Lead-tin perovskite thin film and preparation method and application thereof

Abstract

The invention discloses a lead-tin perovskite thin film and a preparation method and application thereof, and particularly relates to the field of photoelectric materials and devices. Comprising a bottom-buried interface layer, a lead-tin perovskite layer and an upper interface modification layer which are sequentially arranged from bottom to top, the lead-tin perovskite layer is formed by a lead-tin perovskite precursor solution, and the lead-tin perovskite precursor solution comprises the following components: a two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodine, formamidine iodine, stannous fluoride and cesium iodide; and the component of the two-dimensional perovskite single crystal is PEA2PbI4. A two-dimensional perovskite single crystal is added into a Pb-Sn perovskite precursor to serve as a heterogeneous nucleation site, Pb-Sn perovskite is guided to longitudinally grow in the direction perpendicular to a substrate, transverse grain boundaries are reduced, and the crystallization quality is improved; meanwhile, as a buried interface and an upper interface modification layer, efficient transmission and extraction of photon-generated carriers in a Pb-Sn perovskite thin film and high efficiency and stability of a Pb-Sn perovskite cell can be realized.

Description

A lead-tin perovskite thin film, its preparation method and application Technical Field

[0001] This application relates to the field of optoelectronic materials and devices, and in particular to a lead-tin perovskite thin film, its preparation method, and its application. Background Technology

[0002] All-perovskite tandem solar cells achieve tiered absorption and energy conversion of the solar spectrum by vertically integrating two types of cells with different bandgap: a wide-bandgap (approximately 1.7-1.8 eV) perovskite top cell and a narrow-bandgap (approximately 1.2-1.3 eV) lead-tin (Pb-Sn) hybrid perovskite bottom cell. Among these, the narrow-bandgap Pb-Sn perovskite sub-cell, as a key component for absorbing near-infrared light, directly affects the current matching and energy conversion efficiency of the entire tandem device, thus becoming the core focus of current research.

[0003] Currently, the highest reported efficiency of tin-lead perovskite photovoltaic devices has increased from the initial 4.2% to over 24% recently, with the corresponding all-perovskite tandem solar cells exceeding 30% efficiency, demonstrating great potential. Despite significant progress, Pb-Sn narrow-bandgap perovskite solar cell devices still face problems of low efficiency and poor stability, which are the main factors limiting the acquisition of high-efficiency all-perovskite tandem photovoltaic devices. This is because the random orientation of Pb-Sn perovskite thin film crystal growth and the presence of numerous defects within the crystal and at the interfaces lead to poor carrier transport and are prone to carrier recombination due to the formation of many defects. Summary of the Invention

[0004] The main objective of this application is to provide a lead-tin perovskite thin film, its preparation method, and its application, aiming to solve the problem of poor carrier transport in existing Pb-Sn perovskite thin films.

[0005] To achieve the above objectives, this application provides a lead-tin perovskite thin film, comprising a lead-tin perovskite layer formed by a lead-tin perovskite precursor solution. The lead-tin perovskite precursor solution comprises: a two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide. The two-dimensional perovskite single crystal is composed of PEA2PbI4, and its raw materials include lead oxide, phenylethyl ammonium iodide, hydroiodic acid, and hypophosphite. The molar mass ratio of lead oxide, phenylethyl ammonium iodide, hydroiodic acid, and hypophosphite is (4-6): (1-2):230:75.

[0006] Optionally, it also includes a buried interface layer, with a lead-tin perovskite layer covering the surface of the buried interface layer; the material of the buried interface layer is a first organic solution of a two-dimensional perovskite single crystal.

[0007] Optionally, it also includes an upper interface modification layer, which covers the surface of the lead-tin perovskite layer; the material of the upper interface modification layer is a second organic solution of a two-dimensional perovskite single crystal.

[0008] Optionally, the molar mass ratio of two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride and cesium iodide is (0.005-0.015): 0.5: 0.5: (0.25-0.35): (0.7-0.6): 0.05:0.05.

[0009] Optionally, the first organic solution is a mixture of dimethyl sulfoxide and N,N-dimethylformamide, and the second organic solution is an isopropanol solution.

