Blue-light perovskite light-emitting diode based on ethylamine trifluoroacetic acid modification and preparation method thereof

Abstract

The invention is suitable for the field of light-emitting diodes, and provides a blue-light perovskite light-emitting diode based on ethylamine trifluoroacetic acid modification and a preparation method thereof. The invention discloses an application of ethylamine trifluoroacetic acid in preparation of a blue-light perovskite film, and a method for preparing the blue-light perovskite film comprises the following steps: preparing a blue-light perovskite precursor solution, doping ethylamine trifluoroacetic acid in the perovskite precursor solution, coating the perovskite precursor solution on the surface of a hole transport layer, and drying the hole transport layer to obtain the blue-light perovskite film. And after annealing, a blue light perovskite film is formed on the surface of the hole transport layer. The invention also provides a blue-light perovskite light-emitting diode based on the blue-light perovskite film. Through modification of ethylamine trifluoroacetic acid, crystallinity, electrical properties, quasi-two-dimensional phase distribution and device performance of perovskite are all effectively improved, and through a series of gradient doping, the device performance and stability are significantly changed.

Description

Technical Field

[0001] The invention relates to a perovskite light-emitting device, in particular to a blue light perovskite light-emitting diode modified with ethylaminetrifluoroacetic acid and a preparation method thereof. Background Art

[0002] Metal halide perovskites are promising materials for next-generation display technologies because they combine low cost and solution processability with excellent luminescent properties. To improve the performance of perovskite light-emitting diodes (LEDs), strategies such as additive engineering, interface modification, ligand engineering, and quasi-2D phase regulation have been shown to be effective. These efforts have resulted in external quantum efficiencies (EQEs) of over 30% for green, red, and near-infrared perovskite LEDs, which are comparable to the electroluminescence (EL) efficiencies of established technologies such as organic LEDs and inorganic quantum dot LEDs. However, the EL efficiencies of state-of-the-art blue perovskite LEDs have generally remained below 25%, far behind their blue organic and quantum dot counterparts. This requires new approaches to achieve high-performance perovskite LEDs in the blue region. The quasi-2D chlorine-bromine hybrid system is currently the most common system for high-efficiency blue PeLEDs, due to its simple preparation process and high exciton binding energy. However, most state-of-the-art blue devices constructed from quasi-2D perovskites suffer from poor charge transport properties and inefficient energy transfer processes, which hinder the development of high-performance blue perovskite LEDs. Therefore, in order to achieve efficient quasi-two-dimensional blue light emission, it is of great significance to finely control the quasi-two-dimensional phase, passivate halogen vacancy defects, and improve the radiative recombination efficiency, which is of great significance for improving the application prospects of PeLEDs. Summary of the invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a preparation method of a blue light perovskite light-emitting diode based on ethylaminetrifluoroacetate (EATFA) modification. The present invention adds ethylaminetrifluoroacetate to the blue light perovskite to regulate the quasi-two-dimensional perovskite phase, thereby improving the crystallinity of the perovskite, optimizing the perovskite film morphology, enhancing the charge injection balance, and realizing a high-efficiency blue light perovskite light-emitting diode.

[0004] The purpose of the present invention is to disclose a blue light perovskite light emitting diode modified based on ethylamine trifluoroacetic acid and a preparation method thereof, which are used to improve the device efficiency of the blue light perovskite light emitting diode.

