Perovskite thin film based on selective growth of crystal structure and preparation method and application of perovskite thin film

Abstract

The invention belongs to the technical field of solar cell preparation, and particularly relates to a perovskite thin film based on selective growth of a crystal structure and a preparation method and application thereof. The perovskite cell comprises a conductive substrate, an electron transport layer, a perovskite light absorption layer, a hole transport layer and a metal electrode which are arranged in sequence. According to the method, the mixed crystal orientation of perovskite is manually controlled, so that the dependence on a complex passivator in the traditional preparation process is avoided, and the perovskite film can be modified only by optimizing crystal arrangement; a new crystal growth mode is established, and energy loss caused by grain boundary defects is greatly reduced by weakening the negative influence of stress on perovskite crystals, so that the crystallization quality of a perovskite film is remarkably improved, the photoelectric property of a perovskite cell is optimized, and the stability is improved. According to the perovskite solar cell provided by the invention, the quality of the perovskite thin film and the photoelectric property of the cell are synchronously improved under the condition that the process complexity and the cost are not increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cell preparation, and particularly relates to a perovskite thin film based on selective growth of crystal structure, and a preparation method and application thereof. Background Art

[0002] Perovskite solar cells (PSCs), as an emerging material in the third-generation photovoltaic technology, have attracted extensive attention worldwide in the past decade due to their excellent optoelectronic properties, low cost, and convenient preparation process. Perovskite materials have unique optoelectronic properties, including a high light absorption coefficient, a long charge carrier diffusion distance, and an adjustable bandgap structure, which make them show great potential in optoelectronic conversion applications. From an initial photovoltaic conversion efficiency (PCE) of less than 4% to a recent record-breaking efficiency of over 27%, the rapid development of PSCs has made them a strong competitor for next-generation solar cell technology.

[0003] The perovskite layer, as the core functional material of perovskite solar cells, the quality of its thin film is crucial for the optoelectronic properties of the device, and the regulation of crystal morphology plays an important role in the preparation of high-quality thin films. Different crystal planes of perovskite have different optoelectronic properties and carrier transport characteristics, and the (001) and (111) crystal planes have the best photovoltaic performance. Compared with the (110) crystal plane, the (001) and (111) crystal planes can optimize the surface grain boundary characteristics, reduce the non-radiative recombination loss of carriers, and significantly improve the carrier mobility. Therefore, precisely controlling the microstructure of perovskite crystals to construct a thin film with a dominant orientation is the key to improving the performance and stability of perovskite solar cells.

[0004] In the formation process of perovskite crystals, solvent engineering is crucial, and its evaporation rate, evaporation gradient, and the type of solvent directly determine the crystal growth kinetics. The perovskite thin film based on a one-step anti-solvent process will obtain a polycrystalline thin film with a random orientation, and the lattice mismatch between grain boundaries will reduce the defect formation energy. Therefore, in an environment of light, water, and oxygen, ion migration and decomposition are likely to occur at the interface, resulting in the generation of new defects and a decrease in device performance. By controlling the crystallization of PbI2 through a two-step method, it is easier to control the direction of the optimal self-energy of the crystal plane during the crystal growth process.

[0005] Since perovskite is an ionic crystal prepared by solution method, the precise control of its crystal growth process and crystal plane orientation is of high technical difficulty. The crystallization rate of polycrystalline perovskite thin film is extremely fast, and it is not easy to control its orientation. To solve the defects and interface problems of perovskite thin film, researchers have proposed various solutions, including the reasonable design of perovskite solution formula, which can directly determine the nucleation and growth direction of crystals, and additive regulation. Nucleation promoters, such as ligand molecules like dimethyl sulfoxide (DMSO) and methylguanidine (MGA), form complexes with precursor metal ions (such as Pb 2+ ) to reduce the nucleation energy barrier, thereby controlling the nucleation process and so on. So far, most studies have focused on optimizing the grain size, crystallinity and morphology of perovskite thin film to effectively reduce grain boundaries and defects. Although these methods have improved the efficiency and stability of perovskite solar cells to a certain extent, they generally have the following problems: complex operation process, dependence on expensive or special chemicals, difficulty in precisely controlling the treatment effect, and most of them are not suitable for large-scale production. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a preparation method of perovskite thin film based on selective growth of crystal structure. The perovskite battery thin film includes a conductive substrate, an electron transport layer, a lead iodide layer, and a perovskite light absorption layer arranged in sequence, and the treatment methods include deposition, coating, and annealing.

