Patent Application
20210399246
The invention provides a process for producing a multi-junction device comprising a layer of a crystalline A/M/X material. Also provided are a multi-junction device obtainable or obtained by the process of the invention, a multi-junction device comprising at least two photoactive regions, wherein at least one of the photoactive regions comprises a layer of a crystalline A/M/X material and a multi-junction device comprising at least three photoactive regions, wherein each one of the photoactive regions comprises a layer of a crystalline A/M/X material.
When the first report of a perovskite solar cell was made in 2009, the solar light to electrical power conversion efficiency stood at 3%. By 2012, perovskite photovoltaic devices achieving 9.2% and 10.9% had been achieved. Since then, there has been burgeoning research into the field of perovskite photovoltaics and photovoltaic devise based on other A/M/X materials, with such materials showing the promise to completely transform the energy landscape. Perovskite-based photovoltaic devise have since achieved certified efficiencies in excess of 23%.
Apart from the obvious lure of high power conversion efficiencies, one of the most attractive features of A/M/X materials is the relative simplicity with which high-quality films of this material can be manufactured. Perovskite films can be fabricated through a variety of methods, including one-step spin-coating, vapour deposition and dip-coating, as well as various combinations of these three routes. One-step spin-coating, however, remains the simplest and quickest method with the added bonus of not requiring the use of particularly expensive equipment. Many variations of this method have been developed, such as the inclusion of an additional step in the form of anti-solvent quenching. It is expected that solution processing manufacturing methodologies such as inkjet printing, spray-coating, slot dye coating, blade coating and gravure printing, will be able to undertaken, using slight modifications from spin-coating methods developed in laboratories.
While perovskite solar cells are of significant importance in photovoltaic research, there remain some concerns with respect to the viability of this material for market purposes. One is the stability of the material and the anomalous hysteresis, which is frequently observed in the J-V characteristics of these devices. The cause of this hysteresis has been shown to be due to ion motion, and many attempts to mitigate this effect have been made. The so called inverted positive-intrinsic-negative (p-i-n) structure has been shown to exhibit little to negligible hysteresis, while for the regular negative-intrinsic-positive (n-i-p) structure, the replacement of TiO2, often used as the n-type charge collection layer, by an organic electron acceptor such as C60 or phenyl-C61-butyric acid methyl ester (PCBM), or the inclusion of a thin layer of such materials on top of the TiO2 layer, has been quite successful in the reduction of hysteresis, and this results in a significant increase in the steady-state power output of the device.
To date, most reports of perovskite films manufactured via solution methods use high boiling point, polar, aprotic solvents (see, for instance, Eperon et al, Morphological Control for High Performance, Solution-Processed Planar Heterojunction Perovskite Solar Cells, Adv. Funct. Mater. 2013). While the most frequently used solvent is dimethylformamide (DMF), other solvents include dimethylsulfoxide (DMSO), γ-butyrolactone and dimethylacetamide (DMA). The choice of solvent is, in this case, limited by the lead halide salts which tend to be either sparingly, or completely insoluble in most of the solvents commonly used in the processing of organic semiconductors and dye-sensitized solar cell materials. One of the disadvantages to using solvents such as these is the need to heat films to fairly high temperatures (≥100° C.) to induce crystallisation of the perovskite or A/M/X material film. This can be somewhat circumvented by the use of a so called anti-solvent quenching method, where a film is drenched in an anti-solvent at a specified time during spin-coating, causing the immediate crystallisation of the perovskite material. However, this can complicate the process by requiring an additional anti-solvent quenching step.
As discussed in WO 2017/153752, there are several problems associated with existing solution-based methods for forming films of A/M/X materials. The solvents used at present (such as DMF, DMSO, γ-butyrolactone and DMA) have been chosen because they are able to dissolve the precursor compounds for A/M/X materials, and particularly the metal halide precursors. However, these solvents have high boiling points, increasing the energy requirements or complexity of solution processing. They also have a tendency to remove pre-existing organic layers during device production. These solvents are known to be toxic and can be correspondingly difficult to handle and may be prohibitive for large volume manufacturing due to toxicological concerns. Finally, these solvents cause problems for atmosphere purification units, and are hence challenging to employ in manufacturing.
An additional concern is the solubility of other components of multi-junction devices (such as organic, electron-accepting layers in photovoltaic devices) in high boiling point solvents such as DMF, the most commonly used perovskite solvent. Both C60 and PCBM are sparingly soluble in DMF. Upon deposition of the perovskite layer, this can cause two problems: (i) the almost complete washing away of the electron selective contact in the worst case scenario; or (ii) the formation of pinholes, and thus shunting pathways, in the best case scenario. Even if the partial washing away of the electron selective contact only occurs to a very small degree, this introduces another problem: irreproducibility in device performance due to constant changes in both the thickness and the uniformity of the n-type acceptor.
Multi-junction device architectures can increase the power conversion efficiency of photovoltaic cells beyond the single-junction thermodynamic limit that most currently commercial cells operate within. Monolithic tandem solar cells with solution processed perovskite layers have traditionally had to remain a combination of silicon PV cells with a single perovskite solar cell junction.
Metal halide perovskite semiconductors exhibit high performance when integrated in optoelectronic devices such as light-emitting-diodes (LEDs), photo-detectors, lasers and solar cells. These perovskites typically have a general chemical formula ABX3 allowing their band gap to be tuned by substituting their chemical constituents, i.e. the A-site cation (methylammonium, formamidinium, cesium), B-site metal cation (lead or tin), or X-site anions (iodide, bromide, chloride). This enables halide perovskite semiconductors to be tuned to absorb specific regions of the solar spectrum, and employed in multiple-junction applications, which have the capability of surpassing the Shockley-Queisser and the Tiedje-Yablonovitch thermodynamic efficiency limits. By reducing the difference between the photon energy and the electronic band gap energy, the charge-carrier thermalization losses can be minimized, thus increasing the maximum obtainable power conversion efficiency (PCE). In order to reduce the conversion of photon energy into heat, multiple absorber materials with a wide range of band gaps are required. Recently, efficient solar cells employing wide-band gap perovskites have been fabricated by partial substitution of the organic A-site cation with cesium (Cs) to improve their structural, thermal, and light stability. Furthermore, narrow band gap materials have also been explored through modifications to the B-site cation, where the partial substitution of lead (Pb) with tin (Sn) results in an anomalous band gap bowing behavior, leading to band gaps approaching 1.2 eV.
Given the potential advantages afforded by perovskite semiconductors described above, in particular the ability to alter the chemical composition to tune the band gap as necessary, it is highly desirable to be able to construct all-perovskite multi-junction solar cells.
Recent interest in all-perovskite multi-junction solar cells has demonstrated that these devices are challenging to produce, particularly by solution-based methods. This is in part due to the inability to easily construct multiple junction solar cells, one on top of the other using solvents such as DMF and DMSO. DMF and DMSO are both strongly coordinating solvents used in the dissolution of perovskite salts. These solvents, used for processing uniform and high quality perovskite films, readily interpenetrate the layers upon which they are processed and this results in washing away, or chemically destructing, any perovskite layer already processed beneath.
Perovskite solar cells exhibiting record efficiencies have been processed via solution-based fabrication methods, reaching 23% in a single junction device. The ability to fabricate high quality absorber materials from solution-based processes, in combination with their exceptional optoelectronic properties, has led to the rapid rise of perovskite solar cells. In recent years, significant breakthroughs have been made in four-terminal (4T) and two-terminal (2T) perovskite-on-silicon, perovskite-on-Cu(In,Ga)Se2 (CIGS), perovskite-on-Cu2ZnSn(S,Se)4 (CZTSSe) and also perovskite-on-perovskite tandem cells. Tandem solar cells require a semi-transparent electrode and/or recombination layers between each sub-cell, which can be fabricated using a variety of materials and processing methods. These highly conductive transparent layers have been fabricated using silver nanowires (Ag-NWs), N4,N4,N4″,N4″-tetra([1,1′-biphenyl]-4-yl)-[1,1′:4′,1″-terphenyl]-4,4″-diamine doped 2,2′-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (TaTm:F6-TCNNQ), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), aluminum doped zinc oxide (AZO), and most notably indium tin oxide (ITO). These materials can also be processed using different deposition techniques such as: spray-coating, film transfer lamination, vacuum deposition, and sputter coating. Sputtered ITO has gained considerable attraction due to its high optical transparency throughout the visible and near-infrared (NIR) region, combined with a low resistivity. Due to its dense and compact nature, the sputtered ITO can serve as a physical barrier to the solvents which are used to process the subsequent material layers. These solvents rapidly re-dissolve any underlying perovskite layers unless they are protected by a dense pin-hole free layer, such as indium oxide tin oxide (ITO).
As recently shown, monolithic all-perovskite tandem cells, with power conversion efficiencies (PCEs) of over 17%, can be fabricated using a dense, sputtered ITO layer. These sputter coated TCOs require high vacuum deposition systems and dense buffer layers comprised of nanoparticle (NP) or atomic layer deposition (ALD) layers to prevent the organic and perovskite layers from sputter damage. Furthermore, the lower refractive index of ITO, in comparison to the perovskite absorber layers, introduces significant internal reflective losses, thus limiting the maximum feasible power conversion efficiency. The re-dissolution problem has thus far prevented any experimental realization of an all-solution-processed multi-junction perovskite solar cell, without employing sputter coated ITO or other more complex processing techniques.
To date, it has not been possible to construct multiple junction all-perovskite solar cells entirely via solution processing. To try to protect the first perovskite layer, and allow the fabrication of all-perovskite solar cells a number of strategies have been employed as discussed below.
In Eperon et al. (Perovskite-perovskite tandem photovoltaics with optimized bandgaps, Science, 2016) to protect the underlying first perovskite layer from damage from the solvent used for deposition of the second perovskite layer, the recombination layer used comprises a layer of tin oxide sputter coated with indium tin oxide. This recombination layer provides a physical barrier between the perovskite layers through which solvents such as DMF/DMSO cannot pass. However, this requires more complicated processing techniques such as sputter coating which lead to a more complex, lengthy and costly manufacturing process.
In Heo et al. (CH3NH3PbBr3—CH3NH3PbI3 Perovskite-Perovskite Tandem Solar Cells with Exceeding 2.2 V Open Circuit Voltage, Adv. Mater. 2016, 28, 5121-5125) the issue of solvent damage to the underlying perovskite layer is circumvented by manufacturing the top and bottom parts of the solar cell separately, then laminating them together. A thick hole-transport layer is required to maintain adhesiveness between the front and back cells. The PCE obtained for these solar cells is around 10.8%. This process requires a more complex series of manufacturing steps, including lamination, and is therefore not fully solvent-based.
In Sheng et al, Monolithic Wide Band Gap Perovskite/Perovskite Tandem Solar Cells with Organic Recombination Layers, J. Phys. Chem. C 2017, 121, 27256-27262, to avoid solution processing the second perovskite layer with DMF, a sequential vapour-solution processing method is employed. The resulting tandem solar cell has a PCE of 5.9%. Such a process is not well suited to large-scale printing techniques as it requires thermal evaporation of the precursors.
In Jiang et al A two-terminal perovskite/perovskite tandem solar cell J. Mater. Chem 2016, 4, 1208-1213, anti-solvent quenching techniques are used to deposit the perovskite layers and a film transfer-lamination technique is utilised to place the recombination layer onto the bottom cell. These more complex techniques also prevent such a method being employed on a large scale.
None of these strategies provide a simple, all-solution method for preparing multi-junction devices.
The present invention enables construction of A/M/X multi-junction devices without having to resort to complex processing techniques such as sputter coating, lamination or vapour deposition, thereby enabling an all-solution route to multi-junction devices that allows cheap and easy manufacture of such devices using conventional printing techniques, for instance solution processing manufacturing methodologies such as inkjet printing, spray-coating, slot dye coating, blade coating and gravure printing, as well as spin-coating. In particular, the invention provides both solution-processed perovskite layers, and solution-processed charge recombination layers including tunnel junctions.
By employing a highly volatile, low boiling point aprotic solvent/organic amine-based solvent system, it is shown that perovskite junctions can be stacked on one another to create all-solution processed all-perovskite multi-junction solar cells. The solvation strength of such a solvent system can be tuned by altering the amount of organic amine present. This means that the solvent used has the solvation strength necessary to dissolve the A/M/X precursor materials, but with minimal excess organic amine, thereby eliminating the risk of damage to the underlying layers in the device. Thus, the solvents used have been found to not wash off existing organic layers or underlying perovskite layers during the production of multi-junction devices. This improves the reproducibility and efficiency of produced devices.
The inventors have developed a recombination layer that can be disposed between the various photoactive layers using solution-based techniques. The charge recombination layer described herein can be deposited using solution-based methods. This means that no complex techniques such as sputter-coating, lamination or vacuum deposition are required, making the multi-junction devices simpler to produce. In addition, it also means that thin (<100 nm) charge recombination layers can be manufactured leading to a reduction in internal reflective losses and an increase in power conversion efficiency.
This all-solution processed architecture has the potential of being applied to the manufacturing of large area films on both rigid and flexible substrates, using deposition techniques such as roll-to-roll (R2R) processing, blade coating, slot dye coating, gravure printing or inkjet printing. The invention therefore provides a route to fully solution-processed multi-junction solar cells. These findings open new possibilities for large-scale, low-cost, printable perovskite multi-junction solar cells.
Accordingly, the present invention provides a process for producing a multi-junction device comprising a layer of a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c, wherein: [A] comprises one or more A cations; [M] comprises one or more M cations which are metal or metalloid cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18; and wherein the process comprises forming the layer of the crystalline A/M/X material by disposing a film-forming solution on a substrate, wherein the film-forming solution comprises:
The invention also provides a multi-junction device obtainable or obtained by the process of the invention as defined above.
The invention also provides a multi-junction device comprising:
In contrast to a dense, sputtered ITO layer which introduces significant internal reflective losses due to the lower refractive index of ITO compared to the A/M/X absorber layers, the nanoparticles result in a non-continuous layer which is not only solution-processable, but also able to scatter light through any subsequent light absorbing layers, thus increasing the light absorption of the device.
The invention also provides a multi-junction device comprising:
The invention also provides a multi-junction device comprising
The invention can also advantageously be employed to produce multi-junction light emitting devices, where multiple junctions of different band gap light emitting diodes result in a combined white light emission.
The term “crystalline” as used herein indicates a crystalline compound, which is a compound having an extended 3D crystal structure. A crystalline compound is typically in the form of crystals or, in the case of a polycrystalline compound, crystallites (i.e. a plurality of crystals having particle sizes of less than or equal to 1 μm). The crystals together often form a layer. The crystals of a crystalline material may be of any size. Where the crystals have one or more dimensions in the range of from 1 nm up to 1000 nm, they may be described as nanocrystals.
The terms “organic compound” and “organic solvent” as used herein have their typical meaning in the art and would readily be understood by the skilled person.
The term “crystalline A/M/X material”, as used herein, refers to a material with a crystal structure which comprises one or more A ions, one or more M ions, and one or more X ions. A ions and M ions are cations. X ions are anions. A/M/X materials typically do not comprise any further types of ions.
The term “perovskite”, as used herein, refers to a material with a three-dimensional crystal structure related to that of CaTiO3 or a material comprising a layer of material, which layer has a structure related to that of CaTiO3. The structure of CaTiO3 can be represented by the formula ABX3, wherein A and B are cations of different sizes and X is an anion. In the unit cell, the A cations are at (0,0,0), the B cations are at (½, ½, ½) and the X anions are at (½, ½, 0). The A cation is usually larger than the B cation. The skilled person will appreciate that when A, B and X are varied, the different ion sizes may cause the structure of the perovskite material to distort away from the structure adopted by CaTiO3 to a lower-symmetry distorted structure. The symmetry will also be lower if the material comprises a layer that has a structure related to that of CaTiO3. Materials comprising a layer of perovskite material are well known. For instance, the structure of materials adopting the K2NiF4-type structure comprises a layer of perovskite material. The skilled person will appreciate that a perovskite material can be represented by the formula [A][B][X]3, wherein [A] is at least one cation, [B] is at least one cation and [X] is at least one anion. When the perovskite comprise more than one A cation, the different A cations may distributed over the A sites in an ordered or disordered way. When the perovskite comprises more than one B cation, the different B cations may distributed over the B sites in an ordered or disordered way. When the perovskite comprise more than one X anion, the different X anions may distributed over the X sites in an ordered or disordered way. The symmetry of a perovskite comprising more than one A cation, more than one B cation or more than one X cation, will be lower than that of CaTiO3. For layered perovskites the stoichiometry can change between the A, B and X ions. As an example, the [A]2[B][X]4 structure can be adopted if the A cation has a too large an ionic radii to fit within the 3D perovskite structure. The term “perovskite” also includes A/M/X materials adopting a Ruddleson-Popper phase. Ruddleson-Popper phase refers to a perovskite with a mixture of layered and 3D components. Such perovskites can adopt the crystal structure, An-1A′2MnX3n+1, where A and A′ are different cations and n is an integer from 1 to 8, or from 2 to 6. The term “mixed 2D and 3D” perovskite is used to refer to a perovskite film within which there exists both regions, or domains, of AMX3 and An-1A′2MnX3n+1 perovskite phases.
The term “metal halide perovskite”, as used herein, refers to a perovskite, the formula of which contains at least one metal cation and at least one halide anion.
The term “mixed halide perovskite” as used herein refers to a perovskite or mixed perovskite which contains at least two types of halide anion.
The term “mixed cation perovskite” as used herein refers to a perovskite of mixed perovskite which contains at least two types of A cation.
The term “mixed metal perovskite” as used herein refers to a perovskite of mixed perovskite which contains at least two types of metal M cations.
The term “organic-inorganic metal halide perovskite”, as used herein, refers to a metal halide perovskite, the formula of which contains at least one organic cation.
The term “monocation”, as used herein, refers to any cation with a single positive charge, i.e. a cation of formula A+ where A is any moiety, for instance a metal atom or an organic moiety. The term “dication”, as used herein, refers to any cation with a double positive charge, i.e. a cation of formula A2+ where A is any moiety, for instance a metal atom or an organic moiety. The term “trication”, as used herein, refers to any cation with a triple positive charge, i.e. a cation of formula A3+ where A is any moiety, for instance a metal atom or an organic moiety. The term “tetracation”, as used herein, refers to any cation with a quadruple positive charge, i.e. a cation of formula A4+ where A is any moiety, for instance a metal atom.
The term “alkyl”, as used herein, refers to a linear or branched chain saturated hydrocarbon radical. An alkyl group may be a C1-20 alkyl group, a C1-14 alkyl group, a C1-10 alkyl group, a C1-6 alkyl group or a C1-4 alkyl group. Examples of a C1-10 alkyl group are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. Examples of C1-6 alkyl groups are methyl, ethyl, propyl, butyl, pentyl or hexyl. Examples of C1-4 alkyl groups are methyl, ethyl, i-propyl, n-propyl, t-butyl, s-butyl or n-butyl. If the term “alkyl” is used without a prefix specifying the number of carbons anywhere herein, it has from 1 to 6 carbons (and this also applies to any other organic group referred to herein).
The term “cycloalkyl”, as used herein, refers to a saturated or partially unsaturated cyclic hydrocarbon radical. A cycloalkyl group may be a C3-10 cycloalkyl group, a C3-8 cycloalkyl group or a C3-6 cycloalkyl group. Examples of a C3-8 cycloalkyl group include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl, cyclohex-1,3-dienyl, cycloheptyl and cyclooctyl. Examples of a C3-6 cycloalkyl group include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.
The term “alkenyl”, as used herein, refers to a linear or branched chain hydrocarbon radical comprising one or more double bonds. An alkenyl group may be a C2-20 alkenyl group, a C2-14 alkenyl group, a C2-10 alkenyl group, a C2-6 alkenyl group or a C2-4 alkenyl group. Examples of a C2-10 alkenyl group are ethenyl (vinyl), propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl or decenyl. Examples of C2-6 alkenyl groups are ethenyl, propenyl, butenyl, pentenyl or hexenyl. Examples of C2-4 alkenyl groups are ethenyl, i-propenyl, n-propenyl, s-butenyl or n-butenyl. Alkenyl groups typically comprise one or two double bonds.
The term “alkynyl”, as used herein, refers to a linear or branched chain hydrocarbon radical comprising one or more triple bonds. An alkynyl group may be a C2-20 alkynyl group, a C2-14 alkynyl group, a C2-10 alkynyl group, a C2-6 alkynyl group or a C2-4 alkynyl group. Examples of a C2-10 alkynyl group are ethynyl, propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl or decynyl. Examples of C1-6 alkynyl groups are ethynyl, propynyl, butynyl, pentynyl or hexynyl. Alkynyl groups typically comprise one or two triple bonds.
The term “aryl”, as used herein, refers to a monocyclic, bicyclic or polycyclic aromatic ring which contains from 6 to 14 carbon atoms, typically from 6 to 10 carbon atoms, in the ring portion. Examples include phenyl, naphthyl, indenyl, indanyl, anthrecenyl and pyrenyl groups. The term “aryl group”, as used herein, includes heteroaryl groups.
The term “heteroaryl”, as used herein, refers to monocyclic or bicyclic heteroaromatic rings which typically contains from six to ten atoms in the ring portion including one or more heteroatoms. A heteroaryl group is generally a 5- or 6-membered ring, containing at least one heteroatom selected from O, S, N, P, Se and Si. It may contain, for example, one, two or three heteroatoms. Examples of heteroaryl groups include pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, furanyl, thienyl, pyrazolidinyl, pyrrolyl, oxazolyl, oxadiazolyl, isoxazolyl, thiadiazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, quinolyl and isoquinolyl.
The term “substituted”, as used herein in the context of substituted organic groups, refers to an organic group which bears one or more substituents selected from C1-10 alkyl, aryl (as defined herein), cyano, amino, nitro, C1-10 alkylamino, di(C1-10)alkylamino, arylamino, diarylamino, aryl(C1-10)alkylamino, amido, acylamido, hydroxy, oxo, halo, carboxy, ester, acyl, acyloxy, C1-10 alkoxy, aryloxy, halo(C1-10)alkyl, sulfonic acid, thiol, C1-10 alkylthio, arylthio, sulfonyl, phosphoric acid, phosphate ester, phosphonic acid and phosphonate ester. Examples of substituted alkyl groups include haloalkyl, perhaloalkyl, hydroxyalkyl, aminoalkyl, alkoxyalkyl and alkaryl groups. When a group is substituted, it may bear 1, 2 or 3 substituents. For instance, a substituted group may have 1 or 2 substitutents.
