Patent Application
20210388261
The present invention relates to composite perovskite materials and, in particular, to composite perovskite materials for application in various lighting systems.
Lead halide perovskites, as direct bandgap semiconductors, show very low efficiency of light emission at room temperature in bulk crystals, dominated by carrier trapping. Measured values of the exciton binding energy in lead halide perovskite, typical CsPbBr3, range from 19 meV to about 60 meV. At room temperature, such shallow excitons are ionized to free carriers in a very short time, so energy transport occurs mainly by free and/or shallow-trapped carriers, and radiative recombination should obey second-order kinetics for the most part. However, low-dimensional lead halide perovskites become promising candidates to beat the second-order kinetics bottleneck, and have been researched intensively ever since the near unity of photoluminescence quantum yield were first reported in 2012. This is because the nanometer scale spatial confinement of electrons and holes promotes the probability of geminate recombination, which consequently leads to the picosecond decay and enhanced absorption strength.
Motivated by the merits of nanostructured halide perovskites, many approaches to low-dimensional perovskites have been studied in various synthesis methods including 3D structure (nanoparticles, nanowires, and nanoplates) and layered structure (quasi-2D). In general, organic surfactants or organic cations are required to either chemically terminate the crystal growth or create the mechanical exfolication between perovskite sheets. Although the ligand-assisted methods benefit good reproducibility and high yield, the organic additives attached the crystal surfaces and significantly hindered the charge transport due to extremely low conductivity of the organic compounds. Meanwhile, the small molecule surfactants were blamed for one of the critical reasons for the poor stability of halide perovskite films when it loses the support of surrounding solution. In the past few years, great efforts were made to understand and stabilize the low dimensional lead halide perovskites towards high resistivity to moisture and heat, however, the robustness of the perovskite LEDs is still a challenge.
In view of these disadvantages, composite perovskite compositions are described herein exhibiting desirable lighting characteristics and robustness. In one aspect, composite nanoparticles are provided. In some embodiments, a composite nanoparticle comprises a host matrix comprising A4BX6-zYz, and ABX3-pYp inclusions dispersed within the host matrix of the composite nanoparticle, wherein A is an alkali metal, B is an element selected from the group consisting of transition metals, Group IVA elements and rare earth elements and X and Y are independently selected from Group VIIA elements, 0≤z≤6, and 0≤p<3. When z equals 6, X assumes the subscript of zero, thereby making the formula A4BY6. In being dispersed within the host matrix of A4BX6-zYz, the ABX3-pYp inclusions reside in the bulk of the host matrix. In some embodiments, for example, the ABX3-pYp inclusions are not present on surfaces of the host matrix.
The ABX3-pYp inclusions can be photoluminescent and/or electroluminescent. The ABX3-pYp inclusions, for example, can emit light in the visible region of the electromagnetic spectrum. In some embodiments, composition of the ABX3-pYp inclusions can be varied to emit red, green or blue light. The ABX3-pYp inclusions can have peak emission from 500-550 nm, 600-700 nm or 400-500 nm. The emission can have a full width half maximum of 20 nm or less, in some embodiments. The ABX3-pYp inclusions can form a Type I band offset with the A4BX6-zYz host, in some embodiments. In non-limiting embodiments, the host matrix comprises Cs4PbBr6 and inclusions are CsPbBr3 and/or CsPbI3. In other embodiments, the host matrix comprises Cs4PbBr6 and inclusions are CsPbI2Br. As described further herein, the host matrix comprising A4BX6-zYz and/or ABX3-pYp inclusions can be crystalline.
Additionally, a capping layer can reside between the ABX3-pYp inclusions and host matrix. The capping layer can have a composition different form the ABX3-pYp inclusions and the A4BX6-zYz host matrix. In some embodiments, the capping layer exhibits a Br gradient. Moreover, the capping layer can partially or fully surround an ABX3-pYp inclusion and/or have thickness less than 5 nm.
