Patent Application
20240188435
Electrically driven light emitting diodes (LEDs) have a number of applications, ranging, for example, from full-color displays to solid-state lighting. Numerous types of light emitting materials and device configurations have been explored to date for use in electrically driven LEDs, including epitaxially grown inorganic semiconductors based LEDs, organic LEDs, and quantum dot LEDs.
Despite the rapid pace of development, electrically driven LEDs have not achieved their full potential in terms of performance, cost efficiency, and other metrics. Therefore, identifying new low-cost materials for high performance LEDs that can be easily processed is of great scientific and practical interest.
Embodiments of the subject invention provide novel and advantageous organic metal halide hybrids (OMHHs) that can be used as improved materials (e.g., emitter materials) for electrically driven LEDs, as well as methods of fabricating the same. The OMHHs can be highly luminescent and conductive zero-dimensional (0D) OMHHs. Embodiments also provide efficient LEDs that include one or more of the OMHHs described herein. For example, the OMHH can be (and the LEDs can be based on) solution processed TPPcarzSbBr4 thin films (PLQE of 86.1%). The LEDs can exhibit external quantum efficiencies (EQEs) of, for example at least 5.12%, with a peak luminance of, for example, at least 5957 candelas per square meter (cd/m2), which are the highest values achieved to date for electroluminescence devices based on 0D OMHHs.
In an embodiment, an OMHH can have the formula (Cat)aM+bXy, where Cat is a phosphonium cation comprising a phosphorus atom substituted with three aryl C1-C20 hydrocarbyl substituents and one heteroaryl C1-C20 hydrocarbyl substituent, where M is a metal, where b is the oxidation state of the metal, and where X is a halogen. For example, a+b can equal y. The heteroaryl C1-C20 hydrocarbyl substituent can comprise a carbazole moiety, such as a phenyl-carbazole moiety. The three aryl C1-C20 hydrocarbyl substituents can be phenyl. The phosphonium cation can be, for example, triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium with the structure shown in
In another embodiment, an electrically driven LED can comprise: a first electrode; a light emitting layer comprising an OMHH as disclosed herein; and a counter electrode. The light emitting layer can be disposed between the first electrode and the counter electrode. The device can further comprise at least one of: a hole transporting layer disposed between the first electrode and the light emitting layer; and an electron transporting layer disposed between the counter electrode and the light emitting layer. The device can be a hole-only device. The device can be an electron-only device.
Embodiments of the subject invention provide novel and advantageous organic metal halide hybrids (OMHHs) that can be used as improved materials (e.g., emitter materials) for electrically driven LEDs, as well as methods of fabricating the same. The OMHHs can be highly luminescent and conductive zero-dimensional (0D) OMHHs. Embodiments also provide efficient LEDs that include one or more of the OMHHs described herein. For example, the OMHH can be (and the LEDs can be based on) solution processed TPPcarzSbBr4 thin films (PLQE of 86.1%) and/or TPPcarzSbBr4 single crystals (PLQE of 93.8%). The LEDs can exhibit external quantum efficiencies (EQEs) of, for example at least 5% (e.g., 5.12% or about 5.12%), with a peak luminance of, for example, at least 5000 candelas per square meter (cd/m2) (e.g., 5957 cd/m2 or about 5957 cd/m2), which are the highest values achieved to date for electroluminescence devices based on 0D OMHHs.
In the related art, metal halide perovskites and perovskite-related materials have emerged as light emitting materials with remarkable and highly tunable optical properties. Efficient near-infrared (NIR), red, green, and blue perovskite LEDs have been demonstrated with external quantum efficiencies (EQEs) of up to 22.2%, 24.4%, 28.1%, and 13.8%, respectively. While perovskite LEDs have great potential, lead-containing devices represent a major environmental and health concern that could limit their wide commercialization. Moreover, most halide perovskites and perovskite-related structures are metastable under normal atmospheric conditions, which is another obstacle to achieve for devices with long lifetimes.
Zero-dimensional (0D) organic metal halide hybrids (OMHHs) are a new class of light emitting materials with exceptional color tunability. While near-unity photoluminescence quantum efficiencies (PLQEs) have been obtained for a large number of 0D OMHHs, it remains challenging to employ them successfully as emitters for electrically driven LEDs, likely due to the low conductivity of wide band gap organic cations.
