Perovskite precursor solution additive, perovskite solar cell and preparation method

Abstract

The invention relates to the technical field of perovskite solar cells, in particular to a perovskite precursor solution additive, a perovskite solar cell and a preparation method. The additive is selected from any one of thieno [3, 2-B] thiophene, thieno [3, 4-B] thiophene, bithiophene [3, 2-B: 2, 3 '-D] thiophene, bithiophene (3, 4-B: 3, 4-D) thiophene and tetrathiophene, and the concentration of the additive is 0.1 to 0.4 mg / mL. According to the invention, the additive of the surface non-conductive passivation molecules is introduced at the perovskite interface, and the non-radiative recombination of carriers is reduced by passivating the defects at the interface, so that the performance and stability of the device are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite solar cells, and in particular to a perovskite precursor solution additive, a perovskite solar cell and a preparation method thereof. Background Art

[0002] Perovskite solar cells, due to their abundant raw materials, low cost, short production process, strong radiation resistance, excellent photoelectric properties, lightweight, and good flexibility, are expected to break through commercial bottlenecks and have a profound impact on the photovoltaic market. However, as perovskite solar cells are photovoltaic devices with a typical layered structure, they are subject to interface and surface defects, which accelerate carrier recombination and reduce carrier collection, thereby limiting their photoelectric conversion efficiency and affecting their long-term stability.

[0003] Existing technologies usually introduce interface modifiers at the interface between the perovskite layer and the carrier transport layer to optimize the performance of perovskite solar cells. However, there are few passivation sites and only a single type of defect can be passivated, resulting in poor charge transfer and poor device stability. Summary of the Invention

[0004] To address the deficiencies of the prior art, the present invention provides a perovskite precursor solution additive, a perovskite solar cell, and a preparation method. The present invention introduces a surface non-conductive passivation molecule additive at the perovskite interface. By passivating defects at the interface, it reduces non-radiative carrier recombination and improves device performance and stability.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a perovskite precursor solution additive, wherein the additive is selected from any one of thieno[3,2-B]thiophene, thieno[3,4-B]thiophene, dithieno[3,2-B:2,3'-D]thiophene, dithieno(3,4-B:3,4-D)thiophene, and tetrathiophene, and the concentration of the additive is 0.1 to 0.4 mg / mL.

[0007] Preferably, the concentration of the additive is 0.1 to 0.3 mg / mL.

[0008] Preferably, the concentration of the additive is 0.1-0.2 mg / mL.

[0009] In a second aspect, the present invention provides a perovskite precursor solution comprising the above-mentioned additive.

[0010] In a third aspect, the present invention provides a perovskite solar cell, wherein the perovskite absorption layer of the perovskite solar cell contains the above-mentioned additive.

[0011] Preferably, the structure of the perovskite solar cell includes a transparent conductive substrate, an electron transport layer, a lead iodide film, a perovskite absorption layer, a hole transport layer, and a metal electrode.

[0012] Preferably, the oxide material of the transparent conductive substrate is selected from any one or more of indium tin oxide (ITO), fluorine-doped tin oxide (FTO) and aluminum-doped zinc oxide (AZO).

[0013] Preferably, the material of the electron transport layer is selected from titanium dioxide (TiO2), tin dioxide (SnO2), fullerene derivatives (PCBM), fullerene (C 60 ), any one or more of molybdenum disulfide (MoS2).

[0014] Preferably, the material structure of the perovskite absorption layer is ABX3, wherein A is an organic cation selected from CH3NH 3 + , NH2CHNH 2+ 、Cs + , Rb + 、Na + , K + Any one of: B is selected from Pb 2+ 、Sn 2+ Any one or more of; X is I, Br, Cl or a hybrid halogen ion.

[0015] Preferably, the material of the hole transport layer is selected from any one or more of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD), nickel oxide (NiOx), (4-(3,6-dimethyl-9H-carbazole-9-yl)butyl)phosphonic acid (Me-4PACZ), 3,4-ethylenedioxythiophene monomer (PEDOT:PSS), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA).