In another aspect, thin perovskite films are provided. In some embodiments, a thin film comprises a continuous host matrix comprising A4BX6-zYz, and ABX3-pYp inclusions dispersed within the host matrix, wherein A is an alkali metal, B is an element selected from the group consisting of transition metals, Group IVA elements and rare earth elements and X and Y are independently selected from Group VIIA elements, 0≤z≤6, and 0≤p<3. In being dispersed within the host matrix, the ABX3-pYp inclusions reside in the bulk of the host matrix. In some embodiments, for example, the ABX3-pYp inclusions are not present on surfaces of the host matrix or surfaces of the thin film.
The ABX3-pYp inclusions can be photoluminescent and/or electroluminescent. The ABX3-pYp inclusions, for example, can emit light in the visible region of the electromagnetic spectrum. In some embodiments, composition of the ABX3-pYp inclusions can be varied to emit red, green or blue light. The ABX3-pYp inclusions can have peak emission from 500-550 nm, 600-700 nm or 400-500 nm. The emission can have a full width half maximum of 20 nm or less, in some embodiments. The ABX3-pYp inclusions can form a Type I band offset with the A4BX6-zYz host, in some embodiments. In non-limiting embodiments, the host matrix comprises Cs4PbBr6 and inclusions are CsPbBr3 and/or CsPbI3. In other embodiments, the host matrix comprises Cs4PbBr6 and inclusions are CsPbI2Br. As described further herein, the host matrix comprising A4BX6-zYz and/or ABX3-pYp inclusions can be crystalline.
Additionally, a capping layer can reside between the ABX3-pYp inclusions and host matrix. The capping layer can have a composition different form the ABX3-pYp inclusions and the A4BX6-zYz host matrix. In some embodiments, the capping layer exhibits a Br gradient. Moreover, the capping layer can partially or fully surround an ABX3-pYp inclusion and/or have thickness less than 5 nm.
The thin perovskite film can have any desired thickness. In some embodiments, thickness of the thin film is at least 100 nm. The thin perovskite film, for example can have thickness of 100 nm to 1 μm.
In a further aspect, electroluminescent devices are described herein. An electroluminescent device comprises a first electrode and a second electrode and a light emitting layer positioned between the first and second electrodes, the light emitting layer comprising a continuous host matrix comprising A4BX6-zYz, and ABX3-pYp inclusions dispersed within the host matrix, wherein A is an alkali metal, B is an element selected from the group consisting of transition metals, Group IVA elements and rare earth elements and X and Y are independently selected from Group VIIA elements, 0≤z≤6, and 0≤p<3. In being dispersed within the host matrix, the ABX3-pYp inclusions reside in the bulk of the host matrix. In some embodiments, for example, the ABX3-pYp inclusions are not present on surfaces of the host matrix or surfaces of the light emitting layer.
The ABX3-pYp inclusions are electroluminescent. The ABX3-pYp inclusions, for example, can emit light in the visible region of the electromagnetic spectrum. In some embodiments, composition of the ABX3-pYp inclusions can be varied to emit red, green or blue light. The ABX3-pYp inclusions can have peak emission from 500-550 nm, 600-700 nm or 400-500 nm. The emission can have a full width half maximum of 20 nm or less, in some embodiments. The ABX3-pYp inclusions can form a Type I band offset with the A4BX6-zYz host matrix in some embodiments. In non-limiting embodiments, the host matrix comprises Cs4PbBr6 and inclusions are CsPbBr3 and/or CsPbI3. In other embodiments, the host matrix comprises Cs4PbBr6 and inclusions are CsPbI2Br. As described further herein, the host matrix comprising A4BX6-zYz and/or ABX3-pYp inclusions can be crystalline. The presence of a host matrix comprising A4BX6-zYz can sufficiently passivate the light emitting ABX3-pYp inclusions, thereby precluding the use or presence of organic ligands, such as CH3NH3Br (MABr).