[0007] The present invention regulates the crystallization of lead iodide thin film, thereby regulating the orientation of the mixed crystal of perovskite, avoiding the need to use complex passivators or multi-step post-treatment processes. In this method, by precisely controlling the crystal growth mode, the influence of stress on perovskite crystals is significantly weakened, and at the same time, grain boundary defects and energy loss are reduced, thereby improving the film quality and interface stability.

[0008] The present invention provides a perovskite thin film based on selective growth of crystal structure, including a conductive substrate, an electron transport layer, a lead iodide layer, and a perovskite light absorption layer arranged in sequence; the lead iodide layer is obtained by coating a solution containing lead iodide on the surface of the electron transport layer and then regulating the crystallization of the lead iodide thin film through post-treatment; the post-treatment method is annealing or standing, the annealing temperature is 60-80°C, the annealing time is not more than 120 s, and the standing time is 0-60 min;

[0009] The perovskite thin film has a mixed crystal plane orientation, including (100) crystal plane and (111) crystal plane.

[0010] The perovskite light absorption layer of the present invention is prepared by a two-step method. By designing the lead iodide thin film, it changes from a single (001) and single (111) crystal plane to a uniform proportion mixture of (001) and (111) crystal planes, obtaining a perovskite thin film with a mixed orientation.

[0011] Preferably, the lead iodide film does not have a strong lattice orientation, and the thickness of the lead iodide film is 300 - 400 nm; the thickness of the perovskite film is 800 - 900 nm.

[0012] Preferably, the conductive substrate is a semiconductor material, and the semiconductor material is selected from conductive glass or silicon wafers.

[0013] Further, the conductive substrate is selected from fluorine-doped tin oxide glass (FTO).

[0014] Preferably, the perovskite film grown by selective crystal structure does not require any additives and passivation treatment.

[0015] The present invention also provides a method for preparing the above perovskite film grown by selective crystal structure, comprising the following steps:

[0016] S1: Depositing an electron transport material on the surface of the conductive substrate to form an electron transport layer;

[0017] S2: Coating a lead iodide precursor solution on the surface of the electron transport layer, annealing to form a lead iodide film;

[0018] S3: Coating a perovskite precursor solution on the surface of the lead iodide film, annealing to form a perovskite light-absorbing layer, obtaining the perovskite film grown by selective crystal structure; the solute in the perovskite precursor solution includes formamidinium hydroiodide (FAI), methylammonium iodide (MAI), and methylammonium chloride (MACl).

[0019] Preferably, in step S1, the conductive substrate is immersed in a chemical bath deposition solution at 60 - 80 °C for 4 - 5 h, then washed and annealed to obtain the electron transport layer; the chemical bath deposition solution includes tin chloride, urea, thioglycolic acid, hydrochloric acid, and water.

[0020] Preferably, in the lead iodide precursor solution, the solvent is selected from dimethylformamide and dimethyl sulfoxide; the volume ratio of dimethylformamide to dimethyl sulfoxide is 9:1.

[0021] Preferably, in step S3, the annealing temperature is 110 °C and the time is 25 - 30 min.

[0022] It should be noted that, by controlling the crystallization of the lead iodide thin film, the present invention artificially controls the orientation of the mixed crystal of perovskite, avoiding the dependence on complex passivators in the traditional preparation process, and only by optimizing the crystal arrangement, the perovskite thin film can be modified; at the same time, a new crystal growth mode is established, by weakening the negative impact of stress on perovskite crystals, significantly reducing the energy loss caused by grain boundary defects, thus significantly improving the crystallization quality of the perovskite thin film, and further optimizing the optoelectronic performance of the perovskite solar cell and enhancing the stability.

