Perovskite light absorption layer, film forming method and prepared photovoltaic device

Abstract

The invention relates to a perovskite light absorption layer, a film forming method and a prepared photovoltaic device, and the method comprises the following steps: evaporating a perovskite light absorption layer material, and depositing the gaseous perovskite light absorption layer material on a substrate at a first temperature to form a first film layer; the substrate is heated and maintained at a second temperature, evaporation is continued to form a second film layer, and the first temperature is lower than the second temperature; and the temperature of the substrate is reduced to 0-15 DEG C at a set rate, a third film layer is formed in the cooling process, and the first film layer, the second film layer and the third film layer jointly form an evaporation part of the perovskite light absorption layer. The prepared perovskite light absorption layer is uniform and orderly in crystal grain growth, the problems of different sizes and uneven distribution of crystal grains are avoided, the electrical performance of the perovskite cell is remarkably improved, and the internal resistance difference is reduced.

Description

Technical Field

[0001] The present invention relates to a perovskite light-absorbing layer, a film-forming method and a prepared photovoltaic device, belonging to the field of photovoltaics. Background Art

[0002] Against the backdrop of the continuous growth of global energy demand and the increasing emphasis on environmental protection, solar energy, as a clean and renewable energy source, has received extensive attention in its development and utilization. As a key device for converting solar energy into electrical energy, the performance and cost of solar cells directly affect the large-scale application of solar energy. Among various types of solar cells, perovskite solar cells have become a research hotspot in recent years due to their significant advantages.

[0003] The reasons why perovskite solar cells have attracted much attention are mainly reflected in the following aspects. First of all, they have a relatively high power conversion efficiency. In a laboratory environment, remarkable achievements have been made in the power conversion efficiency of perovskite solar cells, and some research results even approach the efficiency level of traditional crystalline silicon solar cells, and there is still great room for improvement. Secondly, from the perspective of cost, the preparation materials of perovskite solar cells are relatively abundant and the cost is relatively low. Compared with some rare and expensive materials required for the preparation of traditional solar cells, they have obvious cost advantages. In addition, their preparation process is relatively simple and does not require complex and expensive equipment and processes like traditional crystalline silicon solar cells, which provides favorable conditions for their large-scale industrial production.

[0004] In the structure of perovskite solar cells, the perovskite layer, as a key part for absorbing photons and generating photo-generated carriers, its preparation process is crucial for the performance of the battery. At present, the evaporation coating process is a relatively commonly used method for preparing the perovskite layer. However, there are many problems that cannot be ignored in the widely used constant-temperature evaporation coating process.

[0005] During the constant-temperature evaporation coating process, the contact effect between the perovskite layer and the substrate is not good, resulting in insufficient bonding between the two, forming a relatively large interfacial resistance, which hinders the smooth transfer of charges from the perovskite layer to the substrate and affects the fill factor and overall output power of the battery. At the same time, the constant-temperature environment is not conducive to the growth of perovskite layer grains, making the grains unable to grow in the expected way and affecting the electrical properties of the perovskite layer. In addition, for the perovskite layer prepared by constant-temperature evaporation coating, a large number of defects will appear on its surface, which will capture photo-generated carriers, increase the recombination probability of carriers, and reduce the power conversion efficiency of solar cells.

[0006] Therefore, developing a new preparation process for the perovskite layer to solve the problems existing in the constant-temperature evaporation coating process and improve the performance and stability of perovskite solar cells is of great significance for promoting the development of perovskite solar cell technology. Summary of the Invention

[0007] In order to solve at least one of the problems in the prior art, such as the poor adhesion between the perovskite layer formed by thermal evaporation and the substrate, uneven grain growth, and serious surface defects, the present invention proposes a film-forming method for a perovskite light-absorbing layer. This method uses variable-temperature evaporation to fabricate the perovskite layer in a perovskite solar cell. By precisely controlling the temperature change during the evaporation process, one or more of the following problems can be effectively solved:

[0008] 1. The insufficient adhesion between the perovskite layer and the substrate results in a large interfacial resistance, which hinders the smooth transfer of charges from the perovskite layer to the substrate, affecting the fill factor and overall output power of the battery.

[0009] 2. In a constant-temperature environment, the perovskite layer grains cannot grow in the expected manner, affecting the electrical properties of the perovskite layer.

[0010] 3. A large number of defects exist on the surface layer of the perovskite layer prepared by the constant-temperature evaporation process, which can capture photo-generated carriers, increase the recombination probability of carriers, and reduce the photoelectric conversion efficiency of the solar cell.

[0011] 4. It is difficult to effectively control the growth rate and thickness of the passivation layer in the prior art, which affects the uniform denseness and passivation effect of the passivation layer and restricts the improvement of the photoelectric conversion ability.