[0005] A method for preparing a blue light perovskite light-emitting diode based on ethylamine trifluoroacetic acid modification, the method comprising the following steps: Step 1: Clean the ITO substrate with detergent, deionized water, ethanol, and isopropanol in sequence, dry it at 100 °C, and place it in a drying cabinet for standby use; Step 2: Place the dried ITO substrate in step 1 in a UV ozone machine for 15 minutes to remove surface impurities and improve the hydrophilicity of the substrate; Step 3: Spin coating the hole transport layer on the ITO substrate in step 2, and perform annealing treatment; Step 4: CsBr, PbBr2, PbCl2, PEABr, KBr, and FABr are dissolved in a dimethyl sulfoxide solvent at a molar ratio of 2.8:1.3:0.7:1.0:0.3:0.3, and heated and stirred at 20-35 °C for 3-6 hours until all the powders are dissolved, and filtered to obtain a perovskite precursor solution, and ethylamine trifluoroacetic acid is added to the precursor solution, and the concentration of ethylamine trifluoroacetic acid is 0.0025 mmol / mL to form a modified solution; Step 5: Spin-coat the modified solution in step 4 onto the surface of the substrate in step 3, and obtain a blue light perovskite film after annealing; Step 6: depositing an electron transport layer, a cathode modification layer and a cathode on the blue light perovskite film in step 5 in sequence by high vacuum thermal evaporation to obtain a blue light perovskite light emitting diode modified with ethylamine trifluoroacetic acid; The hole transport layer is at least one of PEDOT:PSS, PVK, CBP, and Poly-TPD; The perovskite precursor solution has a CsBr concentration of 0.14 mmol / mL; The spin coating conditions of the blue perovskite film were 4000 rpm for 60 s, and the annealing conditions were constant temperature annealing at 70 °C for 7 min; The electron transport layer is one or more of TPBi, CNT2T, POT2T, TmPyPB and B3PYMPM; The electrode modification layer is one of LiF, Liq and CsF; The metal cathode electrode is an aluminum electrode or a silver electrode.

[0006] A blue light perovskite light emitting diode based on ethylamine trifluoroacetic acid modification prepared by the above method.

[0007] By means of the above scheme, the present invention has at least the following advantages: The present invention discloses the application of ethylamine trifluoroacetic acid in the preparation of blue light perovskite light-emitting diodes. By adding ethylamine trifluoroacetic acid as a phase-cutting additive into a perovskite precursor solution, the method has the following advantages compared with the prior art: 1) By introducing ethylamine cation (EA + ) can be combined with phenylethylamine (PEA) with greater adsorption energy +) ligands compete for coordination sites to enhance the formation of large n phase; at the same time, trifluoroacetic acid (TFA - ) anions pass through PEA + The strong interaction between them can delay PEA + The process of combining with the lead octahedron, thereby inhibiting the formation of the small n phase, and the two work together to achieve precise phase tailoring of quasi-two-dimensional perovskite; 2) TFA - Through the combination of C=O and CF multiple sites with uncoordinated lead ions, halogen vacancy defects are passivated, ion migration is inhibited, and the radiation recombination rate is increased; 3) The introduction of EATFA improves the crystallinity of perovskite and effectively improves the morphology of perovskite film; 4) The introduction of EATFA improves charge injection, and the brightness, efficiency and stability of the prepared perovskite light-emitting diodes are improved, with the device efficiency reaching 23.68%.

[0008] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is the surface morphology of the blue perovskite film; Figure 2 is the XRD pattern of the blue perovskite film; Figure 3 is the steady-state photoluminescence spectrum, photoluminescence quantum yield and time-resolved photoluminescence decay curve of the blue light perovskite film; Figure 4 It is the steady-state absorption spectrum and logarithmic photoluminescence spectrum of the blue light perovskite film; Figure 5 It is a device performance diagram of blue light perovskite light-emitting diode. DETAILED DESCRIPTION

[0010] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Example

[0011] A blue light perovskite light-emitting diode based on ethylamine trifluoroacetic acid modification is constructed using a device structure of glass / indium tin oxide (ITO) / PEDOT:PSS / perovskite / TPBi / LiF / Al. ITO is the anode, PEDOT:PSS is the hole transport layer, and the (Cs / FA / PEA)Pb(Cl / Br)3 perovskite layer is the blue light perovskite light-emitting layer, which is doped with ethylamine trifluoroacetic acid. TPBi is the electron transport layer with a thickness of 45 nm, and LiF is the electrode modification layer with a thickness of 1.1 nm. Al is the metal cathode with a thickness of 80 nm.

[0012] The preparation method is as follows: (1) The ITO transparent conductive glass substrate was cleaned with detergent, deionized water, ethanol, and isopropanol in turn, and dried in a hot oven at 100 °C for use. The dried ITO substrate was then treated with a UV ozone machine, and a hole transport layer PEDOT:PSS was deposited on the treated ITO substrate. Specifically, when depositing the hole transport layer, a portion of the PEDOT:PSS solution was drawn with a needle, filtered with a filter head, and spin-coated on the cleaned ITO transparent conductive glass at a rotation speed of 6000 rpm for 40 s, and annealed at 140 °C for 15 minutes to form a hole transport layer.