[0023] The perovskite solar cell and its preparation method provided by the present invention achieve the simultaneous improvement of the quality of the perovskite thin film and the optoelectronic performance of the solar cell without increasing the process complexity and cost.

[0024] The present invention also provides a solar cell, including a perovskite thin film selectively grown based on the crystal structure as described in any one of claims 1-4, a hole transport layer, and a metal electrode arranged in sequence; the thickness of the hole transport layer is 200-300 nm, obtained by spin-coating a hole transport layer material; the thickness of the metal electrode is 50-150 nm, obtained by evaporation.

[0025] A metal electrode is evaporated on the surface of the hole transport layer by using a thermal evaporation instrument, and the evaporation rate of the evaporation is 0.7 nm / s, and the evaporation pressure is 1×10 -5 Pa.

[0026] The present invention also provides the application of the perovskite thin film selectively grown based on the crystal structure in perovskite solar cells, tandem solar cells, quantum dot solar cells or photodetectors.

[0027] Preferably, the metal electrode is a silver electrode or a gold electrode.

[0028] Specifically, the preparation method of the solar cell includes the following steps:

[0029] S1: Mix stannous chloride, urea, thioglycolic acid, hydrochloric acid and deionized water and stir to obtain a chemical bath deposition solution, and put the conductive substrate together with the chemical bath deposition solution into a staining beaker; place the staining beaker in an oven at 90 °C for 4.5 hours, wash it with deionized water and ethanol in sequence to obtain a preliminarily deposited tin oxide thin film; after the washing is completed, place the prepared thin film sample on a preheated heating table and anneal it at 170 °C for 60 min to dry the residual solvent to form a tin oxide thin film with a thickness of 30-80 nm. Wait for the substrate to cool to room temperature and perform ultraviolet cleaning for 30 min;

[0030] S2: Dissolve lead iodide in dimethylformamide and dimethyl sulfoxide, stir evenly to obtain a lead iodide solution; take the lead iodide solution and drop it onto the tin oxide thin film, spin-coat it at a rate of 1500 revolutions per minute for 30 s, and anneal it at 70 °C for less than 120 s to obtain a lead iodide thin film; dissolve formamidinium hydroiodide, methylammonium iodide, and methylammonium chloride in isopropanol, stir evenly to obtain a perovskite precursor solution; drop the perovskite precursor solvent onto the lead iodide thin film, spin-coat it at a rate of 2000 revolutions per minute for 30 s; anneal it at 110 °C in air for 25 min to obtain a highly crystalline bright black perovskite thin film, forming a perovskite light-absorbing layer with a thickness of 800 - 900 nm;

[0031] S3: After cooling to room temperature, spin-coat the hole transport layer material of the hole transport layer at a rate of 2000 revolutions per minute, with a thickness of 200 - 300 nm;

[0032] S4: Transfer the substrate to a thermal evaporation instrument, and evaporate a metal electrode with a thickness of 50 - 150 nm at an evaporation rate of 0.7 nm / s, and the evaporation pressure is 1×10 -5 Pa.

[0033] It should be further noted that different temperatures and annealing times will have different effects on the performance of the device, and different temperatures and annealing times can reflect the optimization effect of the selective growth of the crystal structure and the device performance.

[0034] Furthermore, the step of irradiating the electron transport layer with ultraviolet light after annealing and cooling aims to increase the hydrophilicity of the film surface, facilitate subsequent spin-coating, and prepare a uniform and dense film.

[0035] Furthermore, the steps S2 to S4 are all completed in a glove box to isolate the influence of the external environment on the device.

[0036] Furthermore, in step S2, the spin-coating method is used to coat the lead iodide thin film, and the spin-coating speed is 1000 - 1500 revolutions per minute.