The term “halide” as used herein indicates the singly charged anion of an element in group VIII of the periodic table. “Halide” includes fluoride, chloride, bromide and iodide.
The term “halo” as used herein indicates a halogen atom. Exemplary halo species include fluoro, chloro, bromo and iodo species.
As used herein, an amino group is a radical of formula —NR2, wherein each R is a substituent. R is usually selected from hydrogen, alkyl, alkenyl, cycloalkyl, or aryl, wherein each of alkyl, alkenyl, cycloalkyl and aryl are as defined herein. Typically, each R is selected from hydrogen, C1-10 alkyl, C2-10 alkenyl, and C3-10 cycloalkyl. Preferably, each R is selected from hydrogen, C1-6 alkyl, C2-6 alkenyl, and C3-6 cycloalkyl. More preferably, each R is selected from hydrogen and C1-6 alkyl.
A typical amino group is an alkylamino group, which is a radical of formula —NR2 wherein at least one R is an alkyl group as defined herein. A C1-6 alkylamino group is an alkylamino group wherein at least one R is an C1-6 alkyl group.
As used herein, an imino group is a radical of formula R2C═N— or —C(R)═NR, wherein each R is a substituent. That is, an imino group is a radical comprising a C═N moiety, having the radical moiety either at the N atom or attached to the C atom of said C═N bond. R is as defined herein: that is, R is usually selected from hydrogen, alkyl, alkenyl, cycloalkyl, or aryl, wherein each of alkyl, alkenyl, cycloalkyl and aryl are as defined herein. Typically, each R is selected from hydrogen, C1-10 alkyl, C2-10 alkenyl, and C3-10 cycloalkyl. Preferably, each R is selected from hydrogen, C1-6 alkyl, C2-6 alkenyl, and C3-6 cycloalkyl. More preferably, each R is selected from hydrogen and C1-6 alkyl.
A typical imino group is an alkylimino group, which is a radical of formula R2C═N— or —C(R)═NR wherein at least one R is an alkyl group as defined herein. A C1-6 alkylimino group is an alkylimino group wherein the R substituents comprise from 1 to 6 carbon atoms.
The term “ester” as used herein indicates an organic compound of the formula alkyl-C(═O)—O-alkyl, wherein the alkyl radicals are the same or different and are as defined herein. The alkyl radicals may be optionally substituted.
The term “ether” as used herein indicates an oxygen atom substituted with two alkyl radicals as defined herein. The alkyl radicals may be optionally substituted, and may be the same or different.
As used herein, the term “ammonium” indicates an organic cation comprising a quaternary nitrogen. An ammonium cation is a cation of formula R1R2R3R4N+. R1, R2, R3, and R4 are substituents. Each of R1, R2, R3, and R4 are typically independently selected from hydrogen, or from optionally substituted alkyl, alkenyl, aryl, cycloalkyl, cycloalkenyl and amino; the optional substituent is preferably an amino or imino substituent. Usually, each of R1, R2, R3, and R4 are independently selected from hydrogen, and optionally substituted C1-10 alkyl, C2-10 alkenyl, C3-10 cycloalkyl, C3-10 cycloalkenyl, C6-12 aryl and C1-6 amino; where present, the optional substituent is preferably an amino group; particularly preferably C1-6 amino. Preferably, each of R1, R2, R3, and R4 are independently selected from hydrogen, and unsubstituted C1-10 alkyl, C2-10 alkenyl, C3-10 cycloalkyl, C3-10 cycloalkenyl, C6-12 aryl and C1-6 amino. In a particularly preferred embodiment, R1, R2, R3, and R4 are independently selected from hydrogen, C1-10 alkyl, and C2-10 alkenyl and C1-6 amino. Further preferably, R1, R2, R3, and R4 are independently selected from hydrogen, C1-6 alkyl, C2-6 alkenyl and C1-6 amino.
As used herein, the term “iminium” indicates an organic cation of formula (R1R2C═NR3R4)+, wherein R1, R2, R3, and R4 are as defined in relation to the ammonium cation. Thus, in a particularly preferred embodiment, of the iminium cation, R1, R2, R3, and R4 are independently selected from hydrogen, C1-10 alkyl, C2-10 alkenyl and C1-6 amino. In a further preferable embodiment of the iminium cation, R1, R2, R3, and R4 are independently selected from hydrogen, C1-6 alkyl, C2-6 alkenyl and C1-6 amino. Often, the iminium cation is formamidinium, i.e. R1 is NH2 and R2, R3 and R4 are all H.
The term “multi-junction device”, as used herein, refers to a single device comprising two or more optoelectronic devices, connected electronically in series with each other and positioned sequentially on top of each other. The optoelectronic device could comprise a perovskite absorber layer sandwiched between a hole and electron accepting layer. A charge recombination layer which may be a tunnel junction, separates each optoelectronic device within the multi-junction device, which are stacked on top of each other in the multi-junction device. It is typically that the band gaps of the optoelectronic semiconductors in the multi-junction device will be different from one another.
Examples of multi-junction devices include a photovoltaic device, a solar cell, a photovoltaic diode, a photo detector, a photodiode, a photosensor, a chromogenic device, a light emitting transistor, a light-sensitive transistor, a phototransistor, a solid state triode, a light-emitting device, a laser or a light-emitting diode. The terms “solar cell” and “photovoltaic diode” are used interchangeably herein. The term “optoelectronic device”, as used herein, refers to devices which source, control or detect light. Light is understood to include any electromagnetic radiation. Examples of optoelectronic devices include photovoltaic devices, photodiodes (including solar cells), phototransistors, photomultipliers, photoresistors, and light emitting diodes.
The term “consisting essentially of” refers to a composition comprising the components of which it consists essentially as well as other components, provided that the other components do not materially affect the essential characteristics of the composition. Typically, a composition consisting essentially of certain components will comprise greater than or equal to 95 wt % of those components or greater than or equal to 99 wt % of those components.
The terms “disposing on” or “disposed on”, as used herein, refers to the making available or placing of one component on another component. The first component may be made available or placed directly on the second component, or there may be a third component which intervenes between the first and second component. For instance, if a first layer is disposed on a second layer, this includes the case where there is an intervening third layer between the first and second layers. Typically, “disposing on” refers to the direct placement of one component on another.
The term “layer”, as used herein, refers to any structure which is substantially laminar in form (for instance extending substantially in two perpendicular directions, but limited in its extension in the third perpendicular direction). A layer may have a thickness which varies over the extent of the layer. Typically, a layer has approximately constant thickness. The “thickness” of a layer, as used herein, refers to the average thickness of a layer. The thickness of layers may easily be measured, for instance by using microscopy, such as electron microscopy of a cross section of a film, or by surface profilometry for instance using a stylus profilometer.
The term “band gap”, as used herein, refers to the energy difference between the top of the valence band and the bottom of the conduction band in a material. The skilled person of course is readily able to measure the band gap of a semiconductor (including that of a perovskite) by using well-known procedures which do not require undue experimentation. For instance, the band gap of a semiconductor can be estimated by constructing a photovoltaic diode or solar cell from the semiconductor and determining the photovoltaic action spectrum. Alternatively the band gap can be estimated by measuring the light absorption spectra either via transmission spectrophotometry or by photo thermal deflection spectroscopy. The band gap can be determined by making a Tauc plot, as described in Tauc, J., Grigorovici, R. & Vancu, a. Optical Properties and Electronic Structure of Amorphous Germanium. Phys. Status Solidi 15, 627-637 (1966) where the square of the product of absorption coefficient times photon energy is plotted on the Y-axis against photon energy on the x-axis with the straight line intercept of the absorption edge with the x-axis giving the optical band gap of the semiconductor. Alternatively, the optical band gap may be estimated by taking the onset of the incident photon-to-electron conversion efficiency, as described in [Barkhouse D A R, Gunawan O, Gokmen T, Todorov T K, Mitzi D B. Device characteristics of a 10.1% hydrazine processed Cu2ZnSn(Se,S)4 solar cell. Progress in Photovoltaics: Research and Applications 2012; published online DOI: 10.1002/pip.1160.]
The term “semiconductor” or “semiconducting material”, as used herein, refers to a material with electrical conductivity intermediate in magnitude between that of a conductor and a dielectric. A semiconductor may be an negative (n)-type semiconductor, a positive (p)-type semiconductor or an intrinsic (i) semiconductor. A semiconductor may have a band gap of from 0.5 to 3.5 eV, for instance from 0.5 to 2.5 eV or from 1.0 to 2.0 eV (when measured at 300 K).
The term “n-type region”, as used herein, refers to a region of one or more electron-transporting (i.e. n-type) materials. Similarly, the terms “n-type layer” refers to a layer of an electron-transporting (i.e. an n-type) material. An electron-transporting (i.e. an n-type) material could be a single electron-transporting compound or elemental material, or a mixture of two or more electron-transporting compounds or elemental materials. An electron-transporting compound or elemental material may be undoped or doped with one or more dopant elements.
The term “p-type region”, as used herein, refers to a region of one or more hole-transporting (i.e. p-type) materials. Similarly, the term “p-type layer” refers to a layer of a hole-transporting (i.e. a p-type) material. A hole-transporting (i.e. a p-type) material could be a single hole-transporting compound or elemental material, or a mixture of two or more hole-transporting compounds or elemental materials. A hole-transporting compound or elemental material may be undoped or doped with one or more dopant elements.
The term “electrode material”, as used herein, refers to any material suitable for use in an electrode. An electrode material will have a high electrical conductivity. The term “electrode” as used herein indicates a region or layer consisting of, or consisting essentially of, an electrode material.
The term “nanoparticle”, as used herein, means a microscopic particle whose size is typically measured in nanometres (nm). A nanoparticle typically has a particle size of from 0.1 nm to 500 nm, for instance from 0.5 nm to 500 nm. A nanoparticle may for instance be a particle having size of from 0.1 nm to 300 nm, or for example from 0.5 nm to 300 nm. Often, a nanoparticle has a particle size of from 0.1 nm to 100 nm, for instance from 0.5 nm to 100 nm. A nanoparticle may have a high sphericity, i.e. it may be substantially spherical or spherical. A nanoparticle with a high sphericity may for instance have a sphericity of from 0.8 to 1.0. The sphericity may be calculated as π1/3(6Vp)2/3/Ap where Vp is the volume of the particle and Ap is the area of the particle. Perfectly spherical particles have a sphericity of 1.0. All other particles have a sphericity of lower than 1.0. A nanoparticle may alternatively be non-spherical. It may for instance be in the form of an oblate or prolate spheroid, and it may have a smooth surface. Alternatively, a non-spherical nanoparticle may be plate-shaped, needle-shaped, tubular or take an irregular shape.
The invention provides a process for producing a multi-junction device comprising a layer of a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c, wherein: [A] comprises one or more A cations; [M] comprises one or more M cations which are metal or metalloid cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18; and wherein the process comprises forming the layer of the crystalline A/M/X material by disposing a film-forming solution on a substrate, wherein the film-forming solution comprises:
Typically, the process involves disposing the film-forming solution on the charge recombination layer. Thus, typically, the substrate comprises the following layers in the following order:
Thus, typically, the multi-junction device produced according to the present invention comprises the following layers in the following order:
The photoactive material in the substrate may be soluble in dimethylformamide (DMF). Often, at least one component of the charge recombination layer in the substrate is soluble in dimethylformamide (DMF). For instance, both the photoactive material in the substrate and at least one component of the charge recombination layer in the substrate may be soluble in dimethylformamide (DMF). Typically, the photoactive material in the substrate is soluble in dimethylformamide (DMF), dimethysulfoxide (DMSO) or a mixture thereof. Often, at least one component of the charge recombination layer in the substrate is soluble in dimethylformamide (DMF), dimethysulfoxide (DMSO) or a mixture thereof. For instance, both the photoactive material in the substrate and at least one component of the charge recombination layer in the substrate may be soluble in dimethylformamide (DMF), dimethysulfoxide (DMSO) or a mixture thereof.
Both the photoactive material in the substrate and the charge recombination layer in the substrate may be soluble in dimethylformamide (DMF). Typically, both the photoactive material in the substrate and the charge recombination layer in the substrate are soluble in dimethylformamide (DMF), dimethysulfoxide (DMSO) or a mixture thereof.
Typically, the aprotic solvent does not comprise dimethylformamide (DMF). Preferably, the aprotic solvent does not comprise dimethylformamide, dimethylsulfoxide (DMSO) or mixtures thereof.
The aprotic solvent may be a polar aprotic solvent. Such solvents are known to the skilled person. For instance, the aprotic solvent may comprise a compound selected from the group consisting of chlorobenzene, acetone, butanone, methylethylketone, acetonitrile, propionitrile or a mixture thereof.
The aprotic solvent may be an non-polar aprotic solvent. Such solvents are known to the skilled person. For instance, the aprotic solvent may comprise toluene.
Typically, the aprotic solvent comprises a compound selected from the group consisting of chlorobenzene, acetone, butanone, methylethylketone, acetonitrile, propionitrile, toluene or a mixture thereof. Preferably, the aprotic solvent comprises acetonitrile. For instance, greater then or equal to 80 vol % of the aprotic solvent may be acetonitrile.
Typically, the organic amine is an unsubstituted or substituted alkylamine or an unsubstituted or substituted arylamine.
An alkylamine is an organic compound comprising an alkyl group and an amine group, which amine group may be a primary, secondary or tertiary amine group. The alkylamine compound may be a primary amine RANH2, wherein RA is an alkyl group which may be substituted or unsubstituted, or a secondary amine RA2NH, wherein each RA is an alkyl group which may be substituted or unsubstituted, or a tertiary amine RA3N, wherein each RA is an alkyl group which may be substituted or unsubstituted. Typically, the alkylamine is a primary alkylamine.
Typically, the organic amine is an unsubstituted or substituted (C1-10 alkyl) amine. For instance, the alkylamine compound may be a primary amine RANH2, wherein RA is unsubstituted or substituted C1-10 alkyl, or unsubstituted or substituted C1-8 alkyl, for instance unsubstituted or substituted C1-6 alkyl. For instance, RA may be methyl, ethyl, propyl, isopropyl, butyl (i.e. n-butyl), pentyl (n-pentyl) or hexyl (n-hexyl).
Preferably, the organic amine is an unsubstituted (C1-10 alkyl) amine or a (C1-10 alkyl) amine substituted with a phenyl group. For instance, the organic amine may be an unsubstituted (C1-8 alkyl) amine, for example an unsubstituted (C1-6 alkyl) amine, for example methylamine, ethylamine, propylamine, butylamine or pentylamine, or hexylamine. The organic amine may be a (C1-8 alkyl) amine substituted with a phenyl group, for instance a (C1-6 alkyl) amine substituted with a phenyl group, for example benzyl amine or phenyl ethyl amine.
The organic amine may therefore be methylamine, ethylamine, propylamine, butylamine or pentylamine, hexylamine, benzyl amine or phenyl ethyl amine, or mixtures thereof. For instance, the organic amine may be methylamine, propylamine or butylamine. Preferably, the organic amine is methylamine.
The solvent may comprise two or more organic amine compounds as defined herein. For instance, the solvent may comprise methylamine, butylamine, phenylethylamine, hexylamine, octylamine, ocatadecylamine, alkylamine, naphthylamine and benzylamine, Methoxypolyethylene glycol amine.
An arylamine is an organic compound comprising an aryl group and an amine group. Typically, an aryl amine is derived from ammonia by replacing one or more of the hydrogen atoms with aryl groups.
The arylamine may comprise an amine group which may be a primary, secondary or tertiary amine group. The arylamine compound may be a primary amine RBNH2, wherein RB is an aryl group which may be substituted or unsubstituted. For instance, RB may be selected from phenyl, naphthyl, indenyl, indanyl, anthrecenyl and pyrenyl groups. Typically RB is a phenyl group, hence the arylamine may be phenylamine (aniline).
The arylamine may be a secondary amine, for instance a secondary amine of the formula RBRANH, wherein RA is an alkyl group as described herein and RB is an aryl group as described herein. The arylamine may be tertiary amine, for instance a tertiary amine of the formula RBRA2N, wherein each RA is an alkyl group as described above and RB is an aryl group as described above.
Typically, the solvent in the process of the invention is produced by adding the organic amine to the aprotic solvent, either as a gaseous organic amine, a liquid organic amine or a solution of an organic amine. Thus, the process may further comprise a step of producing the solvent by adding the organic amine to the aprotic solvent. A gaseous organic amine may be added to a solvent by bubbling the organic amine through the solvent.
The amount of organic amine in the solvent may vary depending on requirements. Typically, the amount of organic amine present in the solvent is sufficient to fully solvate the M cations. When A cations and X anions are also present in the film-forming solution, the amount of organic amine present in the solvent may be sufficient to fully solvate the M cations, the A cations and the X anions. Therefore, typically the solvent comprises the amount of organic amine in an amount sufficient to maintain the film-forming solution at its critical solution point. Preferably, only a small excess of organic amine is present, i.e. just enough amine to dissolve the components should usually be present in the solvent. Typically, the percent by volume of amine in the solvent is less than or equal to 50%, more typically less than 25%, for instance less than 10%.
It is desirable to have a film-forming solution in which the minimum amount of organic amine is used to solvate the M cations, and optionally any A cations and X anions that may be present. Such a solution is able to evenly deposit the M cations, and optionally any A cations and X anions on the substrate without dissolving the underlying layers, for instance the charge recombination layer, the photoactive region or any charge transporting layer (if present).
Typically, the film-forming solution is prepared by a process comprising the following steps:
As the skilled person would appreciate, the solubility of the M cations, and optionally any A cations and X anions present, will vary depending on the concentrations and nature of the ions. The method above permits the amount of organic amine to be tailored such that the appropriate amount to fully solvate all ions with minimum excess is used.
Typically, the solution in which the M cations, and optionally any A cations and X anions that may be present, are fully solvated by an excess of organic amine is prepared by a process comprising the following steps:
Typically, the film-forming solution is disposed on the substrate by solution phase deposition, for instance gravure coating, slot dye coating, screen printing, ink jet printing, doctor blade coating, spray coating, roll-to-roll (R2R) processing, or spin-coating. Typically, disposing the film-forming composition on the substrate comprises a step of spin-coating the film-forming solution on the substrate.
Typically, the spin coating is performed at a speed of at least 1000 RPM, for instance at least 2000 RPM, at least 3000 RPM or at least 4000 RPM, for example between 1000 and 10000 RPM, between 2000 and 8000 RPM, between 2500 and 7500 RPM, preferably about 5000 RPM. Typically, the spin coating is performed for a time of at least one second, at least 5 seconds or at least 10 seconds, for example from 1 second to 1 minute, from 10 seconds to 30 seconds, preferably about 20 seconds.
Typically, the process further comprises removing the solvent to form the layer comprising the crystalline A/M/X material. Removing the solvent may comprise heating the solvent, or allowing the solvent to evaporate.
The solvent is usually removed by heating the film-forming solution treated substrate. For instance, the film-forming solution treated substrate may be heated to a temperature of from 30° C. to 400° C., for instance from 50° C. to 200° C. Preferably, the film-forming solution treated is heated to a temperature of from 50° C. to 200° C. for a time of from 5 to 200 minutes, preferably from 10 to 100 minutes.
The process of the present invention may comprise a further step of disposing on the substrate a composition comprising one or more A cations and optionally one or more X anions. The film-forming solution used in the process of the present invention may not comprise any A cations and/or X anions. In this case, the A cations and/or X anions may be added to the substrate in a separate step, so that the crystalline A/M/X material is formed on the substrate. Alternatively, the film-forming solution used in the process of the present invention may comprise A cations and/or X anions, and the further step of disposing a composition comprising one or more A cations and optionally one or more X anions on the substrate is performed as a post treatment step on the layer of the crystalline A/M/X material.
Typically the composition comprising one or more A cations and optionally one or more X anions is a solution. Thus, the process of the present invention may further comprise a step of disposing on the substrate a solution comprising one or more A cations and optionally one or more X anions. The process of the present invention may further comprise a step of disposing on the substrate a composition comprising one or more A cations and one or more X anions, for example a solution comprising one or more A cations and one or more X anions.
The solution comprising one or more A cations and one or more X anions may be formed by dissolving one or more compounds of formula AX in a solvent, wherein A and X are as defined herein. The solvent may be different or the same as the solvent in the film-forming solution. Typically, the solvent is different to the solvent in the film-forming solution. Therefore, the solvent may be a solvent that is orthogonal to the solvent in the film-forming solution. Importantly, the solvent should not dissolve the underlying perovskite film. For instance, the solvent may be isopropanol (2-propanol), ethanol (EtOH), methanol (MeOH), and butanol. The solvent may be toluene. The solvent could also be a mixture of solvents, for instance the above mentioned alcohols with aprotic solvents such as toluene, anisole, chlorobenzene.
Typically, the solution comprising one or more A cations and one or more X anions is spin-coated on to the substrate. Typically, the spin coating is performed at a speed of at least 1000 RPM, for instance at least 2000 RPM, at least 3000 RPM or at least 4000 RPM, for example between 1000 and 10000 RPM, between 4000 and 8000 RPM, preferably about 6000 RPM. Typically, the spin coating is performed for a time of at least one second, at least 5 seconds or at least 10 seconds, for example from 1 second to 1 minute, from 10 seconds to 30 seconds, preferably about 20 seconds.
The solvent is usually removed by heating the film-forming solution treated substrate. For instance, the film-forming solution treated substrate may be heated to a temperature of from 30° C. to 400° C., for instance from 50° C. to 200° C. Preferably, the film-forming solution treated is heated to a temperature of from 50° C. to 200° C. for a time of from 5 to 200 minutes, preferably from 10 to 100 minutes.
Compound of Formula [A]a[M]b[X]c
The process of the present invention produces a multi-junction device comprising a layer of a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c, wherein: [A] comprises one or more A cations; [M] comprises one or more M cations which are metal or metalloid cations; [X] comprises one or more X anions; a is a number from 1 to 6; b is a number from 1 to 6; and c is a number from 1 to 18. a is often a number from 1 to 4, b is often a number from 1 to 3, and c is often a number from 1 to 8.
