Perovskite solar cell and preparation method and application thereof

Abstract

The invention provides a preparation method of a perovskite solar cell, and the method comprises the following steps: S1, carrying out the spin coating of a SnO2 precursor on the surface of a substrate, and carrying out the annealing; s2, spin-coating a ZnO precursor on the surface of the annealed SnO2 precursor, and annealing; s3, spin-coating a perovskite precursor on the surface of the annealed ZnO precursor, then heating the perovskite precursor to 100 DEG C, and annealing; s4, spin-coating an organic solution of PTAA on the surface of the annealed perovskite precursor, and annealing; and S5, sequentially depositing a MoO3 layer and an electrode on the annealed PTAA surface through vacuum thermal evaporation. The perovskite precursor is a 1M CsPbI2Br precursor solution obtained by dissolving CsI, PbI2 and PbBr2 in DMSO according to a molar ratio of 2: 1: 1. The invention also provides the perovskite solar cell prepared by the method and application thereof.

Description

Technical Field

[0001] This invention relates to a method for preparing CsPbI2Br perovskite thin films, belonging to the field of solar cell materials. Background Technology

[0002] Poorly formed pores at the buried interface are commonly found in all-inorganic perovskite films prepared using traditional gradient thermal annealing processes, and their formation mechanism remains unclear. This study found that residual DMSO plays a crucial role in the formation of these pores during thermal annealing, and promoting DMSO evaporation can effectively eliminate them. Spin-coating annealing technology can rapidly remove residual solvents before perovskite crystallization, resulting in highly crystalline and pore-free CsPbI₂Br films. Furthermore, we experimentally observed for the first time the phase transition pathway of the PbI₂-DMSO / PbBr₂-DMSO adduct intermediate phase in the initial film gradually transforming into the PbI₂ / PbBr₂ precursor, ultimately forming the CsPbI₂Br product. Due to reduced bulk charge recombination, the CsPbI₂Br solar cell treated with the TSCA process achieved 15.72 mA / cm². -2 The short-circuit current density, high open-circuit voltage of 1.32V, and power conversion efficiency (PCE) of 14.89% are significantly improved compared to the 12.70% PCE of GTA process devices. This study provides an effective strategy for eliminating thin-film pores in the fabrication of high-performance all-inorganic perovskite solar cells by controlling the residual solvent evaporation behavior.

[0003] Due to its inherently excellent thermal stability and superior photoelectric properties, the all-inorganic perovskite CsPbX3 (X = I, Br, Cl) has attracted widespread attention in recent years for the development of high-performance solar cells. Among all inorganic lead halide perovskites, mixed halide perovskites (such as CsPbI2Br) are promising candidates due to their stable phase structure and tunable optical band gap. However, obtaining spatially uniform and pore-free CsPbI2Br perovskite films, and constructing the key active layer for this efficient and stable all-inorganic solar cell, remains a challenge.

[0004] Dimethyl sulfoxide (DMSO), a commonly used solvent for CsPbI₂Br perovskites, can effectively regulate crystallization kinetics to improve film morphology. However, due to its high boiling point (189°C), DMSO often remains inside the film during thermal annealing, leading to undesirable defects (such as pores) in the perovskite film. PbI₂-DMSO adducts and residual DMSO, which are difficult to remove from the perovskite film, can cause structural distortion and stability problems. Although anti-solvent cleaning (such as isopropanol and chlorobenzene) can remove DMSO residues, this method has limitations such as a narrow processing window (<10 seconds) and poor reproducibility. The strong coordination between DMSO and PbI₂ forms PbI₂-DMSO adducts, which need to be converted to PbI₂ by removing the DMSO solvent to obtain cubic CsPbI₂Br perovskite. However, the removal of DMSO solvent depends on its effective mass transport from the bottom to the top of the solidified perovskite surface. If the transport path of residual DMSO is blocked by a dense surface layer, lateral transport and local enrichment beneath the perovskite layer will be significantly enhanced. In this case, thin film pores will eventually form at the DMSO enrichment sites, leading to a decrease in device efficiency and long-term stability.