[0016] Preferably, the material of the metal electrode is selected from any one or more of Ag, Au, Al, Cu, and Ni.

[0017] Preferably, the structure of the perovskite solar cell further includes a passivation layer.

[0018] In a fourth aspect, the present invention provides a method for preparing a perovskite solar cell, comprising preparing a perovskite absorption layer by spin-coating the precursor solution on a substrate and then annealing the resulting layer.

[0019] Preferably, the concentration of the additive in the precursor solution is 0.1-0.4 mg / mL.

[0020] Preferably, the method for preparing the perovskite solar cell further comprises cleaning the transparent conductive substrate, preparing an electron transport layer, preparing a hole transport layer, and preparing a metal electrode.

[0021] The beneficial effects of the present invention are:

[0022] The perovskite precursor solution additive provided by the present invention is a thiophene molecule, which has the following advantages: (1) the S atom of the additive and the Pb in the perovskite precursor 2+ The strong interaction between the S atoms can enhance the crystallinity of the film and promote the growth of high-quality, defect-free perovskite films. In addition, the S atoms have uncoordinated electron pairs on their surfaces, which effectively passivate the uncoordinated Pb 2+ , inhibiting Pb 0 The generation of defects. That is, the synergistic effect of reducing the film defect density and enhancing the film crystallinity together achieves the effect of passivating defects. (2) The additive can interact with the molecules in the precursor solution to form a highly π-conjugated semiconductor, which can give the perovskite better charge transport properties and promote the growth of perovskite crystals. (3) The additive can effectively reduce the excess PbI2 content in the perovskite and improve the stability of the device.

[0023] In the perovskite solar cell preparation process of the present invention, the additive is innovatively introduced into the perovskite absorption layer to achieve precise control of the material interface. The additive can effectively passivate the interface defect states of the perovskite film and significantly suppress the non-radiative recombination loss of carriers, thereby simultaneously improving the photoelectric conversion efficiency and long-term operation stability of the device. The process parameters of the present invention are widely adaptable, in-situ doping can be achieved without complex equipment modification, and the raw material cost is low. The present invention breaks through the industrial bottleneck of the difficulty in co-optimizing efficiency and stability, and provides a practical technical path for promoting the large-scale industrial production of perovskite solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The efficiency box diagram of the formal structure solar cells prepared by comparative example 1, embodiment 2 and embodiments 6 to 9 (left figure) and the efficiency box diagram of the formal structure solar cells prepared by embodiments 1 to 4 and comparative example 1 (right figure) are shown.

[0025] Figure 2 JV curves of the regular structure solar cells prepared in Example 2 and Comparative Example 1.

[0026] Figure 3 Photoluminescence spectra of the perovskite absorption layers of the solar cells prepared in Example 2 and Comparative Example 1.

[0027] Figure 4TRPL test graphs of the perovskite absorption layer of the solar cell prepared in Example 2 and Comparative Example 1.

[0028] Figure 5 XRD patterns of the perovskite absorption layers of the solar cells prepared in Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0030] In order to solve the problem that the existing technology of using interface modifiers to optimize the performance of perovskite solar cells has a limited number of passivation sites and can only passivate a single type of defect, resulting in poor charge transfer and poor device stability, the present invention first provides a perovskite precursor solution additive, the additive is selected from any one of thieno[3,2-B]thiophene, thieno[3,4-B]thiophene, dithieno[3,2-B:2,3'-D]thiophene, dithieno(3,4-B:3,4-D)thiophene, and tetrathiophene, and the concentration of the additive is 0.1 to 0.4 mg / mL.

[0031] The perovskite precursor solution additive provided by the present invention is a thiophene molecule, which has the following advantages: (1) the S atom of the additive and the Pb in the perovskite precursor 2+ The strong interaction between the S atoms can enhance the crystallinity of the film and promote the growth of high-quality, defect-free perovskite films. In addition, the S atoms have uncoordinated electron pairs on their surfaces, which effectively passivate the uncoordinated Pb 2+ , inhibiting Pb 0 The generation of defects. That is, the synergistic effect of reducing the film defect density and enhancing the film crystallinity together achieves the effect of passivating defects. (2) The additive can interact with the molecules in the precursor solution to form a highly π-conjugated semiconductor, which can give the perovskite better charge transport properties and promote the growth of perovskite crystals. (3) The additive can effectively reduce the excess PbI2 content in the perovskite and improve the stability of the device.