Each of a, b and c may or may not be an integer. For instance, a, b or c may not be an integer where the compound adopts a structure having vacancies such that the crystal lattice is not completely filled. The method of the invention provides very good control over stoichiometry of the product and so is well-suited for forming structures where a, b or c is not an integer (for instance a structure having vacancies in one or more of the A, M or X sites). Accordingly, in some embodiments, one or more of a, b and c is a non-integer value. For example, one of a, b and c may be a non-integer value. In one embodiment, a is a non-integer value. In another embodiment, b is a non-integer value. In yet another embodiment, c is a non-integer value.
In other embodiments, each of a, b and c are integer values. Thus, in some embodiments, a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18. a is often an integer from 1 to 4, b is often an integer from 1 to 3, and c is often an integer from 1 to 8.
In the compound of formula [A]a[M]b[X]c, generally:
Preferably the compound of formula [A]a[M]b[X]c comprises a perovskite. The compound of formula [A]a[M]b[X]c often comprises a metal halide perovskite.
[M] comprises one or more M cations which are metal or metalloid cations. [M] may comprise two or more different M cations. [M] may comprise one or more monocations, one or more dications, one or more trications or one or more tetracations.
Typically, the one or more M cations are selected from Ca2+, Sr2+, Cd2+, Cu2+, Ni2+, Mn2+, Fe2+, Co2+, Pd2+, Ge2+, Sn2+, Pb2+, Yb2+, Eu2+, Bi3+, Sb3+, Pd4+, W4+, Re4+, Os4+, Ir4+, Pt4+, Sn4+, Pb4+, Ge4+ or Te4+. Preferably, the one or more M cations are selected from Cu2+, Pb2+, Ge2+ or Sn2+.
Typically, [M] comprises one or more metal or metalloid dications. For instance, each M cation may be selected from Ca2+, Sr2+, Cd2+, Cu2+, Ni2+, Mn2+, Fe2+, Co2+, Pd2+, Ge2+, Sn2+, Pb2+, Yb2+ and Eu2+, preferably Sn2+, Pb2+, Cu2+, Ge2+, and Ni2+; preferably Sn2+ and Pb2+. In some embodiments, [M] comprises two different M cations, typically where said cations are Sn2+ and Pb2+.
The film-forming solution used in the process of the present invention comprises: (a) one or more M cations as described herein; and (b) a solvent as described herein. The process of the present invention may comprise a step of forming the film-forming solution by dissolving at least one M precursor in the solvent. As is discussed in more detail below, an M precursor is a compound comprising one or more M cations present in [M]. Where [M] (that is, [M] in the compound of formula [A]a[M]b[X]c) comprises only one type of M cation, only one M precursor is necessary in the process of the invention.
The M precursor typically comprises one or more counter-anions. Thus, typically, the film-forming solution comprises one or more counter-anions. Many such counter-anions are known to the skilled person. The one or more M cations and the one or more counter anions may both be from a first precursor compound, which is dissolved in the solvent as described herein to form the film-forming solution.
The counter-anion may be a halide anion, a thiocyanate anion (SCN−), a tetrafluoroborate anion (BF4−) or an organic anion. Preferably, the counter-anion as described herein is a halide anion or an organic anion. The film-forming solution may comprise two or more counter-anions, e.g. two or more halide anions.
Typically, the counter-anion is an anion of formula RCOO−, ROCOO−, RSO3−, ROP(O)(OH)O− or RO−, wherein R is H, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C3-10 cycloalkyl, substituted or unsubstituted C3-10 heterocyclyl or substituted or unsubstituted aryl. For instance R may be H, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C3-10 cycloalkyl or substituted or unsubstituted aryl. Typically R is H substituted or unsubstituted C1-6 alkyl or substituted or unsubstituted aryl. For instance, R may be H, unsubstituted C1-6 alkyl or unsubstituted aryl. Thus, R may be selected from H, methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl and phenyl. Often, (one or more) counter-anions are selected from halide anions (e.g. F−, Cl−, Br− and I−) and anions of formula RCOO−, wherein R is H or methyl.
Typically, the counter-anion is F−, Cl−, Br−, I−, formate or acetate. Preferably, the counter-anion is Cl−, Br−, I− or F−. More preferably, the counter-anion is Cl−, Br− or I−.
Typically, the M precursor is a compound of formula MY2, MY3, or MY4, wherein M is a metal or metalloid cation as described herein, and Y is said counter-anion.
Thus, the M precursor may be a compound of formula MY2, wherein M is Ca2+, Sr2+, Cd2+, Cu2+, Ni2+, Mn2+, Fe2+, Co2+, Pd2+, Ge2+, Sn2+, Pb2+, Yb2+ or Eu2+ and Y is F−, Cl−, Br−, I−, formate or acetate. Preferably M is Cu2+, Pb2+, Ge2+ or Sn2+ and Y is Cl−, Br−, I−, formate or acetate, preferably Cl−, Br− or I−.
Typically, the M precursor is lead (II) acetate, lead (II) formate, lead (II) fluoride, lead (II) chloride, lead (II) bromide, lead (II) iodide, tin (II) acetate, tin (II) formate, tin (II) fluoride, tin (II) chloride, tin (II) bromide, tin (II) iodide, germanium (II) acetate, germanium (II) formate, germanium (II) fluoride, germanium (II) chloride, germanium (II) bromide or germanium (II) iodide. In some cases, the first precursor compound comprises lead (II) acetate. In some cases, the first precursor compound comprises lead (II) iodide.
The M precursor is typically a compound of formula MY2. Preferably, the M precursor is a compound of formula SnI2, SnBr2, SnCl2, PbI2, PbBr2 or PbCl2.
The M precursor may be a compound of formula MY3, wherein M is Bi3+ or Sb3+ and Y is F−, Cl−, Br−, I−, SCN−, BF4−, formate or acetate. Preferably M is Bi3+ and Y is Cl−, Br− or I−. In that case, the A/M/X material typically comprises a bismuth or antimony halogenometallate.
The M precursor may be a compound of formula MY4, wherein M is Pd4+, W4+, Re4+, Os4+, Ir4+, Pt4+, Sn4+, Pb4+, Ge4+ or Te4+ and Y is F−, Cl−, Br−, I−, SCN−, BF4−, formate or acetate. Preferably M is Sn4+, Pb4+ or Ge4+ and Cl−, Br− or I−. In that case, the A/M/X material typically comprises a hexahalometallate.
Typically, the total concentration of [M] cations in the film-forming solution is between 0.01 and 10 M, for instance between 0.1 and 5 M, 0.25 and 2.5 M, 0.5 and 1.5 M, preferably between 0.75 and 1.25 M.
In general, said one or more A cations are monocations. [A] typically comprises one or more A cations which may be organic and/or inorganic monocations. For instance, [A] may comprise at least two A cations which may be organic and/or inorganic monocations. Thus, the compound of formula [A]a[M]b[X]c may be a mixed cation perovskite. [A] may comprise at least one A cation which is an organic cation and at least one A cation which is an inorganic cation. [A] may comprise at least two A cations which are both organic cations. [A] may comprise at least two A cations which are both inorganic cations.
Where an A species is an inorganic monocation, A is typically an alkali metal monocation (that is, a monocation of a metal found in Group 1 of the periodic table), for instance Li+, Na+, K+, Rb+, Cs+, for example Cs+ or Rb+. Typically, [A] comprises at least one organic monocation. Where an A species is an organic monocation, A is typically an ammonium cation, for instance methylammonium, or an iminium cation, for instance formamidimium.
Each A cation may be selected from: an alkali metal cation, for instance Li+, Na+, K+, Rb+, Cs+; a cation of the formula [R1R2R3R4N]+, wherein each of R1, R2, R3, R4 is independently selected from hydrogen, unsubstituted or substituted C1-20 alkyl, and unsubstituted or substituted C6-12 aryl, and at least one of R1, R2, R3 and R4 is not hydrogen; a cation of the formula [R5R6N═CH—NR7R8]+, wherein each of R5, R6, R7 and R8 is independently selected from hydrogen, unsubstituted or substituted C1-20 alkyl, and unsubstituted or substituted C6-12 aryl; and C1-10 alkylamammonium, C2-10 alkenylammonium, C1-10 alkyliminium, C3-10 cycloalkylammonium and C3-10 cycloalkyliminium, each of which is unsubstituted or substituted with one or more substituents selected from amino, C1-6 alkylamino, imino, C1-6 alkylimino, C1-6 alkyl, C2-6 alkenyl, C3-6 cycloalkyl and C6-12 aryl.
Preferably, each A cation is selected from Cs+, Rb+, methylammonium [(CH3NH3)+], ethylammonium [(CH3CH2NH3)+], propylammonium [(CH3CH2CH2NH3)+]. Butylammonium [(CH3CH2CH2CH2NH3)+], pentylammoium [(CH3CH2CH2CH2CH2NH3)+], hexylammonium [(CH3CH2CH2CH2CH2CH2NH3)+], heptylammonium [(CH3CH2CH2CH2CH2CH2CH2NH3)+], octylammonium [(CH3CH2CH2CH2CH2CH2CH2CH2NH3)+], tetramethylammonium [(N(CH3)4)+], formamidinium [(H2N—C(H)═NH2)+], 1-aminoethan-1-iminium [(H2N—C(CH3)═NH2)+] and guanidinium [(H2N—C(NH2)═NH2)+].
[A] usually comprises one, two or three A monocations. [A] may comprises a single cation selected from methylammonium [(CH3NH3)+], ethylammonium [(CH3CH2NH3)+], propylammonium [(CH3CH2CH2NH3)+], dimethylammonium [(CH3)2NH+], tetramethylammonium [(N(CH3)4)+], formamidinium [(H2NC(H)═NH2)+], 1-aminoethan-1-iminium [(H2NC(CH3)═NH2)+], guanidinium [(H2N—C(NH2)═NH2)+], Cs+ and Rb+. For instance [A] may comprise a single cation that is methylammonium [(CH3NH3)+].
Alternatively, [A] may comprise two cations selected from this group, for instance Cs+ and formamidinium [(H2N—C(H)═NH2)+], or for instance Cs+ and Rb+, or for instance methylammonium [(CH3NH3)+] and formamidinium [(H2N—C(H)═NH2)+].
Typically, in the process of the present invention, [A] comprises a cation of the formula [R1NH3]+, wherein R1 is unsubstituted C1-10 alkyl and the organic amine comprises an unsubstituted (C1-10 alkyl) amine. The identity of the organic amine in the solvent may be matched to the alkylamine which, when protonated, corresponds to the cation A. Therefore, the C1-10 alkyl group on the A cation of formula [R1NH3]+ and the C1-10 alkyl group on the unsubstituted (C1-10 alkyl) amine may be the same. For example, the A cation may be methylammonium and the organic amine may comprise methylamine, or the A cation may be ethylammonium and the organic amine may comprise ethylamine, or the A cation may be propylammonium and the organic cation may comprise propylamine, or the A cation may be butylammonium and the organic amine may comprise butylamine, or the A cation may be pentylammonium and the organic amine may comprise pentylamine, or the A cation may be hexylammonium and the organic amine may comprise hexylamine, or the A cation may be heptylammonium and the organic amine may comprise heptylamine, or the A cation may be octylammonium and the organic amine may comprise octylamine. In a preferred embodiment, [A] comprises methylammonium and the organic amine comprises methylamine.
[X] comprises one or more X anions. Typically, [X] comprises one or more halide anions, i.e. an anion selected from F−, Br−, Cl− and I−. Typically, each X anion is a halide. [X] typically comprises one, two or three X anions and these are generally selected from Br−, Cl− and I−. Typically, [X] comprises two or more different halide anions. [X] may for instance consist of two X anions, such as Cl and Br, or Br and I, or Cl and I. Therefore, the compound of formula [A]a[M]b[X]c often comprises a mixed halide perovskite. When [A] comprises one or more organic cations, the compound of formula [A]a[M]b[X]c may be an organic-inorganic metal halide perovskite.
The film-forming solution may further comprise one or more A cations as described herein. Accordingly, it may be preferred that the film-forming solution comprises each of the one or more A cations present in [A]. The process of the present invention may comprise a step of forming the film-forming solution by dissolving at least one A precursor in the solvent. As is discussed in more detail below, an A precursor is a compound comprising one or more A cations present in [A]. Where [A] (that is, [A] in the compound of formula [A]a[M]b[X]c) comprises only one type of A cation, only one A precursor is necessary in the process of the invention.
The film-forming solution may further comprise one or more X anions as described herein. As regards the source of X anions in the process of the invention, it may not be necessary to provide a separate X precursor in the process of the invention. This is because in some embodiments, the A precursor (or where the process involves a plurality of A precursors, at least one of them) and/or the M precursor (or where the process involves a plurality of M precursors, at least one of them) is salt comprising one or more X anions, for instance a halide salt. In a preferred embodiment, the A precursor (or where present the plurality of A precursors) and the M precursor (or where present the plurality of M precursors) together comprise each of the X cations present in [X].
A further X anion, for instance fluoride (F−) or chloride (Cl−), may be added to the film forming solution as a “dopant”, for instance by adding SnF2 or SnCl2 respectively to the film forming solution as an additive. Pb:Sn perovskites in particular can benefit from adding further SnF2 to the solution.
The film-forming solution typically further comprises one or more A cations as described herein and one or more X anions as described herein. In this embodiment, the film forming solution comprises one or more A cations, one or more M cations and one or more X anions. Thus, in one embodiment the film-forming solution may comprise all of the ions required to make the compound of formula [A]a[M]b[X]c.
The A cations and X anions may both be from the same precursor compound or compounds, which are dissolved in the solvent as described herein to form the film-forming solution. Preferably, the A/X precursor compound is a compound of formula [A][X] wherein: [A] comprises the one or more A cations as described herein; and [X] comprises the one or more X anions as described herein. The A/X precursor compound is typically a compound of formula AX, wherein X is a halide anion and the A cation is as defined herein. When more than one A cation or more than one X anion is present in the compound of formula [A]a[M]b[X]c, more than one compound of formula AX may be dissolved in the film-forming solution.
The A/X precursor compound (or compounds) may, for example, be selected from CH3NH3Cl, CH3NH3Br, CH3NH3I, CH3CH2NH3Cl, CH3CH2NH3Br, CH3CH2NH3I, CH3CH2CH2NH3Cl, CH3CH2CH2NH3Br, CH3CH2CH2NH3I, N(CH3)4Cl, N(CH3)4Br, N(CH3)4I, (H2NC(H)═NH2)Cl, (H2NC(H)═NH2)Br, (H2NC(H)═NH2)I, (H2N—C(CH3)═NH2)Cl, (H2NC(CH3)═NH2)Br, (H2NC(CH3)═NH2)I, (H2N—C(NH2)═NH2)Cl, (H2N—C(NH2)═NH2)Br, (H2N—C(NH2)═NH2)I, CsCl, CsBr, CsI, RbCl, RbBr and RbI.
In one embodiment, the film-forming solution comprises an excess of A cations to M cations. In this context, the term “excess” means that the molar ratio of one ion to another is greater than that required by the stoichiometry in the target compound of formula [A]a[M]b[X]c. Typically, the ratio of A cations to M cations in the film-forming solution is from 1:1 to 5:1, for instance from 1:1 to 4:1, 1:1 to 3:1, 1:1 to 2:1, 1:1 to 1.5:1, 1:1 to 1.25:1 or 1:1 to 1.1:1.
In one embodiment, the film-forming solution comprises an excess of M cations to A cations. Typically, the ratio of M cations to A cations in the film-forming solution is from 1:1 to 5:1, for instance from 1:1 to 4:1, 1:1 to 3:1, 1:1 to 2:1, 1:1 to 1.5:1, 1:1 to 1.25:1 or 1:1 to 1.2:1. This is preferred when the compound of formula [A]a[M]b[X]c comprises two M cations, preferably wherein [M] comprises Pb2+ and Sn2+.
Thus, typically, the total concentration of [A] cations in the film-forming solution is between 0.01 and 10 M, for instance between 0.1 and 5 M, 0.25 and 2.5 M, 0.5 and 1.5 M, preferably between 0.6 and 1.4 M.
Typically, the total concentration of X anions depends on the total concentration of A and/or M cations. For instance, when an A/X precursor compound and/or an M precursor compound comprising one or more X anions are used, the total concentration of X anions will depend on the total amount of A/X precursor compound and/or an M precursor compound present, as described above.
Compound of Formula [A]a[M]b[X]c—Further Detail
Typically, a=1, b=1 and c=3. Thus, the compound of formula [A]a[M]b[X]c may be a compound of formula [A][M][X]3, wherein [A], [M] and [X] are as described herein. Typically, the crystalline A/M/X material comprises: a perovskite of formula (I):
[A][M][X]3 (I)
wherein: [A] comprises one or more A cations which are monocations; [M] comprises one or more M cations which are metal or metalloid dications; and [X] comprises one or more anions which are halide anions.
In some embodiments, the perovskite of formula (I) comprises a single A cation, a single M cation and a single X cation. i.e., the perovskite is a perovskite of the formula (IA):
AMX3 (IA)
wherein A, M and X are as defined above. In a preferred embodiment, A is selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2N—C(NH2)═NH2)+, Cs+ and Rb+; M is Pb2+ or Sn2+ and X is selected from Br−, Cl− and I−.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IA) selected from APbI3, APbBr3, APbCl3, ASnI3, ASnBr3 and ASnCl3, wherein A is a cation as described herein.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IA) selected from CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, CsPbI3, CsPbBr3, CsPbCl3, CsSnI3, CsSnBr3, CsSnCl3, (H2N—C(H)═NH2)PbI3, (H2N—C(H)═NH2)PbBr3, (H2N—C(H)═NH2)PbCl3, (H2N—C(H)═NH2)SnI3, (H2N—C(H)═NH2)SnBr3 and (H2N—C(H)═NH2)SnCl3, in particular CH3NH3PbI3 or CH3NH3PbBr3, preferably CH3NH3PbI3.