[0005] To eliminate these pores, Wang et al. introduced ethyl acrylate (EA) to form a volatile DMSO-EA complex for co-evaporation; other studies have used solid carbazide to partially replace DMSO solvent to suppress interfacial pore formation. Despite these advances in the field of organic-inorganic perovskites, poor buried interfacial pores are still prevalent in all-inorganic perovskite films prepared by conventional gradient thermal annealing. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing high-quality all-inorganic perovskite thin films.

[0007] A second objective of this invention is to provide an all-inorganic perovskite thin film prepared by the method described above.

[0008] A third objective of this invention is to provide an application of the aforementioned all-inorganic perovskite thin film.

[0009] This invention is achieved through the following technical solution: A method for fabricating a perovskite solar cell includes the following steps: S1 is annealed after spin-coating SnO2 precursor onto the substrate surface; S2 spin-coated ZnO precursor onto the surface of annealed SnO2 precursor, followed by annealing; S3 spin-coated the perovskite precursor onto the surface of the annealed ZnO precursor, and then heated the perovskite precursor to 100°C for annealing. S4 spin-coated an organic solution of PTAA onto the surface of the annealed perovskite precursor, followed by annealing; S5 is finally obtained by vacuum thermal evaporation to sequentially deposit a MoO3 layer and an electrode on the annealed PTAA surface; The perovskite precursor was obtained by dissolving CsI, PbI2 and PbBr2 in DMSO in a molar ratio of 2:1:1.

[0010] The SnO2 precursor in S1 was obtained by diluting a 12 wt% SnO2 colloidal solution with water at a weight ratio of 1:4. The annealing temperature in S1 is 150°C, and the annealing time is 30 minutes. The spin coating speed in S1 is 5000 rpm, and the time is 30 seconds.

[0011] The annealing temperature in S2 is 150°C, and the annealing time is 30 minutes. The spin coating speed in S2 is 5000 rpm, and the time is 30 seconds; The ZnO precursor in S2 was obtained by diluting a 2.5 wt% ZnO colloidal solution with anhydrous ethanol at a weight ratio of 1:4.

[0012] The spin coating in S3 includes the steps of spin coating at 1000 rpm for 10 seconds and then spin coating at 3000 rpm for 40 seconds; The heating in S3 includes a step of heating the substrate with hot air at 100°C at a distance of 3.5-4 cm.

[0013] The annealing temperature in S3 is 200°C, and the annealing time is 10 minutes. The annealing temperature in S4 is 100°C, and the annealing time is 15 minutes. The spin coating speed in S4 is 4000 rpm; The concentration of PTAA in the organic solution in S4 is 10 mg / mL; The solvent in the organic solution of PTAA in S4 includes chlorobenzene.

[0014] The substrate includes an ITO glass substrate; The ITO glass substrate includes an ITO glass substrate obtained after ultraviolet-ozone treatment.

[0015] The thickness of the MoO3 layer is 6 nm; The thickness of the electrode is 85 nm; The electrode includes a silver electrode.

[0016] The perovskite solar cell prepared by the aforementioned method is a perovskite solar cell.

[0017] The perovskite solar cells described above are used in solar power generation. Attached Figure Description

[0018] Figure 1 A schematic diagram showing solvent residues affecting the formation of voids within perovskite films is presented. Figure 1 This illustrates the role of solvent residue in influencing porosity formation within perovskite films. If solvent residue is trapped at the embedment interface of the perovskite film due to rapid crystallization and the sealing of the top molecular transport channels, porosity will form at the bottom of the perovskite film. In contrast, if the solvent residue is completely evaporated before the top gas transport channels are sealed, particles will grow undisturbed by the solvent residue, forming a porosity-free perovskite film.

[0019] Figure 2 The top, bottom, and cross-sectional morphology of the CsPbI2Br perovskite film, along with photographs of the actual sample, are shown. The bottom image was obtained after peeling the perovskite film from the ITO glass substrate. Perovskite films prepared using different heat treatment methods are shown: (ad) direct thermal annealing at 200℃; (eh) gradient thermal annealing (GTA); (il) spin-coating annealing.

[0020] Figure 3 The XRD patterns of CsPbI2Br films prepared by different methods are shown as follows: (a) top and (b) bottom XRD patterns of the initial cast CsPbI2Br films after pre-annealing at 50°C for different durations and (d) after being treated with thermal spin coating (TSC) at 100°C for different durations.