[0032] In some embodiments of the present invention, the concentration of the additive is any one of 0.1 mg / mL, 0.2 mg / mL, 0.3 mg / mL, 0.4 mg / mL, or a value therebetween. Preferably, the concentration of the additive is 0.1 to 0.3 mg / mL. Preferably, the concentration of the additive is 0.1 to 0.2 mg / mL.

[0033] In a second aspect, the present invention provides a perovskite precursor solution comprising the above-mentioned additive.

[0034] In a third aspect, the present invention provides a perovskite solar cell, wherein the perovskite absorption layer of the perovskite solar cell contains the above-mentioned additive.

[0035] Preferably, the mass of the additive in the perovskite absorber layer of the perovskite solar cell is 0.005 to 0.02 mg. In some embodiments of the present invention, the mass of the additive in the perovskite absorber layer of the perovskite solar cell is any one of 0.005 mg, 0.01 mg, 0.015 mg, 0.02 mg, or a value between the two. Preferably, the mass of the additive in the perovskite absorber layer of the perovskite solar cell is 0.005 to 0.015 mg. Preferably, the mass of the additive in the perovskite absorber layer of the perovskite solar cell is 0.005 to 0.01 mg.

[0036] The structure of the perovskite solar cell of the present invention can be a regular structure or a trans structure.

[0037] In some embodiments of the present invention, the structure of the perovskite solar cell includes a transparent conductive substrate, an electron transport layer, a lead iodide film, a perovskite absorption layer, a hole transport layer, and a metal electrode.

[0038] The oxide material of the transparent conductive substrate of the present invention is selected from any one or more of indium tin oxide (ITO), fluorine-doped tin oxide (FTO) and aluminum-doped zinc oxide (AZO).

[0039] The material of the electron transport layer of the present invention is selected from titanium dioxide (TiO2), tin dioxide (SnO2), fullerene derivatives (PCBM), fullerene (C 60 ), any one or more of molybdenum disulfide (MoS2).

[0040] The material structure of the perovskite absorption layer of the present invention is ABX3, wherein A is an organic cation selected from CH3NH 3 + , NH2CHNH 2+ 、Cs + , Rb + 、Na + , K + Any one of: B is selected from Pb 2+ 、Sn 2+ Any one or more of; X is I, Br, Cl or a hybrid halogen ion.

[0041] The material of the hole transport layer of the present invention is selected from any one or more of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD), nickel oxide (NiOx), (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACZ), 3,4-ethylenedioxythiophene monomer (PEDOT:PSS), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA).

[0042] The material of the metal electrode of the present invention is selected from any one or more of Ag, Au, Al, Cu and Ni.

[0043] The structure of the titanite solar cell of the present invention further includes a passivation layer.

[0044] In a fourth aspect, the present invention provides a method for preparing a perovskite solar cell, comprising: preparing a perovskite absorption layer by spin-coating the precursor solution on a substrate and then annealing the substrate.

[0045] Preferably, the concentration of the additive in the precursor solution is 0.1 to 0.4 mg / mL. Preferably, the concentration of the additive is 0.1 to 0.3 mg / mL. Preferably, the concentration of the additive is 0.1 to 0.2 mg / mL.

[0046] In some embodiments of the present invention, the method for preparing the perovskite solar cell adopts a two-step method.

[0047] The method for preparing the perovskite solar cell of the present invention further comprises cleaning the transparent conductive substrate, preparing an electron transport layer, preparing a hole transport layer, and preparing a metal electrode.

[0048] In the perovskite solar cell fabrication process of the present invention, the additive is innovatively introduced into the perovskite absorber layer, enabling precise control of the material interface. The additive effectively passivates the interface defect states of the perovskite film, significantly suppressing non-radiative carrier recombination losses, thereby simultaneously improving the device's photoelectric conversion efficiency and long-term operational stability.

