Preparation method and application of core-shell structure tin-based perovskite nanocrystal

Abstract

The application relates to a preparation method and application of a core-shell structure tin-based perovskite nanocrystal. The application adjusts the feeding ratio of a cesium source and a stannous source and the proportion of oleylamine and oleic acid, and through one-step hot injection, obtains a nanocrystal with a cesium bromide shell and a tin-based perovskite core; and further, a light emitting diode device is prepared by using the nanocrystal. The tin-based perovskite nanocrystal has a sustained and stable high fluorescence quantum yield, and the light emitting diode device prepared based on the nanocrystal has a very high light emitting efficiency.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic devices, specifically to a method for preparing core-shell structured tin-based perovskite nanocrystals and their applications. Background Technology

[0002] Halide perovskite nanocrystals possess excellent photoelectric conversion properties, yielding disruptive results in the photovoltaic field. They exhibit a tunable bandgap structure and extremely narrow spectrum, meeting the color gamut requirements of BT.2020 displays. Furthermore, due to their solution-processable nature, they offer a significant price advantage compared to traditional inorganic semiconductors. The presence of quantum confinement effects results in extremely high luminescence quantum yields. Therefore, halide perovskite nanocrystals are considered strong contenders for next-generation electroluminescent diode (LED) materials. However, existing high-efficiency perovskite LEDs are primarily lead-based, thus limiting their widespread application in everyday life. Therefore, improving the performance of lead-free perovskites is one of the important development directions for perovskites.

[0003] Tin and lead have similar electronic structures, thus tin and halogens can form stable octahedral structures with good photoelectric properties. However, divalent tin is very easily oxidized, so its stability greatly limits the improvement and application of tin-based perovskites. Although ligands can isolate perovskites from oxygen to some extent, the synthesis and washing of nanocrystals often take place in an atmospheric environment, further necessitating improvements in the stability of tin-based perovskites. Therefore, innovation in raw materials and synthesis methods is required. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing core-shell structured tin-based perovskite nanocrystals. This invention uses more stable stannous acetate as the tin source and achieves the synthesis of core-shell structured nanocrystals through a one-step thermal injection method. The core layer of the nanocrystals is tin-based perovskite, and the shell layer is cesium bromide. By adjusting the ratio of stannous acetate to cesium acetate and the ratio of oleylamine oleic acid ligands during the synthesis process, the nanocrystals can achieve high stability and high fluorescence yield: their initial luminescence quantum yield is close to 80%, and it only decays to half of its initial value after being placed in air for more than 1200 hours.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing core-shell structured tin-based perovskite nanocrystals, characterized by comprising the following steps:

[0007] Step 1: Mix stannous acetate and cesium acetate, add them to a mixture of 1-octadecene, oleic acid and oleylamine, and stir.

[0008] Step 2: Place the mixture obtained in Step 1 under vacuum conditions and maintain it at a constant temperature for a period of time;

[0009] Step 3: Inert gas is introduced into the reaction system and the temperature is kept constant for a period of time to obtain the precursor liquid;

[0010] Step 4: Add trimethylbromosilane to the reaction system and cool to room temperature to obtain a colloidal solution;

[0011] Step 5: After centrifuging the colloidal solution obtained in Step 4, the precipitate is dispersed and washed with n-hexane to obtain core-shell structured tin-based perovskite nanocrystals with high photoluminescence fluorescence yield.

[0012] Based on the above plan,

[0013] The molar ratio of stannous acetate to cesium acetate in step 1 is 1:3 to 1:1.

[0014] The mixture of 1-octadecene, oleic acid and oleylamine described in step 1, wherein the volume ratio of oleic acid to oleylamine is 3:1-4:1, and the volume ratio of 1-octadecene to the above mixture of oleic acid and oleylamine is 7:4-6:5;

[0015] The concentration of stannous acetate in the mixture obtained in step 1 is 0.02 mol / L. -1 ;

[0016] The constant temperature maintenance mentioned in step 2 is specifically maintained at 100-110℃ for 1 hour to remove water and oxygen;

[0017] The constant temperature maintenance mentioned in step 3 is specifically maintained at 175-180℃ for 10 minutes;

[0018] The volume ratio of trimethylbromosilane to the precursor solution in step 4 is 3:100-4:100; trimethylbromosilane is rapidly added to the reaction system and reacted for 10 seconds before being cooled to room temperature.