[0010] To achieve the above objectives, this application provides a method for preparing a lead-tin perovskite thin film, comprising: spin-coating a first organic solution of a two-dimensional perovskite single crystal onto a substrate to form a buried interface layer on the substrate; dissolving the two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodine, formamidinium iodine, stannous fluoride, and cesium iodide in dimethyl sulfoxide and N,N-dimethylformamide to obtain a perovskite precursor; spin-coating the lead-tin perovskite precursor solution onto the buried interface layer to form a lead-tin perovskite layer; and spin-coating a second organic solution of the two-dimensional perovskite single crystal onto the lead-tin perovskite layer to form an upper interface modification layer, thereby obtaining a lead-tin perovskite thin film.

[0011] Optionally, the concentration of the lead-tin perovskite precursor solution is 1.8-1.9 mmol / mL.

[0012] Optionally, the preparation method of two-dimensional perovskite single crystals includes: adding lead oxide powder to a mixed solution of hydroiodic acid and hypophosphoric acid, reacting at a temperature of 120-130℃ to obtain a clear and bright yellow liquid; adding phenylethyl ammonium iodide crystals to the yellow liquid, reacting at 120-130℃ to obtain a reaction solution, and cooling the reaction solution for 4-6 hours to obtain a yellow two-dimensional perovskite single crystal.

[0013] To achieve the above objectives, this application provides an application of lead-tin perovskite thin film in solar cells.

[0014] Optionally, the solar cell includes a substrate, a hole transport layer, a lead-tin perovskite thin film, an electron transport layer, an interface modification layer, and a metal back electrode stacked sequentially.

[0015] Compared with the prior art, the beneficial effects of this application are as follows: The lead-tin perovskite thin film of this invention incorporates a PEA2PbI4 two-dimensional perovskite single crystal into the Pb-Sn perovskite precursor as a heterogeneous nucleation site, guiding the Pb-Sn perovskite to grow longitudinally perpendicular to the substrate, reducing lateral grain boundaries, and improving crystal quality; simultaneously, as a buried interface, the organic cations (PEA2PbI4) in PEA2PbI4... + It possesses reducing and hydrophobic properties, and can form a protective environment locally, slowing down the oxidation of Sn; PEA + The strong coordination ability of PEA can suppress the precipitation of SnI2, regulate the crystal growth direction and longitudinal component distribution of the thin film, and realize the efficient transport and extraction of photogenerated carriers in Pb-Sn perovskite thin films. PEA2PbI4 two-dimensional perovskite is used as the upper interface modification layer. The huge PEA organic chains in its structure are hydrophobic and densely arranged, which can block moisture and improve the stability of the film.

[0016] The method for preparing lead-tin perovskite thin films of the present invention is simple to operate. By introducing an appropriate proportion of PEA2PbI4 two-dimensional perovskite single crystals into the perovskite precursor solution, high-quality Pb-Sn perovskite thin films can be obtained in one step, which can easily meet the needs of large-scale production and manufacturing.

[0017] The lead-tin perovskite thin film of the present invention is used in solar cells. The Pb-Sn narrow bandgap perovskite thin film has a vertical substrate orientation growth distribution. This crystal structure effectively reduces the barrier of charge carriers during longitudinal transport, making charge carrier transport smooth and preventing the accumulation of photogenerated charges at the interface. While promoting the photoelectric conversion process, it also inhibits the perovskite structure decomposition caused by the accumulation of photogenerated electrons, resulting in a significant improvement in the efficiency and stability of its solar cells. Attached Figure Description

[0018] Figure 1 is a schematic diagram illustrating the function of the lead-tin perovskite layer prepared in this application; Figure 2 is a schematic diagram illustrating different stages of the fabrication process of the two-dimensional perovskite PEA2PbI4 single crystal prepared in this application in the lead-tin perovskite layer; Figure 3 is a schematic diagram illustrating the device structure of the lead-tin perovskite solar cell prepared in this application; Figure 4 is an optical microscope image of the perovskite precursor solution of Example 1 and the comparative example during the annealing process; Figure 5 is a crystal structure and calculation diagram of lead and tin vacancy defects in the lead-tin perovskite layer of Example 1 and the comparative example of this application. Figure 6 shows the planar scanning electron microscope (SEM) images of the lead-tin perovskite layers of Examples 1 and 2 and the comparative examples; Figure 7 shows the SEM images of the lower interface after peeling off the film of Examples 1, 2 and the comparative examples; Figure 8 shows the cross-sectional SEM images of Examples 1, 2, 3 and the comparative examples; Figure 9 shows the X-ray diffraction (XRD) patterns of the lead-tin perovskite layers of Examples 1, 2, 3 and the comparative examples; Figure 10 shows the electrochemical impedance spectroscopy (EIS) diagrams of the perovskite solar cells of Examples 1, 2, 3 and the comparative examples.