[0012] On the one hand, the technical solution adopted by the present invention is: a film-forming method for a perovskite light-absorbing layer, including the following steps

[0013] S01 Place the substrate in an evaporation environment;

[0014] S02 Evaporate the perovskite light-absorbing layer material, and the gaseous perovskite light-absorbing layer material is deposited on the substrate to form a first film layer. During the deposition of the first film layer, the substrate is maintained at a first temperature, and the first temperature is a low temperature, preferably -20 to -10 °C; at this stage, the disordered movement of molecules can be reduced, so that perovskite molecules can more fully find the best attachment sites on the substrate surface, enhancing the interaction force with the substrate and laying a good foundation for the subsequent growth of the perovskite layer.

[0015] S03 Evaporate the perovskite light-absorbing layer material, and the gaseous perovskite light-absorbing layer material is deposited on the first film layer to form a second film layer. During the deposition of the second film layer, the temperature of the substrate is heated to a second temperature at a set rate and maintained at the second temperature until the second film layer reaches the set film thickness. The second temperature is a high temperature, preferably 70 to 100 °C; S04 Evaporate the perovskite light-absorbing layer material, and the gaseous perovskite light-absorbing layer material is deposited on the second film layer to form a third film layer. During the deposition of the third film layer, the substrate temperature is cooled from the second temperature to a third temperature at a set rate, and the third temperature is 0 - 15 °C;

[0016] The first film layer, the second film layer, and the third film layer form the perovskite light-absorbing layer; or the first film layer, the second film layer, and the third film layer form the vapor deposition part (vapor deposition layer) of the perovskite light-absorbing layer, and then the perovskite light-absorbing layer is formed by combining the solution method. For example, the inorganic part of the perovskite is obtained by vapor deposition, and then the precursor solution of the organic part is coated on the vapor deposition layer, and annealed to form the perovskite light-absorbing layer.

[0017] As a preferred method, the heating rate in step S02 of the film-forming method is 9 - 13 °C / min.

[0018] As a preferred method, the film thickness of the second film layer in step S02 of the film-forming method is: 300 - 550 nm, preferably 450 - 550 nm.

[0019] As a preferred method, the cooling rate in step S03 of the film-forming method is 16 - 18 °C / min.

[0020] As a preferred method, the vapor deposition rates of the perovskite light-absorbing layer materials in step S02, step S03, and step S04 of the film-forming method are the same or different, preferably different. The vapor deposition rate in step S03 is greater than the vapor deposition rate in step S02. The vapor deposition of the perovskite light-absorbing layer materials in step S02, step S03, and step S04 is single-source, dual-source, triple-source, or quadruple-source co-evaporation.

[0021] As a preferred method, a hole transport layer material is deposited on the substrate, and the perovskite light-absorbing layer is deposited on the hole transport layer material. The hole transport layer material is MeO-2PACz, Me-2PACz, Me-2PACz, 4PADCB, PTAA, etc.

[0022] Once again preferably, the vapor deposition source of the perovskite light-absorbing layer material is: PbI 2 , CsBr, PbCl 2 , FAI, FABr, MACl, MASCN, PbBr 2 , one or more of FAI, and preferably the evaporation source is PbI 2 , CsBr, PbCl 2 , FAI, PbBr 2 One or more of them.

[0023] On the other hand, the present invention also provides a perovskite light-absorbing layer, which can be prepared by the above preparation method. The obtained perovskite light-absorbing layer includes a first film layer, a second film layer, and a third film layer sequentially distributed from near the hole transport layer to near the electron transport layer. The molecular structure of the first film layer is extremely compact, and the grain diameter is about 100 - 130 nm, 1 mm 2The number of grains per unit area is about 30 - 50, and the thickness is about 30 - 60 nm. The grain density of the second film layer is lower than that of the first film layer, and the porosity of the second film layer is 10 - 15%. If the porosity is too large, the overall light absorption ability will decrease, affecting the photoelectric conversion efficiency. If the porosity is too small, the inside of the light absorption layer is relatively dense, and the scattering opportunity of light during its propagation will decrease, resulting in a relatively short optical path and reducing the light absorption rate. The thickness of the second film layer is about 480 - 520 nm, and the grain diameter is about 200 - 230 nm. As the main component of the light absorption layer, it can effectively absorb photons and generate electron-hole pairs. The molecular structure of the third film layer is compact, the porosity is lower than 8%, the grain diameter is about 100 - 130 nm, and the thickness is about 30 - 60 nm.

[0024] As an optimization, the first film layer can firmly form a tight chemical bond with the substrate, laying a stable foundation for the entire device. The molecular structure of the third film layer is compact, the grains are small, and the thickness is also about 30 - 60 nm. It can be closely connected with the next electron transport layer to form a chemical bond and efficiently transport electrons. In addition, due to the tight crystal structure of the first film layer and the third film layer, the stability of the perovskite solar cell device can be significantly enhanced.