[0019] The centrifugation conditions described in step 5 are: 10,000 rpm for 10 min.

[0020] Another objective of this invention is to provide a method for preparing a core-shell structured tin-based perovskite nanocrystalline thin film.

[0021] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0022] A method for preparing a core-shell structured tin-based perovskite nanocrystalline thin film, characterized by comprising the following steps:

[0023] The core-shell structured tin-based perovskite nanocrystals prepared by the above method were dispersed in n-hexane. After ultrasonic treatment of the dispersion, the aggregated nanocrystals were removed by filtration to obtain a spin-coating solution. The spin-coating solution was spin-coated onto a substrate and annealed to obtain a core-shell structured tin-based perovskite nanocrystal film.

[0024] Based on the above plan,

[0025] The concentration of the spin coating solution is 6-10 mg / mL; the spin coating step is 2000 rpm for 60 s; and the annealing conditions are 60℃ for 5 min.

[0026] Another object of the present invention is to provide a core-shell structured tin-based perovskite nanocrystal light-emitting diode device.

[0027] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0028] A core-shell structured tin-based perovskite nanocrystal light-emitting diode device, characterized in that:

[0029] It includes, in sequence, an ITO glass, a hole transport layer, a core-shell structured tin-based perovskite nanocrystalline thin film, an electron transport layer, an electron injection layer, and a metal electrode layer; wherein the hole transport layer is composed of a PEDOT:PSS layer and a poly-N-vinylcarbazole layer deposited sequentially.

[0030] Another objective of this invention is to provide a method for fabricating a core-shell structured tin-based perovskite nanocrystal light-emitting diode device.

[0031] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0032] A method for fabricating a core-shell structured tin-based perovskite nanocrystalline light-emitting diode device, characterized by comprising the following steps:

[0033] Step 1: Mix stannous acetate and cesium acetate, add a mixture of 1-octadecene, oleic acid and oleylamine, and stir.

[0034] Step 2: Place the mixture obtained in Step 1 under vacuum conditions and maintain it at a constant temperature for a period of time;

[0035] Step 3: Inert gas is introduced into the reaction system and the temperature is kept constant for a period of time to obtain the precursor liquid;

[0036] Step 4: Add trimethylbromosilane to the reaction system and cool to room temperature to obtain a colloidal solution;

[0037] Step 5: After centrifuging the colloidal solution obtained in Step 4, the precipitate is dispersed and washed with n-hexane to obtain core-shell structured tin-based perovskite nanocrystals with high photoluminescence fluorescence yield.

[0038] Step 6: Spin-coat the PEDOT:PSS solution onto the ITO glass and then anneal it to obtain the ITO glass loaded with the PEDOT:PSS layer.

[0039] Step 7: Spin-coat the poly-N-vinylcarbazole (PVK) solution onto the PEDOT:PSS layer obtained in step 6 and then anneal it;

[0040] Step 8: Disperse the core-shell structured tin-based perovskite nanocrystals obtained in step 5 in n-hexane, sonicate the dispersion, filter out the aggregated nanocrystals, and obtain a spin-coating solution. Spin-coat the solution onto the N-vinylcarbazole layer obtained in step 7 and anneal to obtain a core-shell structured tin-based perovskite nanocrystal film.

[0041] Step 9: Evaporate an electron transport layer onto the core-shell structured tin-based perovskite nanocrystalline thin film obtained in Step 8.

[0042] Step 10: Deposit an electron injection layer onto the electron transport layer obtained in step 9;

[0043] Step 11: A metal electrode layer is deposited on the electron injection layer obtained in step 10 to obtain a core-shell structured tin-based perovskite nanocrystalline light-emitting diode device.