In searching for efficient lead-free perovskite-related light emitting materials with high stability, progress has been made with 0D OMHHs that include light emitting metal halide polyhedra fully isolated and surrounded by bulky organic cations. Due to the complete site isolation, 0D OMHHs may possess a desirable “host-dopant” structure, with light emitting metal halide species periodically embedded in a large bandgap organic host matrix. While high PLQEs of up to near-unity have been achieved in numerous 0D OMHHs, their application in electrically driven LEDs has not been widely considered. The poor conductivity and wide band gap of organic cations are some of the factors responsible for the inferior charge transport and energy level alignment in these low performance LEDs based on 0D OMHHs.
There remains a need for improved materials for electrically driven LEDs, such as OMHHs. There also remains a need for an effective molecular engineering-based approach for the preparation of highly luminescent and conductive 0D OMHHs for use as emitter materials in electrically driven LEDs. Embodiments of the subject invention address one or more of these needs.
Embodiments provide molecular engineering approaches for the preparation of highly luminescent and conductive 0D OMHHs for use as emitter materials in electrically driven LEDs. In some embodiments, room temperature co-crystallization of a semiconducting organic halide (e.g., TPPcarzBr) and a metal halide (e.g., SbBr3) results in the 0D OMHH (e.g., 0D organic antimony halide hybrid—TPPcarzSbBr4), which may be in the form of single crystals or a thin film. The 0D OMHH (e.g., TPPcarzSbBr4) can exhibit red emission peaked at 653 nm with PLQEs of at least 90% (e.g., 93.8% or about 93.8%).
Embodiments also provide electrically driven LEDs, including high performance electrically driven LEDs based on solution processed thin films of 0D OMHHs (e.g., TPPcarzSbBr4 thin films, PLQE of at least 86.1%), which exhibit EQEs of at least 5% (e.g., 5.12% or about 5.12%) with a peak luminance of at least 5000 cd/m2 (e.g., 5957 cd/m2 or about 5957 cd/m2), which are the highest such values achieved to date for electroluminescence devices based on 0D OMHHs.
In some embodiments, the OMHHs have a structure (e.g., a unit cell) according to the following formula:
(Cat)aM+bXy formula (I),
where Cat is a phosphonium cation comprising a phosphorus atom substituted with three aryl substituents, such as three aryl C1-C20 hydrocarbyl substituents, and one heteroaryl substituent, such as one heteroaryl C1-C20 hydrocarbyl substituent; where M is a metal; where b is the oxidation state of the metal; and where X is a halogen. In some embodiments, a+b=y. As used herein, the phrase “heteroaryl” refers to a hydrocarbyl that is aromatic and includes at least one heteroatom, such as a nitrogen.
In some embodiments, the heteroaryl C1-C20 hydrocarbyl substituent comprises a carbazole moiety, such as a phenyl-carbazole moiety. In some embodiments, the aryl C1-C20 hydrocarbyl substituents are phenyl. In some embodiments, the phosphonium cation is triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium (TPPcarz+), which has the structure shown in
The metal (i.e., “M”) can be any metal capable of forming an OMHH material, as described herein. For example, M can be antimony (Sb). In many embodiments, M is not lead (Pb). X can be, for example, fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). In some embodiments, X is Br.
In some embodiments, the OMHH has a 0D crystal structure. In some embodiments, the OMHH has a crystal structure comprising light emitting antimony bromide dimer anions (Sb2Br82−) surrounded and isolated by the phosphonium cations, such as triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium cations. In some embodiments, the organic metal halide hybrid has a structure of the following formula:
(triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium)+SbBr4.
The organic metal halide hybrids described herein may be in any physical form. In some embodiments, the OMHHs are in the form of discrete crystals (i.e., “single crystals”). The discrete crystals can have a PLQE of at least 90%, or at least 93%. In some embodiments, the OMHHs are in the form of a thin film. The thin film can have a PLQE of at least 85%, or at least 88%.