[0025] On the other hand, the present invention also provides a photovoltaic device prepared from the above-mentioned perovskite light absorption layer.

[0026] The beneficial effects produced by the present invention include:

[0027] 1. By regulating the substrate temperature, the present invention regulates the crystallization performance of the perovskite film layer and then regulates the battery performance; 2. By making the deposition temperatures of the first film layer and the second film layer differ by 60 - 120 °C, the grains are transitioned from a dense state to a non-dense state, ensuring both the stable combination of the perovskite layer and the hole transport layer and the light absorption rate;

[0028] 3. By reducing the substrate temperature to -20 °C - -10 °C at the initial stage of evaporation coating, the perovskite material molecules can be more evenly and tightly attached to the substrate surface during slow movement, greatly enhancing the bonding force between the perovskite layer and the substrate, effectively reducing the interface resistance, providing good conditions for the efficient transport of charges from the perovskite layer to the substrate, and thus improving the fill factor and overall output power of the battery;

[0029] 4. After evaporating to a certain thickness, the temperature is uniformly increased, providing a suitable temperature environment and energy for the growth of grains, promoting the uniform and orderly growth of grains, avoiding the problems of uneven grain size and distribution, significantly improving the electrical properties of the perovskite layer, reducing the internal resistance difference, reducing carrier scattering, increasing the carrier mobility, and ultimately enhancing the photoelectric conversion efficiency of the solar cell;

[0030] 5. When the evaporation coating is about to be completed, rapidly reduce the temperature to quickly fix the atoms on the surface of the perovskite layer, forming a dense surface structure, significantly reducing the generation of surface defects, decreasing the carrier recombination probability, improving the collection efficiency of photo-generated carriers, enhancing the chemical stability of the perovskite layer, and extending the service life of the solar cell, laying a solid foundation for large-scale commercial applications. Description of the Drawings

[0031] Figure 1 Schematic structural diagram of the evaporation coating device;

[0032] Figure 2 Evaporation coating temperature change curve of Example 1;

[0033] Figure 3 Evaporation coating temperature change curve of Example 2;

[0034] Figure 4 Evaporation coating temperature change curve of Example 3;

[0035] Figure 5 Fill factor test data of Example 1 and Comparative Example 1;

[0036] Figure 6 Open circuit voltage test data of Example 1 and Comparative Example 1;

[0037] Figure 7 Current density test data of Example 1 and Comparative Example 1;

[0038] Figure 8 Photoelectric efficiency test data of Example 1 and Comparative Example 1;

[0039] Figure 9 Voltage-current test data of Example 2 and Comparative Example 2;

[0040] Figure 10 Voltage-current test data of Example 3 and Comparative Example 3;

[0041] 1. Mounting plate, 2. Mold temperature controller, 3. Substrate, 4. Evaporation coating source, 5. Chamber. Detailed Description of the Invention

[0042] The present invention will be further described below in conjunction with the specific embodiments, but it should not be understood that the protection scope of the present invention is limited by the specific embodiments.

[0043] In the present invention, the perovskite light-absorbing layer is formed by variable-temperature evaporation coating. The substrate is a conductive glass or a silicon-based bottom cell on which a hole transport layer has been deposited. The perovskite light-absorbing layer is prepared by an evaporation coating process on the hole transport layer, and then a perovskite single-junction cell or a tandem cell is obtained. The device used is as Figure 1, including an evaporation coating device, on which there is a mounting plate 1 for fixing an evaporation coating substrate. The mounting plate 1 is connected to a mold temperature controller 2, which is used to adjust the temperature of the mounting plate 1 and thus can control the temperature of the substrate 3. In order to facilitate the rapid transfer of temperature from the mounting plate 1 to the substrate 3, a high thermal conductivity material such as metal can be used. Of course, other materials or other methods can also be used to heat the substrate 3. The film forming method adopted in the present invention specifically includes the following steps:

[0044] (1) Prepare the substrate of the perovskite solar cell and the perovskite material for evaporation coating, and ensure that the surface of the substrate is clean and flat to ensure the uniform growth of the perovskite layer;

[0045] (2) Place the substrate 3 in an evaporation coating environment to prepare for evaporation coating. The evaporation coating environment generally refers to the chamber 5 of the evaporation coating device, and fix the substrate 3 on the mounting plate 1;