[0021] Figure 4 The ¹H NMR spectrum of a primary-cast CsPbI₂Br perovskite thin film prepared using DMSO solvent is shown; wherein, Figure 4 (a) Comparison of spectra after annealing at 50℃ and hot spin coating for different durations; Figure 4 (b) The change in the amount of DMSO solvent residue in the film after different heat treatment times, calculated by ¹H NMR spectrum; Figure 4 (c) is the spectrum of the newly cast CsPbI2Br thin film after annealing for 10 seconds in the temperature range of 30-200°C; Figure 4 (d) shows the change in the amount of DMSO solvent remaining in the film after 10 seconds of treatment at different annealing temperatures, estimated by ¹H NMR spectra.

[0022] Figure 5 The photoelectric properties and device performance characterization of the CsPbI2Br thin film are shown, among which, Figure 5 (a) The UV-Vis absorption spectrum of CsPbI2Br thin films prepared by gradient annealing and hot spin coating annealing; Figure 5(b) Steady-state photoluminescence spectra of ITO / SnO2 / ZnO / CsPbI2Br films prepared by gradient annealing and hot spin coating annealing; Figure 5 (c) shows the transient photovoltage attenuation curve; Figure 5 (d) is 100 mW cm -2 Current density-voltage characteristic curve under illumination; Figure 5 (e) is the external quantum efficiency spectrum; Figure 5 (f) shows the current density-voltage curve under dark conditions; (all data are taken from CsPbI2Br solar cells prepared by gradient annealing and hot spin coating annealing methods). Figure 6 The performance of CsPbI₂Br solar cells prepared by gradient annealing and hot spin coating annealing methods is shown; wherein: Figure 6 (a) is the Nyquist plot of a CsPbI2Br solar cell; Figure 6 (b) shows the state trap density (tDOS) distribution of the CsPbI2Br solar cell; Figure 6 (c) Light intensity dependent open-circuit voltage test of CsPbI2Br solar cell. Detailed Implementation

[0023] The materials involved in the specific embodiments of the present invention are as follows: Cesium iodide (CsI, 99.999%), lead iodide (PbI2, 99.999%), lead bromide (PbBr2, 99.99%), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA, molecular weight 6000-15000), and molybdenum trioxide (MoO3, 99.999%) were purchased from Xi'an Yuri Solar Co., Ltd. Chlorobenzene (CB, 99.8%) was purchased from Sigma-Aldrich. Dimethyl sulfoxide (DMSO, 99.7%) was purchased from Adamas.

[0024] The characteristics involved in specific embodiments of the present invention are as follows: Crystal structure analysis was performed using a Bruker D8 ADVANCE diffraction system, and XRD patterns were obtained using a copper target Kα-ray source (λ = 1.5418 Å). Surface morphology and cross-sectional microstructure images were acquired using a Navi innovative scanning electron microscope and a Helios NanoLab G3 UC dual-system scanning electron microscope. Optical absorption properties were measured using a Thermo Scientific Evolution 201 spectrophotometer in the 300–900 nm wavelength range. Photoluminescence (PL) spectra were acquired using an lHR 320 spectral system with an excitation wavelength of 337 nm (LDHD-C-405 laser, PicoQuant). Current density-voltage (JV) characteristics were measured under AM 1.5G standard spectral irradiation (100 mW cm⁻¹). -2 The measurements were performed using a xenon lamp solar simulator (Newport Oriel 66902) and a Keithley 2450 source meter. For the electrical behavior of electron-dedicated and hole-dedicated devices, JV curves were recorded in dark conditions using a Keithley 2450 source meter. The external quantum efficiency (EQE) response curves were measured directly using an external quantum efficiency testing system (EnliTechnology). UV-Vis absorption spectra were obtained using a Thermo Scientific Evolution 201 spectrophotometer. ¹H NMR spectra were acquired using a Bruker AVANCE III 600 MHz nuclear magnetic resonance spectrometer. The NMR liquid sample preparation method is as follows: First, perovskite thin films (size: 14.95 mm × 14.95 mm × 5 films) were prepared on a substrate using spin coating, and treated accordingly according to different heat treatment methods. Then, the perovskite thin films were carefully scraped off the glass substrate using a special stainless steel blade. The perovskite powder was quickly transferred to a glass bottle containing 550 μL of heavy water, thoroughly stirred, and filtered to obtain a uniformly mixed heavy water solution, which was then added to an NMR tube for characterization. To accurately determine the trend of residual solvent content changes in the film, the internal standard method was used for testing and calculation: For pure DMSO precursor solution samples, 6 μL of DMF was added as an internal standard to every 550 μL of heavy water. The trend of residual solvent content changes was analyzed using MestReNova software by comparing the integrated area ratio of the residual solvent characteristic peak to the internal standard characteristic peak. Transient photovoltage (TPV) measurements were performed using a xenon lamp solar simulator (Newport Oriel 66902), a pulsed nitrogen laser (NL100, 337 nm), and a digital oscilloscope (Tektronix MDO 3102). Thermal conductance spectroscopy (ATS) analysis was performed on capacitance-voltage (CV) and capacitance-frequency (CF) characteristics measured using an electrochemical workstation (Ivium Vertex, Netherlands).