In one embodiment, the perovskite is a perovskite of the formula (IB):
[AIxAII1-x]MX3 (IB)
wherein AI and AII are as defined above with respect to A, wherein M and X are as defined above and wherein x is greater than 0 and less than 1. In a preferred embodiment, AI and AII are each selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2N—C(NH2)═NH2)+, Cs+ and Rb+; M is Pb2+ or Sn2+ and X is selected from Br−, Cl− and I−. AI and AII may for instance be (H2N—C(H)═NH2)+ and Cs+ respectively, or they may be (CH3NH3)+ and (H2N—C(H)═NH2)+ respectively. Alternatively, they may be Cs+ and Rb+ respectively.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IB) selected from (CsxRb1-x)PbBr3, (CsxRb1-x)PbCl3, (CsxRb1-x)PbI3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]PbCl3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]PbBr3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]PbI3, [(CH3NH3)x(Cs1-x]PbCl3, [(CH3NH3)xCs1-x]PbBr3, [(CH3NH3)xCs1-x]PbI3, [(H2N—C(H)═NH2)xCs1-x]PbCl3, [(H2N—C(H)═NH2)xCs1-x]PbBr3, [(H2N—C(H)═NH2)xCs1-x]PbI3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]SnCl3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]SnBr3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]SnI3, [(CH3NH3)xCs1-x]SnCl3, [(CH3NH3)xCs1-x]SnBr3, [(CH3NH3)xCs1-x]SnI3, [(H2N—C(H)═NH2)xCs1-x]SnCl3, [(H2N—C(H)═NH2)xCs1-x]SnBr3, and [(H2N—C(H)═NH2)xCs1-x]SnI3, where x is greater than 0 and less than 1, for instance x may be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In one embodiment, the perovskite is a perovskite compound of the formula (IC):
AM[XIyXII1-y]3 (IC)
wherein A and M are as defined above, wherein XI and XII are as defined above in relation to X and wherein y is greater than 0 and less than 1. In a preferred embodiment, A is selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2N—C(NH2)═NH2)+, Cs+ and Rb+; M is Pb2+ or Sn2+; and XI and XII are each selected from Br−, Cl− and I−.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IC) selected from APb[BryI1-y]3, APb[BryCl1-y]3, APb[IyCl1-y]3, ASn[BryI1-y]3, ASn[BryCl1-y]3, ASn[IyCl1-y]3, where y is greater than 0 and less than 1, and wherein A is a cation as described herein. y may be from 0.01 to 0.99. For instance, y may be from 0.05 to 0.95 or 0.1 to 0.9.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IC) selected from CH3NH3Pb[BryI1-y]3, CH3NH3Pb[BryCl1-y]3, CH3NH3Pb[IyCl1-y]3, CH3NH3Sn[BryI1-y]3, CH3NH3Sn[BryCl1-y]3, CH3NH3Sn[IyCl1-y]3, CSPb[BryI1-y]3, CSPb[BryCl1-y]3, CSPb[IyCl1-y]3, CsSn[BryI1-y]3, CsSn[BryCl1-y]3, CsSn[IyCl1-y]3, (H2N—C(H)═NH2)Pb[BryI1-y]3, (H2N—C(H)═NH2)Pb[BryCl1-y]3, (H2N—C(H)═NH2)Pb[IyCl1-y]3, (H2N—C(H)═NH2)Sn[BryI1-y]3, (H2N—C(H)═NH2)Sn[BryCl1-y]3, and (H2N—C(H)═NH2)Sn[IyCl1-y]3, where y is greater than 0 and less than 1, for instance y may be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In a preferred embodiment, the perovskite is a perovskite of the formula (ID):
[AIxAII1-x]M[XIyXII1-y]3 (ID)
wherein AI and AII are as defined above with respect to A, M is as defined above, XI and XII are as defined above in relation to X and wherein x and y are both greater than 0 and less than 1. In a preferred embodiment, AI and AII are each selected from ((CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2N—C(NH2)═NH2)+, Cs+ and Rb+; M is Pb2+ or Sn2+; and XI and XII are each selected from Br−, Cl− and I−.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (ID) selected from (CsxRb1-x)Pb(BryCl1-y)3, (CsxRb1-x)Pb(BryI1-y)3, and (CsxRb1-x)Pb(ClyI1-y)3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[BryCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[IyCl1-y]3, [(CH3NH3)xCs1-x]Pb[BryI1-y]3, [(CH3NH3)xCs1-x]Pb[BryCl1-y]3, [(CH3NH3)xCs1-x]Pb[IyCl1-y]3, [(H2N—C(H)═NH2)xCs1-x]Pb[BryI1-y]3, [(H2N—C(H)═NH2)xCs1-x]Pb[BryCl1-y]3, [(H2N—C(H)═NH2)xCs1-x]Pb[IyCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[BryCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[IyCl1-y]3, [(CH3NH3)xCs1-x]Sn[BryI1-y]3, [(CH3NH3)xCs1-x]Sn[BryCl1-y]3, [(CH3NH3)xCs1-x]Sn[IyCl1-y]3, [(H2N—C(H)═NH2)xCs1-x]Sn[BryI1-y]3, [(H2N—C(H)═NH2)xCs1-x]Sn[BryCl1-y]3, and [(H2N—C(H)═NH2)xCs1-x]Sn[IyCl1-y]3, where x and y are both greater than 0 and less than 1, for instance x and y may both be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In one embodiment, the perovskite is a perovskite of the formula (IE):
A[MIzMII1-z]X3 (IE)
wherein MI and MII are as defined above with respect to M, A and X are as defined above, and wherein z is greater than 0 and less than 1. In a preferred embodiment, A is selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2N—C(NH2)═NH2)+, Cs+ and Rb+; MI is Pb2+ and MII is Sn2+; and X is selected from Br−, Cl− and I−.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IE) selected from CH3NH3[PbzSn1-z]Cl3, CH3NH3[PbzSn1-z]Br3, CH3NH3[PbzSn1-z]I3, Cs[PbzSn1-z]Cl3, Cs[PbzSn1-z]Br3, Cs[PbzSn1-z]I3, (H2N—C(H)═NH2)[PbzSn1-z]Cl3, (H2NC(H)═NH2)[PbzSn1-z]Br3, and (H2NC(H)═NH2)[PbzSn1-z]I3, where z is greater than 0 and less than 1, for instance z may be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In one embodiment, the perovskite is a perovskite of the formula (IF):
[AIxAII1-x][MIzMII1-z]X3 (IF)
wherein AI and AII are as defined above with respect to A, MI and MII are as defined above with respect to M, and X is as defined above and wherein x and z are both greater than 0 and less than 1. In a preferred embodiment, AI and AII are each selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2NC(H)═NH2)+, (H2NC(CH3)═NH2)+, (H2NC(NH2)═NH2)+, Cs+ and Rb+; MI is Pb2+ and MII is Sn2+; and X is selected from Br−, Cl− and I−. AI and AII may for instance be (H2NC(H)═NH2)+ and Cs+ respectively, or they may be (CH3NH3)+ and (H2N—C(H)═NH2)+ respectively. Alternatively, they may be Cs+ and Rb+ respectively.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IF) selected from [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]Cl3, [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]Br3, [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]I3, [(CH3NH3)xCs1-x][PbzSn1-z]Cl3, [(CH3NH3)xCs1-x][PbzSn1-z]Br3, [(CH3NH3)xCs1-x][PbzSn1-z]I3, [(H2NC(H)═NH2)xCs1-x][PbzSn1-z]Cl3, [(H2N—C(H)═NH2)xCs1-x][PbzSn1-z]Br3, [(H2NC(H)═NH2)xCs1-x][PbzSn1-z]I3, where x and z are both greater than 0 and less than 1, for instance x and z may each be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In one embodiment, the perovskite is a perovskite compound of the formula (IG):
A[MIzMII1-z][XIyXII1-y]3 (IG)
wherein A is as defined above, MI and MII are as defined above with respect to M, and wherein XI and XII are as defined above in relation to X and wherein y and z are both greater than 0 and less than 1. In a preferred embodiment, A is selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2NC(H)═NH2)+, (H2NC(CH3)═NH2)+, (H2NC(NH2)═NH2)+, Cs+ and Rb+; MI is Pb2+ and MII is Sn2+; and XI and XII are each selected from Br−, Cl− and I−.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IG) selected from A[PbzSn1-z][BryI1-y]3, A[PbzSn1-z][BryCl1-y]3, A[PbzSn1-z][IyCl1-y]3, where y and z are both greater than 0 and less than 1, and wherein A is a cation as described herein. y and z may each be from 0.01 to 0.99. For instance, y and z may each be from 0.05 to 0.95 or 0.1 to 0.9.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IG) selected from CH3NH3[PbzSn1-z][BryI1-y]3, CH3NH3[PbzSn1-z][BryCl1-y]3, CH3NH3[PbzSn1-z][IyCl1-y]3, Cs[PbzSn1-z][BryI1-y]3, Cs[PbzSn1-z][BryCl1-y]3, Cs[PbzSn1-z][IyCl1-y]3, (H2NC(H)═NH2)[PbzSn1-z][BryI1-y]3, (H2N—C(H)═NH2)[PbzSn1-z][BryCl1-y]3, and (H2NC(H)═NH2)[PbzSn1-z][IyCl1-y]3, where y and z are both greater than 0 and less than 1, for instance y and z may each be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In a preferred embodiment, the perovskite is a perovskite of the formula (IH):
[AIxAII1-x][MIzMII1-z][XIyXII1-y]3 (IH)
wherein AI and AII are as defined above with respect to A, MI and MII are as defined above with respect to M, XI and XII are as defined above in relation to X and wherein x, y and z are each greater than 0 and less than 1. In a preferred embodiment, AI and AII are each selected from ((CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2NC(H)═NH2)+, (H2NC(CH3)═NH2)+, (H2NC(NH2)═NH2)+, Cs+ and Rb+; MI is Pb2+ and MII is Sn2+; and XI and XII are each selected from Br−, Cl− and I−.
For instance, the crystalline A/M/X material may comprise, or consist essentially of, a perovskite compound of formula (IH) selected from [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z][BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z][BryCl1-y]3, (CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z][IyCl1-y]3, [(CH3NH3)xCs1-x][PbzSn1-z][BryI1-y]3, [(CH3NH3)xCs1-x][PbzSn1-z][BryCl1-y]3, [(CH3NH3)xCs1-x][PbzSn1-z][IyCl1-y]3, [(H2N—C(H)═NH2)xCs1-x][PbzSn1-z][BryI1-y]3, [(H2NC(H)═NH2)xCs1-x][PbzSn1-z][BryCl1-y]3, and [(H2NC(H)═NH2)xCs1-x][PbzSn1-z][IyCl1-y]3, where x, y and z are each greater than 0 and less than 1, for instance x, y and z may each be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9.
In one embodiment, a=2, b=1 and c=4. In that embodiment, the crystalline A/M/X material comprises a compound (a “2D layered perovskite”) of formula (II):
[A]2[M][X]4 (II)
wherein: [A] comprises one or more A cations which are monocations; [M] comprises one or more M cations which are metal or metalloid dications; and [X] comprises one or more X anions which are halide anions. In this embodiment, the A and M cations, and the X anions, are as defined above.
In another embodiment, a=2, b=1 and c=6. In that embodiment, the crystalline A/M/X material may in that case comprise a hexahalometallate of formula (III):
[A]2[M][X]6 (III)
wherein: [A] comprises one or more A cations which are monocations; [M] comprises one or more M cations which are metal or metalloid tetracations; and [X] comprises one or more X anions which are halide anions.
The hexahalometallate of formula (III) may in a preferred embodiment be a mixed monocation hexahalometallate. In a mixed monocation hexahalometallate, [A] comprises at least two A cations which are monocations; [M] comprises at least one M cation which is a metal or metalloid tetracation (and typically [M] comprises a single M cation which is a metal or metalloid tetracation); and [X] comprises at least one X anion which is a halide anion (and typically [X] comprises a single halide anion or two types of halide anion). In a mixed metal hexahalometallate, [A] comprises at least one monocation (and typically [A] is a single monocation or two types of monocation); [M] comprises at least two metal or metalloid tetracations (for instance Ge4+ and Sn4+); and [X] comprises at least one halide anion (and typically [X] is a single halide anion or two types of halide anion). In a mixed halide hexahalometallate, [A] comprises at least one monocation (and typically [A] is a single monocation or two types of monocation); [M] comprises at least one metal or metalloid tetracation (and typically [M] is a single metal tetra cation); and [X] comprises at least two halide anions, for instance Br− and Cl− or Br− and I−.
[A] may comprise at least one A monocation selected from any suitable monocations, such as those described above for a perovskite. In the case of a hexahalometallate, each A cation is typically selected from Li+, Na+, K+, Rb+, Cs+, NH4+ and monovalent organic cations. Monovalent organic cations are singly positively charged organic cations, which may, for instance, have a molecular weight of no greater than 500 g/mol. For instance, [A] may be a single A cation which is selected from Li+, Na+, K+, Rb+, Cs+, NH4+ and monovalent organic cations. [A] preferably comprises at least one A cation which is a monocation selected from Rb+, Cs+, NH4+ and monovalent organic cations. For instance, [A] may be a single inorganic A monocation selected from Li+, Na+, K+, Rb+, Cs+ and NH4+. In another embodiment, [A] may be at least one monovalent organic A cation. For instance, [A] may be a single monovalent organic A cation. In one embodiment, [A] is (CH3NH3)+. In another embodiment, [A] is (H2N—C(H)═NH2)+.
Preferably, [A] comprises two or more types of A cation. [A] may be a single A monocation, or indeed two A monocations, each of which is independently selected from K+, Rb+, Cs+, NH4+, (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (N(CH2CH3)4)+, (N(CH2CH2CH3)4)+, (H2N—C(H)═NH2)+ and (H2N—C(CH3)═NH2)+.
[M] may comprise one or more M cations which are selected from suitable metal or metalloid tetracations. Metals include elements of groups 3 to 12 of the Periodic Table of the Elements and Ga, In, Tl, Sn, Pb, Bi and Po. Metalloids include Si, Ge, As, Sb, and Te. For instance, [M] may comprise at least one M cation which is a metal or metalloid tetracation selected from Ti4+, V4+, Mn4+, Fe4+, Co4+, Zr4+, Nb4+, Mo4+, Ru4+, Rh4+, Pd4+, Hf4+, Ta4+, W4+, Re4+, Os4+, Ir4+, Pt4+, Sn4+, Pb4+, Po4+, Si4+, Ge4+, and Te4+. Typically, [M] comprises at least one metal or metalloid tetracation selected from Pd4+, W4+, Re4+, Os4+, Ir4+, Pt4+, Sn4+, Pb4+, Ge4+, and Te4+. For instance, [M] may be a single metal or metalloid tetracation selected from Pd4+, W4+, Re4+, Os4+, Ir4+, Pt4+, Sn4+, Pb4+, Ge4+, and Te4+.
Typically, [M] comprises at least one M cation which is a metal or metalloid tetracation selected from Sn4+, Te4+, Ge4+ and Re4+. In one embodiment [M] comprises at least one M cation which is a metal or metalloid tetracation selected from Pb4+, Sn4+, Te4+, Ge4+ and Re4+. For instance, [M] may comprise an M cation which is at least one metal or metalloid tetracation selected from Pb4+, Sn4+, Te4+ and Ge4+. Preferably, [M] comprises at least one metal or metalloid tetracation selected from Sn4+, Te4+, and Ge4+. As discussed above, the hexahalometallate compound may be a mixed-metal or a single-metal hexahalometallate. Preferably, the hexahalometallate compound is a single-metal hexahalometallate compound. More preferably, [M] is a single metal or metalloid tetracation selected from Sn4+, Te4+, and Ge4+. For instance, [M] may be a single metal or metalloid tetracation which is Te4+. For instance, [M] may be a single metal or metalloid tetracation which is Ge4+. Most preferably, [M] is a single metal or metalloid tetracation which is Sn4+.
[X] may comprise at least one X anion which is a halide anion. [X] therefore comprises at least one halide anion selected from F−, Cl−, Br− and I−. Typically, [X] comprises at least one halide anion selected from Cl−, Br− and I−. The hexahalometallate compound may be a mixed-halide hexahalometallate or a single-halide hexahalometallate. If the hexahalometallate is mixed, [X] comprises two, three or four halide anions selected from F−, Cl−, Br− and I−. Typically, in a mixed-halide compound, [X] comprises two halide anions selected from F−, Cl−, Br− and I−.
In some embodiments, [A] is a single monocation and [M] is a single metal or metalloid tetracation. Thus, the crystalline A/M/X material may, for instance, comprise a hexahalometallate compound of formula (IIIA)
A2M[X]6 (IIIA)
wherein: A is a monocation; M is a metal or metalloid tetracation; and [X] is at least one halide anion. [X] may be one, two or three halide anions selected from F−, Cl−, Br− and I−, and preferably selected from Cl−, Br− and I−. In formula (IIIA), [X] is preferably one or two halide anions selected from Cl−, Br− and I−.
The crystalline A/M/X material may, for instance, comprise, or consist essentially of, a hexahalometallate compound of formula (IIIB)
A2MX6-yX′y (IIIB)
wherein: A is a monocation (i.e. the second cation); M is a metal or metalloid tetracation (i.e. the first cation); X and X′ are each independently a (different) halide anion (i.e. two second anions); and y is from 0 to 6. When y is 0 or 6, the hexahalometallate compound is a single-halide compound. When y is from 0.01 to 5.99 the compound is a mixed-halide hexahalometallate compound. When the compound is a mixed-halide compound, y may be from 0.05 to 5.95. For instance, y may be from 1.00 to 5.00.
The hexahalometallate compound may, for instance, be A2SnF6-yCly, A2SnF6-yBry, A2SnF6-yIy, A2SnCl6-yBry, A2SnCl6-yIy, A2SnBr6-yIy, A2TeF6-yCly, A2TeF6-yBry, A2TeF6-yIy, A2TeCl6-yBry, A2TeCl6-yIy, A2TeBr6-yIy, A2GeF6-yCly, A2GeF6-yBry, A2GeF6-yIy, A2GeCl6-yBry, A2GeCl6-yIy, A2GeBr6-yIy, A2ReF6-yCly, A2ReF6-yBry, A2ReF6-yIy, A2ReCl6-yBry, A2ReCl6-yIy or A2ReBr6-yIy, wherein: A is K+, Rb+, Cs+, (R1NH3)+, (NR24)+, or (H2N—C(R1)═NH2)+, wherein R1 is H, a substituted or unsubstituted C1-20 alkyl group or a substituted or unsubstituted aryl group, and R2 is a substituted or unsubstituted C1-10 alkyl group; and y is from 0 to 6. Optionally, y is from 0.01 to 5.99. If the hexahalometallate compound is a mixed-halide compound, y is typically from 1.00 to 5.00. A may be as defined above. For instance, A may be Cs+, NH4+, (CH3NH3)+, (CH3CH2NH3)+, (N(CH3)4)+, (N(CH2CH3)4)+, (H2N—C(H)═NH2)+ or (H2N—C(CH3)═NH2)+, for instance Cs+, NH4+, or (CH3NH3)+.
The hexahalometallate compound may typically be A2SnF6-yCly, A2SnF6-yBry, A2SnF6-yIy, A2SnCl6-yBry, A2SnCl6-yIy, or A2SnBr6-yIy, wherein: A is K+, Rb+, Cs+, (R1NH3)+, (NR24)+, or (H2N—C(R1)═NH2)+, or A is as defined herein, wherein R1 is H, a substituted or unsubstituted C1-20 alkyl group or a substituted or unsubstituted aryl group, or R2 is a substituted or unsubstituted C1-10 alkyl group; and y is from 0 to 6.
In another embodiment, the hexahalometallate compound is A2GeF6-yCly, A2GeF6-yBry, A2GeF6-yIy, A2GeCl6-yBry, A2GeCl6-yIy, or A2GeBr6-yIy, wherein: A is K+, Rb+, Cs+, (R1NH3)+, (NR24)+, or (H2N—C(R1)═NH2)+, or A is as defined herein, wherein R1 is H, a substituted or unsubstituted C1-20 alkyl group or a substituted or unsubstituted aryl group, and R2 is a substituted or unsubstituted C1-10 alkyl group; and y is from 0 to 6.
The hexahalometallate compound may, for instance, be A2TeF6-yCly, A2TeF6-yBry, A2TeF6-yIy, A2TeCl6-yBry, A2TeCl6-yIy, or A2TeBr6-yIy, wherein: A is K+, Rb+, Cs+, (R1NH3)+, (NR24)+, or (H2N—C(R1)═NH2)+, or A is as defined herein, wherein R1 is H, a substituted or unsubstituted C1-20 alkyl group or a substituted or unsubstituted aryl group, and R2 is a substituted or unsubstituted C1-10 alkyl group; and y is from 0 to 6 or y is as defined herein.
Often, y will be from 1.50 to 2.50. For instance, y may be from 1.80 to 2.20. This may occur if the compound is produced using two equivalents of AX′ and one equivalent of MX4, as discussed below.
In some embodiments, all of the ions are single anions or cations. Thus, the crystalline A/M/X material may comprise, or consist essentially of, a hexahalometallate compound of formula (IIIC)
A2MX6 (IlIC)
wherein: A is a monocation; M is a metal or metalloid tetracation; and X is a halide anion. A, M and X may be as defined herein.
The hexahalometallate compound may be A2SnF6, A2SnCl6, A2SnBr6, A2SnI6, A2TeF6, A2TeCl6, A2TeBr6, A2TeI6, A2GeF6, A2GeCl6, A2GeBr6, A2GeI6, A2ReF6, A2ReCl6, A2ReBr6 or A2ReI6, wherein: A is K+, Rb+, Cs+, (R1NH3)+, (NR24)+, or (H2N—C(R1)═NH2)+, wherein R1 is H, a substituted or unsubstituted C1-20 alkyl group or a substituted or unsubstituted aryl group, and R2 is a substituted or unsubstituted C1-10 alkyl group. A may be as defined herein. Preferably, the hexahalometallate compound is Cs2SnI6, Cs2SnBr6, Cs2SnBr6-yIy, Cs2SnCl6-yIy, Cs2SnCl6-yBry, (CH3NH3)2SnI6, (CH3NH3)2SnBr6, (CH3NH3)2SnBr6-yIy, (CH3NH3)2SnCl6- yIy, (CH3NH3)2SnCl6-yBry, (H2N—C(H)═NH2)2SnI6, (H2N—C(H)═NH2)2SnBr6, (H2N—C(H)═NH2)2SnBr6-yIy, (H2N—C(H)═NH2)2SnCl6-yIy or (H2N—C(H)═NH2)2SnCl6-yBry wherein y is from 0.01 to 5.99. For example, the hexahalometallate compound may be (CH3NH3)2SnI6, (CH3NH3)2SnBr6, (CH3NH3)2SnCl6, (H2N—C(H)═NH2)2SnI6, (H2N—C(H)═NH2)2SnBr6 or (H2N—C(H)═NH2)2SnCl6. The hexahalometallate compound may be Cs2SnI6, Cs2SnBr6, Cs2SnCl6-yBry, (CH3NH3)2SnI6, (CH3NH3)2SnBr6, or (H2N—C(H)═NH2)2SnI6.
The crystalline A/M/X material may comprise a bismuth or antimony halogenometallate. For instance, the crystalline A/M/X material may comprise a halogenometallate compound comprising: (i) one or more monocations ([A]) or one or more dications ([B]); (ii) one or more metal or metalloid trications ([M]); and (iii) one or more halide anions ([X]). The compound may be a compound of formula BBiX5, B2BiX7 or B3BiX9 where B is (H3NCH2NH3)2+, (H3N(CH2)2NH3)2+, (H3N(CH2)3NH3)2+, (H3N(CH2)4NH3)2+, (H3N(CH2)5NH3)2+, (H3N(CH2)6NH3)2+, (H3N(CH2)7NH3)2+, (H3N(CH2)8NH3)2+ or (H3N—C6H4—NH3)2+ and X is I−, Br− or Cl−, preferably I−.
In yet further embodiments, the crystalline A/M/X materials may be double perovskites. Such compounds are defined in WO 2017/037448, the entire contents of which is incorporated herein by reference. Typically, the compound is a double perovskite compound of formula (IV):
[A]2[B+][B3+][X]6 (IV);
wherein: [A] comprises one or more A cations which are monocations, as defined herein; [B+] and [B3+] are equivalent to [M] where M comprises one or more M cations which are monocations and one or more M cations which are trications; and [X] comprises one or more X anions which are halide anions.
The one or more M cations which are monocations comprised in [B+] are typically selected from metal and metalloid monocations. Preferably, the one or more M cations which are monocations are selected from Li+, Na+, K+, Rb+, Cs+, Cu+, Ag+, Au+ and Hg+. More preferably, the one or more M cations which are monocations are selected from Cu+, Ag+ and Au+. Most preferably, the one or more M cations which are monocations are selected from Ag+ and Au+. For instance, [B+] may be one monocation which is Ag+ or [B+] may be one monocation which is Au+.
The one or more M cations which are trications comprised in [B3+] are typically selected from metal and metalloid trications. Preferably, the one or more M cations which are trications are selected from Bi3+, Sb+, Cr3+, Fe3+, Co3+, Ga3+, As3+, Ru3+, Rh3+, In3+, Ir3+ and Au3+. More preferably, the one or more M cations which are trications are selected from Bi3+ and Sb3+. For instance, [B3+] may be one trication which is Bi3+ or [B3+] may be one trication which is Sb3+. Bismuth has relatively low toxicity compared with heavy metals such as lead. In some embodiments, the one or more M cations which are monocations (in [B+]) are selected from Cu+, Ag+ and Au+ and the one or more M cations which are trications (in [B3+]) are selected from Bi3+ and Sb3+.
An exemplary double perovskite is Cs2BiAgBr6.
Typically, where the compound is a double perovskite it is a compound of formula (IVa):
A2B+B3+[X]6 (IVa);
wherein: the A cation is as defined herein; B+ is an M cation which is a monocation as defined herein; B3+ is an M cation which is a trication as defined herein; and [X] comprises one or more X anions which are halide anions, for instance two or more halide anions, preferably a single halide anion.
In yet another embodiment, the compound may be a layered double perovskite compound of formula (V):
[A]4[B+][B3+][X]8 (V);
wherein: [A], [B+], [B3+] and [X] are as defined above. In some embodiments, the layered double perovskite compound is a double perovskite compound of formula (Va):
A4B+B3+[X]8 (Va);
wherein: the A cation is as defined herein; B+ is an M cation which is a monocation as defined herein; B3+ is an M cation which is a trication as defined herein; and [X] comprises one or more X anions which are halide anions, for instance two or more halide anions, preferably a single halide anion or two kinds of halide anion.