[0046] (3) Start the mold temperature controller and adjust the temperature of the mounting plate 1 to -20 to -10 °C, so that the temperature of the substrate also reaches -20 to -10 °C. Or directly monitor the substrate temperature with a temperature detector, and the mold temperature controller heats up or cools down according to the monitored substrate temperature. After reaching the required temperature, evaporate the perovskite light-absorbing layer. The evaporation of perovskite can be carried out by single-source evaporation, dual-source co-evaporation or multi-source co-evaporation; the gaseous perovskite light-absorbing layer material is deposited on the substrate to form a first film layer. At this temperature, the molecular thermal motion of the perovskite material is slow and the molecular kinetic energy is low, so that when they reach the surface of the substrate, they can interact more fully with the hole transport layer material on the substrate surface to form chemical bonding. The hydrogen atoms in the polar groups such as amino and hydroxyl in the hole transport layer can form hydrogen bonds with the halogen ions and formamidinium ions in the perovskite light-absorbing layer to enhance the interfacial binding force and stability. The SAM molecules containing aromatic groups can be bonded to the perovskite light-absorbing layer through π–π stacking, and chemically coupled with the hole transport layer through the π–π stacking between the carbazole groups, and then indirectly interact with the perovskite light-absorbing layer. The low porosity and small grain diameter of the first film layer can be closely combined with the hole transport layer, increasing the chemical bonding with the hole layer, forming a tightly connected transition interface, and providing a solid foundation for the growth of the subsequent perovskite layer.

[0047] The thickness of the first film layer is preferably 30 to 60 nm, and the evaporation rate at this stage is preferably: PbI 2 The evaporation rate is The CsI evaporation rate is PbCl 2 The evaporation rate is To ensure that the perovskite material can spread fully on the substrate surface and be tightly combined with the substrate, the arrangement of the first film layer is uniform and consistent in both the transverse and longitudinal directions.

[0048] (4) After the deposition of the first film layer is completed, the substrate temperature is adjusted so that the substrate temperature is heated to the second temperature at a set rate and maintained at the second temperature. In this process, the second film layer is formed. The second film layer is a film layer formed during the heating process and the constant temperature process. The heating rate in this process is 9-13°C / min, and the second temperature is 70-100°C. When the temperature is greater than 100°C, the substrate is prone to fall off and the thermal stability of the second film layer is poor. The grain growth particles are too large, resulting in an increase in porosity. When the temperature is less than 70°C, the grain growth is not obvious and the bonding performance with the first film layer is significantly less than 70-100°C. The threshold value of grain growth affected by temperature is 70°C, and the increase in temperature is conducive to the growth of perovskite crystals. Higher temperatures provide sufficient energy for ions to enable them to diffuse and adhere quickly on the surface of the crystal nucleus, thereby promoting the growth of grains and increasing the grain size. Increasing the temperature of the evaporation surface can increase the grain size, but when the temperature is higher than 100°C, the grain growth becomes partially non-uniform. Too high a temperature will make the perovskite crystal grow too fast and the growth process difficult to control, resulting in abnormal grain growth. The grains may grow rapidly in a certain direction, forming irregular shapes and sizes, destroying the uniformity of the grains and making the grain size distribution range wider, which is not conducive to obtaining an ideal microstructure. The heating method adopted can be: from -20℃ to 70℃ at a rate of 9℃ / min, 10℃ / min, 12℃ / min or 13℃ / min, from -20℃ to 80℃ at a rate of 9℃ / min, 10℃ / min, 12℃ / min or 13℃ / min, from -15℃ to 90℃ at a rate of 9℃ / min, 10℃ / min, 12℃ / min or 13℃ / min, from -10℃ to 100℃ at a rate of 9℃ / min, 10℃ / min, 12℃ / min or 13℃ / min. After heating to the second temperature, maintain the second temperature until the second film layer reaches the set thickness. In this process, the atoms in the perovskite layer obtain more energy and begin to become active, so that the grains can grow uniformly under a suitable temperature environment. At this stage, the evaporation rate needs to be controlled to meet the demand for material supply for grain growth. The evaporation rate of the evaporation source at this stage is preferably: PbI 2 for CsBr PbCl 2 for

[0049] The thickness of the second film layer is 480 - 520 nm. If it is less than 480 nm, the perovskite light-absorbing layer film will be too thin, shortening the absorption path of sunlight, allowing some sunlight to pass through the light-absorbing layer without being fully absorbed, and unable to absorb long-wavelength, low-energy photons, thus affecting the short-circuit current density and photoelectric conversion efficiency of the battery. If it is higher than 520 nm, the probability of non-radiative charge recombination will increase, causing the carriers generated by photoexcitation to recombine in the absorption layer, reducing the carrier mobility.