[0044] Based on the above plan,

[0045] The molar ratio of stannous acetate and cesium acetate in step 1 is 1:3 to 1:1;

[0046] The mixture of 1-octadecene, oleic acid and oleylamine described in step 1, wherein the volume ratio of oleic acid to oleylamine is 3:1-4:1, and the volume ratio of 1-octadecene to the above mixture of oleic acid and oleylamine is 7:4-6:5;

[0047] The concentration of stannous acetate in the mixture obtained in step 1 is 0.02 mol / L. -1 ;

[0048] The constant temperature maintenance mentioned in step 2, at 100-110℃ for 1 hour, removes water and oxygen;

[0049] The constant temperature maintenance mentioned in step 3 is specifically maintained at 175-180℃ for 10 minutes;

[0050] The volume ratio of trimethylbromosilane to the precursor solution in step 4 is 3:100-4:100; trimethylbromosilane is rapidly added to the reaction system and reacted for 10 seconds before being cooled to room temperature;

[0051] The centrifugation conditions described in step 5 are: 10,000 rpm, 10 min;

[0052] The treatment method for the ITO glass in step 6 is as follows: ultrasonically clean it sequentially with washing solution, deionized water, acetone and ethanol for 10 minutes, and then treat it with oxygen plasma for 20-30 minutes.

[0053] The spin coating process described in step 6 is as follows: 4000 rpm, 30 s; annealing conditions are as follows: 150℃, 20-30 min.

[0054] The poly-N-vinylcarbazole solution mentioned in step 7 is: poly-N-vinylcarbazole dissolved in chlorobenzene, with a concentration of 4-6 mg / mL;

[0055] The spin coating step described in step 7 is: 4500 rpm, 60 s; annealing conditions are 120℃, 30 min;

[0056] The concentration of core-shell structured tin-based perovskite nanocrystals in the spin-coating solution described in step 8 is 6-10 mg / mL; the spin-coating process is 2000 rpm for 60 s; and the annealing conditions are 60 °C for 5 min.

[0057] The electron transport layer material described in step 9 has a thickness of 40 nm and a deposition rate of [missing information].

[0058] The electron injection layer thickness in step 10 is 1 nm; the evaporation rate is...

[0059] The metal electrode layer thickness mentioned in step 11 is 100 nm; the evaporation rate is...

[0060] Based on the above plan,

[0061] The electron transport layer materials mentioned in step 9 include: TPBi, B4PymPm, and B3PymPm;

[0062] The electron injection layer material mentioned in step 10 is lithium fluoride;

[0063] The metal electrode layer material mentioned in step 11 is aluminum.

[0064] The method for preparing core-shell structured tin-based perovskite nanocrystals and its application described in this invention have the following beneficial effects:

[0065] 1. By adjusting the feeding ratio of cesium source and tin sub-source, and adjusting the ratio of oleylamine and oleic acid, nanocrystals with cesium bromide as the shell and tin-based perovskite as the core were obtained through a one-step hot injection method. The synthesis method is simple and easy to implement.

[0066] 2. Due to the excellent encapsulation effect of cesium bromide on tin-based perovskites, the initial fluorescence quantum yield of the tin-based perovskite nanocrystals obtained in this invention is close to 80%, and they can be stably stored in air for up to 1200 hours (until the fluorescence quantum yield decays to half of its initial value).

[0067] 3. The perovskite light-emitting diode device fabricated using the above-mentioned tin-based perovskite nanocrystals has a maximum brightness of 16 cd / m². 2 Its highest external quantum efficiency is 0.045%. Attached Figure Description

[0068] The present invention includes the following figures:

[0069] Figure 1 This is a structural diagram of core-shell tin-based perovskite nanocrystals;

[0070] Figure 2 Absorption, excitation, and emission diagrams of the core-shell structured tin-based perovskite nanocrystals prepared in Example 1;

[0071] Figure 3 Fluorescence quantum yield of the core-shell structured tin-based nanocrystals prepared in Example 1;

[0072] Figure 4 The stability of the core-shell structured tin-based nanocrystals prepared in Example 1 when placed in air;

[0073] Figure 5 This is a schematic diagram of the structure of a light-emitting diode (LED) device.

[0074] Figure 6 The J-EQE curve of the light-emitting diode device obtained in Example 2 is shown. Detailed Implementation

[0075] The present invention will be further described in detail below with reference to the accompanying drawings.

[0076] Example 1: Synthesis of core-shell structured tin-based perovskite nanocrystals with high stability and high fluorescence yield.