[0013] (2) Prepare the perovskite precursor solution by: -1 )、PbBr2(0.065mmol mL -1 )、PbCl2(0.035 mmol mL -1 )、PEABr(0.05 mmol mL -1 )、KBr(0.015 mmol mL -1 ) and FABr (0.015 mmol mL -1 ) were weighed and the concentration of each component was 0.0025 mmol mL -1 The above substances were dissolved in DMSO solvent, placed on a heating table at 35°C and heated with stirring for 4 hours, and after complete dissolution, filtered to obtain a perovskite precursor solution.

[0014] (3) The ITO transparent conductive glass substrate on which the PEDOT:PSS hole transport layer was deposited in step (1) was transferred to a glove box, and then the perovskite precursor solution prepared in step (2) was spin-coated on the upper surface of the hole transport layer at a high speed of 4000 rpm for 60 s. After spin coating, the substrate was transferred to a heating table and annealed at 70°C for 7 min to form a blue light perovskite film on the upper surface of the hole transport layer.

[0015] (4) Depositing an electron transport layer, an electrode modification layer and a metal cathode on the blue light perovskite film in step (3) in sequence by high vacuum thermal evaporation to obtain a blue light perovskite light-emitting diode modified with ethylamine trifluoroacetic acid.

[0016] Comparative Example A blue light perovskite light emitting diode, whose structure and preparation method are the same as those in the embodiment, except that ethylamine trifluoroacetic acid is not doped in the blue light perovskite film, and in the preparation process, ethylamine trifluoroacetic acid is not added in step (2) of the embodiment.

[0017] The performance of different blue light perovskite films prepared above was tested, such as Figure 1 As shown in Figs. a and 1b, it can be seen from the SEM images that there are a large number of holes in the comparative film, and the grain sizes are different. In contrast, after the EATFA modification of the embodiment, the film holes are reduced, the film coverage is improved, and the grain size is more uniform. Figure 1 It can also be seen from the AFM images of c and 1d that the surface roughness of the embodiment is reduced and the surface is smoother, which verifies the results of SEM. Figure 2 The XRD patterns of perovskite films with and without EATFA modification show that the peak position does not shift after EATFA modification, indicating that EATFA + and TFA - None of them enter the lattice, but exist in the octahedral gap and surface. At the same time, it can be found that the (200) crystal plane is significantly enhanced, indicating that EATFA can modulate crystallization and enhance the crystallinity of perovskite crystals. The above improvement of crystallization dynamics and optimization of film morphology can have a positive impact on the optoelectronic properties of the film and the device performance of the light-emitting diode.

[0018] Figure 3 a Photoluminescence test of perovskite films with and without EATFA modification. Figure 3 It can be seen from the steady-state fluorescence spectrum of a that the introduction of EATFA significantly enhances the photoluminescence intensity of the perovskite film. Figure 3 It can be seen from the photoluminescence quantum yield of b that the photoluminescence quantum yield increased from 35% to 72% after EATFA modification, and Figure 3 As can be seen from the time-resolved photoluminescence decay curve of c, the exciton lifetime of the example is also significantly enhanced, extending from 23.45 ns to 40.52 ns, indicating that the radiative recombination is significantly enhanced, which can be attributed to the management of defects by EATFA.