Embodiments of the subject invention provide electronic devices, such as electrically driven LEDs. In some embodiments, the electrically driven LEDs can include: an electrode; a layer comprising an OMHH as described herein; and a counter electrode. The layer comprising the OMHH may be disposed between the electrode and the counter electrode. The layer comprising the OMHH may be a light emitting layer. The layer comprising the OMHH can optionally be in direct physical contact with the electrode and/or the counter electrode.
In some embodiments, the electronic device can also include a hole transporting layer and/or an electron transporting layer. The hole transporting layer (if present) can be disposed between the electrode and the layer comprising the OMHH, and the electron transporting layer (if present) can be disposed between the counter electrode and the layer comprising the OMHH. The device may be a hole-only device, or an electron-only device. The hole transporting layer (if present) can be in direct physical contact with the electrode and/or the layer comprising the OMHH. The electron transporting layer (if present) can be in direct physical contact with the counter electrode and/or the layer comprising the OMHH.
In an embodiment, a method of fabricating an OMHH can include performing the method described in Example 1.
The phrases “C1-C20 hydrocarbyl,” and the like, as used herein, generally refer to aliphatic, aryl, or arylalkyl groups containing 1 to 20 carbon atoms. Examples of aliphatic groups, in each instance, include, but are not limited to, an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkadienyl group, a cyclic group, and the like, and includes all substituted, unsubstituted, branched, and linear analogs or derivatives thereof, in each instance having 1 to about 20 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl, octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl and dodecyl. Cycloalkyl moieties may be monocyclic or multicyclic, and examples include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and adamantyl. Additional examples of alkyl moieties have linear, branched and/or cyclic portions (e.g., 1-ethyl-4-methyl-cyclohexyl). Representative alkenyl moieties include vinyl, allyl, 1-butenyl, 2-butenyl, isobutylenyl, 1- pentenyl, 2-pentenyl, 3-methyl-1-butenyl. 2-methyl-2-butenyl, 2,3-dimethyl-2-butenyl, 1- hexenyl, 2-hexenyl, 3-hexenyl, 1-heptenyl, 2-heptenyl, 3-heptenyl, 1-octenyl, 2-octenyl, 3- octenyl, 1-nonenyl, 2-nonenyl, 3-nonenyl, 1-decenyl, 2-decenyl and 3-decenyl. Representative alkynyl moieties include acetylenyl, propynyl, 1-butynyl, 2-butynyl, 1-pentynyl, 2-pentynyl, 3- methyl-1-butynyl, 4-pentynyl, 1-hexynyl, 2-hexynyl, 5-hexynyl, 1-heptynyl. 2-heptynyl, 6- heptynyl, 1-octynyl, 2-octynyl, 7-octynyl, 1-nonynyl, 2-nonynyl, 8-nonynyl, 1-decynyl, 2- decynyl and 9-decynyl. Examples of aryl or arylalkyl moieties include, but are not limited to, anthracenyl, azulenyl, biphenyl, fluorenyl, indan, indenyl, naphthyl, phenanthrenyl, phenyl, 1,2,3,4-tetrahydro-naphthalene, tolyl, xylyl, mesityl, benzyl, and the like, including any heteroatom substituted derivative thereof.