[0025] Example The perovskite solar cell provided in this embodiment is an all-inorganic perovskite solar cell with an ITO / SnO2-ZnO / perovskite / PTAA / MoO3 / Ag structure. The specific preparation process is as follows: The ITO glass substrate was ultrasonically cleaned sequentially with deionized water, acetone and ethanol (15 minutes each), followed by 15 minutes of UV-ozone treatment to obtain a hydrophilic surface. A 12wt% SnO2 colloidal solution was diluted with ultrapure water at a ratio of 1:4, and then spin-coated onto the surface of an ITO glass substrate at 5000 rpm for 30 seconds, followed by annealing at 150°C for 30 minutes. A 2.5 wt% ZnO colloidal solution was diluted with anhydrous ethanol at a ratio of 1:4 and then spin-coated onto an ITO glass substrate coated with SnO2 colloid at 5000 rpm for 30 seconds, followed by annealing at 150°C for 30 minutes. CsI, PbI2, and PbBr2 were dissolved in DMSO in a 2:1:1 molar ratio and stirred at 70°C for 3 hours to prepare a 1M CsPbI2Br solution (i.e., perovskite precursor solution). The perovskite precursor was spin-coated onto the surface of an ITO glass substrate coated with ZnO colloid in two steps: 1000 rpm (10 seconds) followed by 3000 rpm (40 seconds). After spin-coating, the substrate was heated with a hot air gun (100°C, 3.5-4 cm away from the substrate) for 15 seconds, followed by annealing at 200°C for 10 minutes.

[0026] PTAA solution (10 mg / mL chlorobenzene solution) was spin-coated onto the surface of an ITO glass substrate coated with perovskite precursor at 4000 rpm and annealed at 100°C for 15 minutes. Finally, MoO3 (6 nm) and Ag (85 nm) electrodes were deposited sequentially by vacuum thermal evaporation, and the effective area of ​​all devices was 0.08 cm².

[0027] Comparative Example 1 The perovskite solar cell provided in this comparative example is an all-inorganic perovskite solar cell with an ITO / SnO2-ZnO / perovskite / PTAA / MoO3 / Ag structure. The specific preparation process is as follows: The ITO glass substrate was ultrasonically cleaned sequentially with deionized water, acetone and ethanol (15 minutes each), followed by 15 minutes of UV-ozone treatment to obtain a hydrophilic surface. A 12wt% SnO2 colloidal solution was diluted with ultrapure water at a ratio of 1:4, and then spin-coated onto the surface of an ITO glass substrate at 5000 rpm for 30 seconds, followed by annealing at 150°C for 30 minutes. A 2.5 wt% ZnO colloidal solution was diluted with anhydrous ethanol at a ratio of 1:4 and then spin-coated onto an ITO glass substrate coated with SnO2 colloid at 5000 rpm for 30 seconds, followed by annealing at 150°C for 30 minutes. CsI, PbI2, and PbBr2 were dissolved in DMSO in a 2:1:1 molar ratio and stirred at 70°C for 3 hours to prepare a 1M CsPbI2Br solution (i.e., perovskite precursor solution). The perovskite precursor was spin-coated onto the surface of an ITO glass substrate coated with ZnO colloid in two steps at 1000 rpm (10 seconds) followed by 3000 rpm (40 seconds); after heat treatment, it was annealed at 200°C (10 minutes).