[0019] Figure 11 is a statistical graph of the device efficiency of the lead-tin perovskite solar cells of Example 3 and the comparative example; Figure 12 is a curve showing the change of photoelectric conversion efficiency of the unencapsulated device of the lead-tin perovskite solar cells of Example 3 and the comparative example over time in an N2 glove box atmosphere; Figure 13 is the JV curve of the lead-tin perovskite solar cells of Examples 1, 2, 3 and the comparative example; Figure 14 is the PCE of the encapsulated device of the lead-tin solar cells of Example 3 and the comparative example under the ISOS-L-1 protocol.

[0020] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] The first embodiment of the present invention provides a lead-tin perovskite thin film, including a lead-tin perovskite layer formed by a lead-tin perovskite precursor solution. The lead-tin perovskite precursor solution comprises: a two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide. The two-dimensional perovskite single crystal is composed of PEA2PbI4, and its raw materials include lead oxide, phenylethyl ammonium iodide, hydroiodic acid, and hypophosphite. The molar mass ratio of lead oxide, phenylethyl ammonium iodide, hydroiodic acid, and hypophosphite is (4-6): (1-2): 230: 75. The molar mass ratio of two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride and cesium iodide is (0.005-0.015): 0.5: 0.5: (0.25-0.35): (0.7-0.6): 0.05: 0.05.

[0023] In one exemplary embodiment, the lead-tin perovskite thin film further includes a buried interface layer, wherein the lead-tin perovskite layer covers the surface of the buried interface layer. The material of the buried interface layer is a first organic solution of a two-dimensional perovskite single crystal. The first organic solution is a mixture of dimethyl sulfoxide and N,N-dimethylformamide.

[0024] In another exemplary embodiment, the lead-tin perovskite film further includes an upper interface modification layer covering the surface of the lead-tin perovskite layer; the material of the upper interface modification layer is a second organic solution of a two-dimensional perovskite single crystal. The second organic solution is an isopropanol solution.

[0025] Figure 1 shows an illustration of the target device based on a two-dimensional perovskite single crystal of PEA2PbI4 in this embodiment. It can be seen that PEA2PbI4 plays different roles in each step: as an additive, it promotes uniform nucleation and rapid growth of Pb-Sn perovskite; as a seed for burial, it guides vertical crystal growth and promotes charge extraction at the burial interface; and as a passivating agent, it can passivate defects. The effectiveness of the "three-in-one" PEA2PbI4 is described in detail.

[0026] In this embodiment, the PEA2PbI4 two-dimensional perovskite single crystal is used as a component of the lead-tin perovskite precursor solution. It serves as a heterogeneous nucleation site, guiding the Pb-Sn perovskite to grow longitudinally perpendicular to the substrate, reducing lateral grain boundaries and improving crystal quality. Simultaneously, the PEA2PbI4 two-dimensional perovskite single crystal acts as a buried interface, allowing the organic cations (PEA2PbI4) in the PEA2PbI4 to grow longitudinally along the direction perpendicular to the substrate, reducing lateral grain boundaries and improving crystal quality. + It possesses reducing and hydrophobic properties, and can form a protective environment locally, slowing down the oxidation of Sn; and the organic cation (PEA) + The strong coordination ability of PbI₄ can suppress SnI₂ precipitation and regulate the crystal growth direction and longitudinal component distribution of the thin film. The PEA₂PbI₄ two-dimensional perovskite, used as the upper interface modification layer, features large, hydrophobic, and densely packed PEA organic chains that can block moisture and improve film stability. Ultimately, this achieves efficient transport and extraction of photogenerated carriers in Pb-Sn perovskite films and high efficiency and stability of Pb-Sn perovskite solar cells.