Unless otherwise indicated, the term “substituted,” when used to describe a chemical structure or moiety, refers to a derivative of that structure or moiety wherein (i) a multi-valent non-carbon atom (e.g., oxygen, nitrogen, sulfur, phosphorus, etc.) is bonded to one or more carbon atoms of the chemical structure or moiety (e.g., a “substituted” C4 hydrocarbyl may include, but is not limited to, diethyl ether moiety, a methyl propionate moiety, an N,N-dimethylacetamide moiety, a butoxy moiety, etc., and a “substituted” aryl C12 hydrocarbyl may include, but is not limited to, an oxydibenzene moiety, a benzophenone moiety, etc.) or (ii) one or more of its hydrogen atoms (e.g., chlorobenzene may be characterized generally as an aryl C6 hydrocarbyl “substituted” with a chlorine atom) is substituted with a chemical moiety or functional group such as alcohol, alkoxy, alkanoyloxy, alkoxycarbonyl, alkenyl, alkyl (e.g., methyl, ethyl, propyl, t-butyl), alkynyl, alkylcarbonyloxy (—OC(O)alkyl), amide (—C(O)NH-alkyl- or -alkylNHC(O)alkyl), tertiary amine (such as alkylamino, arylamino, arylalkylamino), aryl, aryloxy, azo, carbamoyl (—NHC(O)O-alkyl- or —OC(O)NH-alkyl), carbamyl (e.g., CONH2, as well as CONH-alkyl, CONH-aryl, and CONH-arylalkyl), carboxyl, carboxylic acid, cyano, ester, ether (e.g., methoxy, ethoxy), halo, haloalkyl (e.g., —CCl3, —CF3, —C(CF3)3), heteroalkyl, isocyanate, isothiocyanate, nitrile, nitro, oxo, phosphodiester, sulfide, sulfonamido (e.g., SO2NH2), sulfone, sulfonyl (including alkylsulfonyl, arylsulfonyl and arylalkylsulfonyl), sulfoxide, thiol (e.g., sulfhydryl, thioether) or urea (—NHCONH-alkyl-).
While certain aspects of conventional technologies have been discussed to facilitate disclosure of various embodiments, applicants in no way disclaim these technical aspects, and it is contemplated that the present disclosure may encompass one or more of the conventional technical aspects discussed herein.
The present disclosure may address one or more of the problems and deficiencies of known methods and processes. However, it is contemplated that various embodiments may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the present disclosure should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.
The terms “a,” “an,” and “the” are intended to include plural alternatives, e.g., at least one. For instance, the disclosure of “an antisolvent”, “a triaryl amine”, and the like, is meant to encompass one, or mixtures or combinations of more than one antisolvent, triaryl amine, and the like, unless otherwise specified.
When ranges are used herein, combinations and subcombinations of ranges (e.g., any subrange within the disclosed range) and specific embodiments therein are intended to be explicitly included. When the term “about” is used herein, in conjunction with a numerical value, it is understood that the value can be in a range of 95% of the value to 105% of the value, i.e. the value can be +/−5% of the stated value. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.
A greater understanding of the embodiments of the subject invention and of their many advantages may be had from the following examples, given by way of illustration. The following examples are illustrative of some of the methods, applications, embodiments, and variants of the present invention. They are, of course, not to be considered as limiting the invention. Numerous changes and modifications can be made with respect to embodiments of the invention.
The examples describe a molecular engineering approach to addressing the issues of low conductivity and poor energy alignment in electrically driven LEDs based on 0D OMHHs.
By introducing a simple organic charge transporting unit (phenylcarbazole) to a triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium (TPP+) cation, a semiconducting organic cation—triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium (TPPcarz+) was produced (see also, Xu et al., Ligand-Mediated Release of Halides for Color Tuning of Perovskite Nanocrystals with Enhanced Stability, The Journal of Physical Chemistry Letters, 10 (19), 5836-5840, 2019; which is hereby incorporated by reference herein in its entirety).
A 0D OMHH TPPcarzSbBr4 was then synthesized, in which light emitting antimony bromide dimer anions (Sb2Br82−) were surrounded and isolated by TPPcarz+. Both single crystals and solution processed thin films of TPPcarzSbBr4 were found to exhibit red emission with high PLQEs of 93.8% and 86.1%, respectively.
Electrically driven LEDs with solution processed TPPcarzSbBr4 emitting layer exhibited an EQE of 5.12%, a peak luminance of 5957 cd/m2, and a current efficiency of 14.2 candelas per Amp (cd/A), the best values reported to date for 0D-OMHH-based electroluminescence devices.
Chemicals: poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) (CH8000) was purchased from Heraeus. Antimony(III) bromide, Zinc acetate dihydrate, Triphenylphosphine (TPP, Aldrich, 99%), 3-bromo-9- phenylcarbazole, zinc acetate dihydrate, poly(N-vinylcarbazole) (PVK), lithium fluoride (LiF), dichloromethane (DCM, 99.5%) and diethyl ether (Et2O, anhydrous), dimethylformamide (DMF, anhydrous), and hydrobromic acid (48%) were purchased from Sigma-Aldrich. Chlorobenzene (anhydrous, 99.8%) and ethylene glycol was purchased from VWR. All reagents and solvents were used without further purification unless otherwise stated.