[0050] (5) After the deposition of the second film layer is completed, adjust the substrate temperature to decrease the substrate temperature to the third temperature at a set rate. During this process, the gaseous perovskite light-absorbing layer material is deposited on the second film layer to form the third film layer. The cooling rate is preferably 15 - 20 °C, the cooling time is preferably 1 - 5 min, and the third temperature is preferably 0 - 15 °C. For example, the substrate is cooled from 70 °C to 0 °C at a cooling rate of 15 °C / min, from 80 °C to 0 °C at a cooling rate of 16 °C / min, from 75 °C to 5 °C at a cooling rate of 17 °C / min, from 90 °C to 15 °C at a cooling rate of 18 °C / min, from 100 °C to 15 °C at a cooling rate of 20 °C / min, etc. Rapid cooling at a cooling rate of 15 - 20 °C is beneficial for the atoms on the surface of the perovskite layer to quickly lose energy, and the migration ability of the atoms drops sharply, thus quickly fixing in the current position to form a dense surface structure. The dense surface structure can effectively reduce the number of dangling bonds of surface atoms and greatly reduce the generation probability of surface defects. At the same time, the dense surface structure can also improve the chemical stability of the perovskite layer and reduce the influence of external environmental factors on its performance. In addition, cooling at a rate of 15 - 20 °C can avoid the generation of stress inside the perovskite layer due to too drastic temperature changes, affecting the performance of the battery.

[0051] The first film layer, the second film layer, and the third film layer formed by the above steps together form the perovskite light-absorbing layer.

[0052] The following is a description of the film-forming process in the form of specific examples to further illustrate the present invention.

[0053] Example 1

[0054] In this example, the substrate is a conductive glass deposited with a hole transport layer, the prepared perovskite battery is a single-junction perovskite battery, and the evaporation sources are PbI 2 , CsBr, PbCl 2 , and the evaporation method is co-evaporation of three sources.

[0055] The preparation method of the perovskite battery is as follows:

[0056] 1. Obtain conductive glass;

[0057] 2. Spin-coat and deposit the hole transport layer material MeO-2PACz on the conductive glass. Prepare it by spin-coating in a nitrogen environment, with a spin-coating speed of 4000Rpm, a spin-coating time of 30s. After spin-coating, the annealing temperature is 120°C and the annealing time is 10min.

[0058] 3. The perovskite light-absorbing layer is formed by a two-step wet and dry method. The change of the substrate temperature with the evaporation time during the dry film-forming process is shown in Figure 2 , and the specific steps are as follows:

[0059] a. Place the conductive glass deposited with the hole transport layer material in the evaporation environment, start the mold temperature controller, adjust the temperature of the mounting plate to -20°C, so that the substrate temperature also reaches -20°C. Start the evaporation equipment, and evaporate PbI 2 , CsBr, PbCl 2 respectively at a evaporation rate of . After 5 minutes, stop the deposition to obtain the first film layer, and the thickness of the first film layer is 50nm;

[0060] b. Adjust the substrate temperature so that the substrate temperature rises at the heating rate shown in Figure 2 . At the 20th minute, the temperature rises to 80°C, at the 25th minute, it rises to 90°C, and then remains at 90°C until the 50th minute. During this process, PbI 2 , CsBr, PbCl 2 are evaporated respectively at a evaporation rate of . After the deposition, obtain the second film layer, and the thickness of the second film layer is: 300nm.

[0061] c. Adjust the substrate temperature so that the substrate temperature drops suddenly to 10°C at the 55th minute at the rate shown in Figure 2 . During this process, PbI 2 , CsBr, PbCl 2 are evaporated respectively at a evaporation rate of . After the deposition, obtain the third film layer, and the thickness of the third film layer is: 50nm.

[0062] The inorganic part of the perovskite light-absorbing layer is prepared.

[0063] 4. Wet film formation step: Weigh 38.52 mg of FAI, 28.00 mg of FABr, 3.78 mg of MACl, and 5.04 mg of MASCN, dissolve them in 1 ml of absolute ethanol, stir at a speed of 500 rpm for 20 min, and the stirring temperature is room temperature. The solution is marked as organic. After the evaporation of the inorganic part is completed, transfer it to a spin-coating glove box, take 100 μL of the organic solution for spin-coating deposition, spin at a speed of 2000 rpm for 30 s, with an acceleration of 500, anneal in a nitrogen environment at a temperature of 90 °C for 2 min, and then transfer it to the air for annealing at a temperature of 150 °C for 20 min to form a perovskite light-absorbing layer.

[0064] 5. Evaporate 10 nm of C60 at a rate on the perovskite light-absorbing layer as the electron transport layer;

[0065] 6. Deposit a hole-blocking layer of SnO 2 with 120 cycles;

[0066] 7. Evaporate 200 nm of silver at a rate on the hole-blocking layer as the metal electrode,

[0067] to obtain a perovskite single-junction cell.

[0068] Example 2

[0069] In this example, the substrate is a silicon-based bottom cell deposited with a hole transport layer, and the finally required cell to be prepared is a perovskite-silicon tandem cell. This tandem cell uses the silicon cell as the bottom cell and the perovskite cell as the top cell. The evaporation sources for the perovskite light-absorbing layer are PbI 2 , FAI, CSI, PbBr 2 , and a perovskite light-absorbing layer is formed by the four-source co-evaporation method.

