A CsPbI x Br 3-x Perovskite Thin Films, Their Preparation Methods and Applications

Abstract

The application provides a CsPbI x Br 3‑x Perovskite thin film, and a preparation method and application thereof. The preparation method comprises the following steps: providing a perovskite precursor solution containing lead halide, cesium halide, 4-tert-butylpyridine and a solvent; performing film forming treatment on the precursor solution, and then sequentially performing first annealing treatment and second annealing treatment, so as to obtain a CsPbI x Br 3‑x Perovskite thin film; wherein the temperature of the first annealing treatment is 30-60 DEG C, and the temperature of the second annealing treatment is 200-350 DEG C. In the application, TBP is added to form a metastable Lewis acid-base adduct with lead halide, which releases lead halide in the first annealing treatment to induce heterogeneous nucleation, and in the second annealing treatment, the crystal seeds act as nucleation sites to realize controlled crystal growth, so as to obtain a perovskite thin film with a lower defect state density, and a solar cell containing the perovskite thin film has good photoelectric properties.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cell technology, specifically relating to a CsPbI solar cell. x Br 3-x Perovskite thin films and their preparation methods, and a perovskite solar cell and its preparation method. Background Technology

[0002] Cesium lead-based all-inorganic perovskite solar cells (PSCs), due to the removal of fragile organic components from their structure, have exhibited photovoltaic performance comparable to organic-inorganic hybrid solar cells, while also demonstrating intrinsic thermal stability and stability under ultraviolet light. Among them, CsPbI₂ with mixed halogens... x Br 3-x By balancing the band gap and tolerance factor, a stable photosensitive cubic phase is formed at room temperature, exhibiting excellent absorption in the visible light range of 300–700 nm. This makes CsPbI0.05 x Br 3-x It shows great promise in building-integrated photovoltaics and tandem solar cell applications.

[0003] However, due to rapid crystallization during the annealing process, the cubic α-CsPbI phase prepared directly from the precursor solution... x Br 3-x This introduces ionic defects, such as vacancies, anti-substitution sites, or interstitial defects, as well as macroscopic defects like cracks and voids. These defects increase the defect state density in perovskite films, generating defect energy levels that act as non-radiative recombination centers, leading to significant energy loss. Furthermore, these defects are also vulnerable sites on the film, easily allowing moisture intrusion, which can degrade device performance or even cause failure.

[0004] To improve film quality, existing strategies include precursor engineering, antisolvent engineering, and multi-step annealing. For example, some studies have used precursor materials containing organic components such as HCOOCs, HPbI3, and HPbBr3 to replace traditional CsI, PbI2, and PbBr2, which can improve the tolerance to moisture during perovskite preparation to some extent. Introducing organic halides such as MACl and MAI into the precursor solution can form an intermediate phase, which gradually transforms into CsPbI3 during annealing. x Br 3-x Thin films. However, these strategies all introduce additional organic components that may remain during annealing and introduce uncertainty into device stability over time. Summary of the Invention

[0005] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0006] One of the objectives of this invention is to provide a CsPbI x Br 3-x A method for preparing perovskite thin films includes: providing a perovskite precursor solution comprising lead halide, cesium halide, 4-tert-butylpyridine, and a solvent; performing a film-forming treatment on the precursor solution, followed by a first annealing treatment and a second annealing treatment, thereby obtaining CsPbI x Br 3-x A perovskite thin film; wherein the temperature of the first annealing treatment is 30-60℃, and the temperature of the second annealing treatment is 200-350℃.

[0007] The beneficial effect of this technology lies in the fact that, by introducing 4-tert-butylpyridine (TBP) as a volatile Lewis base monodentate ligand to form a metastable complex with lead halide for a non-uniform nucleation process without antisolvents, the ordered crystal growth strategy of this invention can prepare CsPbI x Br 3-x Perovskite film; specifically, this metastable complex preferentially decomposes during the first annealing process, causing lead halide to desorb. This portion of lead halide acts as a heterogeneous nucleation site, promoting heterogeneous crystallization. During the second annealing process, the crystal further grows and eventually forms a dense perovskite film. In the second annealing process, TBP is completely volatilized and does not remain in the perovskite film.