[0037] Furthermore, in step S2, the spin-coating method is used to coat the perovskite light-absorbing layer, and the spin-coating speed is 1000 - 2000 revolutions per minute.

[0038] Furthermore, in step S3, the spin-coating method is used to coat the hole transport layer, and the spin-coating speed is 1000 - 2000 revolutions per minute.

[0039] The technical solution of the present invention has the following advantages compared with the prior art:

[0040] (1) The present invention adopts a method of artificially controlling the mixed crystal orientation of perovskite to establish a new crystal growth mode.

[0041] (2) The present invention uses a method of artificially controlling the mixed crystal orientation of perovskite to weaken the negative impact of stress on perovskite crystals and reduce the energy loss caused by grain boundary defects, thereby optimizing the optoelectronic performance of perovskite solar cells.

[0042] (3) The present invention uses a method of artificially controlling the mixed crystal orientation of perovskite. After long-term storage, it still maintains high optoelectronic performance, greatly improving the stability of perovskite solar cells.

[0043] (4) The present invention uses a method of artificially controlling the mixed crystal orientation of perovskite. Without increasing the process complexity and cost, it realizes the simultaneous improvement of the optoelectronic performance and stability of perovskite solar cells. Description of the Drawings

[0044] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, where:

[0045] Figure 1 is a scanning electron microscope image of an incompletely crystallized lead iodide film after annealing for 45 s of the lead iodide film prepared in Example 1 of the present invention;

[0046] Figure 2 is a scanning electron microscope image of an uncrystallized lead iodide film after annealing for 0 s of the lead iodide film prepared in Comparative Example 1 of the present invention;

[0047] Figure 3 is a scanning electron microscope image of a completely crystallized lead iodide film after annealing for 90 s of the lead iodide film prepared in Comparative Example 2 of the present invention;

[0048] Figure 4 is an X-ray diffraction analysis diagram of the perovskite films prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0049] Figure 5 is the ratio of the intensities of the (111) crystal plane and the (001) crystal plane in the X-ray diffraction analysis results of the perovskite films prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0050] Figure 6 is a scanning electron microscope image of a perovskite film with a mixed crystal orientation after annealing the lead iodide film prepared in Example 1 of the present invention for 45 s;

[0051] Figure 7 The volt-ampere characteristic (J-V) curve diagram of the perovskite cells prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed Embodiments

[0052] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the exemplified embodiments are not intended to limit the present invention.

[0053] Example 1

[0054] S1. Mix 462 mg of tin chloride (SnCl2), 2500 mg of urea, 50 μL of thioglycolic acid, 2500 μL of hydrochloric acid (HCl) and 200 mL of deionized water and stir to obtain a chemical bath deposition solution. Put the FTO conductive glass together with the chemical bath deposition solution into a staining beaker; place the staining beaker in a preheated oven at 90 °C for 4.5 hours, take it out and wash it with deionized water and ethanol in turn for 10 min to obtain a preliminarily deposited tin oxide film; after the cleaning is completed, place the prepared film sample on a preheated heating table and anneal it at 170 °C for 60 min to dry the residual solvent and form a tin oxide film with a thickness of 30 - 80 nm. Wait for the substrate to cool to room temperature and perform ultraviolet cleaning for 30 min;

[0055] S2. Weigh 691 mg of lead iodide (PbI2) and dissolve it in 1 mL of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), where DMF:DMSO = 9:1, stir for 2 h to prepare a pale yellow lead iodide solution; take 30 μL of the lead iodide solution and drop it on the tin oxide film, spin-coat it at a rate of 1500 r / min for 30 s, and anneal it at 70 °C for 45 s to obtain a transparent pale yellow lead iodide film; weigh 90 mg of formamidinium hydroiodide (FAI), 6.39 mg of methylammonium iodide (MAI) and 9 mg of methylammonium chloride (MACl) respectively, dissolve them in 1 mL of isopropyl alcohol (IPA), stir evenly for 2 h to prepare a transparent and uniform perovskite precursor solution; take 90 μL of the perovskite precursor solution and drop it on the lead iodide film, spin-coat it at a rate of 2000 r / min for 30 s; anneal it at 110 °C in air for 25 min to obtain a highly crystalline bright black perovskite film with a thickness of 800 - 900 nm;