Synthesis of triphenyl(9-phenyl-9H-carbazol-3-yl)phosphonium bromide(TPPcarzBr): The TPPcarzBr was synthesized according to the scheme shown in
Growth of TPPcarzSbBr4 single crystals via antisolvent vapor diffusion: 0.2 mmol SbBr3 and 0.4 mmol TPPcarzBr were mixed at a 1:2 molar ratio and dissolved in 1 mL ethanol and 0.1 mL HBr to form a clear precursor solution. Two ml of Et2O were diffused into this precursor solution at room temperature overnight.
Preparation of ZnO nanocrystals: ZnO nanocrystals were synthesized (see also Shi et al., Strategy of Solution-Processed All-Inorganic Heterostructure for Humidity/Temperature-Stable Perovskite Quantum Dot Light-Emitting Diodes, ACS Nano 12 (2), 1462-1472, 2018; which is hereby incorporated by reference herein in its entirety). Zinc acetate dihydrate (2.29 grams (g)) was dissolved in 10 mL of methanol with vigorous stirring. KOH (1.48 g) was dissolved in 5 mL of methanol and then added slowly into the zinc acetate solution and continuously stirred for an additional 120 minutes (60° C.). The above solution was centrifuged at 4200 revolutions per minute (rpm) for 3 minutes to collect the white precipitate. The white precipitate was dispersed in chlorobenzene to obtain a ZnO nanocrystals solution.
Device fabrication and characterization: The LEDs were fabricated with the configuration of indium tin oxide (ITO)/PEDOT:PSS (40 nm thickness)/PVK (35 nm)/TPPcarzSbBr4 (40 nm)/ZnO (40 nm)/LiF (2 nm)/aluminum (Al) (100 nm). ITO substrates were cleaned by sonication in deionized water, acetone, and isopropanol, followed by nitrogen purge and ultraviolet-ozone treatment for 20 minutes. PEDOT:PSS was spin-coated at 4500 rpm for 60 seconds and baked at 150° C. for 20 minutes. PVK (in chlorobenzene, 8 milligrams per milliliter (mg/mL)) was deposited on top of PEDOT:PSS at 2000 rpm for 45 seconds, followed by drying at 150° C. for 20 minutes. The light-emitting layer was deposited layer by layer by spin coating at 2500 rpm for 45 seconds using a precursor solution (0.2 mmol of SbBr3 and 0.4 mmol of TPPcarzBr in a 1:2 molar ratio in 1 mL DMF). Subsequently, the ZnO nanoparticles solution (chlorobenzene, 3%) were then spin-coated at 2500 rpm for 45 seconds, followed by an annealing treatment at 100° C. for 10 minutes. Finally, 2 nm of LiF and 100 nm of Al were thermally deposited under high vacuum of about 1×10−6 Torr. Devices for capacitance study were fabricated with the configuration of ITO/PEDOT:PSS (40 nm)/PVK (35 nm)/TPPcarzSbBr4 (40 nm)/calcium (Ca) (20 nm)/Al (100 nm). Hole-only and electron-only devices were fabricated using the device structures ITO/PEDOT:PSS (40 nm)/TPPcarzSbBr4 (40 nm)/molybdenum oxide (MoOx) (10 nm)/Al (100 nm) and ITO/tin oxide (SnO2) (30 nm)/TPPcarzSbBr4 (40 nm)/LiF (2 nm)/Al (100 nm), respectively. The electroluminescence (EL) spectra were recorded by a USB4000 spectrometer. The current density-voltage-brightness (I-V-B) curves of the devices were measured with a Keithley 2400 source meter coupled to a silicon (Si) photodiode. All tests of the devices were conducted at room temperature under ambient conditions.