In yet another embodiment, the compound may be a compound of formula (VI):
[A]4[M][X]6 (VI);
wherein: [A], [M] and [X] are as defined above (in relation to, for instance, compounds of formula (I) or (II)). However, preferably the compound is not a compound of formula (VI). Where the compound is a compound of formula (VI), the compound may preferably be a compound of formula (VIA)
[AIAII]4[M][X]6 (VIA);
that is, a compound wherein [A] comprises two types of A monoacation. In other preferred embodiments, the compound of formula (VI) may be a compound of formula (VIB):
[A]4[M][XIXII]6 (VIB);
that is, a compound of formula (VI) wherein [X] comprises two types of X anion. In yet other preferred embodiments, the compound of formula (VI) may be a compound of formula (VIC):
[AIAII]4[M][XIXII]6 (VIC);
that is, a compound of formula (VI) wherein [A] comprises two types of A monoacation and [X] comprises two types of X anion. In formulae (VIa), (VIb) and (VIc), each of: [A], [M] and [X] are as defined above (in relation to, for instance, compounds of formula (I) or (II)).
In another embodiment, a=1, b=1 and c=4. In that embodiment, the crystalline A/M/X material may in that case comprise a compound of formula (VII):
[A][M][X]4 (VII)
wherein: [A] comprises one or more A cations which are monocations; [M] comprises one or more M cations which are metal or metalloid trications; and [X] comprises one or more X anions which are halide anions. The A monocations and M trications are as defined herein. An exemplary compound of formula (VII) is AgBiI4.
It should be understood that the invention also encompasses processes for producing variants of the above-described structures (I), (II), (III), (IV), (V), (VI) and (VII) where one or more of the relevant a, b and c values are non-integer values.
Preferably, the compound of formula [A]a[M]b[X]c is a compound of formula [A][M][X]3, a compound of formula [A]4[M][X]6 or a compound of formula [A]2[M][X]6. For example, in preferred embodiments the compound of formula [A]a[M]b[X]c is a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), or a compound of formula (IIIB), (IIIC), (VIA), (VIB), or (VIC). Generally, the compound of formula [A]a[M]b[X]c is a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH).
In some embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [A] comprises two or more different A cations. For examples, [A] may contain two types of cation. In some embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [X] comprises two or more different X anions. For example, [X] may contain two types of anion, e.g. halide anions. In some embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [M] comprises two or more different M cations. For example, [X] may contain two types of anion, e.g. Sn2+ and Pb2+.
In one aspect of each of these embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [A] comprises two or more different A cations and wherein [X] comprises two or more different X anions. For example, [A] may contain two types of A cation and [X] may contain two types of X anion (e.g. two types of halide anion).
In one aspect of each of these embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [A] comprises two or more different A cations and wherein [M] comprises two or more different M cations. For example, [A] may contain two types of A cation and [M] may contain two types of M cation (e.g. Sn2+ and Pb2+).
In one aspect of each of these embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [X] comprises two or more different X anions and wherein [M] comprises two or more different M cations. For example, [X] may contain two types of X anion (e.g. two types of halide anion) and [M] may contain two types of M cation (e.g. Sn2+ and Pb2+).
In one aspect of each of these embodiments, the compound of formula [A]a[M]b[X]c is a compound wherein [A] comprises two or more different A cations and wherein [X] comprises two or more different X anions and wherein [M] comprises two or more different M cations. For example, [A] may contain two types of A cation, [X] may contain two types of X anion (e.g. two types of halide anion) and [M] may contain two types of M cation (e.g. Sn2+ and Pb2+).
The substrate may comprise one or more further layers. For instance, the substrate may further comprise a layer of a charge transporting material. Preferably the layer of a charge transporting material is disposed on the charge recombination layer. Typically, the layer of a charge transporting material is disposed directly on the charge recombination layer. Alternatively, there may be an intervening layer between the layer of a charge transporting material and the charge recombination layer. Hence, the substrate may comprise the following layers in the following order:
Typically, the layer of a crystalline A/M/X material is disposed directly on the layer of a charge transporting material. Alternatively, there may be is an intervening layer between the layer of a charge transporting material and the layer of a crystalline A/M/X material. Typically, the layer of a charge transporting material is disposed directly on the charge recombination layer, and the layer of a crystalline A/M/X material is disposed directly on the layer of a charge transporting material. Hence, the multi-junction device produced according to the present invention may comprise a the following layers in the following order:
In one embodiment, the layer of a charge transporting material is a layer of an electron transporting (n-type) material. In another embodiment, the layer of a charge transporting material is a layer of a hole transporting (p-type) material. Typically, the layer of a charge transporting material is a layer of an electron transporting (n-type) material.
Typically, the charge transporting material is soluble in dimethylformamide. Thus, the charge transporting material may be soluble in dimethylformamide (DMF), dimethysulfoxide (DMSO) or a mixture thereof.
Typically, the layer of a charge transporting material has a thickness of less than 1000 nm, or less than 500 nm, or less than 250 nm, preferably less than 100 nm. For instance, the layer of a charge transporting material may have a thickness of from 1 to 500 nm, for instance from 5 to 250 nm, or from 10 to 75 nm.
Examples of electron transporting (n-type) materials are known to the skilled person. A suitable n-type material may be an organic or inorganic material. A suitable inorganic n-type material may be selected from a metal oxide, a metal sulphide, a metal selenide, a metal telluride, a perovskite, amorphous Si, an n-type group IV semiconductor, an n-type group III-V semiconductor, an n-type group II-VI semiconductor, an n-type group I-VII semiconductor, an n-type group IV-VI semiconductor, an n-type group V-VI semiconductor, and an n-type group II-V semiconductor, any of which may be doped or undoped. More typically, the n-type material is selected from a metal oxide, a metal sulphide, a metal selenide, and a metal telluride.
Thus, the n-type layer may comprise an inorganic material selected from oxide of titanium, tin, zinc, niobium, tantalum, tungsten, indium, gallium, neodymium, palladium, or cadmium, or an oxide of a mixture of two or more of said metals. For instance, the n-type layer may comprise TiO2, SnO2, ZnO, Nb2O5, Ta2O5, WO3, W2O5, In2O3, Ga2O3, Nd2O3, PbO, or CdO. Other suitable n-type materials that may be employed include sulphides of cadmium, tin, copper, or zinc, including sulphides of a mixture of two or more of said metals. For instance, the sulphide may be FeS2, CdS, ZnS, SnS, BiS, SbS, or Cu2ZnSnS4.
The n-type layer may for instance comprise a selenide of cadmium, zinc, indium, or gallium or a selenide of a mixture of two or more of said metals; or a telluride of cadmium, zinc, cadmium or tin, or a telluride of a mixture of two or more of said metals. For instance, the selenide may be Cu(In,Ga)Se2. Typically, the telluride is a telluride of cadmium, zinc, cadmium or tin. For instance, the telluride may be CdTe.
The n-type layer may for instance comprise an inorganic material selected from oxide of titanium (e.g. TiO2), tin (e.g. SnO2), zinc (e.g. ZnO), niobium, tantalum, tungsten, indium, gallium, neodymium, palladium, cadmium, or an oxide of a mixture of two or more of said metals; a sulphide of cadmium, tin, copper, zinc or a sulphide of a mixture of two or more of said metals; a selenide of cadmium, zinc, indium, gallium or a selenide of a mixture of two or more of said metals; or a telluride of cadmium, zinc, cadmium or tin, or a telluride of a mixture of two or more of said metals.
Examples of other semiconductors that may be suitable n-type materials, for instance if they are n-doped, include group IV elemental or compound semiconductors; amorphous Si; group III-V semiconductors (e.g. gallium arsenide); group II-VI semiconductors (e.g. cadmium selenide); group I-VII semiconductors (e.g. cuprous chloride); group IV-VI semiconductors (e.g. lead selenide); group V-VI semiconductors (e.g. bismuth telluride); and group II-V semiconductors (e.g. cadmium arsenide).
Other n-type materials may also be employed, including organic and polymeric electron-transporting materials, and electrolytes. Suitable examples include, but are not limited to a fullerene or a fullerene derivative (for instance C60, C70, phenyl-C61-butyric acid methyl ester (PCBM), PC71BM (i.e. phenyl C71 butyric acid methyl ester), bis[C60]BM (i.e. bis-C60 butyric acid methyl ester), and 1′,1″,4′,4″-Tetrahydro-di[1,4]methanonaphthaleno[1,2:2′,3′,56,60:2″,3″][5,6]fullerene-C60 (ICBA)), an organic electron transporting material comprising perylene or a derivative thereof, or poly{[N,N0-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,50-(2,20-bithiophene)} (P(NDI2OD-T2)).
Preferably, the n-type material is phenyl-C61-butyric acid methyl ester (PCBM).
Examples of hole transporting (p-type) materials are known to the skilled person. The p-type material may be a single p-type compound or elemental material, or a mixture of two or more p-type compounds or elemental materials, which may be undoped or doped with one or more dopant elements.
The p-type material may comprise an inorganic or an organic p-type material. Typically, the p-type material is an organic p-type material.
Suitable p-type materials may be selected from polymeric or molecular hole transporters. The p-type material may for instance comprise spiro-OMeTAD (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene)), P3HT (poly(3-hexylthiophene)), PCPDTBT (Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]]), PVK (poly(N-vinylcarbazole)), HTM-TFSI (1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), Li-TFSI (lithium bis(trifluoromethanesulfonyl)imide), spiro-OMETAD+-bis(trifluoromethanesulfonyl)imide-(spiro(TFSI)2), tBP (tert-butylpyridine), m-MTDATA (4,4′,4″-tris(methylphenylphenylamino)triphenylamine), MeOTPD (N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine), BP2T (5,5′-di(biphenyl-4-yl)-2,2′-bithiophene), Di-NPB (N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine), α-NPB (N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine), TNATA (4,4′,4″-tris-(N-(naphthylen-2-yl)-N-phenylamine)triphenylamine), BPAPF (9,9-bis[4-(N,N-bis-biphenyl-4-yl-amino)phenyl]-9H-fluorene), spiro-NPB (N2,N7-Di-1-naphthalenyl-N2,N7-diphenyl-9,9′-spirobi[9H-fluorene]-2,7-diamine), 4P-TPD (4,4-bis-(N,N-diphenylamino)-tetraphenyl), polyTPD (i.e. Poly[N,N′-bis(4-butylphenyl)-N,N′-bisphenylbenzidine]), PTAA (i.e. poly(triaryl amine), also known as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) or PEDOT:PSS. The p-type material may comprise carbon nanotubes. Usually, the p-type material is selected from spiro-OMeTAD, P3HT, PCPDTBT, spiro(TFSI)2 and PVK. Preferably, the p-type material is spiro-OMeTAD or spiro(TFSI)2.
Suitable p-type materials also include molecular hole transporters, polymeric hole transporters and copolymer hole transporters. The p-type material may for instance be a molecular hole transporting material, a polymer or copolymer comprising one or more of the following moieties: thiophenyl, phenelenyl, dithiazolyl, benzothiazolyl, diketopyrrolopyrrolyl, ethoxydithiophenyl, amino, triphenyl amino, carbozolyl, ethylene dioxythiophenyl, dioxythiophenyl, or fluorenyl.
The p-type material may be doped, for instance with tertbutyl pyridine and LiTFSI. The p-type material may be doped to increase the hole-density. The p-type material may for instance be doped with NOBF4 (Nitrosonium tetrafluoroborate), to increase the hole-density.
In other embodiments, the p-type layer may comprise an inorganic hole transporter. For instance, the p-type layer may comprise an inorganic hole transporter comprising an oxide of nickel (e.g. NiO), vanadium, copper or molybdenum; CuI, CuBr, CuSCN, Cu2O, CuO or CIS; a perovskite; amorphous Si; a p-type group IV semiconductor, a p-type group III-V semiconductor, a p-type group II-VI semiconductor, a p-type group I-VII semiconductor, a p-type group IV-VI semiconductor, a p-type group V-VI semiconductor, and a p-type group II-V semiconductor, which inorganic material may be doped or undoped. The p-type layer may be a compact layer of said inorganic hole transporter.
The p-type material may be an inorganic p-type material, for instance a material comprising an oxide of nickel, vanadium, copper or molybdenum; CuI, CuBr, CuSCN, Cu2O, CuO or CIS; amorphous Si; a p-type group IV semiconductor, a p-type group III-V semiconductor, a p-type group II-VI semiconductor, a p-type group I-VII semiconductor, a p-type group IV-VI semiconductor, a p-type group V-VI semiconductor, and a p-type group II-V semiconductor, which inorganic material may be doped or undoped. The p-type material may for instance comprise an inorganic hole transporter selected from CuI, CuBr, CuSCN, Cu2O, CuO and CIS.
In one embodiment, the invention comprises a step forming the substrate by disposing a layer of a charge transporting material as described herein on the charge recombination layer. Typically, a composition comprising a the charge transporting material is disposed on the charge recombination layer, preferably a solution comprising the charge transporting material. The solution is comprising the charge transporting material is typically disposed on the charge recombination layer by solution phase deposition, for instance gravure coating, slot dye coating, screen printing, ink jet printing, doctor blade coating, spray coating, roll-to-roll (R2R) processing, or spin-coating, preferably by spin-coating.
Typically, the solvent in the solution comprising the charge transporting is selected from chlorobenzene, chloroform, anisole, toluene, tetrahydrofuran, xylene or mixtures thereof. For instance, the step forming the substrate by disposing a layer of a charge transporting material on the charge recombination layer may comprise:
The process of the present invention may further comprise a step of producing the substrate by disposing the charge recombination layer on the photoactive region by solution deposition.
Typically, the charge recombination layer comprises nanoparticles of a transparent conducting oxide. The nanoparticles create ohmic contact between both electron and hole transporting layers thus allowing for efficient charge transfer into the recombination layer. Further, such nanoparticles are easily processed using solution-based methods to form the substrate.
The nanoparticles of the transparent conducting oxide may comprise indium zinc oxide (IZO), indium tin oxide (ITO), aluminium zinc oxide (AZO), indium cadmium oxide, fluorine doped tin oxide (FTO), antimony doped tin oxide, antimony doped titanium dioxide, niobium doped tin oxide, niobium doped titanium dioxide, barium stannate, strontium vanadate, and calcium vanadate. Preferably, the nanoparticles of the transparent conducting oxide comprises indium tin oxide (ITO). Therefore, the nanoparticles of a transparent conducting oxide may be nanoparticles of indium tin oxide. Preferably, the nanoparticles of a transparent conducting oxide are nanoparticles of indium tin oxide having a size less than 500 nm, preferably less than 250 nm, more preferably less than 100 nm. Typically the size of the nanoparticles can be determined by dynamic light scattering within solution, or transmission electron microscopy of dried films.
The nanoparticles of the transparent conducting oxide may be disposed in a matrix material. The matrix material may be an inorganic or organic matrix material. It is often a dielectric matrix material, for instance an inorganic or organic dielectric matrix material. Alternatively, it may be an electron-transporting matrix material. Usually, the matrix material is an organic matrix material. Typically, the organic matrix material is an electron-transporting organic matrix material. Suitable examples include, but are not limited to a fullerene or a fullerene derivative (for instance C60 or Phenyl-C61-butyric acid methyl ester (PCBM)), an organic electron transporting material comprising perylene or a derivative thereof, or poly{[N,N0-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,50-(2,20-bithiophene)} (P(NDI2OD-T2)). Preferably, the organic matrix material comprises [6,6]-phenyl-C61-butyric acid methyl ester (PCBM).
Typically, the charge recombination layer further comprises a conducting polymer. For instance, the charge recombination layer may comprise p-doped polyTPD, Poly triarylamine (PTAA), polythiophene. Typically, the conducting polymer comprises poly(3,4-ethylenedioxythiophene) (PEDOT) or a derivative thereof. For instance, the conducting polymer may comprise poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) or poly(3,4-ethylenedioxythiophene)-tetramethacrylate (PEDOT:TMA). Preferably the conducting polymer comprises poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS).
The charge recombination layer may comprise nanoparticles of a transparent conducting oxide and a conducting polymer. For instance the charge recombination layer may comprise indium tin oxide (ITO) nanoparticles and poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS). The nanoparticles of a transparent conducting oxide may be evenly distributed in the conducting polymer of the charge recombination layer. Alternatively, the nanoparticles of a transparent conducting oxide and the conducting polymer may form two distinct sub-layers within the charge recombination layer.
Typically, the charge recombination layer has a thickness of less than 1000 nm, for instance less than 750 nm, less than 250 nm, preferably less than 100 nm. For instance, the charge recombination layer may have a thickness of from 5 to 500 nm, from 10 to 250 nm, from 20 to 150 nm, preferably from 25 to 125 nm. In some embodiments, for instance when the charge recombination layer is a tunnel junction, the charge recombination layer has a thickness of less than 50 nm, for instance less than 30 nm, for example less than or equal to 20 nm, or for instance less than or equal to 10 nm.
The charge recombination layer may be a tunnel junction. A tunnel junction is generally a very thin film, for instance a film having a thickness of less than or equal to 20 nm, for instance less than or equal to 10 nm. The film typically comprises a very thin layer of a highly-doped n-type material interfaced with a very thin layer of a highly-doped p-type material. This enables charges to tunnel through the junction.
Accordingly, in one embodiment, the charge recombination layer is a tunnel junction. Typically, the tunnel junction has a thickness of less than 30 nm, for instance less than or equal to 20 nm, or less than or equal to 10 nm. The tunnel junction typically comprises, and more typically consists of, a first sub-layer disposed on a second sub-layer, wherein one of the first and second sub-layers is an n-type material and the other of the first and second sub-layers is a p-type material. The n-type material may comprise any of the n-type materials described herein. The n-type material is generally doped with a dopant. The p-type material may comprise any of the p-type materials described herein. Generally, the p-type material is doped with a dopant. Dopants for doping n- and p-type materials in tunnel junctions are known in the art.
Typically, disposing the charge recombination layer on the photoactive region comprises a step of disposing a solvent dispersion of nanoparticles of a transparent conducting oxide on the photoactive region.
Typically, the solvent is chosen to be orthogonal to those used for the underlying layers, for instance the photoactive region and/or the charge transporting layer, if present. A solvent is orthogonal to another solvent when it does not dissolve the layer of material deposited from the other solvent. For instance, the solvent may be a polar solvent, for instance a polar protic solvent such as an alcohol. It may for instance be isopropanol (2-propanol), methanol, or ethanol. It may be a polar aprotic solvent, for instance, acetone, acetonitrile, methylethylketone.
Typically, the solvent dispersion of nanoparticles of a transparent conducting oxide is a dispersion of indium tin oxide nanoparticles in isopropanol.
Typically, the indium tin oxide nanoparticles comprise less than 75 weight % of the solvent dispersion (total weight of solvent plus nanoparticles), for instance less than 50 weight % of the solvent dispersion. For instance, the indium tin oxide nanoparticles may comprise between 0.001 and 50 weight % of the solvent dispersion, between 0.1 and 10 weight % of the solvent dispersion, between 0.5 and 5 weight % of the solvent dispersion, preferably about 1 weight % of the solvent dispersion.
The solvent dispersion of nanoparticles of a transparent conducting oxide may be disposed on the photoactive region by roll-to-roll (R2R) processing, blade coating, inkjet printing or spin-coating. Typically, the solvent dispersion of nanoparticles of a transparent conducting oxide is disposed on the photoactive region by spin-coating. In one embodiment, the solvent dispersion of nanoparticles of a transparent conducting oxide is spin-coated directly onto the photoactive region. Typically, the spin coating is performed at a speed of at least 1000 RPM, for instance at least 2000 RPM, at least 3000 RPM, at least 4000 RPM or at least 5000 RPM, for example between 2000 and 10000 RPM, between 4000 and 8000 RPM preferably about 6000 RPM. Typically, the spin coating is performed for a time of at least one second, at least 5 seconds or at least 10 seconds, for example from 1 second to 1 minute, from 10 seconds to 30 seconds, preferably about 20 seconds.
Thus, the step of producing the substrate by disposing the charge recombination layer on the photoactive region by solution deposition may comprise spin coating a solvent dispersion of indium tin oxide nanoparticles in isopropanol on to the substrate (photoactive region) at a speed of about 6000 RPM for about 20 seconds.
The charge recombination layer may further comprise a matrix material. The matrix material may be an inorganic or organic matrix material. It may be a dielectric matrix material, for instance an inorganic or organic dielectric matrix material. It is often however an electron-transporting matrix material. Usually, the matrix material is an organic matrix material, as described herein. Accordingly, the solvent dispersion of nanoparticles may further comprise a matrix material, for instance an organic matrix material, as described herein. The matrix material may for instance be a dielectric matrix material, or it may be an electron-transporting matrix material. The matrix material may be organic or inorganic, but is typically organic, for instance an organic electron-transporting matrix material. Disposing the charge recombination layer on the photoactive region may comprise disposing a solvent dispersion of nanoparticles of a transparent conducting oxide and the matrix material, e.g. an organic matrix material, on the photoactive region.
The matrix material and the nanoparticles may be disposed together (e.g. as described above) or separately, in the process of the invention. When they are disposed separately, one option is first to dispose the nanoparticles, e.g. as a solvent dispersion of the nanoparticles, and subsequently to dispose the matrix material, e.g. as a solution or dispersion of the matrix material in a solvent. The matrix material may then percolate into the disposed nanoparticles such that the nanoparticles are dispersed in the matrix material.
When a conducting polymer is present in the charge recombination layer, disposing the charge recombination layer on the photoactive region may comprise disposing a conducting polymer as described above on the photoactive region, and disposing a solvent dispersion of nanoparticles of a transparent conducting oxide on the photoactive region. Preferably, the conducting polymer comprises poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS). Typically, the conducting polymer is dispersed in a solvent. For example, the conducting polymer may be dispersed in an alcohol, water, a mixture of one or more alcohols and water, or a mixture of alcohols, for instance it may be dispersed in isopropanol (2-propanol), ethanol (EtOH), methanol (MeOH), or water or a mixture thereof. Thus, disposing the charge recombination layer on the photoactive region may comprise disposing a dispersion of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) in isopropanol (2-propanol), ethanol (EtOH), methanol (MeOH), water or a mixture thereof on the photoactive region.