[0056] S3. After cooling to room temperature, dynamically spin-coat 25 μL of the hole transport layer material Spiro-OMeTAD at a rate of 2000 r / min, with a thickness of 250 nm; then transfer the substrate to a thermal evaporation instrument and evaporate a 100-nm-thick silver electrode at an evaporation rate of 0.7 nm / s. The evaporation source is silver and the evaporation pressure is 1×10 -5 Pa.

[0057] According to the above steps, a perovskite solar cell is prepared, which includes, from bottom to top in sequence: a transparent conductive substrate, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and a metal electrode. The material of the transparent conductive substrate is fluorine-doped tin oxide glass (FTO), and the material of the electron transport layer is tin oxide thin film.

[0058] Example 2

[0059] A perovskite solar cell is prepared according to the method of Example 1, except that: the lead iodide thin film is not annealed and is left standing for 10 min to allow the solvent in the lead iodide thin film to slowly volatilize.

[0060] Comparative Example 1

[0061] A perovskite solar cell is prepared according to the method of Example 1, except that: the annealing time of the lead iodide thin film is changed to 0 s.

[0062] Comparative Example 2

[0063] A perovskite solar cell is prepared according to the method of Example 1, except that: the annealing time of the lead iodide thin film is changed to 90 s.

[0064] Effect Evaluation 1

[0065] Photovoltaic performance test of the perovskite solar cell:

[0066] (1) After annealing the lead iodide thin film prepared in Example 1 for 45 s, the SEM test is carried out on the incompletely crystallized lead iodide thin film, the lead iodide thin film prepared in Comparative Example 1 after annealing for 0 s (uncrystallized lead iodide thin film), and the lead iodide thin film prepared in Comparative Example 2 after annealing for 90 s (completely crystallized lead iodide thin film). The results are as Figure 1 、 Figure 2 、 Figure 3 shown.

[0067] Figure 1 、 Figure 2 、 Figure 3 In contrast, in Example 1 of the present invention, after annealing the lead iodide thin film for 45 s, the incompletely crystallized lead iodide thin film does not have a very strong lattice orientation, and there are holes on the surface of the thin film, which is convenient for the subsequent infiltration of the perovskite solution.

[0068] (2) X-ray diffraction analysis is carried out on the perovskite thin films prepared in Example 1, Comparative Example 1, and Comparative Example 2. The curve graph is as Figure 4 shown.

[0069] From Figure 4 it can be found that when the lead iodide thin film is annealed for 45 s, the perovskite thin film grows with a mixed orientation of (001) and (111) crystal planes; while when the lead iodide thin film is annealed for 0 s and 90 s, the perovskite thin film grows with a single orientation of (001) and (111) crystal planes respectively.

[0070] (3) In the X-ray diffraction analysis results of the perovskite thin films prepared in Example 1, Comparative Example 1, and Comparative Example 2, the ratio of the intensities of the (111) crystal plane and the (001) crystal plane was analyzed, and the results are as Figure 5 shown.

[0071] Figure 5 It shows that compared with Comparative Example 1 and Comparative Example 2, when the lead iodide thin film was annealed for 45 s, the (001) and (111) crystal planes grew in a uniform proportion and a perovskite thin film with a uniform mixed orientation was obtained.

[0072] (4) SEM tests were performed on the incompletely crystallized lead iodide thin film and the perovskite thin film with a uniform mixed crystal orientation prepared in Example 1, and the results are as Figure 6 shown.