Characterization: Single crystal X-ray crystallography data was collected using Rigaku XtaLAB Synergy-S diffractometer equipped with a HyPix-6000HE Hybrid Photon Counting (HPC) detector and copper (Cu) microfocus sealed X-ray sources at 295 Kelvin (K). The powder X-ray diffraction patterns were obtained using a Rigaku Smartlab powder diffractometer equipped with a Cu Kα X-ray source. 1H NMR B500 was equipped with a high resolution 5 millimeter (mm) TXI (H-C/N-D) Zg probe. TGA was obtained on a TA instruments TGA 550 system. The sample was heated from room temperature to 700° C. at a rate of 5° C./minute. Absorption spectra were conducted using an Agilent Technologies Cary 5000 UV-Vis-NIR spectrophotometer. PL measurements were done at an excitation wavelength of 365 nm via an Edinburgh FS5 steady state spectrometer with a 150 W xenon lamp. The corresponding time-resolved PL spectra were recorded by the same instrument which equipped a 365 nm laser (Edinburgh Instruments). The carrier lifetimes were fitted with a single exponential function, as follows: y=A1×exp(−x/τ1)+y0. PLQE measurements were carried out at an excitation wavelength of 365 nm using a quantaurus absolute QY Spectrometer from Hamamatsu. The PLQE values were calculated by the equation: ηQE=Is/(ER−ES), where Is represents the emission spectra of samples, ER represents the spectra of the excitation light for the reference (blank substrate), and Es represents the excitation spectra for exciting the sample.
Cyclic voltammetry data were collected using Epsilon E2 electrochemical analyzer in an electrolyte (0.1 moles per liter 9 mol/L) solution of tetrabutylammonium hexylfluorophosphate in dichloromethane) initially de-aerated by argon (Ar). Measurements were conducted in a three-electrode electrochemical cell: platinum (Pt) counter electrode, silver (Ag) pseudo reference electrode, and glassy carbon electrodes working and with a 100 millivolt per second (mV/s) of potential scan rate. The potentials were determined versus Fc+/Fc (ferrocene) reference potential. The AFM picture was captured with a Bruker Icon scanning probe microscope in tapping-mode. The SEM pictures were captured by Nova NanoSEM 400 (FEI Company) at 3.0 kilovolts (kV) scanning voltage. The ultrafast transient absorption data were collected using a femtosecond (fs) pump-probe system. The output from a Ti:sapphire laser was split into two beams: one was used to generate the pump; another beam was sent to a spectrometer to generate the probe (420-800 nm) by focusing the 800 nm fundamental onto a Sapphire crystal. Electrochemical impedance spectroscopy was obtained at a 0 V reverse direct current (DC) bias and 100 mV alternating current (AC) amplitude applied at a frequency range of 1 Hertz (Hz)-1 megahertz (MHz) using a Gamry Interface 1000E potentiostat. The charge-carrier mobility (μ) was determined using Mott-Gurney (M-G) analysis in trap-controlled space-charge limited current (SCLC) region of the J-V curves. The SCLC region shows a quadratic response, μ=(8JL3)/(9εε0V2), where ε0 is the dielectric constant of vacuum, ε is the dielectric constant of TPPcarzSbBr4 obtained by the via capacitance measurements, and μ is the carrier mobility (see also, Worku et al., Band Edge Control of Quasi-2D Metal Halide Perovskites for Blue Light-Emitting Diodes with Enhanced Performance, Advanced Functional Materials, 31 (45), 2103299, 2021; which is hereby incorporated by reference herein in its entirety).