[0077] Preparation of precursors for hot injection method: Stannous acetate (Sn(OAc)2) and cesium acetate (Cs(OAc)) were dissolved in a mixture of 1-octadecene, oleic acid, and oleylamine at a molar ratio of 1:2, with a ratio of 6:4:1; the concentration of stannous acetate in the above precursor solution was 0.02 mol / L. -1 .

[0078] Thermal injection synthesis method: The reaction system is first replaced with an inert gas 3-4 times, and then kept at 100°C under vacuum for 1 hour to remove water and oxygen; then an inert gas is introduced and the temperature is raised to 180°C and held for 10 minutes. Then 0.2-0.3 mL of trimethylbromosilane (the purity of trimethylbromosilane can be 90%, and the volume ratio of trimethylbromosilane to precursor liquid is 3:100) is injected. The reaction is carried out for about 10 seconds and then rapidly cooled to room temperature to obtain core-shell structured tin-based perovskite nanocrystals with orange light emission.

[0079] like Figures 2-4 As shown, the synthesized orange luminescent core-shell structured tin-based perovskite nanocrystals were tested, and the results showed that:

[0080] The nanocrystals exhibit a broad-spectrum orange light with a peak emission value of around 620 nm and a full width at half maximum (FWHM) of around 120 nm, and show a significant Stokes shift. The photoluminescence quantum yield is 78.2%, and it demonstrates excellent stability: the photoluminescence quantum yield decays to half of its initial value in more than 1200 hours, and the spectrum remains unchanged.

[0081] Example 2: Fabrication of a light-emitting diode device based on the nanocrystals obtained in Example 1.

[0082] The structure of the light-emitting diode device is glass / ITO / PEDOT: PSS / PVK / NCs / B3PymPm / LiF / Al (e.g.) Figure 5 ).

[0083] First, the ITO substrate is cleaned by ultrasonic cleaning with detergent, deionized water, acetone and ethanol for 20 minutes in sequence. Then, the cleaned ITO glass is dried with nitrogen gas and treated with oxygen plasma for 15-30 minutes.

[0084] After the ITO glass is processed, we first spin-coat a PEDOT:PSS solution in an air environment, and then anneal it on a hot plate at 150°C for 20-30 minutes.

[0085] It was then transferred to a glove box and spin-coated with PVK (PVK / chlorobenzene solution, concentration 6 mg / mL) at 4500 rpm for 60 s and annealed at 120 °C for 30 minutes.

[0086] The core-shell structured tin-based perovskite nanocrystals obtained in Example 1 were dispersed in n-hexane at a concentration of 6-10 mg / mL, sonicated for 10 minutes, and then filtered (using a 0.22-micron organic filter) before being spin-coated onto the hole transport layer PVK (2000 rpm, 60 s). The spin-coated wet film was then transferred to a 60°C hot plate for annealing for 5 minutes (completing the spin-coating preparation of the nanocrystalline thin film for the light-emitting diode device).

[0087] The device was then transferred to a thermal evaporation vacuum chamber, where the pressure dropped to 5 × 10⁻⁶. -4 After the pressure drops below Pa, the electron transport layer is deposited by vapor deposition. The electron transport layer material is B3PymPm, with a thickness of 40 nanometers, and the deposition rate is controlled at [value missing].

[0088] After the electron transport layer is deposited, a 1-nanometer-thick layer of lithium fluoride is deposited onto the electron transport layer, with the deposition rate controlled at [value missing].

[0089] After replacing the upper electrode mask, a 100-nanometer-thick aluminum layer was deposited onto the lithium fluoride layer, with the deposition rate controlled at [value missing]. The core-shell structured tin-based perovskite nanocrystal light-emitting diode device was finally obtained.

[0090] Since this embodiment uses a full-size ITO substrate, the area of ​​the dotted aluminum electrode is the same as the area of ​​the device.

[0091] The vapor-deposited devices are transferred using a sealed device to a nitrogen glove box in another testing device to complete the performance testing of the light-emitting diode devices.

[0092] like Figure 5 The structure shown indicates that, due to charge injection and the presence of a shell barrier, the light-emitting diode device has a peak emission of around 450 nm at low voltage, corresponding to the emission of cesium bromide in the shell. As the voltage increases, charge carriers are injected into the core layer, resulting in the emission of tin-based perovskite.