Additionally, a capping layer can reside between the ABX3-pYp inclusions and host matrix. The capping layer can have a composition different form the ABX3-pYp inclusions and the A4BX6-zYz host matrix. In some embodiments, the capping layer exhibits a Br gradient. Moreover, the capping layer can partially or fully surround an ABX3-pYp inclusion and/or have thickness less than 5 nm.
The light emitting layer can have any desired thickness. In some embodiments, thickness of the thin film is at least 100 nm. The thin perovskite film, for example can have thickness of 100 nm to 1 um.
The first and/or second electrode can be radiation transmissive, thereby enabling top emitting devices. In some embodiments, the radiation transmissive first and/or second electrodes are metal or alloy. In other embodiments, a radiation transmissive electrode may be a conductive metal oxide. Radiation transmissive conducting oxides can include one or more of indium tin oxide (ITO), gallium indium tin oxide (GITO), aluminum tin oxide (ATO) and zinc indium tin oxide (ZITO). In some embodiments, a radiation transmissive first and/or second electrode is formed of a radiation transmissive polymeric material such as polyanaline (PANT) and its chemical relatives or 3,4-polyethylenedioxythiophene (PEDOT). Further, a radiation transmissive first and/or second electrode can be formed of a carbon nanotube layer having a thickness operable to at least partially pass visible electromagnetic radiation. An additional radiation transmissive material can comprise a nanoparticle phase dispersed in a polymeric phase. The electroluminescent device may be connected to a direct current source, thereby functioning as a light emitting diode. In other embodiments, the electroluminescent device may be connected to an alternating current source.
In some embodiments, one or more hole transport layers (HTL) are positioned between the anode and perovskite light emitting layer(s). Similarly, one or more electron transport layers (ETL) can be positioned between the cathode and perovskite light matting layer(s). Specific compositional identity of HTLs and ETLs can be dependent upon the electronic structure of the organic-inorganic perovskite nanocrystal layer(s) and electrode composition. In some embodiments, for example, a HTL comprises poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (poly-TPD), poly(9-vinylcatbazole) (PVK), 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (CBP), or PEDOT:PSS. In some embodiments, an ETL comprises 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) or phenyl-dipyrenylphosphine oxide (POPy2).
In some embodiments, the electroluminescent device further comprises a current injection gate positioned between the first electrode and the light emitting layer or between the second electrode and the light emitting layer, wherein the current injection gate comprises a semiconductor layer of electronic structure restricting injected current flow from the first or second electrode through the semiconductor layer as a function of alternating current voltage frequency applied to the first and second electrodes. In such embodiments, the electroluminescent device may be connected to an alternating current source.
Semiconducting materials demonstrating frequency dependent restriction of injected current from the first or second electrode can serve as the current injection gate in the electroluminescent device architecture. Suitable gate semiconductor materials can comprise inorganic semiconductors and organic semiconductors. For example, in some embodiments, inorganic gate semiconductors comprise transition metal oxides, including titanium oxide. In some embodiments, inorganic gate semiconductors are selected from Tables I and II.
Moreover, organic gate semiconductors can comprise small molecule semiconductors including acene and/or acene derivatives such as anthracene, tetracene, pentacene, hexacene, heptacene or rubrene. In some embodiments, small molecule gate semiconductor is selected from Table III.
Additionally, organic gate semiconductor can comprise one or more conjugated polymeric materials including polyacetylene, polyacetylene derivatives, poly(9,9-di-octylfluorene-alt-benzothiadiazole) (F8BT), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] [MEH-PPV], P3HT, poly(3,4-ethylenedioxythiophene) (PEDOT), PEDOT:PSS or mixtures thereof. In some embodiments, gate semiconductor is formed of carbon nanoparticles, such as those listed in Table IV.
Gate semiconductors can be intrinsic or doped. Further, suitable inorganic and/or organic gate semiconductors can demonstrate a bandgap of at least 2 eV or at least 3 eV. In some embodiments, gate semiconductor material has a bandgap of 2 to 4 eV or 2.5 to 3.5 eV.
A semiconductor layer of a current injection gate can have any thickness not inconsistent with the objectives of the present invention. In some embodiment, a gate semiconductor layer has a thickness selected from Table V.