[0028] PTAA solution (10 mg / mL chlorobenzene solution) was spin-coated onto the surface of an ITO glass substrate coated with perovskite precursor at 4000 rpm and annealed at 100°C for 15 minutes. Finally, MoO3 (6 nm) and Ag (85 nm) electrodes were deposited sequentially via vacuum thermal evaporation, with all devices having an effective area of ​​0.08 cm². 2 .

[0029] Comparative Example 2 The perovskite solar cell provided in this comparative example is an all-inorganic perovskite solar cell with an ITO / SnO2-ZnO / perovskite / PTAA / MoO3 / Ag structure. The specific preparation process is as follows: The ITO glass substrate was ultrasonically cleaned sequentially with deionized water, acetone and ethanol (15 minutes each), followed by 15 minutes of UV-ozone treatment to obtain a hydrophilic surface. A 12wt% SnO2 colloidal solution was diluted with ultrapure water at a ratio of 1:4, and then spin-coated onto the surface of an ITO glass substrate at 5000 rpm for 30 seconds, followed by annealing at 150°C for 30 minutes. A 2.5 wt% ZnO colloidal solution was diluted with anhydrous ethanol at a ratio of 1:4 and then spin-coated onto an ITO glass substrate coated with SnO2 colloid at 5000 rpm for 30 seconds, followed by annealing at 150°C for 30 minutes. CsI, PbI2, and PbBr2 were dissolved in DMSO in a 2:1:1 molar ratio and stirred at 70°C for 3 hours to prepare a 1M CsPbI2Br solution (i.e., perovskite precursor solution). The perovskite precursor was spin-coated onto the surface of an ITO glass substrate coated with ZnO colloid in two steps at 1000 rpm (10 seconds) followed by 3000 rpm (40 seconds). The substrate was first annealed at 50°C to give the film a light brown transition state, and then finally annealed at 200°C (10 minutes).

[0030] PTAA solution (10 mg / mL chlorobenzene solution) was spin-coated onto the surface of an ITO glass substrate coated with perovskite precursor at 4000 rpm and annealed at 100°C for 15 minutes. Finally, MoO3 (6 nm) and Ag (85 nm) electrodes were deposited sequentially via vacuum thermal evaporation, with all devices having an effective area of ​​0.08 cm². 2 .

[0031] The following provides further explanation of the embodiments and comparative examples.

[0032] This invention provides three methods for preparing CsPbI2Br perovskite thin films: direct thermal annealing at 200℃, pre-annealing at 50℃ followed by high-temperature annealing at 200℃ (i.e., gradient thermal annealing), and thermal spin coating at 100℃ followed by annealing at 200℃. A schematic diagram of the thermal spin coating annealing process is shown below. Figure 1 . Figure 2 The images labeled ad, eh, and il respectively show the top view, bottom view, cross-sectional SEM images, and optical photographs of thin films prepared by direct thermal annealing, gradient thermal annealing, and spin coating annealing methods. All samples were prepared using a one-step method with DMSO solution as a precursor for CsI, PbI2, and PbBr2. Figure 2 As shown in Figure ac, the CsPbI2Br thin film treated with direct thermal annealing exhibits numerous pores on both the surface and bottom, and the grain morphology displays a distinctly discontinuous characteristic. Interestingly, when the initial cast thin film is treated with gradient thermal annealing ( Figure 2 e.g., the discontinuous grain morphology was significantly improved. This indicates that pre-annealing at 50℃ can accelerate the evaporation of residual DMSO solvent before crystallization of the CsPbI2Br perovskite film, thereby effectively suppressing the formation of pores. Inspired by this, we used a hot spin-coating annealing method to further accelerate the evaporation rate of DMSO solvent before perovskite crystallization, and successfully obtained a CsPbI2Br perovskite film with regular crystal planes and no pores. Figure 2 The optical images of the thin films prepared by the three methods show coffee rings (ik). Figure 2 d) Flowing stripes ( Figure 2 h) and uniform pattern ( Figure 2 (l). These results demonstrate that, compared to direct thermal annealing and gradient thermal annealing, the spin coating annealing process achieves rapid and thorough solvent removal, effectively avoiding the lateral transport and accumulation of DMSO solvent, thus forming a pore-free, spatially uniform perovskite film. In summary, SEM images and optical characterization together prove that thorough removal of residual solvent and achieving uniform solvent evaporation play a crucial role in suppressing pore formation in CsPbI₂Br perovskite films.

