A preparation method of nickel oxide thin film and its application in perovskite solar cells

Abstract

The present invention discloses a preparation method of nickel oxide thin film and its application in perovskite solar cells, belonging to the technical field of new material solar cells. In the synthesis step of nickel oxide nanocrystals, the present invention introduces a ligand protection method. Lithium stearate, which can stably exist in the reaction system and is easy to adhere to nickel oxide nanoparticles, is added to the reaction system. Lithium stearate acts as a ligand to coat the surface of nickel oxide, reducing the reaction activity of nickel oxide and preventing it from being reduced to nickel during high-temperature and long-time reaction processes, and finally obtaining high-purity nickel oxide. The inverted planar perovskite solar cell prepared with pure nickel oxide thin film as the hole transport layer has higher photoelectric conversion efficiency and better stability, providing a new idea for the preparation of high-efficiency and high-stability perovskite solar cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of new material solar cells, and relates to the preparation of a hole transport layer and its application in perovskite solar cells. Background Art

[0002] In recent years, an organic-inorganic halide perovskite has shown broad application prospects due to its low-cost solution processability and excellent optoelectronic conversion performance. The perovskite materials have good light absorption coefficients, long charge diffusion lengths, tunable bandgaps, solution processability, and the advantages of being able to prepare flexible, transparent, and tandem cells, etc., which have attracted the attention of many researchers.

[0003] Perovskite solar cells are a new type of solar cell that has developed the fastest so far. In just a few years, its efficiency has exceeded 20%, and it has the potential to achieve higher efficiency and low manufacturing costs. However, poor material stability and short battery life have always been the main factors restricting its development. Currently, its commonly used hole transport materials can be divided into three categories: inorganic, polymer, and small molecule. Although inorganic hole transport materials have high hole mobilities, the processing solvents have a certain solubility in perovskite, which affects the stability of the device. Polymer hole transport materials also have some disadvantages, such as poor solubility, complex purification processes during synthesis, and uncertain molecular weights. Small molecule hole transport materials have monodispersity and have a definite molecular weight, which is a good choice, but their bottlenecks are also obvious, such as long synthesis steps, instability to ultraviolet light, low purity, and low yield.

[0004] Nickel oxide has the advantages of low cost, high transparency, high hole mobility, and good chemical stability. As a hole transport layer, good device performance has been obtained in perovskite cells. However, during the synthesis of nickel oxide nanocrystals, nickel oxide is easily reduced to nickel at high temperatures and during long reaction processes, which greatly affects the purity of the nickel oxide thin film and further affects the use efficiency and stability of perovskite solar cells. Summary of the Invention

[0005] The object of the present invention is to solve at least one of the above problems and / or defects and provide at least the advantages described hereinafter.

[0006] To achieve these objects and other advantages in accordance with the present invention, a method for preparing a nickel oxide thin film is provided, specifically including the following steps:

[0007] Step 1. Synthesis of nickel oxide nanocrystals: Weigh a certain proportion of nickel stearate, lithium stearate, and octadecanol and dissolve them in a certain amount of 1-octadecene. Heat and stir, and evacuate to remove air and moisture in the reaction system. After a period of time, heat to 250-320 °C under argon protection, condense and reflux until the reaction ends to obtain nickel oxide nanocrystals protected by lithium stearate ligands.

[0008] Step 2. Preparation of nickel oxide nanocrystal solution: Pour the mixture obtained in Step 1 into a beaker, add ethyl acetate, and let it stand at room temperature for 10-14 h. Then transfer it to a centrifuge tube, centrifuge at 4000-6000 r / min for 4-6 min, pour off the supernatant, dissolve the precipitate completely with n-hexane, add absolute ethanol, and then centrifuge at 8000-12000 r / min for 4-6 min. Repeat centrifugation multiple times, collect the precipitate and freeze-dry it, and then dissolve it in chlorobenzene to prepare a chlorobenzene solution of nickel oxide with a certain concentration to obtain a nickel oxide nanocrystal solution.

[0009] Step 3. Preparation and cleaning of nickel oxide thin film: Take a conductive glass as the substrate, take the nickel oxide nanocrystal solution obtained in Step 2 as the coating liquid, and spread the nickel oxide nanocrystal solution on the surface of the conductive glass substrate by spin coating. Subsequently, put the conductive glass substrate coated with the nickel oxide nanocrystal solution into a vacuum tube furnace, anneal at 350-380 °C for 15-20 min under argon atmosphere protection to obtain a nickel oxide thin film on the surface of the conductive glass.