In further embodiments, a current injection gate having frequency dependent behavior can be a composite formed of organic and inorganic components. For example, a current injection gate composite can comprise inorganic particles dispersed in a polymeric matrix. In some embodiments, one or more ceramic particles (e.g. metal carbides, metal oxides, metal carbonitrides, metal nitrides, metal oxynitrides and/or metal oxycarbonitrides) can be dispersed in a conjugated or semiconducting polymeric matrix to provide a current injection gate exhibiting a frequency dependent restriction of injected current from the first or second electrode. A current injection gate composite can employ up to about 90 wt % inorganic particles with the balance polymeric matrix. In some embodiments, a current injection gate comprises 15-75 wt. % inorganic particles with the balance polymeric matrix. Suitable inorganic particles and conjugated polymer for the current injection gate composite are described in this Section C. Inorganic particles for the composite current injection gate can have any average particle size not inconsistent with the objectives of the present invention. For example, in some embodiments, the inorganic particles are nanoparticles having an average size less than 1 μm. In some embodiments, the inorganic particles have an average size from 10 μm to 500 μm. Alternatively, the inorganic particles can have an average size greater than 1 μm. A current injection gate composite, in some embodiments, has a thickness selected from Table V.
An electroluminescent device may also be encapsulated in a hydrophobic of water resistant material, such as a polysiloxane or other elastomer. Moreover, electroluminescent devices described herein are flexible, in some embodiments. Additionally, electroluminescent devices described herein can exhibit lighting efficiencies of at least 100 lm/W or at least 200 lm/W and lifetimes in excess of 1,000 hours, 5,000 hours or 10,000 hours. In some embodiments, an electroluminescent device described herein has a lighting efficiency of 150-250 lm/W and/or a lifetime of 5,000-15,000 hours.
These and other embodiments are further described in the detailed description which follows.
Embodiments described herein can be understood more readily by reference to the following detailed description, examples and drawings. Elements, apparatus, and methods described herein, however, are not limited to the specific embodiments presented in the detailed description, examples and drawings. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.
As described herein, composite nanoparticles comprise a host matrix comprising A4BX6-zYz, and ABX3-pYp inclusions dispersed within the host matrix of the composite nanoparticle, wherein A is an alkali metal, B is an element selected from the group consisting of transition metals, Group IVA elements and rare earth elements and X and Y are independently selected from Group VIIA elements, 0≤z≤6, and 0≤p<3. In some embodiments, the host matrix and inclusions present a core shell architecture. In the present example, CsPbBr3 nano-inclusions embedded Cs4PbBr6 matrix, is illustrated in
The CsPbBr3—Cs4PbBr6 thin film on glass substrate was clear with yellow tint in room light (
The CsPbBr3—Cs4PbBr6 device showed an electroluminescence (EL) peak with the full width of half maximum (FWHM) of 20.9 nm solely from the imbedded CsPbBr3 nanoinclusions, which was sharper than the emission from CsPbBr3 NC device (FWHM=27.4 nm,
Even though the solid cap significantly improved the device lifetime, the Cs4PbBr6 lattice was not chemically stable directly contacting water. As shown in
To investigate the thermal robustness, a CsPbBr3—Cs4PbBr6 device was heated and maintained for 30 s. Due to the half micrometer of the total device thickness, the heat could spread over the sample in a short period of time. The devices were then cooled back to 25° C. (room temperature) before the luminous and electrical measurements. As shown in
Instead of rigid glass, the flexible PET was also used as substrate to build the CsPbBr3—Cs4PbBr6 LED. Device flexibility on plain and ITO coated PET substrates was investigated. In the irrigative bending tests with a constant current (62.5 mA/cm2), the ITO free device maintained over 90% of the initial brightness (70 cd/m2) up to 4,000 bending cycles as shown in
The ligand assisted CsPbBr3 nanocrystals have a good stability in liquid suspension. However, once the nanocrystals are processed into the thin film, it suffers the stability issue and the surface agents become unwanted. There are three reasons: (1) The remained surface agents are normally sensitive to air not as stable as in solution. The instability of nanocrystal emitter in solid form is one of the major problems leading to the short lifetime of EL device. The loss of surface ligands could also cause the nanocrystals fusion or phase transition, which ultimately have negative impacts on radiative efficiency. (2) The excessive organic ligands in chemical synthesis make it difficult to dry the film because of the strong bonds between solvent molecules and the surface agents. The bottom “wet” film is a major issue for the deposition of top functional layer. (3) The organic ligands normally have high resistivity which increase the barrier for carrier injection to emitter under electric field. The consequences are higher driving voltage and low power efficiency which accelerate the device degradation.