[0033] Comparative analysis revealed that the evolution of the intermediate phase and the formation of the cubic phase in CsPbI2Br perovskite films are greatly influenced by the preparation steps and parameters. This invention presents X-ray diffraction (XRD) analysis of CsPbI2Br perovskite films prepared by direct thermal annealing, gradient thermal annealing, and hot spin coating annealing processes. Figure 3 ab shows the XRD patterns measured from the top and bottom of the films, respectively. All samples show a cubic phase structure of CsPbI2Br perovskite. The characteristic diffraction peaks at 2θ = 14.6° and 29.5° indicate that the crystal exhibits a preferred orientation along the cubic (100) plane.

[0034] from Figure 3 As can be clearly seen, regardless of whether the X-rays are incident from the top or the bottom, the XRD peak intensity of the hot spin-coated annealed sample is the strongest, while that of the DTA sample is the weakest. This variation in XRD peak intensity is consistent with the changes in crystallinity and morphology of the CsPbI2Br perovskite film.

[0035] To understand how pre-annealing affects the intermediate state during crystallization, this invention subjected CsPbI2Br films to pre-annealing at 50°C for different durations. For example... Figure 3 As shown in Figure c, PbI2-DMSO and PbBr2-DMSO intermediate phases can be observed in the film. When the film is pre-annealed at 50°C, these intermediate phases are transformed into crystalline PbI2 or PbBr2. This phenomenon is different from the process of lead halide and methyl ammonium halide (such as MAI-PbI2-DMSO) forming intermediate phases in organic-inorganic perovskites. Even with the extended pre-annealing time of 50°C, the PbI2-DMSO and PbBr2-DMSO intermediate phases still exist. Importantly, the disappearance of PbI2 and PbBr2 is accompanied by the initial formation of the perovskite phase, indicating that this phase transformation process lays the foundation for the subsequent formation of cubic CsPbI2Br perovskite. When the film is prepared using a 100°C hot spin coating process, the XRD pattern shows that the orientation degree of the (100) crystal plane increases with the extension of the hot spin coating treatment time ( Figure 3 d). Spin coating significantly promoted the transformation of the PbI₂-DMSO and PbBr₂-DMSO mesophases to the CsPbI₂Br perovskite cubic phase. This result is attributed to the rapid removal of DMSO residue by the spin coating process, thereby promoting the formation of high-quality CsPbI₂Br perovskite films during subsequent annealing (e.g., ...). Figure 1 (As shown in the schematic diagram). Therefore, the method provided by this invention, in preparing CsPbI2Br films, follows a film formation path from the initial PbI2-DMSO / PbBr2-DMSO adduct intermediate phase in the film, to the PbI2 / PbBr2 precursor, and finally to the formation of the CsPbI2Br film.

[0036] To reveal the mechanism by which the evaporation behavior of residual solvent DMSO affects the formation of pores at the buried interface, this invention uses hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy to quantitatively analyze the amount of residual DMSO in CsPbI₂Br perovskite films during the thermal annealing process. Based on Figure 4 The integral peak area ratio of DMSO to internal standard in a was calculated. Figure 4 The residual DMSO content shown in b reveals a significant difference in the residual content evolution between gradient thermal annealing and thermal spin coating annealing. Figure 4 b. A comparison was made between the changes in DMSO content relative to the initial state under hot spin coating and 50℃ pre-annealing treatments with heat treatment time. The results showed that the DMSO content in the hot spin coating group decreased significantly faster than that in the 50℃ pre-annealing group. This indicates that hot spin coating can remove DMSO more quickly, consistent with XRD data ( Figure 3 c) This corroborates each other, further confirming that achieving uniform solvent removal before crystal growth is crucial for forming high-quality CsPbI₂Br films. However, the 50°C pre-annealing method has proven ineffective in eliminating DMSO solvent residue. Analysis of samples annealed at different temperatures for 10 seconds... Figure 4 CD data shows that as the pre-annealing temperature increases, the amount of DMSO residue in the film gradually decreases relative to the initial state. Spin-coating annealing enables more uniform solvent evaporation and effectively delays the closure of gas transport channels at the top of the film.