In order to turn TPP+ into a semiconducting organic cation, one phenyl ring in TPP+ was replaced with phenylcarbazole, a charge transporting unit to give TPPcarz+, as shown in
TPPcarzBr was first synthesized according to the scheme shown in
TPPcarzSbBr4 single crystals were prepared by diffusing an antisolvent (diethyl ether in this example, though any suitable antisolvent could be used) into a dichloromethane precursor solution of antimony tribromide (SbBr3) and TPPcarzBr in a 1:2 molar ratio at room temperature (see
The thermal stability of TPPcarzSbBr4 was characterized using thermal gravimetric analysis (TGA), which showed little to no decomposition up to 220° C. (see
For electrically driven LEDs, emitting layers in the form of smooth thin films were tested. In order to make TPPcarzSbBr4 thin films, a TPPcarzSbBr4 precursor solution containing 1:2 molar ratio of SbBr3:TPPcarzBr was spin casted. The same solution used for the preparation of single crystals was used here. The fabricated thin films showed almost identical optical properties as those of single crystals under ambient and UV (365 nm) lights (see
The photophysical properties of both TPPcarzSbBr4 single crystals and solution processed thin films were characterized with absorption spectroscopy (see
An excited-state lifetime of 2.3 microseconds (μs) upon excitation at 365 nm was recorded, which suggested the phosphorescence nature of the emission. Such a broadband emission with a large Stokes shift and a long lifetime has been observed in Sb-based 0D OMHHs (see also He et al., Highly Stable Organic Antimony Halide Crystals for X-ray Scintillation, ACS Materials Letters 20, 2 (6), 633-638, 2020; which is hereby incorporated by reference herein in its entirety). Excitation power-dependent PL spectra (
The surface morphology of solution processed TPPcarzSbBr4 thin films was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM), as shown in
SEM images also confirmed the formation of smooth thin films with uniformly distributed crystalline phases without any deep grain boundaries. The high quality of solution processed thin films was mainly attributed to the relatively high viscosity of TPPcarzBr, which likely played a key role in the crystallization process during the film formation (see also; Riera-Galindo et al., Role of Polymorphism and Thin-Film Morphology in Organic Semiconductors Processed by Solution Shearing, ACS Omega, 3 (2), 2329-2339, 2018; and Kundu et al., High-Tg Carbazole Derivatives as Blue-Emitting Hole-Transporting Materials for Electroluminescent Devices, Advanced Functional Materials, 13 (6), 445-452, 2003; both of which are hereby incorporated by reference herein in their entireties). With high PLQE and excellent film morphology achieved in solution processed TPPcarzSbBr4 thin films, suitable electronic properties were the last major requirement for them to act as emitting layer in electrically driven LEDs.
In order to support the design of conductive thin films based on 0D OMHHs, electrochemical impedance spectroscopy (EIS) was performed to probe the conductivity of solution processed TPPcarzSbBr4 thin films. The Nyquist plots of devices with a structure of ITO/PEDOT:PSS (40 nm)/PVK (35 nm)/TPPcarzSbBr4 (40 nm)/Ca (20 nm)/Al (100 nm) measured at a reverse bias voltage of 0 V are shown in
The charge transport resistance (Rct), the series resistance (Rs), and the chemical capacitance (Cct) were obtained by fitting electrochemical impedance spectroscopy (EIS) data according to the relevant equivalent circuit. Also tested was the conducting performance of a device based on TPP2SbBr5 for comparison (inset of
Single-carrier devices were fabricated in order to further verify the improved charge transport capabilities of TPPcarzSbBr4 thin films over TPP2SbBr5 thin films.
The device characteristics for the electron-only devices (ITO/tin oxide (SnO2) (30 nm)/TPPcarzSbBr4 (40 nm)/LiF (2 nm)/Al (100 nm)) and the hole-only devices (ITO/PEDOT:PSS (40 nm)/TPPcarzSbBr4 (40 nm)/MoOx (10 nm)/Al (100 nm)) are shown in
As compared to devices based on TPP2SbBr5 thin films, devices based on TPPcarzSbBr4 thin films exhibited much higher current density with more balanced charge injection. The hole and electron charge carrier mobilities of TPPcarzSbBr4 thin films were determined to be 1.3×10−6 square centimeters per Volt per second (cm2/V-s) and 3.2×10−6 cm2/V-s, respectively (see
In this example, electrically driven LEDs were fabricated using the device structure as shown in
An external quantum efficiency (EQE) of 5.12%, a luminance of 5957 cd/m2, and a current efficiency of 14.2 cd/A (see
The spectral stability was evaluated by varying bias from 5V to 8 V (see
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.
This application claims the benefit of U.S. Provisional Application Ser. No. 63/385,106, filed Nov. 28, 2022, the disclosure of which is hereby incorporated by reference in its entirety, including all figures, tables, and drawings.
This invention was made with government support under Contract Nos. 2204466 and 1912911, awarded by the National Science Foundation (NSF). The government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 63385106 | Nov 2022 | US |