[0010] Preferably, in Step 1, the molar ratio of nickel stearate, lithium stearate, and octadecanol is 0.98-1.02:0.39-0.41:5.88-6.12; the purity of the argon is above 99.99%.

[0011] Preferably, in Step 2, the concentration of nickel oxide nanocrystals in the chlorobenzene solution is 8-12 mg / mL.

[0012] Preferably, in Step 3, the size of the conductive glass is 1.5 cm × 1.5 cm.

[0013] Preferably, in Step 3, the dropping amount of the nickel oxide nanocrystal solution on the conductive glass is 60 μL.

[0014] Application of a nickel oxide thin film prepared by the method for preparing a nickel oxide thin film as claimed in claim 1 as a hole transport layer in a perovskite solar cell, wherein:

[0015] The layers of the perovskite solar cell structure are, from bottom to top in sequence: conductive glass, nickel oxide thin film - nickel oxide hole transport layer, perovskite layer, PCBM layer, silver electrode layer;

[0016] The preparation method of the perovskite solar cell is as follows:

[0017] Ⅰ. Take a conductive glass - ITO glass sheet (1.5 cm × 1.5 cm), ultrasonically clean the ITO glass sheet with acetone, dishwashing detergent water, deionized water, and isopropanol for 10 - 20 min. After thorough cleaning, dry it with a nitrogen gun and put it into a plasma processor for surface treatment with ultraviolet ozone for 8 - 12 min;

[0018] Ⅱ. Take the cleaned ITO glass in Ⅰ as the substrate and nickel oxide nanocrystal solution as the coating liquid. Spread the nickel oxide nanocrystal solution on the surface of the ITO glass by spin coating. Then put the conductive glass substrate coated with the nickel oxide nanocrystal solution into a vacuum tube furnace and anneal it at 350 - 380 °C for 15 - 20 min under the protection of an argon atmosphere to obtain a high-purity nickel oxide thin film on the surface of the cleaned ITO glass, obtaining battery precursor A. Immediately put it into a glove box protected by high-purity nitrogen for standby;

[0019] Ⅲ. Take the ITO glass - battery precursor A with a nickel oxide thin film on its surface in Ⅱ as the substrate and perovskite solution as the coating liquid. Drop the perovskite solution onto the slowly rotating nickel oxide thin film at 80 °C, then adjust the rotation speed to 4000 - 6000 r / min and maintain it for 25 - 35 s; at 12 - 18 s, uniformly drop 1 mL of toluene to the center of the sample; then, anneal it at 105 - 115 °C for 4 - 6 min and at 125 - 135 °C for 8 - 12 min. After cooling to room temperature, obtain a dense and hole-free perovskite thin film on the surface of the nickel oxide thin film, obtaining battery precursor B;

[0020] Ⅳ. Take the battery precursor B substrate obtained in Ⅲ and 15 - 20 mg / mL PCBM solution as the coating liquid. Spread the PCBM solution on the surface of the perovskite thin film on the battery precursor B by spin coating to obtain battery precursor C;

[0021] Ⅴ. Take the battery precursor C obtained in Ⅳ and put it into the chamber of a vacuum coating machine. Evaporate a 70 - 80 nm thick Ag electrode on the surface of the PCBM thin film on the battery precursor C under vacuum conditions; wipe out a photoanode with γ-butyrolactone, and then use an ultrasonic soldering iron to solder an indium wire at the wiped photoanode to obtain a perovskite solar cell.

[0022] Preferably, in step I, the ultrasonic cleaning frequency is 30 - 50KHZ; in step II, the spin coating speed of the nickel oxide nanocrystal solution spread on the surface of the ITO glass is 2800 - 3000r / min, and the spin coating time is 8 - 12s; in step III, the perovskite solution is a dimethyl sulfoxide solution containing methylammonium lead iodide at 0.6 - 0.8g / mL; in step IV, the PCBM solution is a chlorobenzene solution containing fullerene, the spin coating speed is 4000 - 6000r / min, and the spin coating time is 25 - 35s.

[0023] Preferably, the perovskite solar cell is a reverse planar perovskite solar cell.

[0024] A preparation method of a nickel oxide thin film and its application in a perovskite solar cell provided by the present invention has at least the following beneficial effects:

[0025] Compared with the nickel oxide thin film prepared by the traditional synthesis method, by the method of ligand protection, the reaction activity of the nickel oxide nanocrystal is reduced, and it is prevented from being reduced to nickel during the reaction at high temperature and for a long time, and a pure nickel oxide thin film is obtained. The reverse planar perovskite solar cell prepared with the pure nickel oxide thin film as the hole transport layer has higher photoelectric conversion efficiency and better stability, providing a new idea for the preparation of high-efficiency and high-stability perovskite solar cells.