[0008] In some embodiments, the solvent can combine with lead halide to form a complex. Furthermore, the decomposition temperature of the complex formed by the solvent and lead halide is higher than the decomposition temperature of the complex formed by 4-tert-butylpyridine and lead halide.

[0009] In some embodiments, the 4-tert-butylpyridine is soluble in the solvent in any proportion.

[0010] In some preferred embodiments, the solvent includes at least one of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF). O-Pb exists between dimethyl sulfoxide and N,N-dimethylformamide and lead halide. 2+ Coordination results in complexes with suitable binding forces, while TBP and lead halides form N-Pb complexes. 2+The coordination bonds are weaker, therefore, during the first low-temperature annealing process, the desorption process of lead halide bound to dimethyl sulfoxide and / or N,N-dimethylformamide is slower than that of lead halide bound to TBP. This portion of lead halide mainly participates in film formation during the second high-temperature annealing process, achieving the goal of ordered, stepwise controlled crystal growth. Furthermore, the lead halide, TBP, and DMSO / DMF system provided by this invention can achieve good ordered crystal growth through a two-step annealing process because the binding forces between lead halide and TBP, and between lead halide and DMSO / DMF, are significantly different. This allows for seed crystal formation and crystal growth in two temperature ranges with significant temperature differences. Since the temperature ranges of the two annealing steps differ considerably, there is no need to worry about temperature errors affecting ordered crystal growth during actual production, resulting in lower requirements for equipment temperature control precision and suitability for industrial applications. The solvent preferably includes dimethyl sulfoxide because lead halide, cesium halide, and 4-tert-butylpyridine have greater solubility in dimethyl sulfoxide.

[0011] In some embodiments, the concentration of 4-tert-butylpyridine in the precursor solution is 1%-20% v / v. Within this concentration range, the formed grain size is preferred; if the concentration is below this range, the heterogeneous crystallization process is not significant; if the concentration is above this range, the evaporation of a large amount of 4-tert-butylpyridine will result in obvious porosity in the film. The concentration of 4-tert-butylpyridine in the precursor solution is preferably 1%-10% v / v, more preferably 4%-8% v / v, which can further improve the photoelectric performance of the device, for example, further improve the photoelectric conversion efficiency of the solar cell.

[0012] In some embodiments, the first annealing treatment time is 20 seconds to 10 minutes. If the first annealing treatment time is too short, it will not promote the desorption of TBP and lead halides; if the time is too long, some lead halides complexed with the solvent will participate in film formation, failing to achieve the purpose of orderly control of crystal growth. The preferred first annealing treatment time is 20 seconds to 10 minutes, resulting in perovskite films with better morphology and properties.

[0013] In some embodiments, the second annealing process takes 5 seconds to 1 hour.

[0014] In some embodiments, the lead halide includes PbI2 and / or PbBr2, but is not limited thereto.

[0015] In some embodiments, the cesium halide includes CsI and / or CsBr, but is not limited thereto.

[0016] In some embodiments, the molar ratio of lead halide to cesium halide is 1:0.9 to 1.1. Preferably, it is 1:1.

[0017] In some embodiments, the film-forming process includes: uniformly coating the precursor solution onto the substrate surface to form a liquid film.

[0018] Furthermore, the precursor solution is uniformly coated onto the substrate using a spin coating method, which includes a first spin coating process and a second spin coating process. The precursor solution is uniformly distributed on the substrate through step-by-step spin coating.

[0019] Furthermore, the spin coating speed of the first spin coating process is 500-1500 rpm, and the spin coating time is 5-10 s.

[0020] Furthermore, the spin coating speed for the second spin coating process is 2000–4000 rpm, and the spin coating time is 80–100 s. The beneficial effect of this technical solution is that if the spin coating time for the second spin coating process is too short, it will lead to uneven crystallization caused by the accumulation of the precursor solution at the edges, resulting in obvious stripe defects at the film edges. Extending the spin coating time within a certain range can eliminate these stripe defects; however, if the time is too long, the film will become too thin, affecting the light absorption efficiency.