[0027] The second embodiment of the present invention provides a method for preparing a lead-tin perovskite thin film. As shown in Figure 2, firstly, a two-dimensional perovskite single crystal (SC) of PEA2PbI4 is dropped onto a substrate, and PEA2PbI4 is obtained as a buried interface through spin coating and annealing. Then, a lead-tin perovskite precursor solution containing the PEA2PbI4 two-dimensional perovskite single crystal is obtained by spin coating and annealing to obtain a passivated perovskite thin film. Finally, the upper interface modification solution of the PEA2PbI4 two-dimensional perovskite single crystal is obtained by spin coating and annealing to obtain a PEA2PbI4 capping passivation layer. Specifically, the method includes the following steps: Step S1, the first organic solution of the PEA2PbI4 two-dimensional perovskite single crystal is spin-coated onto a substrate, and a buried interface layer is formed on the substrate through spin coating and annealing. It is worth noting that the buried interface layer in this embodiment is prepared on the hole transport layer, so the substrate in step S1 refers to the hole transport layer in the solar cell.

[0028] Specifically, in step S11, lead oxide powder is added to a mixed solution of hydroiodic acid and hypophosphorous acid, and an acid-base neutralization reaction is carried out at a temperature of 120-130℃. Lead oxide is an amphoteric, slightly alkaline oxide, which will rapidly neutralize with the strongly acidic hydroiodic acid to produce soluble lead iodide and water, resulting in a clear, bright yellow liquid. Phenylethyl ammonium iodide crystals are then added to the yellow liquid, using hypophosphorous acid to prevent oxidation, and a solvothermal synthesis reaction is carried out at 120-130℃ to promote crystal growth. The reaction solution is then cooled. After 4-6 hours, yellow two-dimensional perovskite single crystals are obtained. In step S12, 19.2-38.4 mg of the two-dimensional perovskite single crystals are dissolved in a 1 mL mixture of 250-400 µL LDMSO and 750-600 µL LDMMF. The mixture is stirred until completely dissolved to obtain the first organic solution of the two-dimensional perovskite single crystals, namely the buried interface solution. The buried interface solution is evenly coated onto the substrate using a pipette. The spin coating conditions are 5000 rpm for 45 s, and the substrate is annealed at 100 °C for 10 min to form a buried interface layer on the substrate.

[0029] Step S2: PEA2PbI4 two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide are dissolved in dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) to obtain a lead-tin perovskite precursor. The volume ratio of DMSO to DMF precursor components is (1-2):3, and the total volume of the mixture is 1 mL, yielding a lead-tin perovskite precursor solution. The two-dimensional perovskite single crystal is dissolved and dispersed in the perovskite precursor. The concentration of the lead-tin perovskite precursor solution is 1.8-1.9 mmol / mL. Lead-tin perovskite precursor solution was spin-coated onto a buried interface layer using an anti-solvent spin-coating process, followed by annealing to obtain a PEA2PbI4 passivated lead-tin perovskite layer. Specifically, 50 µL of lead-tin perovskite precursor solution was dropped onto the buried interface layer and spin-coating was initiated at 1000 rpm for 10 s. At 35 s, 350 µL of chlorobenzene anti-solvent was rapidly added to crystallize the film, and the spin-coating conditions were 5000 rpm for 45 s. Annealing was then performed on a hot plate at 100°C for 10 min to obtain the lead-tin perovskite layer. Step S3 involves... The second organic solution of the perovskite single crystal is spin-coated onto the lead-tin perovskite layer to form an upper interface modification layer, thus obtaining a lead-tin perovskite thin film. Specifically, the two-dimensional perovskite single crystal is dissolved in isopropanol solution and stirred until completely dissolved to obtain the second organic solution of the two-dimensional perovskite single crystal, i.e., the upper interface modification solution. The upper interface modification solution is spin-coated onto the lead-tin perovskite layer under spin-coating conditions of 4000 rpm for 30 s, and then annealed on a hot stage at 100°C for 10 min to obtain a PEA2PbI4 capped passivation layer lead-tin perovskite thin film.