[0093] like Figure 6 As shown, the highest brightness of the light-emitting diode made based on this nanocrystal is 16 cd / m2, and its highest external quantum efficiency is 0.045%, which is the highest efficiency of the tin-based perovskite nanocrystal light-emitting diode as of June 2023.

[0094] In addition, by modifying some conditions in Example 1, other orange luminescent core-shell structured tin-based perovskite nanocrystals can be prepared, as shown in Table 1 below:

[0095] Table 1

[0096]

[0097]

[0098] Based on the nanocrystals obtained in any one of Examples 1-11, by modifying some conditions in Example 2, other core-shell structured tin-based perovskite nanocrystal light-emitting diode devices can be fabricated, as shown in Table 2 below:

[0099] Table 2

[0100] The difference from Example 2 is that the conditions are different. Example 12 Based on Example 1, the electron transport layer is B3PymPm. Example 13 Based on Example 1, the electron transport layer is TPBi. Example 14 Based on Example 1, the PVK / chlorobenzene solution concentration was 4 mg / mL. Example 15 Based on Example 1, the PVK / chlorobenzene solution concentration was 5 mg / mL.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, it is intended to include any modifications and variations that fall within the scope of the claims and their equivalents.

[0102] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for preparing a core-shell structure tin-based perovskite nanocrystal, characterized in that, Comprising the following steps: Step 1, tin acetate and cesium acetate are mixed and added to a mixture of 1-octadecene, oleic acid and oleylamine, and stirred; Step 2, the mixture obtained in step 1 is kept at a constant temperature for a period of time under vacuum conditions; Step 3, inert gas is filled into the reaction system and kept at a constant temperature for a period of time to obtain a precursor solution; Step 4, trimethylsilyl bromide is added to the reaction system and cooled to room temperature to obtain a colloidal solution; Step 5, the colloidal solution obtained in step 4 is centrifuged, and the precipitate is dispersed and washed with n-hexane to obtain a core-shell structure tin-based perovskite nanocrystal; The molar ratio of tin acetate and cesium acetate in step 1 is 1:3-1:1 The mixture of 1-octadecene, oleic acid and oleylamine in step 1, wherein the volume ratio of oleic acid and oleylamine is 3:1-4:1, and the volume ratio of 1-octadecene to the above mixture of oleic acid and oleylamine is 7:4-6:5; The concentration of stannous acetate in the mixture obtained in Step 1 is 0.02 mol L -1 ; The constant temperature keeping for a period of time in step 2 is 100-110 ℃ for 1 h to remove water and oxygen; The constant temperature keeping for a period of time in step 3 is 175-180 ℃ for 10 min; The volume ratio of trimethylsilyl bromide to the precursor solution in step 4 is 3:100-4:100; trimethylsilyl bromide is quickly added to the reaction system and reacts for 10 s, and then cooled to room temperature; The centrifugal treatment condition in step 5 is 10000 rpm for 10 min.

2. A method for preparing a core-shell structured tin-based perovskite nanocrystal thin film, characterized in that, Comprising the following steps: The core-shell structure tin-based perovskite nanocrystal prepared by the method of claim 1 is dispersed in n-hexane, the above dispersion is ultrasonically treated, and the aggregated nanocrystals are removed by filtration to obtain a spin coating solution, which is spin coated on a substrate, and a core-shell structure tin-based perovskite nanocrystal thin film is obtained by annealing.

3. The preparation method of a core-shell structure tin-based perovskite nanocrystal thin film according to claim 2, characterized in that: The concentration of the spin coating solution is 6-10 mg / mL; the spin coating step is 2000 rpm for 60 s; and the annealing condition is 60 ℃ for 5 min.

4. A core-shell structure tin-based perovskite nanocrystal light-emitting diode device comprising a core-shell structure tin-based perovskite nanocrystal thin film prepared by the method of claim 2 or 3, characterized in that: It comprises ITO glass, hole transport layer, core-shell structure tin-based perovskite nanocrystal thin film, electron transport layer, electron injection layer and metal electrode layer which are sequentially stacked; wherein the hole transport layer is composed of PEDOT:PSS layer and poly-N-vinyl carbazole layer deposited in order.