[0019] Figure 4Figure a shows the UV-visible steady-state absorption spectra of perovskite films with and without EATFA modification. It can be seen from the figure that there are four shoulder peaks in the film, which are the exciton absorption signal at around 392 nm corresponding to n = 1, the exciton absorption signal at around 418 nm corresponding to n = 2, the exciton absorption signal at around 442 nm corresponding to n = 3, and the exciton absorption signal at around 465 nm corresponding to n ≥ 4. It can be seen from the figure that the signals of n = 1 and n = 2 of the small n phase are significantly weakened, and the signal of n = 3 is significantly enhanced, which indicates that EATFA can inhibit the formation of the small n phase and promote the formation of the large n phase. There is a strong exciton-phonon coupling in the n ≤ 2 phase, which is not conducive to the effective radiative recombination of excitons. The suppression of the small n phase and the enhancement of the large n phase are conducive to the energy transfer and radiative recombination of excitons. At the same time, the same conclusion can be drawn from the normalized Log-PL diagram ( Figure 4 b). From the normalized Log-PL graph of the comparative example, it can be seen that there are obvious fluorescence peak signals at 389 nm and 416 nm, corresponding to the signals of n = 1 and n = 2, respectively. After EATFA modification, these two signals almost disappeared, indicating that the phase in the perovskite film tends to be distributed in a large n phase, and EATFA achieves precise phase regulation of the quasi-two-dimensional phase.

[0020] Figure 5 The following are the device performances before and after EATFA modification. Figure 5 As shown in a, with the increase of driving voltage, the EATFA-modified PeLEDs showed excellent EL spectrum stability, and the emission peak of the device always remained at 490 nm without shifting, proving the effective suppression of halide ion migration. According to the current density-voltage brightness (JVL) characteristic curve ( Figure 5 b) Both current injection and brightness are improved by EATFA modification. The reduced leakage current at lower bias and the increased injection current at higher bias reflect the optimization of charge transport during operation. The maximum brightness of EATFA-modified PeLEDs reaches 1756 cd m -2 , is the original device (1105 cd m -2 ), indicating that the radiative recombination in the EATFA-modified perovskite film is significantly enhanced. More importantly, the maximum EQE is increased from 13.56% to 23.68% ( Figure 5 c), making the optimized device among the most advanced blue PeLEDs reported to date. Figure 5 d describes 1 mA cm -2 Device operating life at constant current density. The half-life T of the EATFA-modified device 50It was also extended from 216 s in the control device to 522 s, which was attributed to the effective suppression of non-radiative recombination by EATFA, reducing the Joule heat generation channel.

[0021] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a blue light perovskite light-emitting diode modified with ethylamine trifluoroacetic acid, characterized in that: The method comprises the following steps: Step 1: Clean the ITO substrate with detergent, deionized water, ethanol, and isopropanol in sequence, dry it at 100 °C, and place it in a drying cabinet for standby use; Step 2: Place the dried ITO substrate in step 1 in a UV ozone machine for 15 minutes to remove surface impurities and improve the hydrophilicity of the substrate; Step 3: Spin coating the hole transport layer on the ITO substrate in step 2, and perform annealing treatment; Step 4: CsBr, PbBr2, PbCl2, PEABr, KBr, and FABr are dissolved in a dimethyl sulfoxide solvent at a molar ratio of 2.8:1.3:0.7:1.0:0.3:0.3, and heated and stirred at 20-35 °C for 3-6 hours until all the powders are dissolved, and filtered to obtain a perovskite precursor solution, and ethylamine trifluoroacetic acid is added to the precursor solution, and the concentration of ethylamine trifluoroacetic acid is 0.0025 mmol / mL to form a modified solution; Step 5: Spin-coat the modified solution in step 4 onto the surface of the substrate in step 3, and obtain a blue light perovskite film after annealing; Step 6: depositing an electron transport layer, a cathode modification layer and a cathode on the blue light perovskite film in step 5 in sequence by high vacuum thermal evaporation to obtain a blue light perovskite light emitting diode modified with ethylamine trifluoroacetic acid; The hole transport layer is at least one of PEDOT:PSS, PVK, CBP, and Poly-TPD; The perovskite precursor solution has a CsBr concentration of 0.14 mmol / mL; The spin coating conditions of the blue perovskite film were 4000 rpm for 60 s, and the annealing conditions were constant temperature annealing at 70 °C for 7 min; The electron transport layer is one or more of TPBi, CNT2T, POT2T, TmPyPB and B3PYMPM; The electrode modification layer is one of LiF, Liq and CsF; The metal cathode electrode is an aluminum electrode or a silver electrode.

2. A blue light perovskite light emitting diode based on ethylamine trifluoroacetic acid modification prepared by the method of claim 1.

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