The Cs4PbBr6 solid capping is an efficient and facile method to stabilize CsPbBr3 nanocrystals without additives. Unlike fuzzy organic ligands, the Cs4PbBr6 shell was demonstrated to be thick and compact which seals the CsPbBr3 nanocrystals air tight. There is barely moisture and air penetrations into the emission centers which significantly improved stability of CsPbBr3—Cs4PbBr6 system. Crystalized by anti-solvent or/and thermal annealing. The CsPbBr3—Cs4PbBr6 thin film is hard and flat in terms of morphology which eases the deposition of top layers. The solvent annealing is also a low temperature process which enables the devices on flexible plastic substrates. Meanwhile, the solid Cs4PbBr6 shell acts as a mechanical shield to reduce the friction between CsPbBr3 nanocrystals in distortional substrates. The type I heterojunction at the CsPbBr3—Cs4PbBr6 interface constructs a quantum well for the efficient exciton radiative recombination. Unlike carrier tunneling through organic ligands, the e-h pairs are formed in Cs4PbBr6 (˜3.7 eV) and transferred to CsPbBr3 (˜2.4 eV). The e-h pairs are trapped in CsPbBr3 confinement, then recombine leading to the photon emission. However, more works are required to carry out for a deep understanding of the energy transfer mechanism in the heterojunction to further improve the CsPbBr3—Cs4PbBr6 LEDs' quantum efficiency.
Top-emitting structure of thin film LEDs allows driving transistors implemented under the LEDs, facilitating display contrast as well as its compatibility with the active driving circuits. Furthermore, due to the metal electrode replacing ITO, the top-emitting structure used dual metal electrodes which has a significantly improvement on the stabilities such as luminance, emission efficiency, and color accuracy.
Since OLED technology was first commercialized in 1997 by Tohoku Pioneer, the OLED display market has been well developed in the past two decades and is expected to garner $37.2 billion by 2020. However, the cost of OLED technology is still higher than its competitors such as LCD display. One of the main holds is the cost of high-purity, efficient, and stable organic semiconductors that require extremely high standard synthetic conditions and purification processes. For instant, the green emissive pi-conjugated materials are costly about 10 USD per m2 in an industrial scale comparing to 0.6 USD per m2 of Cs—Pb—Br materials. Regardless, the Cs—Pb—Br perovskite LED provides a dramatic high color purity that the organic semiconductor cannot compete. Even comparing with the state-of-the-art CdSe or InP quantum dots, the Cs—Pb—Br perovskite shows narrower FWHM and low cost, more importantly the ease of in-situ preparation. Nonetheless, typical type-I CdSe or InP QDs with rather thin (1-2 nm) shells are susceptible to becoming charged in actual devices, particularly at high current densities, resulting in substantial efficiency decrease and poor device stabilities.
Materials and Methods
Cs—Pb—Br precursor was prepared by adding PbBr2 and CsBr in 5 ml vials with the molar ratio of 1:1.5 into Dimethyl sulfoxide (DMSO). The mixture was stirred for 2 hours at 65° C. until completely dissolved.