[0030] A third embodiment of the present invention provides an application of a lead-tin perovskite thin film in a solar cell. The solar cell includes a substrate, a hole transport layer, a lead-tin perovskite thin film, an electron transport layer, an interface modification layer, and a metal back electrode, which are stacked sequentially.

[0031] Specifically, the substrate is ITO conductive glass, and the above-mentioned solar cell preparation method includes: step S10, cleaning and drying the ITO conductive glass and then performing ultraviolet hydrophilic treatment, followed by spin coating of poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) (PEDOT:PSS) and annealing to obtain a hole transport layer; step S20, preparing a lead-tin perovskite thin film on the hole transport layer; see steps S1-3 for details; step S30, spin coating a solution of [6,6]-phenyl-C61-butyrate isomethyl ester (PCBM) on the lead-tin perovskite thin film to obtain an electron transport layer; the PCBM solution is prepared by dissolving PCBM in chlorobenzene to obtain a chlorobenzene (CB) solution with a concentration of 18 mg / mL; step S40, vacuum evaporating an interface modification layer and a metal back electrode on the electron transport layer to obtain a solar cell. The interface modification layer is made of 2,9-dimethyl-4,7-diphenyl-1,10-o-phenanthroline (BCP) with a deposition thickness of 6 nm, and the metal back electrode is made of Ag with a deposition thickness of 100 nm.

[0032] Example 1 Preparation of Cs 0.05 MA 0.35 FA 0.6 Pb 0.5 Sn 0.5 In step S100 of I3, 19.2-38.4 mg of two-dimensional perovskite single crystals are dissolved in a 1 mL mixture of 250-400 µL DDMSO and 750-600 µL DMF, and stirred until completely dissolved to obtain the first organic solution of the two-dimensional perovskite single crystals, namely the buried interface solution.

[0033] According to the molar ratio of 0.015 : 0.5 : 0.5 : 0.3 : 0.65 : 0.05 : 0.05, two-dimensional perovskite single crystals, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide were dissolved in DMSO and DMF and stirred until completely dissolved to obtain lead-tin perovskite precursors; 0.5-1 mg of two-dimensional perovskite single crystals were dissolved in 1 mL of isopropanol solution and stirred until completely dissolved to obtain the upper interface modification solution; in step S200, ITO transparent conductive glass was treated with ethanol (30 min) - ultrapure water plus cleaning agent (30 min) - ultrapure water (30 min) - acetone (30 min) - ethanol. The ITO substrate was ultrasonically cleaned for 30 minutes, dried with a nitrogen gun, and then placed in an oven to dry, resulting in a clean ITO substrate. In step S300, the ITO substrate underwent UV-ozone surface treatment for 20 minutes. 30 μL of PEDOT:PSS was pipetted onto the clean ITO substrate and uniformly coated using a spin coater at 5000 rpm for 50 seconds. After spin coating, the substrate was annealed on a hot plate at 150°C for 20 minutes to form a uniform, dense, and robust PEDOT:PSS hole transport layer on the ITO surface. Then, the ITO substrate was... TO is transferred to the N2 glove box; in step S400, 30 μL of the buried interface solution is pipetted and uniformly coated onto the hole transport layer under spin coating conditions of 5000 rpm for 45 s, and annealed at 100°C for 10 min to obtain the buried interface layer; in step S500, 50 μL of lead-tin perovskite precursor solution is added to the buried interface layer and spin coating is started under spin coating conditions of 1000 rpm for 10 s. At the 35th second, 350 μL of chlorobenzene antisolvent is rapidly added to crystallize the film under spin coating conditions of 5000 rpm for 45 s, and annealed on a hot plate at 100°C for 1 min. In step S600, a lead-tin perovskite thin film was obtained after 0 min. In step S700, 30 μL of the upper interface modification layer solution was pipetted and spin-coated at 4000 rpm for 30 s, followed by annealing at 100 °C for 5 min to obtain the upper interface modification layer. In step S800, 30 μL of the prepared PCBM solution was pipetted and spin-coated at 1000 rpm for 45 s to obtain the electron transport layer. In step S800, a 6 nm interface modification layer and a 100 nm metal back electrode were sequentially deposited by vacuum evaporation on the electron transport layer to obtain the solar cell.