[0049] The above is a detailed description of the technical solution of the present invention, and the following are embodiments of the present invention.

[0050] Example 1

[0051] A method for preparing a formal structured perovskite solar cell comprises the following steps:

[0052] (1) Cleaning the transparent conductive substrate: Place the ITO substrate in a UV ozone cleaning machine and irradiate it with UV light for 15 minutes to clean away impurities on the substrate surface and improve the substrate wettability.

[0053] (2) Preparation of electron transport layer: Spin-coat SnO2 nanocrystal solution (concentration of 13 mg / mL, amount of 40 μL) on a transparent conductive substrate using dynamic spin coating at a rotation speed of 2000 rpm / s. After spin coating for 30 seconds, place it on a hot plate at 150°C for annealing for 30 minutes.

[0054] (3) Preparation of lead iodide film: Spin-coat PbI2 solution (each 1 mL of solution contains DMF: 0.9 mL, DMSO: 0.1 mL, PbI2: 691 mg) on ​​the electron transport layer using static spin coating at a rotation speed of 1500 rpm / s. After spin coating for 40 seconds, place it on a 70°C hot plate for annealing for 1 minute.

[0055] (4) Preparation of perovskite absorption layer: Spin coating a precursor solution containing thieno[3,2-B]thiophene (90 mg of FAI and 9 mg of MACl per 1 mL of solution) on the lead iodide film using a quasi-dynamic spin coating method at a speed of 2000 rpm / s and a dosage of 50 μL. After spin coating for 30 seconds, place the film on a hot plate at 150°C in air for annealing for 30 minutes.

[0056] The added concentration of thieno[3,2-B]thiophene is 0.1 mg / mL, and the structural formula of thieno[3,2-B]thiophene is:

[0057] (5) Preparation of hole transport layer: Spin-coat the perovskite absorption layer with Spiro-oMeTAD solution (100 mg of Spiro-oMeTAD, 40 μL of tetra-tert-butylpyridine, 6 mg of lithium bis(trifluoromethanesulfonylimide), and 12 mg of cobalt(III) bis(trifluoromethanesulfonylimide per 1 mL of solution, in a dosage of 40 μL) using a dynamic spin-coating method at a rotation speed of 4500 rpm / s for 30 s.

[0058] (6) Preparation of metal electrodes: Evaporation of Ag electrodes with a thickness of 100 to 120 nm.

[0059] Example 2

[0060] The same as Example 1, except that: in step (4) when preparing the perovskite absorption layer, the added concentration of thieno[3,2-B]thiophene is 0.2 mg / mL.

[0061] Example 3

[0062] The same as Example 1, except that: in step (4) when preparing the perovskite absorption layer, the added concentration of thieno[3,2-B]thiophene is 0.3 mg / mL.

[0063] Example 4

[0064] The same as Example 1, except that: in step (4) when preparing the perovskite absorption layer, the added concentration of thieno[3,2-B]thiophene is 0.4 mg / mL.

[0065] Example 5

[0066] A method for preparing an inverted perovskite solar cell comprises the following steps:

[0067] (1) Cleaning the transparent conductive substrate: Place the ITO substrate in a UV ozone cleaning machine and irradiate it with UV light for 15 minutes to clean away impurities on the substrate surface and improve the substrate wettability;

[0068] (2) Preparation of hole transport layer: NiOx (concentration of 20 mg / mL, amount of 40 μL) was spin-coated in air by dynamic spin coating at a speed of 3000 rpm / s for 30 s. After spin coating, the mixture was placed on a hot plate at 150°C for annealing for 15 min. Subsequently, Me-4PACZ solution (concentration of 0.5 mg / mL, amount of 50 μL) was spin-coated by dynamic spin coating at a speed of 3000 rpm / s for 30 s as a hole transport layer.

[0069] (3) Preparation of lead iodide film: PbI2 solution (40 μL per 1 mL of solution containing 0.9 mL of DMF, 0.1 mL of DMSO, and 691 mg of PbI2) was spin-coated on the hole transport layer by static spin coating at a speed of 1500 rpm / s for 30 s, and then annealed on a hot plate at 70°C for 1 min.