[0037] Pre-annealing can affect the quality of perovskite films. Figure 5 A shows the optical absorption spectra of thin films prepared by gradient annealing and spin coating annealing. All samples exhibit an absorption edge near 650 nm. The absorption intensity of the thin films prepared by spin coating annealing is significantly enhanced, which is attributed to their superior crystallinity. Figure 3 (This is corroborated by XRD spectra). On the other hand, the steady-state photoluminescence (PL) spectrum of the SnO2 / ZnO / perovskite heterostructure shows (…). Figure 5 (b) The luminescence intensity of the spin-coated annealed film was significantly quenched compared to the gradient-annealed sample, indicating enhanced photogenerated carrier extraction capability at the electron transport layer / perovskite interface. Carrier recombination dynamics were characterized using transient photovoltage decay (TPV) spectroscopy. Figure 5 c shows that the carrier recombination lifetime of the hot spin-coated annealed device is extended to 3.34 μs, which is significantly higher than the 1.09 μs of the gradient annealed device, indicating that the crystallinity of the hot spin-coated annealed sample is improved and the defects of non-radiative recombination centers are effectively suppressed.

[0038] This invention further fabricated a planar solar cell with a glass / ITO / SnO2 / ZnO / CsPbI2Br / PTAA / MoO3 / Ag structure. The hot-spin-coating annealed device achieved a power conversion efficiency (PCE) of 14.89%, while also obtaining a high open-circuit voltage (VOC) of 1.32 V and a voltage of 15.72 mA cm⁻¹. - ² Short-circuit current density (JSC) Figure 5 d), its performance is significantly better than PCE (12.70%), VOC (1.30 V), and JSC (15.02 mA cm⁻¹). - Gradient annealing device. Figure 5 The external quantum efficiency (EQE) spectrum of the thermally spin-coated annealed device shows a significant enhancement in response across the entire spectral range, with an integrated current density reaching 15.31 mA cm⁻¹. -2 The measured value is 15.72 mA cm⁻¹. -2 There is only a tiny deviation of 2.61%. Figure 5 The results show that the dark current density of the TSCA device is reduced by 1-2 orders of magnitude compared to the GTA device. These results demonstrate that the efficiency improvement stems from the suppression of bulk charge recombination and the acceleration of interfacial carrier extraction.

[0039] This invention uses impedance spectroscopy to demonstrate the differences in carrier transport and recombination kinetics between CsPbI2Br solar cells prepared by gradient annealing and thermal spin coating annealing methods. Figure 6 Figure a shows the Nyquist plot and the corresponding equivalent circuit model. The device fabricated by the hot spin coating annealing method exhibits a significantly reduced series resistance (Rs) and an order-of-magnitude increase in recombination resistance (Rrec). This significant improvement in electrical properties indicates that nonradiative carrier recombination in the TSCA device is effectively suppressed, consistent with the aforementioned PL test results. Figure 6 b. The relationship between the state trap density (tDOS) and energy level was characterized using thermal admittance spectroscopy. Compared to gradient-annealed devices, the trap density of the thermally spin-coated annealed device was significantly reduced in the shallow energy level region (0.3-0.4 eV), confirming that the pores at the buried interface significantly affect the formation of shallow energy level traps. To further elucidate charge recombination behavior, this invention measured the device in the 20-100 mW cm⁻¹ range. -2 Open-circuit voltage dependence characteristics within the light intensity range ( Figure 6 c). The slope of the nKBT / q curve versus the logarithmic value of light intensity reflects the degree of nonradiative recombination and the trap density, where n is the ideality factor, KB is the Boltzmann constant, q represents the elementary charge, and T is the absolute temperature. When the value of n approaches 1, nonradiative recombination is suppressed and the trap density is minimized. The fitting results show that the thermally spin-coated annealed device has a smaller slope value (1.45 KBT / q), indicating that interface pores affect carrier transport by enhancing trap-assisted recombination.