[0070] The preparation method of the perovskite-silicon tandem cell is as follows:

[0071] 1. Obtain a silicon-based bottom cell;

[0072] 2. Spin-coat and deposit a hole transport layer material Me-4PACz on the light-absorbing surface of the silicon-based bottom cell at a spin speed of 4000 Rpm for 30 s, with an acceleration of 1000, and the heating temperature after spin-coating is 120 °C for 20 min;

[0073] 3. Form the perovskite light-absorbing layer. The variation of the evaporation temperature with time during the film formation process is as Figure 3 , a Place the conductive glass deposited with the hole transport layer material in the evaporation environment, start the mold temperature controller, adjust the temperature of the mounting plate to -15 °C, so that the substrate temperature also reaches -15 °C, start the evaporation equipment, and make PbI 2, FAI, CSI, PbBr 2 Evaporate at the evaporation rate of respectively, stop deposition after 5 minutes, and obtain the first film layer with a film thickness of 50 nm;

[0074] b Adjust the substrate temperature so that the substrate temperature rises at the Figure 3 shown heating rate. At the 20th minute, the temperature rises to 76 °C, at the 25th minute it rises to 80 °C, and then it is maintained at 80 °C until the 50th minute. During this process, PbI 2 , FAI, CsI, PbBr 2 Evaporate at the evaporation rate of respectively, and obtain the second film layer after the deposition ends. The thickness of the second film layer is 500 nm: c Adjust the substrate temperature so that the substrate temperature drops suddenly to 10 °C at the 55th minute at the Figure 2 shown rate. During this process, PbI 2 , FAI, CSI, PbBr 2 Evaporate at the evaporation rate of respectively, and obtain the third film layer after the deposition ends. The thickness of the third film layer is: 50 nm to prepare the perovskite light-absorbing layer.

[0075] 4. Evaporate 10 nm of C60 at the rate on the perovskite light-absorbing layer as the electron transport layer;

[0076] 5. Deposit the hole-blocking layer SnO 2 on the electron transport layer for 120 cycles;

[0077] 6. Sputter 70 nm of ITO on the hole-blocking layer as the transparent conductive electrode layer.

[0078] 7. Evaporate 200 nm of silver at the rate on the transparent conductive electrode layer as the metal electrode.

[0079] Obtain the perovskite-silicon tandem cell.

[0080] Example 3

[0081] In this example, the substrate is a silicon bottom cell deposited with a hole transport layer. The finally required cell to be prepared is a perovskite-silicon tandem cell. This tandem cell uses the silicon cell as the bottom cell and the perovskite cell as the top cell. The evaporation sources of the perovskite light-absorbing layer are PbI 2 , FAI, CsI, PbBr 2 , and the perovskite light-absorbing layer is formed by the four-source co-evaporation method.

[0082] The preparation method of the perovskite-silicon tandem cell is as follows:

[0083] 1. Obtain a silicon-based battery;

[0084] 2. Spin-coat and deposit the hole transport layer material 4PADCB on the light-absorbing surface of the silicon-based battery at a spin-coating speed of 4000Rpm for 30s. After spin-coating, heat at 120°C for 20min.

[0085] 3. Form a perovskite light-absorbing layer. The variation of the evaporation temperature with time during the film-forming process is as Figure 4 , and the film-forming steps are as follows:

[0086] a. Place the silicon-based battery deposited with the hole transport layer material in the evaporation environment, start the mold temperature controller, adjust the temperature of the mounting plate to -10°C, so that the substrate temperature also reaches -10°C. Start the evaporation equipment to evaporate PbI 2 , FAI, CSI, PbBr 2 respectively at evaporation rates. After 5 minutes, stop deposition to obtain the first film layer with a thickness of 50nm;

[0087] b. Adjust the substrate temperature to increase at the heating rate shown in Figure 4 . At the 20th minute, the temperature rises to 80°C, and at the 25th minute, it rises to 90°C, and then remains at 90°C until the 50th minute. During this process, PbI 2 , FAI, CSI, PbBr 2 respectively at evaporation rates. After deposition, obtain the second film layer with a thickness of 500nm;

[0088] c. Adjust the substrate temperature to rapidly drop to 10°C at the 55th minute at the rate shown in Figure 4 . During this process, PbI 2 , FAI, CSI, PbBr 2 respectively at evaporation rates. After deposition, obtain the third film layer with a thickness of 50nm;

[0089] Prepare the perovskite light-absorbing layer.

[0090] 4. Evaporate 10nm of C60 at a rate on the perovskite light-absorbing layer as the electron transport layer;

[0091] 5. Deposit the hole blocking layer SnO 2 on the electron transport layer for 120 cycles;

[0092] 6. Sputter 70 nm of ITO on the hole blocking layer as the transparent conductive electrode layer.

[0093] 7. Evaporate 200 nm of silver on the transparent conductive electrode layer at a rate as the metal electrode.

[0094] Obtain a perovskite-silicon tandem cell.