[0034] The difference between Example 2 and Example 1 is that step S100 does not involve the preparation of the buried interface solution and the upper interface modification solution; and does not include steps S400 and S600.

[0035] The difference between Example 3 and Example 1 is that step S100 does not involve the preparation of the upper interface modification solution; and step S400 is not included.

[0036] The difference between the comparative example and Example 3 is that step S100 does not involve the preparation of the buried interface solution and the upper interface modification solution, and the perovskite precursor does not contain two-dimensional perovskite single crystals; steps S400 and S600 are not included.

[0037] Cs in Examples 1-3 0.05 MA 0.35 FA 0.6 Pb 0.5 Sn 0.5 I3 and the comparative examples were characterized by precursor solutions, perovskite thin films, and perovskite solar cells, as shown in Figure 4-14.

[0038] The optical microscope images of the lead-tin perovskite precursor solutions of Example 1 and the comparative example are shown in Figure 4. It can be seen that the introduction of two-dimensional perovskite single crystals in Example 1 makes the nucleation sites in the lead-tin perovskite precursor solution more uniformly distributed, with more identifiable crystal domains, showing faster and more extensive grain growth, and having larger and denser crystal clusters.

[0039] Figure 5 shows the crystal structure and calculated formation energy of lead and tin vacancy defects in the lead-tin perovskite layers of Example 1 and the comparative example. It can be clearly seen that the introduction of the two-dimensional perovskite PEA2PbI4 single crystal additive increases the formation energy of lead and tin vacancy defects, which is beneficial to improving the efficiency and stability of perovskite solar cells.

[0040] The planar scanning electron microscope (SEM) images of the perovskite layers of Example 1 and the comparative example are shown in Figure 6. From Figure 6(a) and (b), it can be seen that the grain size of Example 1 is significantly increased. The SEM images of the buried interface after film removal for the comparative example, Example 1, and Example 3 are shown in Figure 7. It is clearly visible that obvious pores appear in the comparative example, while Example 3 has no pores but cracks. In Example 1, the perovskite buried interface is uniform and smooth without pores or cracks. From the SEM cross-sectional image in Figure 8, it can be seen that the perovskite grains in Example 1 grow more orderly, and the crystal growth direction changes from the transverse growth of the comparative example to the longitudinal growth of Example 1. The X-ray diffraction (XRD) patterns of the perovskite layers of Examples 1, 2, 3, and the comparative example are shown in Figure 9. It can be seen that the introduction of the PEA2PbI4 two-dimensional perovskite single crystal causes the disappearance of the lead iodide phase in the lead-tin perovskite layer, and the main peak is stronger, indicating better crystal quality.

[0041] The electrochemical impedance spectroscopy (EIS) diagrams of the solar cells obtained in Examples 1, 2, 3, and the comparative example are shown in Figure 10. It can be seen that the carrier recombination resistance of the lead-tin perovskite thin film in Example 1 is significantly increased, indicating that the carrier transport is more efficient. The device efficiency statistics of the solar cells obtained in Example 1 and Comparative Example 1 are shown in Figure 11. It can be seen from the figure that the overall device efficiency of Example 1 is significantly increased and the variance is smaller.

[0042] Using the solar cells prepared in Example 1 and the comparative example, the photoelectric conversion efficiency (PCE) of the unencapsulated device under N2 glove box atmosphere is shown in Figure 12. The figure shows that Example 1 exhibits significantly enhanced stability. The JV curves of the solar cells prepared in Examples 1, 2, 3, and the comparative example are shown in Figure 13. It can be seen that the photovoltaic device prepared in Example 1 has superior efficiency; the PCE increases from 20% in the comparative example to 23.86% in Example 1, where V... OC From 0.832 V to 0.88 V, J SC From 32 mA / cm 2 Increased to 33.72 mA / cm 2 The fill factor FF increased from 75.2% to 80.4%, and the hysteresis decreased from 5.35% to 1.93%.

[0043] Figure 14 shows the PCE variation of the solar cells obtained in Example 1 and the comparative example under the ISOS-L-1 protocol. It can be clearly seen that after 2000 hours under the ISOS-L-1 protocol, the encapsulated device of Example 1 retained >92% of the initial PCE, while the comparative example only had 82.6%.