[0026] Other features and advantages of the present disclosure will be described in the following description, or, some features and advantages can be inferred from the description or determined without doubt, or can be learned by implementing the above technologies of the present disclosure. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of the reverse perovskite solar cell of the present invention;

[0028] Figure 2 is the X-ray diffraction characterization of the nickel oxide nanocrystal in Example 1 of the present invention;

[0029] Figure 3 is the SEM characterization diagram of the nickel oxide nanocrystal thin film with a conductive glass as the substrate in Example 1 of the present invention;

[0030] Figure 4 is the efficiency comparison diagram of the inverted perovskite solar cell prepared in Example 1 of the present invention and a common reverse perovskite solar cell;

[0031] Figure 5 is the stability comparison diagram of the inverted perovskite solar cell prepared in Example 1 of the present invention and a common reverse perovskite solar cell. Detailed Embodiments

[0032] The following describes the specific solutions proposed by the present invention in more detail with several specific embodiments.

[0033] Please refer to Figure 1 , a perovskite solar cell with an inverted structure, and its layers from bottom to top are successively: a conductive glass, a nickel oxide thin film, a perovskite layer, a PCBM layer, and a silver electrode layer.

[0034] Example 1:

[0035] S1. A preparation method of a nickel oxide thin film specifically includes the following steps:

[0036] S11. Synthesis of nickel oxide nanocrystals: Weigh 1 mmol of nickel stearate, 0.4 mmol of lithium stearate, 6 mmol of octadecanol, and 10 mL of 1-octadecene into a three-necked flask, add a magnetic stirrer, connect a vacuum pump to the left side of the three-necked flask, install a condenser in the middle, and install a thermometer and a thermocouple on the right side;

[0037] Control the reaction temperature through the thermometer and the thermocouple, heat to 180 °C, stir magnetically and evenly, and evacuate to remove air and moisture in the three-necked flask. After 30 minutes, pass argon gas and heat to 280 °C for condensation reflux until the reaction ends to obtain nickel oxide nanocrystals protected by lithium stearate ligands;

[0038] S12. Preparation of nickel oxide nanocrystal solution: Pour all the products obtained in the first step into a beaker, add 40 mL of ethyl acetate, and place it at room temperature for 12 h. Then place it in several centrifuge tubes respectively, centrifuge at 5000 r / min for 5 min, pour off the supernatant, add 4 mL of n-hexane to dissolve all the precipitates, then add 6 mL of absolute ethanol, and then centrifuge at 10000 r / min for 5 min, and centrifuge four times repeatedly. Collect the centrifuged precipitate and freeze-dry it, and then dissolve it in chlorobenzene to prepare a 10 mg / mL nickel oxide nanocrystal solution;

[0039] S13. Preparation and cleaning of nickel oxide thin film: Take a conductive glass as a substrate and the nickel oxide nanocrystal solution as a coating liquid, and spread the nickel oxide nanocrystal solution on the surface of the conductive glass substrate by spin coating. Subsequently, place the conductive glass substrate coated with the nickel oxide nanocrystal solution into a vacuum tube furnace, and anneal it at 380 °C for 20 min under the protection of an argon atmosphere to obtain a nickel oxide thin film on the conductive glass surface;

[0040] Among them, the spin coating speed is 3000 r / min, and the dropping amount of the nickel oxide nanocrystal solution on the surface of each conductive glass substrate is 60 μL.

[0041] S2. Application of nickel oxide thin film surface-modified with nickel stearate in perovskite solar cells, specifically including the following steps:

[0042] S21. Conductive Glass - The ITO glass sheet (1.5 cm * 1.5 cm) is ultrasonically cleaned with acetone, 10% (by mass) dishwashing detergent solution, deionized water, and isopropanol for 15 min in sequence. After thorough cleaning, it is dried with a nitrogen gun and then put into a plasma processor for 10 min of surface treatment by ultraviolet ozone cleaning;

[0043] Among them, the ultrasonic cleaning frequency is 40 KHZ; the set temperature for ultraviolet ozone cleaning in the plasma processor is 30 °C;

[0044] S22. Take the cleaned ITO glass processed in S21 as the substrate and the nickel oxide nanocrystal solution as the coating liquid. The nickel oxide nanocrystal solution is spread on the surface of the ITO glass by spin coating to form a nickel oxide thin film. Subsequently, the conductive glass substrate coated with the nickel oxide nanocrystal solution is put into a vacuum tube furnace and annealed at 380 °C for 20 min under the protection of an argon atmosphere to remove the nickel stearate ligand on the surface of the nickel oxide, obtaining the battery precursor A, which is immediately put into a glove box protected by high-purity nitrogen for standby;

[0045] Among them, the spin coating speed is 3000 r / min, the spin coating time is 10 s, and the dropwise addition amount of the nickel oxide nanocrystal solution on the surface of each ITO glass sheet is 60 uL.