[0021] A second objective of this invention is to provide CsPbI obtained according to the above-described preparation method. x Br 3- x Perovskite Thin Film.

[0022] In some embodiments, the CsPbI x Br 3-x The perovskite grain size in the perovskite thin film is 0.5 μm to 3 μm.

[0023] The third objective of this invention is to provide the aforementioned CsPbI x Br 3-x Applications of perovskite thin films in the fabrication of perovskite solar cells, photodetectors, lighting devices, or display devices.

[0024] The fourth objective of this invention is to provide a perovskite solar cell, comprising a conductive glass, an electron transport layer, a perovskite active layer, a hole transport layer, and a metal electrode, wherein the perovskite active layer comprises CsPbI as described in the above-mentioned technical solution. x Br 3-x Perovskite thin films.

[0025] In some embodiments, the conductive glass comprises ITO and / or FTO.

[0026] In some embodiments, the electron transport layer includes at least one of TiO2, ZnO, and SnO2.

[0027] In some embodiments, the hole transport layer includes at least one of Spiro-OMeTAD, PTAA, P3HT, and CuSCN. The hole transport layer preferably includes Spiro-OMeTAD because the valence band top of the perovskite thin film prepared in this invention is close to the HOMO level of Spiro-OMeTAD. Using Spiro-OMeTAD as the hole transport layer not only facilitates hole extraction and reduces device energy loss, but the built-in electric field between the two also facilitates charge transport, thereby improving the device's photovoltage output.

[0028] In some embodiments, the metal electrode includes at least one of Ag, Al, Au and Cu electrodes.

[0029] In some embodiments, the conversion efficiency of the perovskite solar cell is 16.5% or higher.

[0030] The fifth objective of this invention is to provide a method for preparing a perovskite solar cell, the method comprising:

[0031] An electron transport layer is formed on the conductive glass;

[0032] The CsPbIe layer is formed on the side of the electron transport layer away from the conductive glass using the preparation method described in any of the above technical solutions. x Br 3-x Perovskite thin films;

[0033] In the CsPbI x Br 3-x A hole transport layer is formed on the side of the perovskite thin film away from the electron transport layer;

[0034] A metal electrode is formed on the hole transport layer.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention adds 4-tert-butylpyridine (TBP) to the perovskite precursor solution and combines it with a two-step annealing process to promote the crystallization of high-quality perovskite films, resulting in more dense perovskite films with a lower defect state density. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1This is an example of the preparation of CsPbI in this invention. x Br 3-x A schematic diagram of the perovskite thin film process;

[0038] Figure 2 This is a SEM image of the surface of the perovskite thin film prepared in Example 1 of this invention;

[0039] Figure 3 This is a SEM image of the cross-section of the perovskite thin film prepared in Example 1 of this invention;

[0040] Figure 4 This is a SEM image of the surface of the perovskite film prepared in Comparative Example 1 of the present invention.

[0041] Figure 5 This is a SEM image of the cross-section of the perovskite thin film prepared in Comparative Example 1 of this invention;

[0042] Figure 6 This is a schematic diagram of the film-forming mechanism of the preparation method provided by the present invention;

[0043] Figure 7 These are the steady-state emission spectra of the perovskite thin films in Example 1 and Comparative Example 1 of the present invention;

[0044] Figure 8 These are the time-resolved emission spectra of the perovskite thin films in Embodiment 1 and Comparative Example 1 of the present invention;

[0045] Figure 9 It is the transient photovoltage of the solar cells in Embodiment 1 and Comparative Example 1 of the present invention;

[0046] Figure 10 It is the transient photocurrent of the solar cells in Embodiment 1 and Comparative Example 1 of the present invention;

[0047] Figure 11 This is a stability test of the solar cells in Embodiment 1 and Comparative Example 1 of the present invention over 400 hours. Detailed Implementation

[0048] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. Specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and are intended to teach those skilled in the art.