[0040] In summary, the method provided by this invention can effectively remove residual solvent DMSO, resulting in a film with high crystallinity and no pores. Unlike the intermediate state formation process involving lead halides and methyl ammonium halides (such as MAI-PbI2-DMSO) in organic-inorganic perovskites, in this invention, even with extended pre-annealing time at 50°C, the PbI2-DMSO and PbBr2-DMSO intermediate phases still exist; and the disappearance of PbI2 and PbBr2 is accompanied by the initial formation of the perovskite phase, indicating that this phase transition process lays the foundation for the subsequent formation of the cubic CsPbI2Br perovskite phase. Compared to the pre-annealing treatment in gradient annealing methods, the spin coating technology in spin coating annealing is a more effective way to remove residual DMSO solvent. The spin coating process achieves more uniform solvent evaporation by delaying the closure of the gas transport channels at the top of the film. This invention utilizes a hot spin coating annealing technique to fabricate a CsPbI2Br solar cell, achieving a 15.72 mA cm⁻¹ ampere-hour without any additive modification or interface passivation. -2 The invention achieves high short-circuit current density (JSC), a high open-circuit voltage (VOC) of 1.33 V, and a power conversion efficiency (PCE) of 14.89%. By controlling the evaporation behavior of residual solvents, this invention solves the problem of thin-film porosity formation in the production of high-performance all-inorganic perovskite solar cells.

Claims

1. A method for preparing a perovskite solar cell, characterized in that: Includes the following steps: S1 is annealed after spin-coating SnO2 precursor onto the substrate surface; S2 spin-coated ZnO precursor onto the surface of annealed SnO2 precursor, followed by annealing; S3 spin-coated the perovskite precursor onto the surface of the annealed ZnO precursor, and then heated the perovskite precursor to 100°C for annealing. S4 spin-coated an organic solution of PTAA onto the surface of the annealed perovskite precursor, followed by annealing; S5 is finally obtained by sequentially depositing a MoO3 layer and an electrode on the annealed PTAA surface through vacuum thermal evaporation. The perovskite precursor was obtained by dissolving CsI, PbI2 and PbBr2 in DMSO at a molar ratio of 2:1:1 to obtain a 1M CsPbI2Br precursor solution.

2. The method for preparing a perovskite solar cell as described in claim 1, characterized in that: The SnO2 precursor in S1 was obtained by diluting a 12 wt% SnO2 colloidal solution with water at a weight ratio of 1:

4. The annealing temperature in S1 is 150°C, and the annealing time is 30 minutes. The spin coating speed in S1 is 5000 rpm, and the time is 30 seconds.

3. The method for preparing a perovskite solar cell as described in claim 1, characterized in that: The annealing temperature in S2 is 150°C, and the annealing time is 30 minutes. The spin coating speed in S2 is 5000 rpm, and the time is 30 seconds; The ZnO precursor in S2 was obtained by diluting a 2.5 wt% ZnO colloidal solution with anhydrous ethanol at a weight ratio of 1:

4.

4. The method for preparing a perovskite solar cell as described in claim 1, characterized in that: The spin coating in S3 includes the steps of spin coating at 1000 rpm for 10 seconds and then spin coating at 3000 rpm for 40 seconds; The heating in S3 includes a step of heating the substrate with hot air at 100°C at a distance of 3.5-4 cm. The annealing temperature in S3 is 200°C, and the annealing time is 10 minutes.

5. The method for preparing a perovskite solar cell as described in claim 1, characterized in that: The annealing temperature in S4 is 100°C, and the annealing time is 15 minutes.

6. The method for preparing a perovskite solar cell as described in claim 1, characterized in that: The spin coating speed in S4 is 4000 rpm; The concentration of PTAA in the organic solution in S4 is 10 mg / mL; The solvent in the organic solution of PTAA in S4 includes chlorobenzene.

7. The method for preparing a perovskite solar cell according to claim 1, characterized in that: The substrate includes an ITO glass substrate; The ITO glass substrate includes an ITO glass substrate obtained after ultraviolet-ozone treatment.

8. The method for preparing a perovskite solar cell as described in claim 1, characterized in that: The thickness of the MoO3 layer is 6 nm; The thickness of the electrode is 85 nm; The electrode includes a silver electrode.

9. The perovskite solar cell prepared by the method described in claim 1.

10. The application of the perovskite solar cell as described in claim 9, characterized in that: It is used in solar power generation.

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