[0046] S23. Take the ITO glass - battery precursor A with a nickel oxide thin film covered on its surface in S22 as the substrate and the perovskite solution as the coating liquid. The perovskite solution is dropped onto the slowly rotating nickel oxide thin film at 80 °C, and then the rotation speed is adjusted to 5000 r / min and maintained for 30 s; at 15 s, 1 mL of toluene is uniformly dropped onto the center of the nickel oxide thin film. After that, it is annealed in a heating furnace at 110 °C for 5 min and at 130 °C for 10 min. After cooling to room temperature, a dense and hole-free perovskite thin film is obtained on the surface of the nickel oxide thin film, obtaining the battery precursor B;

[0047] Among them, the perovskite solution is a dimethyl sulfoxide solution containing methylammonium lead iodide, and its concentration is 0.744 g / mL; the dropwise addition amount of the perovskite solution on the surface of the nickel oxide thin film is 75 uL.

[0048] S24. Take the battery precursor B obtained in S23 as the substrate and the 20 mg / mL PCBM solution as the coating liquid. The PCBM solution is spread on the surface of the perovskite thin film on the battery precursor B by spin coating to obtain the battery precursor C;

[0049] Among them, the PCBM solution refers to a chlorobenzene solution containing fullerene, the spin coating speed is 5000 r / min, the spin coating time is 30 s, and the dropwise addition amount of the PCBM solution on the surface of each perovskite thin film is 75 uL.

[0050] S25. Take the battery precursor C obtained in S24 and place it in the chamber of a vacuum coating machine. Under vacuum conditions, evaporate a 75-nm-thick Ag electrode on the surface of the PCBM thin film on the battery precursor C. Wipe out a photoanode with γ-butyrolactone, and then use an ultrasonic soldering iron to solder an indium wire at the wiped photoanode to obtain a perovskite solar cell.

[0051] Implementation effect:

[0052] (1) Please refer to Figure 2 , in the XRD pattern of the nickel oxide thin film prepared in this embodiment, there are no impurity peaks, indicating that the nickel oxide nanocrystals obtained in this embodiment have good performance and a single crystal structure.

[0053] (2) Please refer to Figure 3 , the SEM characterization of the nickel oxide thin film prepared in this embodiment shows that the nickel oxide prepared in this embodiment has good film-forming properties.

[0054] (3) Please refer to Figure 4 、 Figure 5 , where the NiO nanocrystals in the figure refer to the nickel oxide nanocrystals protected by nickel stearate ligands in the nickel oxide thin film of the inverted planar perovskite solar cell; NiO refers to the nickel oxide thin film in the inverted planar perovskite solar cell prepared from ordinary nickel oxide nanocrystals; spiro refers to the hole transport layer in the inverted planar perovskite solar cell being a traditional organic hole transport layer material;

[0055] It can be seen that: compared with the inverted planar perovskite solar cell with the nickel oxide thin film prepared by the conventional method as the hole transport layer, the inverted planar perovskite solar cell prepared by the implementation method of this embodiment has higher stability and efficiency; and it is significantly superior in stability to the perovskite solar cell prepared with the traditional organic hole transport layer material spiro.

[0056] The above treatment scale is used to simplify the description of the present invention, and the applications, modifications, and variations of the present invention are obvious to those skilled in the art.