[0095] Comparative Example 1

[0096] The difference from Example 1 lies in the dry film-forming step of the perovskite light-absorbing layer in Step 3. The dry film-forming method used is: deposit at a constant temperature of 90 °C, and the evaporation rate of PbI 2 , CsBr, PbCl 2 is until the thickness of the perovskite light-absorbing layer reaches 400 nm and stop deposition.

[0097] Comparative Example 2

[0098] The difference from Example 2 lies in the film-forming of the perovskite light-absorbing layer in Step 3. The film-forming method used is: deposit at a constant temperature of 100 °C, and the evaporation rate of PbI 2 , FAI, CsI, PbBr 2 is until the thickness of the perovskite light-absorbing layer reaches 600 nm and stop deposition.

[0099] Comparative Example 3

[0100] The difference from Example 3 lies in the film-forming of the perovskite light-absorbing layer in Step 3. The film-forming method used is: deposit at a constant temperature of 80 °C, and the evaporation rate of PbI 2 , FAI, CsI, PbBr 2 is until the thickness of the perovskite light-absorbing layer reaches 600 nm and stop deposition.

[0101] Performance Test

[0102] Test the optoelectronic properties of the cells obtained in Example 1 and Comparative Example 1, and obtain Figures 5 to 8 .

[0103] Figure 5For the fill factor comparison, the fill factor is an important parameter to measure the output characteristics of a solar cell. The higher its value, the higher the efficiency of the cell in converting absorbed light energy into electrical energy. As can be seen from the figure, the average value of the fill factor for variable-temperature evaporation is 79.13%, and the average value of the fill factor for constant-temperature evaporation is 75.50%. Among them, the minimum value of the fill factor for variable-temperature evaporation is 77.96%, which is much higher than the minimum value of the fill factor for constant-temperature evaporation, 73.23%. The data distribution of the fill factor under the variable-temperature evaporation method is generally higher than that of the constant-temperature evaporation, indicating that variable-temperature evaporation can effectively improve the fill factor of the cell and make the cell perform better in energy conversion.

[0104] Figure 6 For the open-circuit voltage comparison. The open-circuit voltage refers to the output voltage of a solar cell under no-load conditions. As shown in the figure, the average value of the open-circuit voltage for variable-temperature evaporation is 1.240 V, and the average value of the open-circuit voltage for constant-temperature evaporation is 1.152 V. Among them, the minimum value of the open-circuit voltage for variable-temperature evaporation is 1.238 V, which is much higher than the minimum value of the open-circuit voltage for constant-temperature evaporation, 1.147 V. The data distribution of the open-circuit voltage for variable-temperature evaporation is relatively more concentrated and has higher values compared to constant-temperature evaporation, indicating that variable-temperature evaporation helps to increase the open-circuit voltage of the cell and enhance the electrical performance of the cell.

[0105] Figure 7 For the current density comparison. The current density reflects the current output ability per unit area of the cell. The average value of the current density for variable-temperature evaporation is 21.36 mA / cm 2 , and the average value of the current density for constant-temperature evaporation is 19.06 mA / cm 2 , among which the minimum value of the current density for variable-temperature evaporation is 20.96 mA / cm 2 , which is much higher than the minimum value of the current density for constant-temperature evaporation, 18.88 mA / cm 2 , and the current density data under variable-temperature evaporation is significantly higher than that of constant-temperature evaporation, indicating that variable-temperature evaporation can increase the current output of the cell and improve the power output ability of the cell.

[0106] Figure 8 For the device efficiency comparison. The device efficiency is a key indicator to measure the comprehensive performance of a solar cell. The average value of the device efficiency for variable-temperature evaporation is 19.54%, and the average value of the device efficiency for constant-temperature evaporation is 16.95%. Among them, the minimum value of the device efficiency for variable-temperature evaporation is 19.38%, which is much higher than the minimum value of the device efficiency for constant-temperature evaporation, 16.41%. The data distribution of the device efficiency for variable-temperature evaporation is in a higher range and is generally higher than that of constant-temperature evaporation, fully demonstrating the significant advantage of variable-temperature evaporation in improving the comprehensive performance of perovskite solar cells.

[0107] The optoelectronic properties of the cells obtained from Test Example 2 and Comparative Example 2 are shown in Figure 9 , which is a J-V curve graph. The open-circuit voltage of the variable-temperature evaporation in Example 2 is 1.89 V, and the current density is 19.94 mA / cm 2, the fill factor is 73.16%, the device efficiency is 26.22%, and the open-circuit voltage of the constant-temperature evaporation coating in Comparative Example 2 is 1.80 V, and the current density is 18.85 mA / cm 2 , the fill factor is 70.94%, the device efficiency is 24.13%. Overall comparison shows that the performance of the variable-temperature evaporation coating device is higher than that of the constant-temperature evaporation coating, especially the voltage comparison is obvious. In the perovskite-silicon tandem solar cell, having a higher voltage at the same bandgap brings many benefits, specifically reflected in improving the cell efficiency, reducing energy loss, and enhancing the driving force of photo-generated carriers: voltage essentially reflects the strength of the internal electric field of the cell. A higher voltage means a stronger built-in electric field, which can provide a greater driving force for photo-generated carriers (electrons and holes), prompting them to be separated more efficiently and move towards the two poles of the cell. At the same bandgap, this stronger driving force can reduce the recombination probability of carriers, enabling more photo-generated carriers to be collected and participate in the circuit, thereby increasing the short-circuit current density of the cell and further enhancing the overall photoelectric conversion efficiency of the cell.