[0070] (4) Preparation of perovskite absorption layer: 50 μL of a precursor solution containing thieno[3,2-b]thiophene (90 mg of FAI and 9 mg of MACl per mL of solution) was spin-coated on the lead iodide film using a quasi-dynamic spin coating method; the concentration of thieno[3,2-b]thiophene was 0.1 mg / mL, the spin coating speed was 2000 rpm / s, and after spin coating for 30 seconds, the film was placed on a hot plate at 150°C in air for annealing for 30 minutes;

[0071] (5) Preparation of electron transport layer: PCBM solution (concentration of 20 mg / mL, amount of 30 μL) was spin-coated by dynamic spin coating at a speed of 1500 rpm / s for 30 s;

[0072] (6) Preparation of passivation layer: BCP solution (concentration of 0.5 mg / mL, amount of 60 μL) was spin-coated as a passivation layer by dynamic spin coating at a speed of 6000 rpm / s for 40 s;

[0073] (7) Preparation of metal electrode: Evaporation of Ag electrode with a thickness of 100 nm.

[0074] Example 6

[0075] The same as Example 1 or 5, except that, in step (4) of preparing the perovskite absorption layer, the precursor solution additive is 0.2 mg / mL of thieno[3,4-B]thiophene, whose chemical structure is:

[0076]

[0077] Example 7

[0078] The same as Example 1 or 5, except that, in step (4), when preparing the perovskite absorption layer, the precursor solution additive is 0.2 mg / mL of dithiophene [3,2-B:2,3'-D] thiophene, whose chemical structure is:

[0079]

[0080] Example 8

[0081] The same as Example 1 or 5, except that, in step (4) of preparing the perovskite absorption layer, the precursor solution additive is 0.2 mg / mL of dithiophene (3,4-B:3,4-D) thiophene, whose chemical structure is:

[0082]

[0083] Example 9

[0084] The same as Example 1 or 5, except that, in step (4) of preparing the perovskite absorption layer, the precursor solution additive is 0.2 mg / mL of quaterthiophene, whose chemical structure is:

[0085]

[0086] Comparative Example 1

[0087] The same as Example 1, except that no additive is added to the precursor solution when preparing the perovskite absorption layer in step (4).

[0088] Effect Example 1 Solar Cell Performance Test

[0089] Figure 1The left figure is a box plot of the efficiency of the solar cells of the formal structure prepared in Comparative Example 1, Example 2, and Examples 6 to 9. As can be seen from the figure, the efficiency of the solar cells obtained by adding the additive of the present invention to the perovskite precursor solution is improved in overall performance compared to Comparative Example 1, and the highest functional conversion efficiency can be obtained. 24.81%. The right figure is a box plot of the efficiency of the solar cells of the formal structure prepared in Examples 1 to 4 and Comparative Example 1. As can be seen from the figure, the highest functional conversion efficiency can be obtained when the concentration of the additive added to the perovskite precursor solution is 0.2 mg / mL.

[0090] Figure 2 The JV curves of the solar cells with the formal structures prepared in Example 2 and Comparative Example 1 are shown. As can be seen from the figure, adding the additive of the present invention to the perovskite precursor solution can improve the overall performance of the device, and a maximum functional conversion efficiency of 24.81% can be achieved at a concentration of 0.2 mg / mL.

[0091] Effect Example 2 Photoluminescence Spectrum Characterization

[0092] The optical properties and defect states of perovskite materials are characterized by photoluminescence (PL) spectroscopy. Figure 3 The photoluminescence spectra of the perovskite absorber layer of the solar cell prepared in Example 2 and Comparative Example 1 are shown in the figure. As can be seen from the figure, compared with Comparative Example 1, the PL peak of Example 2 is higher, indicating that the band gap energy of the perovskite material is higher, the PL intensity is higher, indicating that non-radiative recombination is reduced, the half-peak width is narrower, and the material has better crystal quality and fewer defects. This is because after the additive is added to the perovskite precursor solution of the present invention, the S in the additive thiophene reacts with the uncoordinated Pb 2+ Combined with passivation of surface defects in perovskite films, the defect density can be reduced.