The conducting polymer may be disposed on the photoactive region by roll-to-roll (R2R) processing, blade coating, inkjet printing or spin-coating. Usually, the conducting polymer is disposed on the photoactive region by spin-coating. In one embodiment, the conducting polymer is spin-coated directly onto the photoactive region. Typically, the spin coating is performed at a speed of at least 1000 RPM, for instance at least 2000 RPM, at least 3000 RPM, at least 4000 RPM or at least 5000 RPM, for example between 2000 and 10000 RPM, between 4000 and 8000 RPM preferably about 6000 RPM. Typically, the spin coating is performed for a time of at least one second, at least 5 seconds or at least 10 seconds, for example from 1 second to 1 minute, from 10 seconds to 30 seconds, preferably about 20 seconds.
Typically, disposing the charge recombination layer on the photoactive region comprises two steps:
Typically, both the solvent dispersion of the nanoparticles and the conducting polymer are disposed on the photoactive region by spin-coating. The steps of spin-coating the solvent dispersion of the nanoparticles and (if present) the conducting polymer on the photoactive region may be combined with one or more annealing steps. Typically, the annealing is performed at a temperature of at least 20° C., for instance temperature in the range of 20 to 150° C., for instance 30 to 120° C., 40 to 110° C., 60 to 100° C., 70 to 90° C., preferably about 80° C. Typically the annealing is performed for a period of from 1 to 120 minutes, for instance from 2 to 60 minutes, 3 to 45 minutes, 4 to 30 minutes, from 5 to 15 minutes or about 10 minutes. Thus, the annealing may be performed at a temperature of 20 to 150° C. for a period of from 1 to 120 minutes, for instance at a temperature of 60 to 100° C. for a period of from 4 to 30 minutes, preferably at about 80° C. for about 10 minutes.
In one embodiment, disposing the charge recombination layer on the photoactive region comprises the following steps:
Disposing the charge recombination layer on the photoactive region may comprise simultaneously disposing a conducting polymer and disposing a solvent dispersion of nanoparticles of a transparent conducting oxide on the photoactive region. For instance, the conducting polymer and the nanoparticles of a transparent conducting oxide may be present in the same solvent dispersion. The dispersion comprising the conducting polymer and the nanoparticles of a transparent conducting oxide may be disposed on the photoactive region by spin coating, as described above.
The photoactive material in the photoactive region in the substrate may comprise any suitable photoactive material known to the skilled person. For instance, the photoactive material in the photoactive region may comprise silicon, Cu(In,Ga)Se2 (CIGS), Cu2ZnSn(S,Se)4 (CZTSSe), CuInS (CIS) metal chalcogenide nanocrystals such as PbS, PbSe or PbS1-xSex, chalcogenide thin films such as CdTe, or CdTe1-xSex, or CdTe1-xSx, or a crystalline A/M/X material. Typically, the photoactive material in the photoactive region in the substrate comprises a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c as described herein.
For instance, the photoactive material in the photoactive region may comprise a compound of formula [A]a[M]b[X]c, wherein said compound is a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein. Typically, the photoactive material in the photoactive region comprises a compound of formula [A]a[M]b[X]c, wherein said compound is a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH).
For instance, the photoactive material in the photoactive region may comprise a compound of formula (IA):
AMX3 (IA)
wherein A, M and X are as defined above. In a preferred embodiment, A is selected from (CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2N—C(NH2)═NH2)+, Cs+ and Rb+; M is Pb2+ or Sn2+ and X is selected from Br−, Cl− and I−.
For instance, the photoactive material in the photoactive region may comprise, or consist essentially of, a perovskite compound of formula (IA) selected from APbI3, APbBr3, APbCl3, ASnI3, ASnBr3 and ASnCl3, wherein A is a cation as described herein.
For instance, the photoactive material in the photoactive region may comprise, or consist essentially of, a perovskite compound of formula (IA) selected from CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, CsPbI3, CsPbBr3, CsPbCl3, CsSnI3, CsSnBr3, CsSnCl3, (H2N—C(H)═NH2)PbI3, (H2N—C(H)═NH2)PbBr3, (H2N—C(H)═NH2)PbCl3, (H2N—C(H)═NH2)SnI3, (H2N—C(H)═NH2)SnBr3 and (H2N—C(H)═NH2)SnCl3, in particular CH3NH3PbI3 or CH3NH3PbBr3, preferably CH3NH3PbI3.
For instance, the photoactive material in the photoactive region may comprise a compound of formula (ID):
[AIxAII1-x]M[XIyXII1-y]3 (ID)
wherein AI and AII are as defined above with respect to A, M is as defined above, XI and XII are as defined above in relation to X and wherein x and y are both greater than 0 and less than 1. In a preferred embodiment, AI and AII are each selected from ((CH3NH3)+, (CH3CH2NH3)+, (CH3CH2CH2NH3)+, (N(CH3)4)+, (H2N—C(H)═NH2)+, (H2N—C(CH3)═NH2)+, (H2NC(NH2)═NH2)+, Cs+ and Rb+; M is Pb2+ or Sn2+; and XI and XII are each selected from Br−, Cl− and I−.
For instance, the photoactive material in the photoactive region may comprise, or consist essentially of, a perovskite compound of formula (ID) selected from [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[BryCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[IyCl1-y]3, [(CH3NH3)xCs1-x]Pb[BryI1-y]3, [(CH3NH3)xCs1-x]Pb[BryCl1-y]3, [(CH3NH3)xCs1-x]Pb[IyCl1-y]3, [(H2NC(H)═NH2)xCs1-x]Pb[BryI1-y]3, [(H2N—C(H)═NH2)xCs1-x]Pb[BryCl1-y]3, [(H2NC(H)═NH2)xCs1-x]Pb[IyCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[BryCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[IyCl1-y]3, [(CH3NH3)xCs1-x]Sn[BryI1-y]3, [(CH3NH3)xCs1-x]Sn[BryCl1-y]3, [(CH3NH3)xCs1-x]Sn[IyCl1-y]3, [(H2NC(H)═NH2)xCs1-x]Sn[BryI1-y]3, [(H2N—C(H)═NH2)xCs1-x]Sn[BryCl1-y]3, and [(H2NC(H)═NH2)xCs1-x]Sn[IyCl1-y]3, where x and y are both greater than 0 and less than 1, for instance x and y may both be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9. Preferably, the photoactive material in the photoactive region comprises a perovskite compound of formula [(H2NC(H)═NH2)xCs1-x]Pb[BryI1-y]3 wherein x and y are both from 0.1 to 0.9.
The crystalline A/M/X material deposited on the substrate and the crystalline A/M/X material in the photoactive region may be different or the same. Typically, the crystalline A/M/X material deposited on the substrate and the crystalline A/M/X material in the photoactive region are different. For instance, the crystalline A/M/X material in the photoactive region may comprise, or consist essentially of, a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein, preferably a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH) as described herein, and the crystalline A/M/X material deposited on the substrate may comprise, or consist essentially of, a different compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein, preferably a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH) as described herein.
For instance, the crystalline A/M/X material in the photoactive region may comprise, or consist essentially of, a compound of formula (IA), and the crystalline A/M/X material deposited on the substrate may comprise, or consist essentially of, a compound of formula (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein, for instance a compound of formula (IB), (IC), (ID), (IE), (IF), (IG) or (IH) as described herein, preferably a compound of formula (ID), (IE) or (IF) as described herein.
For example, the crystalline A/M/X material in the photoactive region may comprise, or consist essentially of, a compound of formula APbI3, APbBr3, APbCl3, ASnI3, ASnBr3 or ASnCl3, wherein A is a cation as described herein, preferably APbI3, more preferably CH3NH3PbI3, and the crystalline A/M/X material deposited on the substrate may comprise, or consist essentially of, a compound of formula CH3NH3[PbzSn1-z]Cl3, CH3NH3[PbzSn1-z]Br3, CH3NH3[PbzSn1-z]I3, Cs[PbzSn1-z]Cl3, Cs[PbzSn1-z]Br3, Cs[PbzSn1-z]I3, (H2N—C(H)═NH2)[PbzSn1-z]Cl3, (H2NC(H)═NH2)[PbzSn1-z]Br3, or (H2NC(H)═NH2)[PbzSn1-z]I3, where z is greater than 0 and less than 1, for instance z may be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9, or of formula [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]Cl3, [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]Br3, [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]I3, [(CH3NH3)xCs1-x][PbzSn1-z]Cl3, [(CH3NH3)xCs1-x][PbzSn1-z]Br3, [(CH3NH3)xCs1-x][PbzSn1-z]I3, [(H2NC(H)═NH2)xCs1-x][PbzSn1-z]Cl3, [(H2NC(H)═NH2)xCs1-x][PbzSn1-z]Br3, or [(H2NC(H)═NH2)xCs1-x][PbzSn1-z]I3, where x and z are both greater than 0 and less than 1, for instance x and z may each be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9, preferably a compound of formula CH3NH3[PbzSn1-z]I3 or [(CH3NH3)x(H2N—C(H)═NH2)1-x][PbzSn1-z]I3 wherein x, y and z are each from 0.05 to 0.95 or 0.1 to 0.9.
The photoactive material in the photoactive region may comprise a perovskite compound of formula:
Csz(H2NC(H)═NH2)(1-z)[M][X]3
wherein: [M] is as defined above, and for instance, may comprise Pb, Sn, or a mixture of Pb and Sn; [X] is one or more different halide anions, for instance two or more different halide anions; and z is from 0.01 to 0.99. For instance, the perovskite may be a compound of formula Csz(H2NC(H)═NH2)(1-z)[PbxSn1-x]I3, Csz(H2NC(H)═NH2)(1-z)[PbxSn1-x]Br3 or Csz(H2NC(H)═NH2)(1-z)[PbxSn1-x]IyBr3(1-y), wherein z is as defined above and x is from 0 to 1 (and may for instance be 0.5) and y is from 0.01 to 0.99.
The photoactive material in the photoactive region may comprise a compound of formula:
Csz(H2NC(H)═NH2)(1-z)[M]X3yX′3(1-y)
wherein: [M] is as defined above, and for instance, may comprise Pb, Sn, or a mixture of Pb and Sn; X is a first halide anion selected from I−, Br−, Cl− and F−; X′ is a second halide anion which is different from the first halide anion and is selected from I−, Br−, Cl− and F−; z is from 0.01 to 0.99; and y is from 0.01 to 0.99. For instance, the perovskite may be a compound of formula Csz(H2NC(H)═NH2)(1-z)PbBr3yI3(1-y).
The crystalline A/M/X material in the photoactive region may comprise, or consist essentially of, a compound of formula (ID), and the crystalline A/M/X material deposited on the substrate may comprise, or consist essentially of, a compound of formula (IA), (IB), (IC), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein, for instance a compound of formula (IA), (IB), (IC), (IE), (IF), (IG) or (IH) as described herein, preferably a compound of formula (IA), (IE) or (IF) as described herein.
For example, the crystalline A/M/X material in the photoactive region may comprise, or consist essentially of, a compound of formula [(CH3NH3)4H2NC(H)═NH2)1-x]Pb[BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[BryCl1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Pb[IyCl1-y]3, [(CH3NH3)xCs1-x]Pb[BryI1-y]3, [(CH3NH3)xCs1-x]Pb[BryCl1-y]3, [(CH3NH3)xCs1-x]Pb[IyCl1-y]3, [(H2NC(H)═NH2)xCs1-x]Pb[BryI1-y]3, [(H2NC(H)═NH2)xCs1-x]Pb[BryCl1-y]3, [(H2N—C(H)═NH2)xCs1-x]Pb[IyCl1-y]3, [(CH3NH3)x(H2NC(H)═NH2)1-x]Sn[BryI1-y]3, [(CH3NH3)x(H2N—C(H)═NH2)1-x]Sn[BryCl1-y]3, [(CH3NH3)x(H2NC(H)═NH2)1-x]Sn[IyCl1-y]3, [(CH3NH3)xCs1-x]Sn[BryI1-y]3, [(CH3NH3)xCs1-x]Sn[BryCl1-y]3, [(CH3NH3)xCs1-x]Sn[IyCl1-y]3, [(H2NC(H)═NH2)xCs1-x]Sn[BryI1-y]3, [(H2NC(H)═NH2)xCs1-x]Sn[BryCl1-y]3, or [(H2N—C(H)═NH2)xCs1-x]Sn[IyCl1-y]3, where x and y are both greater than 0 and less than 1, for instance x and y may both be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9, preferably a compound of formula [(CH3NH3)xCs1-x]Pb[BryI1-y]3, where x and y are from 0.05 to 0.95 or 0.1 to 0.9, and the crystalline A/M/X material deposited on the substrate may comprise, or consist essentially of, a compound of formula APbI3, APbBr3, APbCl3, ASnI3, ASnBr3 or ASnCl3, wherein A is a cation as described herein, preferably APbI3, more preferably CH3NH3PbI3; or CH3NH3[PbzSn1-z]Cl3, CH3NH3[PbzSn1-z]Br3, CH3NH3[PbzSn1-z]I3, Cs[PbzSn1-z]Cl3, Cs[PbzSn1-z]Br3, Cs[PbzSn1-z]I3, (H2NC(H)═NH2)[PbzSn1-z]Cl3, (H2N—C(H)═NH2)[PbzSn1-z]Br3, and (H2NC(H)═NH2)[PbzSn1-z]I3, where z is greater than 0 and less than 1, for instance z may be from 0.01 to 0.99 or from 0.05 to 0.95 or 0.1 to 0.9, preferably CH3NH3[PbzSn1-z]I3 where z is from 0.05 to 0.95 or 0.1 to 0.9.
Alternatively, the crystalline A/M/X material deposited on the substrate and the crystalline A/M/X material in the photoactive region may both be compounds of the same formula ((IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein) but have a different chemical composition (for instance one may be CH3NH3PbI3 and the other may be CH3NH3PbBr3, or one may be CH3NH3PbI3 and the other may be CH3NH3SnI3).
Typically, the photoactive region comprises one or more charge transporting layers, for instance two charge transporting layers. The charge transporting layers may be layers of an electron transporting (n-type) material, as described herein, or layers of a hole transporting (p-type) material, as described herein. Typically, the photoactive region comprises two charge transporting layers wherein one of the charge transporting layers is a layer of an electron transporting (n-type) material as described herein, and the other charge transporting layer is a layer of a hole transporting (p-type) material as described herein.
Preferably, the photoactive region comprises a layer of an electron transporting (n-type) material, wherein said electron transporting material comprises PCBM, and the other charge transporting layer is a layer of a hole transporting (p-type) material, wherein said hole transporting material comprises spiro-OMeTAD or spiro(TFSI)2.
Hence, the photoactive region may comprise the following layers in the following order:
The layer of an electron-transporting (n-type) material may for instance comprise a layer of an organic n-type material and a layer of an inorganic n-type material. Often the layer of the organic n-type material (which may be as defined further herein, e.g. it may be PCBM) is disposed on a layer of an inorganic n-type material (which also may be as further defined herein, and may for instance be SnO2). The layer of an electron-transporting (n-type) material typically has this structure when it is in contact with an electrode, for instance when it is in contact with a first electrode which comprises a transparent conducting oxide (such as, for instance, fluorine doped tin oxide (FTO) or indium doped tin oxide (ITO)). Typically, the inorganic n-type layer of the layer of the electron-transporting material (which it often SnO2) is in contact with the transparent conducting oxide, for instance with FTO. Indeed, the present inventors have found that such an inorganic n-type layer improves the electronic contact of the organic n-type layer with the transparent conducting oxide. Similarly, the inventors have found that the organic n-type layer (e.g. PCBM) makes more stable electronic contact to the photoactive material than an inorganic n-type layer, particularly when the photoactive material is a crystalline A/M/X material as defined herein. They have also found that that having a double n-layer helps inhibit pinholes in the n-layer. Thus, the present invention typically employs two n-type layers in between the electrode which comprises a transparent conducting oxide and the photoactive material. The inventors have found in particular that SnO2 improves the electronic contact of PCBM with FTO, and that the double SnO2/PCBM n-type layer is improved compared to SnO2 alone because PCBM makes more stable electronic contact to a perovskite photoactive material.
Typically, the photoactive region, comprising the layer of a photoactive material and optionally the layers of charge transporting material, has a total thickness of from 10 to 5000 nm, for instance from 50 to 3000 nm, from 100 to 2000 nm, from 200 to 1500 nm, preferably from 250 to 1250 nm. Typically, when any layers of charge transporting material are present, they have an individual thickness of less than 200 nm, for instance less than 150 nm or less than 100 nm, from 1 to 100 nm, typically from 10 to 75 nm typically 30 to 60 nm.
The layer of a photoactive material in the photoactive region may also be produced using the aprotic solvent/organic amine solvent system as used in the process of the present invention. For instance, the process of the present invention may further comprise a step of producing the substrate by disposing a layer of a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c as described herein; wherein the process comprises forming the layer of the crystalline A/M/X material by disposing a film-forming solution on a substrate layer, for instance an n-type or p-type layer in the substrate, wherein the film-forming solution comprises:
Alternatively, the layer of a photoactive material in the photoactive region may be produced according to other methods known to the skilled person. For instance, the process of the present invention may further comprise a step of producing the substrate by disposing a layer of a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c as described herein; wherein the process comprises forming the layer of the crystalline A/M/X material by conventional high boiling point solvent deposition methods, for instance by disposing (e.g. by spin coating) a solution of the A/M/X precursor compounds in DMF, DMSO or a mixture thereof, onto the substrate precursor.
In one embodiment, the substrate comprises two separate photoactive regions as described herein, wherein each photoactive region comprises a photoactive material. By two separate photoactive regions it is meant that the substrate comprises two photoactive regions that are not in direct physical contact with each other. When the substrate comprises two separate photoactive regions, the layer of a crystalline A/M/X material formed on the substrate forms a part of a third photoactive region. Thus, the multi-junction device produced according to the process of the present invention may comprise three photoactive regions. Thus, the multi-junction device produced according to the process of the present invention may be a triple-junction device. Typically, at least two of the photoactive regions in the multi-junction device are formed using a film-forming solution as defined herein, with reference to the process of the invention.
In this embodiment, a further charge recombination layer, as described herein, may be disposed between the two photoactive regions in the substrate. Thus, the substrate may comprise two photoactive regions, separated by the further charge recombination layer. For instance, the substrate may comprise the following layers in the following order:
Each photoactive region may be as described above. For instance each photoactive region may comprise one or more charge transporting layers as described herein, for instance two charge transporting layers. The charge transporting layers may be layers of an electron transporting (n-type) material, as described herein, or layers of a hole transporting (p-type) material, as described herein. Typically, each photoactive region comprises two charge transporting layers wherein one of the charge transporting layers is a layer of an electron transporting (n-type) material as described herein, and the other charge transporting layer is a layer of a hole transporting (p-type) material as described herein. These layers are generally disposed either side (above and below, respectively) of a layer of a photoactive material as described herein.
Preferably, each photoactive region comprises a layer of an electron transporting (n-type) material, wherein said electron transporting material comprises PCBM, and the other charge transporting layer is a layer of a hole transporting (p-type) material, wherein said hole transporting material comprises spiro-OMeTAD.
The layer of the electron transporting material in one of the photoactive regions may comprise a layer of an organic n-type material and a layer of an inorganic n-type material. Often the layer of the organic n-type material (e.g. PCBM) is disposed on a layer of an inorganic n-type material (e.g. SnO2). The layer of an electron-transporting (n-type) material typically has this structure when it is in contact with an electrode, for instance when it is in contact with a first electrode which comprises a transparent conducting oxide (such as, for instance, fluorine doped tin oxide, FTO).
Hence, each photoactive region may comprise the following layers in the following order:
Each photoactive material in each photoactive region may comprise a crystalline A/M/X material, which crystalline A/M/X material comprises a compound of formula [A]a[M]b[X]c as described herein. For instance, each photoactive material in the photoactive region may comprise a compound of formula [A]a[M]b[X]c, wherein said compound is a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein. Typically, each photoactive material in the photoactive region comprises a compound of formula [A]a[M]b[X]c, wherein said compound is a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH).
The crystalline A/M/X materials in the two photoactive regions may be the same crystalline A/M/X material or different crystalline A/M/X materials as described herein. Preferably, at least two of the crystalline A/M/X materials selected from the crystalline A/M/X material deposited on the substrate and the crystalline A/M/X materials in the two photoactive regions are different. In one embodiment, all three of the crystalline A/M/X materials selected from the crystalline A/M/X material deposited on the substrate and the crystalline A/M/X materials in the two photoactive regions are different.
For example, the layer of a photoactive material in one photoactive region may comprise a compound of formula ID, the layer of a photoactive material in the other photoactive region may comprise a compound of formula IA, and the crystalline A/M/X material deposited on the substrate may comprise a compound of formula IE.
Preferably, at least one of the layers of crystalline A/M/X material in one of the photoactive regions is deposited using the aprotic solvent/organic amine solvent system as used in the process of the present invention. In one embodiment, each layer of photoactive material in each of the photoactive regions may be deposited using the aprotic solvent/organic amine solvent system as used in the process of the present invention.
Alternatively, one of the layers of photoactive material in one of the photoactive regions is produced according to other methods known to the skilled person. For instance, the layer of a photoactive material may be deposited by conventional high boiling point solvent deposition methods, for instance by spin coating a solution of the A/M/X precursor compounds in DMF, DMSO or a mixture thereof
The substrate typically comprises a first electrode. The first electrode may comprise a metal (for instance silver, gold, aluminium or tungsten) or a transparent conducting oxide (for instance fluorine doped tin oxide (FTO) or indium doped tin oxide (ITO)). Typically, the first electrode comprises a transparent conducting oxide. The thickness of the layer of a first electrode is typically from 5 nm to 100 nm.
The substrate typically comprises:
For manufacture of a triple-junction device, the substrate typically comprises
The first electrode may be deposited on a layer of a transparent material, for instance a layer of glass. The layer of a transparent material may be treated with an anti-reflective coating. Typically, the anti-reflective coating comprises magnesium fluoride (MgF2).
The process may further comprise: disposing a second electrode on the layer of the crystalline A/M/X material disposed on the substrate.
The second electrode may be as defined above for the first electrode. Typically, the second electrode comprises, or consists essentially of, a metal for instance an elemental metal. Examples of metals which the second electrode material may comprise, or consist essentially of, include silver, gold, copper, aluminium, platinum, palladium, or tungsten. The second electrode may be disposed by vacuum evaporation. The thickness of the layer of a second electrode material is typically from 1 to 250 nm, preferably from 5 nm to 100 nm.