[0057] Although the embodiments of the present invention have been disclosed as above, they are not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. Application of nickel oxide thin film as hole transport layer in perovskite solar cell, characterized in that, The layers of the perovskite solar cell structure are, from bottom to top in sequence: conductive glass, nickel oxide thin film - nickel oxide hole transport layer, perovskite layer, PCBM layer, silver electrode layer; Among them, the preparation method of the nickel oxide thin film specifically includes the following steps: Step 1, synthesis of nickel oxide nanocrystals: Weigh a certain proportion of nickel stearate, lithium stearate and octadecanol and dissolve them in a certain amount of 1-octadecene. Heat and stir and evacuate the air and moisture in the reaction system; after a period of time, heat to 250-320 °C under argon protection, condense and reflux until the reaction ends to obtain nickel oxide nanocrystals protected by lithium stearate ligands; Step 2, preparation of nickel oxide nanocrystal solution: Pour the mixture obtained in Step 1 into a beaker, add ethyl acetate, place it at room temperature for 10-14 h, add it to a centrifuge tube, centrifuge at 4000-6000 r / min for 4-6 min, pour off the supernatant, dissolve the precipitate completely with n-hexane, then add absolute ethanol, and then centrifuge at 8000-12000 r / min for 4-6 min. Centrifuge repeatedly for multiple times, collect the precipitate and freeze-dry it, and then dissolve it in chlorobenzene to prepare a chlorobenzene solution of nickel oxide with a certain concentration to obtain a nickel oxide nanocrystal solution; Step 3, preparation and cleaning of nickel oxide thin film: Take conductive glass as the substrate, take the nickel oxide nanocrystal solution in Step 2 as the coating liquid, and spread the nickel oxide nanocrystal solution on the surface of the conductive glass substrate by spin coating. Subsequently, put the conductive glass substrate coated with the nickel oxide nanocrystal solution into a vacuum tube furnace and anneal it at 350-380 °C for 15-20 min under argon atmosphere protection to obtain a nickel oxide thin film on the conductive glass surface; In Step 3, the size of the conductive glass is 1.5 cm × 1.5 cm, and the dropping amount of the nickel oxide nanocrystal solution on the conductive glass is 60 uL; Among them, the manufacturing method of the perovskite solar cell is: Ⅰ. Take a conductive glass - ITO glass sheet, ultrasonically clean the ITO glass sheet with acetone, dishwashing detergent water, deionized water, and isopropanol at 30-50 kHz for 10-20 min, dry it with a nitrogen gun, and perform ultraviolet ozone treatment in a plasma processor for 8-12 min; Ⅱ. Take the treated ITO glass as the substrate and the nickel oxide nanocrystal solution as the coating liquid, spin coat the nickel oxide nanocrystal solution on the surface of the ITO glass at a rotation speed of 2800-3000 r / min for 8-12 s; then place it in a vacuum tube furnace under argon atmosphere and anneal it at 350-380 °C for 15-20 min to obtain a high-purity nickel oxide thin film on the surface of the ITO glass, obtain cell precursor A, and place it in a glove box protected by high-purity nitrogen for standby; Ⅲ. Take the battery precursor A as the substrate, and use the perovskite solution as the coating liquid. The perovskite solution is a dimethyl sulfoxide solution containing lead iodide methylamine with a concentration of 0.6 - 0.8 g / mL. At 80 °C, the perovskite solution is dropped onto the nickel oxide film rotating at a low speed, and then the rotation speed is adjusted to 4000 - 6000 r / min and maintained for 25 - 35 s. At 12 - 18 s, 1 mL of toluene is uniformly dropped onto the center of the sample. Then, it is annealed at 105 - 115 °C for 4 - 6 min and at 125 - 135 °C for 8 - 12 min. After cooling, a dense and hole-free perovskite film is obtained on the surface of the nickel oxide film, and the battery precursor B is obtained. Ⅳ. Take the battery precursor B as the substrate, and use the PCBM solution with a concentration of 15 - 20 mg / mL as the coating liquid. The PCBM solution is a chlorobenzene solution containing fullerene. The PCBM solution is spin-coated on the surface of the perovskite film at a rotation speed of 4000 - 6000 r / min for 25 - 35 s to obtain the battery precursor C. Ⅴ. In a vacuum coating machine, an Ag electrode with a thickness of 70 - 80 nm is evaporated on the surface of the PCBM film on the battery precursor C. Use γ-butyrolactone to wipe out a photoanode, and then use an ultrasonic soldering iron to solder an indium wire at the wiped photoanode to obtain a perovskite solar cell.

2. The application of the nickel oxide thin film as a hole transport layer in a perovskite solar cell according to claim 1, characterized in that, In the first step, the molar ratio of nickel stearate, lithium stearate, and octadecanol is 0.98 - 1.02:0.39 - 0.41:5.88 - 6.12; the purity of the argon gas is above 99.99%.

3. The use of the nickel oxide thin film as a hole transport layer in a perovskite solar cell according to claim 1, wherein In the second step, the concentration of nickel oxide nanocrystals in the chlorobenzene solution is 8 - 12 mg / mL.

4. Use of the nickel oxide thin film as a hole transport layer in a perovskite solar cell according to claim 1, characterized in that, The perovskite solar cell is a reverse planar perovskite solar cell.

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