[0108] Test the optoelectronic performance of the cells obtained in Test Example 3 and Comparative Example 3, as shown in Figure 10 is the J-V curve graph. The open-circuit voltage of the variable-temperature evaporation coating in Example 3 is 1.88 V, and the current density is 19.85 mA / cm 2 , the fill factor is 72.04%, the device efficiency is 26.87%; the open-circuit voltage of the constant-temperature evaporation coating in Comparative Example 3 is 1.80 V, and the current density is 18.21 mA / cm 2 , the fill factor is 70.94%, the device efficiency is 24.13%. Overall comparison shows that the performance of the variable-temperature evaporation coating device is higher than that of the constant-temperature evaporation coating, especially the current density comparison is obvious. In the perovskite-silicon tandem solar cell, a relatively high current density means that the cell per unit area can generate more current under illumination. Increasing the output power enhances the overall photoelectric conversion efficiency of the cell. The perovskite-silicon tandem structure itself is designed to broaden the absorption range of the solar spectrum. When the current density is high, it indicates that the cell has a good response to different wavelengths of light, enabling more photons to be converted into electron-hole pairs, thereby forming a current and reducing the waste of spectral energy.

Claims

1. A method for forming a perovskite light-absorbing layer, characterized in that: The method comprises the following steps: S01 placing the substrate in an evaporation environment; S02: evaporating the perovskite light absorbing layer material, wherein the gaseous perovskite light absorbing layer material is deposited on the substrate to form a first film layer, and during the deposition of the first film layer, the substrate is maintained at a first temperature; S03: evaporating the perovskite light absorbing layer material, wherein the gaseous perovskite light absorbing layer material is deposited on the first film layer to form a second film layer, wherein during the deposition of the second film layer, the temperature of the substrate is increased to a second temperature at a set rate and maintained at the second temperature until the second film layer reaches a set film thickness, and the second temperature is higher than the first temperature; S04: evaporating the perovskite light absorbing layer material, wherein the gaseous perovskite light absorbing layer material is deposited on the second film layer to form a third film layer. During the deposition of the third film layer, the substrate temperature is cooled from the second temperature to the third temperature at a set rate, wherein the third temperature is 0-15° C.; The first film layer, the second film layer, and the third film layer form the perovskite light absorption layer, or the first film layer, the second film layer, and the third film layer form the evaporated deposition part of the perovskite light absorption layer.

2. The method for forming a perovskite light absorbing layer according to claim 1, characterized in that: The heating rate in step S02 is 9-13°C / min.

3. The method for forming a perovskite light absorbing layer according to claim 1, characterized in that: The thickness of the second film layer in step S02 is 300nm-550nm.

4. The method for forming a perovskite light absorbing layer according to claim 1, characterized in that: The cooling rate in step S03 is 16-18°C / min.

5. The method for forming a perovskite light absorbing layer according to claim 1, characterized in that: The evaporation rates of the perovskite light absorbing layer materials in step S02, step S03 and step S04 are the same or different. The evaporation of the perovskite light absorbing layer materials in step S02, step S03 and step S04 is single-source, dual-source, triple-source or co-evaporation of three or more sources.

6. The method for forming a perovskite light absorbing layer according to claim 1, characterized in that: A hole transport layer material is deposited on the substrate, and the perovskite light absorbing layer is deposited on the hole transport layer material. The hole transport layer material is one or a combination of MeO-2PACz, Me-2PACz, Me-2PACz, and 4PADCB.

7. The method for forming a perovskite light absorbing layer according to claim 6, characterized in that: The evaporation source of the perovskite light-absorbing layer material is selected from one or more of PbI2, CsBr, PbCl2, FAI, FABr, MACl, MASCN, PbBr2, and FAI.

8. The method for forming a perovskite light absorbing layer according to claim 1, characterized in that: The first temperature and the second temperature differ by 60 to 120°C, preferably the first temperature is -20 to 10°C, and the second temperature is 70 to 100°C.

9. A perovskite light absorbing layer, characterized in that: The film is prepared by the film forming method according to any one of claims 1 to 8.

10. A photovoltaic device made using the perovskite light-absorbing layer according to claim 9.

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