Preferably, the process comprises disposing a layer of a charge transporting material as described herein on the layer of the crystalline A/M/X material disposed on the substrate, and disposing the second electrode on the charge transporting material. The layer of a charge transporting material may be a layer of an electron transporting (n-type) material, as described herein, or a layer of a hole transporting (p-type) material, as described herein. Typically, the layer of a charge transporting material disposed on the layer of the crystalline A/M/X material is a layer of a hole transporting (p-type) material as described herein, preferably wherein said hole transporting material comprises spiro-OMeTAD.
Thus the multi-junction device produced by the process of the present invention may comprise the following layers in the following order:
In the case of a triple-junction device produced by the process of the present invention, the triple-junction device may comprise the following layers in the following order:
In one embodiment, at least two of the photoactive regions in the multi-junction device are formed using a film-forming solution as described herein. In this embodiment, the process of the invention may comprise forming the layer of the crystalline A/M/X material by disposing a film-forming solution on a substrate, wherein the substrate comprises: one photoactive region comprising a photoactive material, and a charge recombination layer which is disposed on the photoactive region by solution-deposition, then further steps of:
Such a device may therefore comprising the following layers in the following order:
The present invention also relates to a multi-junction device which is obtainable or obtained by the process of the present invention. The multi-junction device may comprise any of the features described above in relation to the process for producing a multi-junction device. For instance, the multi-junction device may comprise any of the combination of layer sequences and materials as set out above. Also, the crystalline A/M/X material(s) may each be as further defined anywhere herein.
In one embodiment, the present invention also relates to a multi-junction device comprising:
The nanoparticles of a transparent conducting oxide may be any nanoparticles of a transparent conducting oxide as described herein. For instance, the nanoparticles of a transparent conducting oxide may be indium tin oxide (ITO) nanoparticles, preferably ITO nanoparticles having a size of less than 100 nm.
The present invention also relates to a multi-junction device comprising:
In the multi-junction devices described above, [A], [M] and [X] may all be as described herein. Each A/M/X material may be as further defined herein. Also, each photoactive region may be as further defined herein, for instance each one, may further comprise a layer of an n-type material and a layer of a p-type material, which n-type and p-type materials may be as further defined herein.
The conducting polymer may be any conducting polymer as described herein. For instance, the conducting polymer may comprise poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS).
In the multi-junction devices described above, the charge recombination layer typically comprises nanoparticles of a transparent conducting oxide and a conducting polymer, both of which may be as further defined anywhere herein. Thus, the charge recombination layer may comprise (i) nanoparticles of indium tin oxide (ITO) and (ii) a polymer which comprises poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate.
In the multi-junction devices above, two of the photoactive regions may comprise a layer of a crystalline A/M/X material as described herein. In one embodiment, the multi-junction devices above comprise at least three photoactive regions. Preferably each photoactive region comprises a layer of a crystalline A/M/X material as described herein. Each crystalline A/M/X material may comprise, or consist essentially of, a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein, preferably a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH) as described herein. Each photoactive region may further comprise n-type and p-type layers as further defined herein.
The present invention also relates to a multi-junction device comprising
In the multi-junction device comprising three photoactive regions, [A], [M] and [X] may all be as described herein.
Typically, at least two charge recombination layers are disposed between the photoactive regions. For instance, the multi-junction device may comprise the following layers in the following order:
Typically, at least one of the charge recombination layers comprises a conducting polymer or nanoparticles of a transparent conducting oxide. For instance, each one of the charge recombination layers comprises a conducting polymer or nanoparticles of a transparent conducting oxide.
Typically, at least one of the charge recombination layers comprises nanoparticles of a transparent conducting oxide and a conducting polymer. For instance, each one of the charge recombination layers may comprise nanoparticles of a transparent conducting oxide and a conducting polymer. The nanoparticles of a transparent conducting oxide and the conducting polymer may be as described herein, for example the nanoparticles of a transparent conducting oxide may be indium tin oxide (ITO) nanoparticles, preferably ITO nanoparticles having a size of less than 100 nm, and the conducting polymer may comprise poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS). Thus, each one of the charge recombination layer or layers may comprise (i) nanoparticles of indium tin oxide (ITO) and (ii) a polymer which comprises poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate.
In the multi-junction devices described above, at least two of the crystalline A/M/X materials may be different from each other. In one embodiment, more than two of the crystalline A/M/X materials are different from one other. For instance, in a multi-junction device in which three crystalline A/M/X materials are present, all three crystalline A/M/X materials may be different from each other. The crystalline A/M/X material in each photoactive region may comprise, or consist essentially of, a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG), (IH), (IIIA), (IIIB), (IIIC), (VIA), (VIB), or (VIC) as described herein, preferably a compound of formula (I), for instance a compound of formula (IA), (IB), (IC), (ID), (IE), (IF), (IG) or (IH) as described herein. Each photoactive region may further comprise at least one, preferably two, charge transporting layers, for instance an n-type layer and a p-type layer as further defined herein.
The multi-junction devices described above may further comprise a first electrode and a second electrode as described herein, wherein the photoactive regions and the charge recombination layer or layers are disposed between the first electrode and the second electrode. Preferably, the first electrode comprises a transparent conducting oxide and the second electrode comprises elemental metal.
Typically, the multi-junction devices described herein are selected from the group consisting of an optoelectronic device, a photovoltaic device, a solar cell, a photo detector, a photodiode, a photosensor, a chromogenic device, a transistor, a light-sensitive transistor, a phototransistor, a solid state triode, a battery, a battery electrode, a capacitor, a super-capacitor, a light-emitting device, a light-emitting diode and a laser. For instance, the multi-junction device may be an optoelectronic device. Examples of optoelectronic devices include photovoltaic devices, photodiodes (including solar cells), phototransistors, photomultipliers, photoresistors, and light emitting devices. Preferably, the multi-junction device is a photovoltaic device or a light-emitting device.
The advantages of the invention will hereafter be described with reference to some specific examples.
Herein, an acetonitrile/methylamine (ACN/MA) composite solvent is employed, which was previously introduced by Noel et al. (N. K. Noel, S. N. Habisreutinger, B. Wenger, M. T. Klug, M. T. Hörantner, M. B. Johnston, R. J. Nicholas, D. T. Moore, H. J. Snaith, Energy Environ. Sci. 2017, 10, 145) to enable the sequential processing of perovskite absorber layers upon underlying perovskite devices. This all-solution processed architecture has the potential of being applied to the manufacturing of large area films on both rigid and flexible substrates, using deposition techniques such as roll-to-roll (R2R) processing, blade coating or inkjet printing. An all-solution processed tandem architecture is presented, reaching over 15% stabilized power conversion efficiency (PCE), and delivering an open circuit voltage (Voc) of 2.18 V. Furthermore, we show that the mixed-metal Sn/Pb perovskite MAPb0.75Sn0.25I3, can also be processed via the ACN/MA solvent system, where the reducing nature of MA obviates the need to use SnF2 to achieve respectable efficiencies, allowing u a scanned PCE of over 11% (stabilized 10.5%) to be obtained employing an n-i-p architecture. Using a mixed-metal MAPb0.75Sn0.25I3 perovskite material to extend the light absorption of the multi-junction to 925 nm, the first monolithic triple-junction perovskite solar is presented with an open circuit voltage (Voc) of 2.83 V. An optical and electronic model is utilized to validate the experimental results, and reveal the optical losses existing within this specific architecture. A triple junction perovskite solar cell is then modeled, using electronic characteristics of currently feasible 1.94/1.57/1.24 eV perovskite materials, showing the possibility of achieving a triple junction device with a 24.3% PCE and corresponding Voc of 3.15 V.
All-perovskite monolithic 2T tandems and multi-junction solar cells require a tunnel junction (TJ) or recombination layer to provide a means to create an electronic series connection between the different sub-cells. In turn, photo-voltage generated from each sub-cell sum resulting in high voltage devices. However, due to charge conservation, the current density flowing out of each sub-cell must match, and hence the current will be limited by the lowest current density generated from any sub-junction. Thus, in order to maximize the photocurrent density in a 2T monolithic tandem, both sub-cells should generate equal current density, which can be achieved through carefully tuning the band gap and thickness of each junction. Recombination layers between the sub cells must fulfill stringent requirements. Firstly, they must to enable ohmic contact to the charge extraction layers, and facilitate recombination of collected electrons and holes without introducing resistive losses. Secondly, they must be as optically transparent as possible to avoid parasitic absorption of light. Thirdly, deposition of the recombination layer should not damage any of the layers beneath, which is typically achieved via introducing “buffer layers” when sputtering, or by using orthogonal solvents for solution processing. Lastly, this interlayer must be a sufficient barrier to solvent penetration to prevent any re-dissolution of underlying perovskite or other electronic layers when subsequently processing another perovskite layer.
Here, a recombination layer and an n-i-p perovskite solar cell architecture are developed that meet these constraints. For the recombination layer, a combination of a PEDOT:PSS layer followed by a ITO nanoparticles layer is found to work well. In the first instance, a “wide band gap”, purely lead-based perovskite tandem cell is developed by processing a 1.94 eV (as determined by a Tauc plot which we show in
For the bottom cell, which is processed on top of the wide-gap cell, the issue of dissolution of the underlying perovskite film must be considered. If one of the standard DMF/DMSO solvent based routes is employed, the underlying perovskite film may be completely solvated and discolored, making it evident that the recombination layer is not impermeable to DMF or DMSO. These high boiling point solvents remain on the surface long enough to slowly percolate through solution-processed interlayers, re-dissolve the underlying perovskite layer, thus limiting their usefulness in all-solution processed tandem solar cells. An ACN/MA based composite solvent system for processing perovskite films has been developed previously, which has several distinct advantages (D. P. McMeekin, Z. Wang, W. Rehman, F. Pulvirenti, J. B. Patel, N. K. Noel, M. B. Johnston, S. R. Marder, L. M. Herz, H. J. Snaith, Adv. Mater. 2017, 1607039). Firstly, it is much more volatile than DMF, enabling very rapid drying. Secondly, the solvation strength can be tuned by varying the amount of methylamine incorporated. The right amount of MA is chosen to enable complete dissolution of the salts, but with minimal excess. It was found that having an excess amount of MA in solution can have a detrimental impact to the device. Unwanted pinholes in the interlayers may result in methylamine percolating and re-dissolving the perovskite underlayer. Thus, by carefully tuning the MA content in the solutions to obtain a solution at its critical solubility point, the chance of re-dissolving the underlayer is minimised. This solubility point is found by slowly adding a ACN/MA perovskite solution to a neat ACN perovskite dispersion, until the mixture becomes a full perovskite solution. Through this route, a robust and reliable protocol for fabrication of all-perovskite multi-junction solar cells was obtained.
To achieve optimal results, careful tuning of the B-site metal ion content was needed for both MAPbI3 and MAPb0.75Sn0.25I3 perovskite material processed via the ACN/MA solvent route. In
In
In an all-solution processed tandem architecture, it is imperative to eliminate the presence of pinholes, to prevent dissolving underlying layers. In
In
In
In this work, the recombination layer comprises PEDOT:PSS and indium tin oxide (ITO) nanoparticle (NP) sublayers. A high conductivity PEDOT:PSS (Heraus H1000) solution is diluted with isopropanol (IPA) and directly spin-coated on the spiro-OMeTAD layer, which acts as both a recombination layer and solvent barrier. An ITO layer is then spin-coated on from a solvent dispersion of ITO nanoparticles (>100 nm). The fabricated ITO nanoparticle layer may be porous and non-continuous. However, these nanoparticles, improve the recombination process, due to their high carrier density, which allow holes from PEDOT:PSS and electrons from PC61BM to recombine. The ITO NP layer creates an ohmic contact between both electron and hole-accepting layers, which allows for efficient charge transfer into the recombination layer.
This tandem device generated a short-circuit current-density (JSC) of 11.5 mA cm2, a fill-factor (FF) of 0.63, an open-circuit voltage (Voc) of 2.18 V, and a power conversion efficiency of 15.2% (stabilized) (
Although neat lead-based devices have led to stable perovskite materials, the drive to narrow the bandgap using less stable tin-based perovskites is still highly desirable for tandem applications. As shown in
Surprisingly, a substantial difference was found in optimum A-site to B-site ratio for tin-lead based perovskite materials compared to neat lead-based perovskites. In the case of Sn/Pb-based perovskite, the research community appears to have consistently observed performance gains when using an excess of tin halides, most notably in the form of tin fluoride (SnF2) or tin chloride (SnCl2) (see D. Zhao, Y. Yu, C. Wang, W. Liao, N. Shrestha, C. R. Grice, A. J. Cimaroli, L. Guan, R. J. Ellingson, K. Zhu, X. Zhao, R.-G. Xiong, Y. Yan, Nat. Energy 2017, 2, 17018; K. P. Marshall, M. Walker, R. I. Walton, R. A. Hatton, Nat. Energy 2016, 1, 16178; S. J. Lee, S. S. Shin, Y. C. Kim, D. Kim, T. K. Ahn, J. H. Noh, J. Seo, S. Il Seok, J. Am. Chem. Soc. 2016, 138, 3974; M. H. Kumar, S. Dharani, W. L. Leong, P. P. Boix, R. R. Prabhakar, T. Baikie, C. Shi, H. Ding, R. Ramesh, M. Asta, M. Graetzel, S. G. Mhaisalkar, N. Mathews, Adv. Mater. 2014, 26, 7122; A. G. Kontos, A. Kaltzoglou, E. Siranidi, D. Palles, G. K. Angeli, M. K. Arfanis, V. Psycharis, Y. S. Raptis, E. I. Kamitsos, P. N. Trikalitis, C. C. Stoumpos, M. G. Kanatzidis, P. Falaras, Inorg. Chem. 2017, 56, 84). The tin fluoride as an additive has readily been used as a reducing agent with the aim of suppressing the tin oxidation from Sn2+ to Sn4+. By suppressing oxidation, Sn2+ vacancies are limited, which causes the undesirable p-type behavior found in Sn-based perovskites. In this study, MA is relied on to act as a reducing agent instead of SnF2, since SnF2 poorly dissolves in the ACN/MA solvent system. Amines have been known to act as reducing agents, a phenomenon most often exploited in the synthesis of metal nanoparticles (see J. D. S. N. and, G. J. Blanchard*, 2006, DOI 10.1021/LA060045Z). Here, the reducing properties of amines is exploited, allowing SnF2 to be effectively replaced with MA.
As reported by Hörantner et al., all-perovskite triple junction solar cells employing perovskite absorbers with similar band gaps to those which we have used in the present work, should be capable of outperforming single and double junction efficiencies. The modelling of H Hörantner et al. shows that an optimized 1.22 eV band gap material should current match the two wider band gap sub-cells of 2.04 eV and 1.58 eV, delivering a theoretical maximum JSC of 12 mA cm−2, a Voc of 3.54 V and a PCE of 36.6% (see M. T. Hörantner, T. Leijtens, M. E. Ziffer, G. E. Eperon, M. G. Christoforo, M. D. McGehee, H. J. Snaith, ACS Energy Lett. 2017, 2, 2506). However, this performance can only be obtained with optically transparent interlayers to reduce parasitic absorption and reflection losses.
To assess the true potential of this fully-solution processed all-perovskite multi-junction solar cell architecture, a similar optical and electrical model to that used by Hörantner et al., was employed to simulate this semiconductor stack and reveal where improvements can be made to further increase the performance of multi-junction devices. Using the experimental thicknesses, in combination with the extracted electrical characteristics of the state-of-the-art single junction perovskite cells,
The fully-solution processed all-perovskite multi-junction solar cells which are presented open new avenues for the large-scale manufacture of highly efficient multi-junction architectures. These tandem architectures can be achieved using a highly volatile ACN/MA-based solvent system, which enabled sequential stacking of different energy gap perovskite absorbers. Using a highly transparent and effective PEDOT:PSS/ITO NPs recombination layer, the first fully-solution processed monolithic FA0.83Cs0.17Pb(Br0.7I0.3)3/MAPbI3 tandem solar cell has been fabricated, reaching a stabilized power conversion efficiency of 15.2%. By adding a narrow band-gap MAPb0.75Sn0.25I3 perovskite junction, the multi-junction's light absorption is extended to 925 nm and fabricated the first triple-junction perovskite solar cell, reaching a record high 2.83 V Voc.
Top Cell (TC) Fabrication: Glass/FTO/SnO2/PC61BM/FA0.83Cs0.17Pb(Br0.7I0.3)3/Spiro-OMeTAD
Substrate Preparation: Devices were fabricated on fluorine-doped tin oxide (FTO) coated glass (Pilkington, 15Ω□−1). Initially, FTO was removed at specific regions where the anode contact will be deposited. This FTO etching was done using a 2M HCl and zinc powder. Substrates were then cleaned sequentially in Hellmanex detergent, acetone, isopropyl alcohol, and dried with a compressed air gun.
Tin Oxide (SnO2) layer fabrication: Immediately prior to spin coating, we prepared a SnO2 precursor solution comprised of 17.5 mg ml−1 tin(IV) chloride pentahydrate (SnCl4.5H2O) (Sigma-Aldrich) dissolved in anhydrous 2-propanol (IPA). The solution was spin-coated in nitrogen at 3000 rpm for 30 s, with a ramp of 200 rpm/s. The substrates were then dried in nitrogen at 100° C. for 10 min. A subsequent annealing step was done in air 180° C. for 90 min.
PC61BM layer fabrication: A Phenyl-C61-butyric acid methyl ester (PC61BM) precursor solution was prepared by dissolving a 7.5 mg ml−1 PC61BM (99%, solenne) in anhydrous chlorobenzene (CB) (Sigma). We doped the PC61BM using dihydro-1H-benzoimidazol-2-yl (N-DBI) derivatives, specifically 3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (N-DMBI) (see S. Rossbauer, C. Müller, T. D. Anthopoulos, Adv. Funct. Mater. 2014, 24, n/a; Z. Wang, D. P. McMeekin, N. Sakai, S. van Reenen, K. Wojciechowski, J. B. Patel, M. B. Johnston, H. J. Snaith, Adv. Mater. 2017, 29, 1604186; S. S. Kim, S. Bae, W. H. Jo, Chem. Commun. 2015, 51, 17413; P. Wei, T. Menke, B. D. Naab, K. Leo, M. Riede, Z. Bao, J. Am. Chem. Soc. 2012, 134, 3999; B. D. Naab, S. Guo, S. Olthof, E. G. B. Evans, P. Wei, G. L. Millhauser, A. Kahn, S. Barlow, S. R. Marder, Z. Bao, J. Am. Chem. Soc. 2013, 135, 15018; P. Wei, J. H. Oh, G. Dong, Z. Bao, J. Am. Chem. Soc. 2010, 132, 8852). We doped the PC61BM precursor solution with N-DMBI at a 0.25% wt %. This solution was then filtered using a 0.45 μm PTFE filter. We spin coated this solution in a nitrogen-filled glovebox at 2000 rpm for 20 s with a ramp rate of 1000 rpm/s, and annealed the substrate at 80° C. for 10 min.
FAI synthesis: Formamidinium iodide (FAI) was synthesized by dissolving formamidine acetate salt (99%, Sigma-Aldrich) in a 1.5× molar excess of hydriodic acid (HI), 57 wt. % in H2O, distilled, stabilized, 99.95% (Sigma-Aldrich). After addition of acid the solution was left stirring for 10 minutes at 50° C. Upon drying in a large glass dish at 100° C. for 2 h, a yellow-white powder was formed. This was then washed three times with diethyl ether. The power was later dissolved in anhydrous ethanol (99.5%, Sigma-Aldrich) and heated at 120° C. in a N2-rich atmosphere to obtain a supersaturated solution. Once fully dissolved, the solution was then slowly cooled to room temperature in a N2-rich atmosphere, until recrystallization occurred. The recrystallization process formed white flake-like crystals. The solution was then placed and in a refrigerator at 4° C., after which it was transferred to a freezer for further crystallization. The powder was later washed with diethyl ether three times. Finally, the powder was dried overnight in a vacuum oven at 50° C.
FA0.83Cs0.17Pb(Br0.7I0.3)3 with 2% K additive perovskite precursor solution preparation: FA/Cs (formamidinium/Cs) with 2% K additive perovskite solutions were prepared by dissolving the precursor salts in anhydrous N,N-dimethylformamide (DMF) to obtain a stoichiometric solution with the desired FA0.83Cs0.17Pb(Br0.7I0.3)3 composition and 2% K additive using a molar ratio of 30% to 70% KI to KBr. The precursor solution was prepared using the following precursor salts: formamidinium iodide (FAI), cesium iodide (CsI) (99.9%, Alfa Aesar), lead iodide (PbI2) (99%, Sigma-Aldrich), lead bromide (PbBr2) (98%, Alfa Aesar), potassium iodide (KI) (99%, Sigma-Aldrich), potassium bromide (99%, KBr) (Sigma-Aldrich). 27.2 μl/ml of hydroiodic acid (HI) (57 wt. % in H2O, distilled, stabilized, 99.95%, Sigma-Aldrich) and 54.8 μl/ml of hydrobromic (HBr) (48 wt. % in H2O) was added to 1 ml of 0.75 M precursor solutions. After the addition of the acids, the perovskite precursor solution was aged for 2 days under a nitrogen atmosphere.
FA0.83Cs0.17Pb(Br0.7I0.3)3 perovskite layer preparation: This aged precursor perovskite solution was spin-coated in a nitrogen-filled glovebox at 1200 rpm for 45 s with a 500 rpm/s ramp rate. The films were dried inside a N2 glovebox on a hot plate at a temperature of 70° C. for 1 minute. The films were then annealed in an oven in an air atmosphere at 185° C. for 90 minutes. During this annealing process, the samples were covered with a large glass container to prevent dust contamination.
Spiro-OMeTAD hole-transporting layer fabrication: The electron-blocking layer was deposited with a 72.5 mg/ml of 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene (spiro-OMeTAD) (Lumtec) solution in chlorobenzene. Additives of 38 μl of lithium bis(trifluoromethanesulfonyl)imide (170 mg/mL in 1-butanol solution) per 1 ml of spiro-OMeTAD solution and 21 μl of 4-tert-butylpyridine (TBP) per 1 mL of spiro-OMeTAD solution. The samples were left to oxidize in a desiccator for 24 h. Spin-coating was carried out in a nitrogen-filled glovebox at 2000 rpm for 20 s with a ramp rate of 1000 rpm/s.