[0093] The dynamic behavior of photogenerated carriers in perovskite materials, especially the carrier recombination process, is studied through time-resolved photoluminescence testing. Figure 4 The TRPL test graphs of the perovskite absorption layer of the solar cell prepared in Example 2 and Comparative Example 1 show that the average carrier lifetime (τ) is obtained by fitting the PL decay curve. The average carrier lifetime of Example 2 of the present invention is significantly higher than that of Comparative Example 1, indicating that the carrier recombination rate is slower. This is because the thieno[3,2-B]thiophene molecules in the additive of the present invention can react with the FAI solution to form a highly π-conjugated semiconductor, which can give the perovskite better charge transport properties, effectively reduce the excess PbI2 content of the perovskite, and improve device stability.

[0094] Effect Example 3 XRD Characterization

[0095] Figure 5 The XRD patterns of the perovskite absorber layer of the solar cell prepared in Example 2 and Comparative Example 1 are shown. As can be seen from the figure, the typical XRD peak of the perovskite material is located at an angle of 14°, corresponding to the crystal plane (001) in its crystal structure. Compared with Comparative Example 1, the XRD peak intensity of the perovskite absorber layer prepared in Example 2 of the present invention is higher, indicating that the additive promotes the crystallization of the perovskite film and improves the crystallinity. This is because the thieno[3,2-b]thiophene molecules can react with the FAI solution to form a highly π-conjugated semiconductor, which can promote the growth of perovskite crystals, and the S and Pb in the thieno[3,2-b]thiophene molecules are more likely to be pi-conjugated than those in the FAI solution. 2+ Form coordination, regulate the growth of perovskite thin crystals, and promote the formation of high-quality, low-defect perovskite films.

[0096] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A perovskite precursor solution additive, characterized in that: The additive is selected from any one of thieno[3,2-B]thiophene, thieno[3,4-B]thiophene, dithieno[3,2-B:2,3'-D]thiophene, dithieno(3,4-B:3,4-D)thiophene, and tetrathiophene, and the concentration of the additive is 0.1-0.4 mg / mL.

2. A perovskite precursor solution, characterized in that The invention comprises the additive according to claim 1.

3. A perovskite solar cell, characterized in that: The perovskite absorption layer of the perovskite solar cell contains the additive according to claim 1.

4. The perovskite solar cell according to claim 3, characterized in that The structure of the perovskite solar cell includes a transparent conductive substrate, an electron transport layer, a lead iodide film, a perovskite absorption layer, a hole transport layer, and a metal electrode.

5. The perovskite solar cell according to claim 4, characterized in that The material of the electron transport layer is selected from any one or more of titanium dioxide, tin dioxide, fullerene derivatives, fullerene, and molybdenum disulfide.

6. The perovskite solar cell according to claim 4, characterized in that The material structure of the perovskite absorption layer is ABX3, wherein A is an organic cation selected from CH3NH 3+ , NH2CHNH 2+ 、Cs + , Rb + 、Na + , K + Any one of: B is selected from Pb 2+ 、Sn 2+ Any one or more of; X is I, Br, Cl or a hybrid halogen ion.

7. The perovskite solar cell according to claim 4, characterized in that The material of the hole transport layer is selected from any one or more of Spiro-OMeTAD, NiOx, Me-4PACZ, PEDOT:PSS, and PTAA.

8. The perovskite solar cell according to any one of claims 4 to 7, characterized in that: The structure of the perovskite solar cell further includes a passivation layer.

9. A method for preparing a perovskite solar cell, characterized in that: The method comprises preparing a perovskite absorption layer by spin-coating the precursor solution according to claim 2 on a substrate and then annealing the substrate.

10. The method for preparing a perovskite solar cell according to claim 9, wherein: The method for preparing the titanium ore solar cell further includes cleaning the transparent conductive substrate, preparing an electron transport layer, preparing a hole transport layer, and preparing a metal electrode.

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