[0044] Table 1 shows the device parameters of lead-tin perovskite solar cells based on Comparative Example 1 and Examples 1-3: Table 1 Device Parameters of Lead-Tin Perovskite Solar Cells

[0045] As can be seen from the table above, the interface enhancement effect of two-dimensional perovskite single crystals makes V OC The enhancement and fill factor FF were significantly improved, and the PCE increased by 3.86%.

[0046] In summary, the results in Figures 4-14 and Table 1 show that, compared with the comparative examples, the precursor solutions in Examples 1-3 have more nucleation sites, the grain packing direction in the film changes from lateral to longitudinal, the lower interface is smoother and free of pores, the film has stronger crystallinity, and the carrier recombination impedance is increased. The photoelectric conversion efficiency of the prepared lead-tin perovskite is improved, and its stability is significantly enhanced.

[0047] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A lead-tin perovskite thin film, characterized in that, The material includes a lead-tin perovskite layer, which is formed by a lead-tin perovskite precursor solution. The lead-tin perovskite precursor solution comprises: a two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide. The two-dimensional perovskite single crystal is composed of PEA2PbI4, and its raw materials include lead oxide, phenylethyl ammonium iodide, hydroiodic acid, and hypophosphite. The molar mass ratio of lead oxide, phenylethyl ammonium iodide, hydroiodic acid, and hypophosphite is (4-6): (1-2):230:

75.

2. The lead-tin perovskite thin film according to claim 1, characterized in that, It also includes a buried interface layer, wherein the lead-tin perovskite layer covers the surface of the buried interface layer; the material of the buried interface layer is a first organic solution of a two-dimensional perovskite single crystal.

3. The lead-tin perovskite thin film according to claim 2, characterized in that, It also includes an upper interface modification layer, which covers the surface of the lead-tin perovskite layer; the material of the upper interface modification layer is a second organic solution of a two-dimensional perovskite single crystal.

4. The lead-tin perovskite thin film according to claim 1, characterized in that, The molar mass ratio of the two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide is (0.005-0.015): 0.5: 0.5: (0.25-0.35): (0.7-0.6): 0.05: 0.

05.

5. The lead-tin perovskite thin film according to claim 3, characterized in that, The first organic solution is a mixture of dimethyl sulfoxide and N,N-dimethylformamide, and the second organic solution is an isopropanol solution.

6. A method for preparing a lead-tin perovskite thin film according to claim 3, characterized in that, include: A first organic solution of a two-dimensional perovskite single crystal is spin-coated onto a substrate to form a buried interface layer. The two-dimensional perovskite single crystal, lead iodide, stannous iodide, methylamine iodide, formamidinium iodide, stannous fluoride, and cesium iodide are dissolved in dimethyl sulfoxide and N,N-dimethylformamide to obtain a perovskite precursor. The lead-tin perovskite precursor solution is spin-coated onto the buried interface layer to form a lead-tin perovskite layer. A second organic solution of the two-dimensional perovskite single crystal is spin-coated onto the lead-tin perovskite layer to form an upper interface modification layer, thus obtaining a lead-tin perovskite thin film.

7. The method for preparing lead-tin perovskite thin films according to claim 6, characterized in that, The concentration of the lead-tin perovskite precursor solution is 1.8-1.9 mmol / mL.

8. The method for preparing lead-tin perovskite thin films according to claim 6, characterized in that, The method for preparing the two-dimensional perovskite single crystal includes: adding lead oxide powder to a mixed solution of hydroiodic acid and hypophosphoric acid, reacting at a temperature of 120-130℃ to obtain a clear and bright yellow liquid; adding phenylethyl ammonium iodide crystals to the yellow liquid, reacting at 120-130℃ to obtain a reaction solution, and cooling the reaction solution for 4-6 hours to obtain a yellow two-dimensional perovskite single crystal.

9. The application of the lead-tin perovskite thin film according to claim 1 in a solar cell.

10. The application of the lead-tin perovskite thin film according to claim 9 in solar cells, characterized in that, The solar cell comprises a substrate, a hole transport layer, a lead-tin perovskite thin film, an electron transport layer, an interface modification layer, and a metal back electrode, which are stacked in sequence.

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