The interlayer is fabricated using both PEDOT:PSS (PH 1000) in water (Heraeus Clevios) and indium-tin oxide, 30 wt. % in isopropanol (IPA), (ITO)>100 nm nanoparticles (NPs) dispersion (Sigma), as precursor solutions. We first deposit a thin layer of PEDOT:PSS directly on top of the existing spiro-OMeTAD layer. The PEDOT:PSS precursor solution was prepared immediately prior to spin coating, by diluting PEDOT:PSS (PH 1000) in anhydrous 2-propanol (IPA) at a volume ratio of 1 to 1.5 (PEDOT:PSS to IPA) and then filtered with a 2.7 μm GF/D membrane filter (Whatman). The substrates were preheated at 80° C., and we then dynamically spin coated the diluted PEDOT:PSS solution, in a dry air atmosphere >10% relative humidity (RHM), at a speed of 6000 rpm for 20 s, and then annealed for at 80° C. for 10 min. We then deposited the ITO NPs layer. We prepared the ITO NPs precursor solution by diluting the 30 wt. % in IPA down to 1 wt. % in IPA. The diluted solution was sonicated, in a sonication bath, for 15 m prior to deposition. We dynamically spin coated the diluted ITO NPs solution, in a dry air atmosphere >10% relative humidity (RHM), at a speed of 6000 rpm for 20 s, and then annealed for at 80° C. for 10 m.
Middle Cell (MC) Fabrication: PC61BM/MAPbI3/Spiro-OMeTAD
PC61BM layer fabrication: A Phenyl-C61-butyric acid methyl ester (PC61BM) precursor solution was prepared by dissolving a 30 mg ml−1 PC61BM (99%, solenne) in a mixture of anhydrous chlorobenzene (CB) (sigma) and anhydrous chloroform (CF) solvents. The solvents were mixed at a volume ratio of 2 to 1, CB to CF. We doped the PC61BM using dihydro-1H-benzoimidazol-2-yl (N-DBI) derivatives, specifically 3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (N-DMBI). We doped the PC61BM precursor solution with N-DMBI at a 0.25 wt %. This solution was then filtered using a 0.45 μm PTFE filter. The substrates were preheated at 80° C., we then dynamically spin coated this solution in a dry air atmosphere >10% relative humidity (RHM) at 4000 rpm for 20 s, and annealed the substrate at 80° C. for 10 min.
In this work, we found that controlling the MA content in the acetonitrile (CH3CN)/methylamine (CH3NH2) (ACN/MA) MAPbI3 solution resulted in better tandem performance with higher reproducibility. Excess MA in the ACN/MA MAPbI3 solution can potentially percolate through pinholes of thin imperfect interlayers, thus partially or completely dissolving the underlying junction. Thus, solutions with the minimal amount of MA required to dissolve the perovskite were employed. Controlling the MA content in the solution can potentially be done by controlling the MA flow rate and stirring speed, however, precisely controlling these parameters was sometimes challenging. Instead, we prepared two ACN MAPbI3 dispersions, one with excess MA content resulting in a full ACN/MA MAPbI3 solution, and another ACN MAPbI3 dispersion without any MA Immediately prior to spin coating, we slowly add the ACN/MA MAPbI3 with excess MA to the ACN MAPbI3 dispersion until this dispersion is fully dissolved, and becomes a full solution. The resulting solution is an ACN/MA MAPbI3 solution at its critical solubility point. The preparations of the ACN/MA MAPbI3 solution and the ACN MAPbI3 dispersion are described below. The ACN MAPbI3 perovskite precursor solution without any MA was prepared, under nitrogen, using precursor salts methylammonium iodide (MAI) (Dyesol) and lead iodide (PbI2) (TCI) added into anhydrous acetonitrile (ACN) (Sigma Aldrich) at a concentration of 1.03 M for MAI and 1 M for PbI2, resulting in a non-stoichiometric solution (1.03:1 MAI:PbI2). This solution was then sonicated, in a sonication bath, for 1 h in order to fully react the MAI with the PbI2, a black perovskite dispersion is then seen at the bottom of the ACN filled vial.
The ACN/MA MAPbI3 perovskite precursor solution was prepared using an adapted method described by Noel et al. (see N. K. Noel, S. N. Habisreutinger, B. Wenger, M. T. Klug, M. T. Hörantner, M. B. Johnston, R. J. Nicholas, D. T. Moore, H. J. Snaith, Energy Environ. Sci. 2017, 10, 145). We first prepare an ACN/MA MAPbI3 perovskite precursor solution with the identical preparation method as described above. In order to dissolve the perovskite in ACN, a solution of methylamine (MA) in ethanol (Sigma Aldrich, 33 wt %) was placed into an aerator which was kept in an ice bath. Nitrogen was then bubbled into the solution, thus degassing the solution of MA. The MA gas which was produced was then passed through a drying tube filled with a desiccant (Drietire and CaO). The gas was bubbled into the black dispersion, while vigorously stirring the ACN/MA MAPbI3 dispersion using a large magnetic stir bar at a speed of approximately 700 rpm. The dispersion was bubbled for 15 minutes, which resulted in a full dissolution of the black perovskite particles, resulting in a clear, light yellow solution. We note this solution has an “excess” amount of MA in the ACN/MA MAPbI3 solution.
ACN/MA MAPbI3 perovskite layer preparation: The ACN/MA MAPbI3 precursor perovskite solution (at it's critical solubility point) is immediately dynamically spin coated in a dry air atmosphere >10% relative humidity (RHM) at 5000 rpm for 20 s. A post treatment of methylammonium chloride (MACl) was then carried out by dynamically spincoating at 6000 rpm for 20 s a 50 μl of MACl (Alfa Aesar, 2 mg/ml in isopropanol). The films were then annealed in an oven in an air atmosphere at 80° C. for 90 minutes. During this annealing process, the samples were covered with a large glass container to prevent dust contamination.
Spiro-OMeTAD hole-transporting layer fabrication: The electron-blocking layer was deposited by dynamically spin coating a 85 mg/ml of 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene (spiro-OMeTAD) (Lumtec) solution in chlorobenzene. Additives of 20 μl of lithium bis(trifluoromethanesulfonyl)imide (520 mg/mL in acetonitrile solution) per 1 ml of spiro-OMeTAD solution and 33 μl of 4-tert-butylpyridine (tBP) per 1 mL of spiro-OMeTAD solution. Spin-coating was done dynamically and carried out in a dry air atmosphere >10% relative humidity (RHM) at 2000 rpm for 30 s. The samples were left to oxidize in a desiccator for 24 h.
Bottom Cell (BC) Fabrication: PC61BM/ACN/MA MA-MAPb0.75Sn0.25I3/Spiro(TFSI)2
PC61BM layer fabrication: A Phenyl-C61-butyric acid methyl ester (PC61BM) precursor solution was prepared by dissolving a 30 mg ml−1 PC61BM (99%, solenne) in a mixture of anhydrous chlorobenzene (CB) (sigma) and anhydrous chloroform (CF) solvents. The solvents were mixed at a volume ratio of 2 to 1, CB to CF. We doped the PC61BM using dihydro-1H-benzoimidazol-2-yl (N-DBI) derivatives, specifically 3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (N-DMBI). We doped the PC61BM precursor solution with N-DMBI at a 0.25% wt %. This solution was then filtered using a 0.45 μm PTFE filter. The substrates were preheated at 80° C., we then dynamically spin coated this solution in a dry air atmosphere >10% relative humidity (RHM) at 4000 rpm for 20 s, and annealed the substrate at 80° C. for 10 min.
ACN/MA-MAPb0.75Sn0.25I3 Perovskite Precursor Solution Preparation:
To obtain a mixed-metal ACN/MA MAPb0.75Sn0.25I3 perovskite precursor solution, we mixed an ACN/MA MAPbI3 with an ACN/MA MAPb0.5Sn0.5I3 (without any MA) at a 1:1 volume ratio, resulting in an ACN/MA MAPb0.75Sn0.25I3. The ACN/MA MAPb0.5Sn0.5I3 solution perovskite precursor solution without any MA was prepared, under nitrogen, using precursor salts methylammonium iodide (MAI) (Dyesol), lead iodide (PbI2) (TCI), and anhydrous tin iodide (SnI2) beads (TCI) added into anhydrous acetonitrile (ACN) (Sigma Aldrich) at a concentration of 0.8 M for MAI, 0.46 M for PbI2 and 0.46 M for SnI2, resulting in a non-stoichiometric solution with 15% excess metal salts (1:1.15 MAI:PbI2+SnI2). This solution was then stirred under nitrogen at 70° C. for 1 h, in order to fully react the MAI with the mixed metals, a black perovskite dispersion is then seen at the bottom of the ACN filled vial. The ACN/MA MAPbI3 perovskite precursor solution was prepared using an adapted method described by Noel et al. We first prepare a ACN/MA MAPbI3 perovskite precursor solution at a 0.8 M for MAI and 0.46 M for PbI2, resulting in a non-stoichiometric solution with 15% excess metal salts (1:1.15 MAI:PbI2). In order to dissolve the perovskite in ACN, a solution of methylamine (MA) in ethanol H2O (Sigma Aldrich, 40 wt %) was placed into an aerator which was kept in an ice bath. Nitrogen was then bubbled into the solution, thus degassing the solution of MA. The MA gas which was produced was then passed through a drying tube filled with a desiccant (Drietire and CaO). The gas was bubbled into the black dispersion, while vigorously stirring the ACN/MA MAPbI3 dispersion using a large magnetic stir bar at a speed of approximately 700 rpm. The dispersion was bubbled for 15 minutes, which resulted in a full dissolution of the black perovskite particles, resulting in a clear, light yellow solution. We note this solution has an “excess” amount of MA in the ACN/MA MAPbI3 solution. The solution was then stored in nitrogen for approximately 3 h with activated 3 Å molecular sieves to remove any H2O that was introduced during the MA bubbling process. ACN/MA MAPb0.75Sn0.25I3 perovskite layer: This precursor perovskite solution is immediately dynamically spin coated in a nitrogen glovebox at 5000 rpm for 20 s. A second subsequent spin coating step was used to deposit a methylammonium chloride (MACl) post treatment. A 2 mg ml−1 solution of MACl in IPA was dynamically spin coated at 6000 rpm for 20 s. The films were then annealed in nitrogen at 80° C. for 90 minutes.
Spiro(TFSI)2 synthesis: The Spiro(TFSI)2 hole-transporting layer used for the MAPb0.75Sn0.25I3 perovskite was prepared using an adapted method described by Nguyen et al. (see W. H. Nguyen, C. D. Bailie, E. L. Unger, M. D. McGehee, J. Am. Chem. Soc. 2014, 136, 10996). We first dissolved 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene (spiro-OMeTAD) (Lumtec) solution in chlorobenzene (CB) at a 2 mg ml−1 concentration. Separately, we dissolved the Silver(I) bis(trifluoromethanesulfonyl)imide (Ag-TFSI) in methanol at a 100 mg ml−1. We slowly mixed identical volumes of both solutions together, while stirring. The final molar ratio is 1 to 0.95 (spiro-OMeTAD to Ag-TFSI). We then left the mixed solution stirring overnight. We filtered the solution with a 2 μm PTFE filter to remove the Ag colloids. We used a rotary evaporation to remove CB until approximately 5% of the original volume is left. We then added toluene to the remaining flask at a volume of 50% of the initial CB volume. We placed the solution in a refrigerator for 24 h, where a fine black powder precipitated. Once, the black powder fully settled, we removed excess toluene using a glass frit filter. We washed the powder with a cold 4° C. toluene. Once the powder was dry, we prepared a 20 mg ml−1 in methanol solution. This black powder should not have low solubility in methanol, which starts the precipitation process. We refrigerated the solution at 4° C. overnight. The black powder collected at the bottom of the vial. We removed the excess toluene using a glass frit filter, and washed with 4° C. methanol. Once dry, we collected and weighed the Spiro(TFSI)2 powder.
Spiro-OMeTAD doped with 10 wt. % Spiro(TFSI)2 hole-transporting layer fabrication: The electron-blocking layer was deposited by dynamically spin coating a spiro(TFSI)2 doped spiro-OMeTAD at 2000 rpm for 30 s in a nitrogen glovebox. This precursor solution was prepared with a 72.5 mg ml−1 wt. % spiro solution composed of a 7.25 mg ml−1 Spiro(TFSI)2 and a 65.25 mg ml−1 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene (spiro-OMeTAD) (Lumtec) solution in chlorobenzene. No additives were added to the spiro-OMeTAD solution.
Bottom Cell (BC) Fabrication: PEDOT:PSS/FA0.83Cs0.17Pb0.5Sn0.5I3/PC61BM/BCP
FA0.83Cs0.17Pb0.5Sn0.5I3 perovskite precursor preparation: A stoichiometric solution of 1.2 M FA0.83Cs0.17Pb0.5Sn0.5I3 was prepared in a nitrogen atmosphere by dissolving FAI (Dyesol), CsI (99.9%, Alfa Aesar), PbI2 (99.999%, Alfa Aesar), and SnI2 (99.999%, Alfa Aesar) in a mixed solvent of 4:1 DMF:DMSO by volume. Also dissolved in the solution is 60 mM tin (II) fluoride (SnF2, 99%, Sigma Aldrich) and 36 mM lead (II) thiocyanate (99.5%, Sigma Aldrich).
Device preparation: Patterned indium tin oxide (ITO) substrates were cleaned by sequentially rinsing in acetone and IPA. Once dried, the substrates were cleaned with an O2-plasma for ten minutes. Immediately following plasma treatment, a PEDOT:PSS solution (PVP AI 4083, Heraeus, in a 1:2 volume ratio with methanol) was spin coated in ambient conditions at 4 krpm for 30 s, followed by annealing at 150° C. in ambient for 10 minutes. The devices were immediately transferred to a N2 glovebox. Just prior to fabricating the perovskite film the PEDOT:PSS coated ITO substrates were annealed again at 120° C. for 10 minutes. The perovskite film was fabricated by spincoating the solution at 3.6 krpm for 14 s with a 6 s ramp. At 13 s after the start of the spincoating program, 200 μL of anisole was dispensed onto the spinning substrate. Once spincoating is finished, a stream of N2 was applied to the film for 15 s and then immediately annealed at 120° C. for 10 minutes. The PC61BM layer was produced by dynamically spincoating 50 uL of a hot solution (90° C.) of PC61BM (20 mg/mL dissolved in a mixed solvent of 3:1 chlorobenzene:1,2-dichlorobenzene by volume) at 2 krpm for 30 s and subsequently annealed at 90° C. for 2 minutes. Once cooled to room temperature, 70 μL of a 0.5 mg/mL solution of bathocuproin (BCP, 98%, Alfa Aesar) was dynamically spincoated at 4 krpm for 20 s.
Electrode: A 100 nm silver or gold electrode was thermally evaporated under vacuum of ≈10−6 Torr, at a rate of ≈0.2 nm·s−1.
Solar cell characterization: The current density-voltage (J-V) curves were measured (2400 Series SourceMeter, Keithley Instruments) under simulated AM 1.5 sunlight at 100 mWcm-2 irradiance generated by an Abet Class AAB sun 2000 simulator, with the intensity calibrated with an NREL calibrated KG5 filtered Si reference cell. The mismatch factor was calculated to be less than 1%. The active area of the solar cell is 0.0919 cm-2. The forward JV scans were measured from forward bias (FB) to short circuit (SC) and the backward scans were from short circuit to forward bias, both at a scan rate of 0.25V s-1. A stabilization time of 5 seconds under 1 sun illumination and forward bias of 0.3V above the expected VOC was done prior to scanning.
EQE characterization: The multi-junction EQEs were measured by optically biasing the sub-cells that are not being measured with a 3 W 470-475 nm LED and a 3 W 730-740 nm LED, for the TC and for the BC, respectively. A negative bias equal to Voc of the sub-junction that is being optically biased was applied to the tandem during the measurement. This allows us to measure the response of the tandem in short-circuit condition.
Transient photoconductivity: The Nd:YAG laser excitation source tuned to 470 nm and pumped at 10 Hz with 7 ns pulses is used at the range of fluences to have various charge carrier density as described in the main text. This pulse light is illuminated in entire sample area to evenly excite the film. A bias of 24 V is applied across the in-plane (lateral) electrodes. Here, as the contact resistance between perovskite film and Au electrode is fairly small compared to sample resistance, we employ two electrodes conductivity measurement. A variable resistor is in series with sample in the circuit to always be <1% of the sample resistance. We monitored the voltage drop on variable series resistor through parallel oscilloscope (1 MΩ) to determine the potential dropped across the two in-plane Au electrodes (4 mm channel to channel distance) in sample. Perovskite film is scribed to have 5 mm channel width, and coated with inert 200 nm PMMA. Transient photoconductivity (Gm) was calculated by the equation
where, Rr is variable resistor, Vbias is bias voltage, 1 is channel-channel length, w is channel width, and t is film thickness.
Overview: We modelled the optical properties of the stack using a generalized transfer matrix method (TMM) (see E. Centurioni, Appl. Opt. 2005, 44, 7532). All the calculations were done in Python with heavy use of the NumPy and SciPy libraries. The wavelength dependent complex refractive index, the layer thicknesses and the incidence angle were fed as input. The TMM model outputs the electric field distribution in the stack. This was used to calculate Transmittance T(E), Reflectance R(E) and the absorption A(E) in each layer. The short circuit current of each sub-cell was then determined by assuming the internal quantum efficiency to be unity:
J
SC
=q∫
0
∞
A(E)·ϕAM1.5(E)·dE
The JV curve from each sub-cell was obtained by combining this modelled JSC with the electrical characteristics of state-of-art single junction cells. To do this, we parametrized the JV curves of state-of-the-art single junctions as per the single diode equivalent model:
Where n, VT, RS, J0 and RSH are respectively the electron charge, thermal voltage at 300K, series resistance, dark current, and shunt resistance. The JV curve of each multi-junction sub-cell is modelled by replacing Jsun in the fitted equation with the JSC calculated from the multijunction stack. As the correlation between Jsun and other fitting parameters is negligible, we can be sure that Jsun can be changed without changing other parameters. The approach of Jain et al. (see A. Jain, A. Kapoor, Sol. Energy Mater. Sol. Cells 2004, 81, 269). was used to solve the single diode model using the Lambert W function. After calculating the JV curves of all sub-cells, we combined them to obtain the multi-junction JV curve (see A. Hadipour, B. de Boer, P. W. M. Blom, Org. Electron. 2008, 9, 617). The maximum point is calculated from this combined JV curve.
Inputs for the Optical and Electrical Models: The refractive indices for ITO, FTO, PEDOT:PSS, PCBM, Spiro-OMeTAD, Ag, MA0.4FA0.6Sn0.6Pb0.4I3 and MAPbI3 were taken from the literature (see T. A. F. König, P. A. Ledin, J. Kerszulis, M. A. Mahmoud, M. A. El-Sayed, J. R. Reynolds, V. V. Tsukruk, ACS Nano 2014, 8, 6182; J. M. Ball, S. D. Stranks, M. T. Hörantner, S. Hiittner, W. Zhang, E. J. W. Crossland, I. Ramirez, M. Riede, M. B. Johnston, R. H. Friend, H. J. Snaith, Energy Environ. Sci. 2015, 8, 602; D. Shi, V. Adinolfi, R. Comin, M. Yuan, E. Alarousu, A. Buin, Y. Chen, S. Hoogland, A. Rothenberger, K. Katsiev, Y. Losovyj, X. Zhang, P. A. Dowben, O. F. Mohammed, E. H. Sargent, O. M. Bakr, Science 2015, 347, 519; V. S. Gevaerts, L. J. A. Koster, M. M. Wienk, R. A. J. Janssen, ACS Appl. Mater. Interfaces 2011, 3, 3252; M. Filipič, P. Löper, B. Niesen, S. De Wolf, J. Krč, C. Ballif, M. Topič, Opt. Express 2015, 23, A263; P. B. Johnson, R. W. Christy, Phys. Rev. B 1972, 6, 4370; M. T. Hörantner, T. Leijtens, M. E. Ziffer, G. E. Eperon, M. G. Christoforo, M. D. McGehee, H. J. Snaith, ACS Energy Lett. 2017, 2, 2506; P. Löper, M. Stuckelberger, B. Niesen, J. Werner, M. Filipič, S.-J. Moon, J.-H. Yum, M. Topič, S. De Wolf, C. Ballif, J. Phys. Chem. Lett. 2015, 6, 66). The extinction co-efficient k of FA0.83Cs0.17Pb(Br0.7I0.3)3 was obtained by measuring the transmittance T and the reflectance R of a thin film of thickness t on glass and using the relations:
α=4πk/λ
Once k(λ) was obtained, we parametrized it in terms of Lorentz oscillators to get an analytical representation, which was transformed into the refractive index n(λ) via the Kramers-Kronig transform:
The electrical characteristics for the MAPbI3 and the MAPb0.75Sn0.25I3 are taken from best reported cells of same or similar class in the literature (see S. S. Shin, E. J. Yeom, W. S. Yang, S. Hur, M. G. Kim, J. Im, J. Seo, 2017, 6620; R. Prasanna, A. Gold-Parker, T. Leijtens, B. Conings, A. Babayigit, H. G. Boyen, M. F. Toney, M. D. McGehee, J. Am. Chem. Soc. 2017, 139, 11117). For the FA0.83Cs0.17Pb(Br0.7I0.3)3 sub-cell, we use the JV curve of our best FA0.83Cs0.17Pb(Br0.7I0.3)3 single junction cell (
Where nITO, nPCBM and fITO are respectively the complex refractive index of ITO, complex refractive index of PCBM and the fraction of ITO in the effective medium.
FA0.83Cs0.17Pb(Br0.7I0.3)3/MAPbI3 simulation—
FA0.83Cs0.17Pb(Br0.7I0.3)3/MAPbI3 (optimized)—
FA0.83Cs0.17Pb(Br0.7I0.3)3/MAPbI3/MA0.4FA0.6Pb0.4Sn0.6I3 (optimized) simulation—
| Number | Date | Country | Kind |
|---|---|---|---|
| 1817166.0 | Oct 2018 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2019/052988 | 10/18/2019 | WO | 00 |