The Cs—Pb—Br precursor solution was spin-coated onto the substrates in N2 filled glove box. The spin speed was accelerated to final speed of 4000 rpm through 1000 rpm in 3 seconds. A wet layer of Cs—Pb—Br perovskite is formed in the first 30 second. Then, two droplets of anti-solvent acetone was applied on the top of the spinning substrates to create a fast crystallization for CsPbBr3—Cs4PbBr6 formation. The duration of the entire spinning coat process is 60 seconds. For devices on glass, the samples were heated to 250° C. for 10 mins to improve the crystallization. For devices on PET substrate, 75° C. was used in post annealing to remove solvent residue.
An integrating sphere was employed to determine the quantum yield (QY) of perovskite samples. The sample was added in a thin cuvette and was excited with a 405 nm blue LED light. The scattered excitation, along with emission, were collected by using a fiber optic coupled spectrometer (FLAME-S-XR1-ES). The whole spectrum was collected for both a reference (cuvette with DMSO only) and for the sample.
The ratio of the number of emission photons over the number of absorbed photons was used to determine the QY as shown in the equation below,
where Sem and Sexc are the integrated signal in the emission and excitation region, respectively, for the sample, and Rem and Rexc are the integrated signal in the emission and excitation region, respectively, for the reference. As a check for the accuracy of the system, the QY of Rhodamine 6G in ethanol was found to be 94.4%, close to the literature value of 95%. (Kubin, R. F.; Fletcher, A. N. Fluorescence quantum yields of some rhodamine dyes. J Lumin. 1982, 27, 455-462.)
The crystalline phase analysis was performed by an X-ray powder diffractometer (Bruker D2 PHASER) in ambient.
The PL of Cs—Pb—Br perovkite layers in different molar ratio was measured by a spectrofluorometer (PerkinElmer LS50B) on glass substrates.
A scanning electron microscope (JEOL 6330) was utilized to analyze the morphology of different molar ratio thin films and CsPbBr3 and Cs4PbBr6 microcrystals.
TEM images of Cs4PbBr6 nanograins were taken on a JEOL JEM-1200EX. CsPbBr3 and Cs4PbBr6 nanograins thin film was peeled off by a blade and placed on copper grid as imaging sample. The selected area electron diffraction patterns were achieved as well.
HT-TEM measurements were performed on an aberration-corrected FEI Titan S 80-300 STEM/TEM microscope equipped with a Gatan OneView camera at an acceleration voltage of 300 kV.
Devices were built on a 2.54 cm×2.54 cm plain glass substrate. The glass substrates are cleaned in an ultrasonic bath with acetone followed by methanol and isopropanol for 1 hour each. A 100 nm thick layer of Al was pre-coated by thermal evaporator as bottom reflective electrode. The substrates were dry-cleaned for 30 min by exposure to an UV-ozone ambient. ZnO nanoparticle suspensions (˜35 nm) were spin-coated onto the Al-coated glass substrates at 4000 rpm for 30 s and baked at 100° C. for 30 min in vacuum oven. The substrates were transferred into glove box for further depositions. CsPbBr4—Cs4PbBr6 perovskite layers were deposited by spin-coating at 4000 rpm for 60 s from 1:1.5 PbBr2-to-CsBr precursor solution. Poly-TPD chlorobenzene solutions (concentration: 10 mg/mL) at 2000 rpm for 30 s were applied for hole transport layer. After baking, MoO3 (9 nm) and Au semi-transparent electrode (15 nm) were deposited using a thermal evaporation system through a shadow mask under a vacuum of 2×10−7 Torr.
The LED devices in this report are measured in on-off mode inside of glove box at room temperature (25° C.) without encapsulation. Current versus voltage characteristics were measured using a Keithley 2400 source measure unit. Simultaneously, luminance (in cd/m2) was directly measured using a photometer (ILT 1400-A) with an optical fiber facing light-emitting pixel. The EL spectra for the devices were collected by an ILT 950 spectroradiometer (International Light Technologies).
Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.
The present invention claims priority pursuant to 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 62/746,369 filed Oct. 16, 2018 which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/056556 | 10/16/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62746369 | Oct 2018 | US |