[0073] Figure 6 It shows that in Example 1 of the present invention, the incompletely crystallized lead iodide thin film and the perovskite thin film with a uniform mixed crystal orientation are uniform and dense, and there are no obvious defects on the surface of the thin film.

[0074] (5) Figure 7 The volt-ampere characteristic (J-V) curve graphs of the perovskite solar cells prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0075] Figure 7 It shows that under the simulated sunlight irradiation of 100 mW / cm 2 , for the perovskite solar cell based on the perovskite thin film with a uniform mixed crystal orientation, its open-circuit voltage is 1.175 V, the short-circuit current density reaches 24.59 mA / cm 2 , the fill factor is 81.04, and the highest photoelectric conversion efficiency is 23.42%.

[0076] It can be found from Figure 7 that with the change of the crystal orientation brought about by the annealing time of lead iodide, the efficiency of the prepared perovskite solar cell also changes significantly. The perovskite solar cell (Example 1) based on the incompletely crystallized lead iodide thin film and the perovskite thin film with a uniform mixed crystal orientation has the best efficiency.

[0077] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A perovskite film selectively grown based on crystal structure, characterized in that: The invention comprises a conductive substrate, an electron transport layer, a lead iodide layer and a perovskite light absorption layer which are arranged in sequence; the lead iodide layer is obtained by coating a solution containing lead iodide on the surface of the electron transport layer and then post-treating the layer; the post-treating method is annealing or standing, the annealing temperature is 60-80°C, the annealing time is not more than 120s, and the standing time is 0-60min; The perovskite film has a mixed crystal plane orientation, including a (100) crystal plane and a (111) crystal plane.

2. The perovskite film selectively grown based on crystal structure according to claim 1, characterized in that: The thickness of the lead iodide film is 300-400nm; the thickness of the perovskite film is 800-900nm.

3. The perovskite film selectively grown based on crystal structure according to claim 1, characterized in that: The conductive substrate is a semiconductor material, and the semiconductor material is selected from conductive glass or silicon wafer.

4. The perovskite film selectively grown based on crystal structure as claimed in claim 3, characterized in that: The conductive substrate is selected from fluorine-doped tin oxide glass.

5. A method for preparing a perovskite film based on crystal structure selective growth according to any one of claims 1 to 4, characterized in that: The steps include: S1: depositing electron transport material on the surface of the conductive substrate to form an electron transport layer; S2: coating a lead iodide precursor solution on the surface of the electron transport layer, and annealing to form a lead iodide film; S3: coating a perovskite precursor solution on the surface of the lead iodide film, annealing, forming a perovskite light-absorbing layer, and obtaining the perovskite film selectively grown based on the crystal structure; the solute in the perovskite precursor solution includes formamidine hydroiodide, methylammonium iodide and methylammonium chloride.

6. The preparation method according to claim 5, characterized in that: In the step S1, the conductive substrate is immersed in a chemical bath deposition solution at 60-80° C. for 4-5 hours, then cleaned and annealed to obtain the electron transport layer; the chemical bath deposition solution includes tin chloride, urea, thioacetic acid, hydrochloric acid and water.

7. The preparation method according to claim 5, characterized in that: In the lead iodide precursor solution, the solvent is selected from dimethylformamide and dimethyl sulfoxide; the volume ratio of dimethylformamide to dimethyl sulfoxide is 9:

1.

8. The preparation method according to claim 5, characterized in that: In step S3, the annealing temperature is 110° C. and the annealing time is 25-30 min.

9. A solar cell, characterized in that: It comprises a perovskite film selectively grown based on a crystal structure as described in any one of claims 1 to 4, a hole transport layer and a metal electrode arranged in sequence; the hole transport layer has a thickness of 200-300nm and is obtained by spin coating the hole transport layer material; the metal electrode has a thickness of 50-150nm and is obtained by evaporation.

10. Application of the perovskite film selectively grown based on crystal structure according to claims 1-4 in perovskite cells, stacked cells, quantum dot cells or photodetectors.

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