5. A method of fabricating a core-shell structure tin-based perovskite nanocrystal light emitting diode device as claimed in claim 4, characterized in that, Comprising the following steps: Step 1, tin acetate and cesium acetate are mixed and added to a mixture of 1-octadecene, oleic acid and oleylamine, and stirred; Step 2, the mixture obtained in step 1 is kept at a constant temperature for a period of time under vacuum conditions; Step 3, inert gas is filled into the reaction system and kept at a constant temperature for a period of time to obtain a precursor solution; Step 4, trimethylsilyl bromide is added to the reaction system and cooled to room temperature to obtain a colloidal solution; Step 5, the colloidal solution obtained in step 4 is centrifuged, and the precipitate is dispersed and washed with n-hexane to obtain a core-shell structure tin-based perovskite nanocrystal; Step 6: spin-coat the PEDOT:PSS solution onto the ITO glass, and then anneal to obtain the ITO glass loaded with the PEDOT:PSS layer; Step 7: spin-coat the poly-N-vinylcarbazole solution onto the PEDOT:PSS layer obtained in step 6, and then anneal; Step 8: disperse the core-shell structured tin-based perovskite nanocrystals obtained in step 5 in n-hexane, and then filter out the aggregated nanocrystals after ultrasonic treatment to obtain a spin-coating solution; spin-coat the spin-coating solution onto the poly-N-vinylcarbazole layer obtained in step 7, and then anneal to obtain a core-shell structured tin-based perovskite nanocrystal thin film; Step 9: evaporate an electron transport layer on the core-shell structured tin-based perovskite nanocrystal thin film obtained in step 8; Step 10: evaporate an electron injection layer on the electron transport layer obtained in step 9; Step 11: evaporate a metal electrode layer on the electron injection layer obtained in step 10 to obtain a core-shell structured tin-based perovskite nanocrystal light-emitting diode device.

6. The preparation method of claim 5, wherein: the molar ratio of stannous acetate to cesium acetate in step 1 is 1:3-1:1; the mixture of 1-octadecene, oleic acid and oleylamine in step 1 has a volume ratio of oleic acid to oleylamine of 3:1-4:1, and a volume ratio of 1-octadecene to the mixture of oleic acid and oleylamine of 7:4-6:5; The concentration of stannous acetate in the mixture obtained in Step 1 is 0.02 mol L -1 ; the constant temperature in step 2 is maintained for a period of time, specifically 100-110 ℃ for 1 h to remove water and oxygen; the constant temperature in step 3 is maintained for a period of time, specifically 175-180 ℃ for 10 min; the volume ratio of trimethylsilyl bromide to the precursor solution in step 4 is 3:100-4:100; trimethylsilyl bromide is quickly added to the reaction system and reacts for 10 s, and then cooled to room temperature; the centrifugal treatment condition in step 5 is 10000 rpm for 10 min; the treatment method of the ITO glass in step 6 is: ultrasonic cleaning the ITO substrate with a washing solution, deionized water, acetone and ethanol for 20 min, and then treating with oxygen plasma for 15-30 min; the spin-coating step in step 6 is 4000 rpm for 30 s; the annealing condition is 150 ℃ for 20-30 min; the poly-N-vinylcarbazole solution in step 7 is: poly-N-vinylcarbazole is dissolved in chlorobenzene, and the concentration is 4-6 mg / mL; the spin-coating step in step 7 is 4500 rpm for 60 s; the annealing condition is 120 ℃ for 30 min; the concentration of the core-shell structured tin-based perovskite nanocrystals in the spin-coating solution in step 8 is 6-10 mg / mL; the spin-coating step is 2000 rpm for 60 s; the annealing condition is 60 ℃ for 5 min; The electron transport layer material described in Step 9 has a thickness of 40 nm, and the evaporation rate is 0.5-1 A s -1 ; The electron injection layer described in Step 10 has a thickness of 1 nm; the evaporation rate is 0.1-0.3 A s -1 ; The thickness of the metal electrode layer described in Step 11 is 100 nm; the evaporation rate is 3-5 A s -1 .

7. The method of claim 6, wherein: the electron transport layer material in step 9 includes TPBi, B4PymPm and B3PymPm; the electron injection layer material in step 10 is lithium fluoride; the metal electrode layer material in step 11 is aluminum.

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