[0049] Figure 6 This is a schematic diagram of the film-forming mechanism of the preparation method provided by the present invention, as shown below. Figure 6As shown, the technical concept of this invention is as follows: Traditional perovskite thin film preparation processes involve uncontrolled crystallization, which easily leads to macroscopic defects such as cracks and microscopic defects such as vacancies. This invention adds TBP to the perovskite precursor solution. Due to the weak interaction between lead halide and TBP, the adduct formed by the two preferentially decomposes and releases lead halide during low-temperature annealing (first annealing treatment). This portion of lead halide acts as heterogeneous nucleation sites, promoting the formation of perovskite seed crystals. Simultaneously, due to the stronger binding force between the solvent (e.g., DMSO, DMF) and lead halide, this portion of lead halide only participates in film formation during the high-temperature annealing stage (second annealing treatment), continuing to grow on the pre-formed seed crystals to form larger grains. This preparation method achieves ordered grain growth without the need for an anti-solvent, thereby obtaining a thin film with large grains and low defect state density.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a CsPbI x Br 3-x Methods for preparing perovskite thin films include:

[0052] Add 1.2 mmol of CsI, 0.6 mmol of PbI2 and 0.6 mmol of PbBr2 to 1 mL of DMSO solvent, and add TBP at a volume concentration of 6% to form a precursor solution. Stir overnight to fully dissolve the precursor solution before use.

[0053] ITO was ultrasonically cleaned sequentially with cleaning solution, distilled water, ethanol, and acetone to obtain clean ITO conductive glass.

[0054] A 0.1 M ZnO sol-gel solution was spin-coated onto the clean ITO surface and then annealed at 170 °C for 1 h to prepare a ZnO layer.

[0055] An aqueous solution of SnO2 was spin-coated onto the ZnO layer and then annealed at 150°C for 30 min to form a ZnO / SnO2 electron transport layer.

[0056] The prepared precursor solution was spin-coated onto the electron transport layer. The spin-coating process consisted of first spin-coating at 1000 rpm for 30 seconds, then spin-coating at 3000 rpm for 100 seconds, followed by annealing at 50°C for 1 minute, and then annealing at 280°C for 10 minutes to obtain CsPbI₂ formed on the electron transport layer. x Br 3-x Perovskite thin films;

[0057] A mixed solution containing 72.3 mg / mL Spiro-OMeTAD, 17.5 μL Li-TFSI (520 mg / mL acetonitrile solution), and 28.8 μL TBP was spin-coated onto the above CsPbI. x Br 3-x A hole transport layer was formed on a perovskite thin film by spin coating at a speed of 3000 rpm for 30 s.

[0058] Then, a 10 nm thick MoO3 electrode and a 100 nm thick Ag electrode are deposited on the hole transport layer to obtain a perovskite solar cell.

[0059] Example 2

[0060] The only difference between Example 2 and Example 1 is that TBP was added at a volume concentration of 1% to form a precursor solution. The rest of the process was the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0061] Example 3

[0062] The only difference between Example 3 and Example 1 is that TBP was added at a volume concentration of 20% to form a precursor solution. The rest is the same as in Example 1. The performance of the perovskite solar cells obtained in Example 3 is shown in Table 1.

[0063] Example 4

[0064] The only difference between Example 4 and Example 1 is that Example 4 was annealed at 30°C for 1 minute and then at 200°C for 10 minutes. The rest of the process was the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0065] Example 5

[0066] The only difference between Example 5 and Example 1 is that Example 5 was annealed at 60°C for 1 minute and then at 350°C for 10 minutes. The rest of the process was the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0067] Example 6

[0068] The only difference between Example 6 and Example 1 is that the spin coating process is to first spin coat at 1000 rpm for 30 seconds, and then spin coat at 3000 rpm for 80 seconds. The rest is the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0069] Example 7

[0070] 0.6 mmol of CsI, 0.3 mmol of PbI2 and 0.3 mmol of PbBr2 were added to 1 mL of N,N-dimethylformamide solvent, and TBP was added at a volume concentration of 6% to form a precursor solution; the rest of the process was the same as in Example 1, and the performance of the resulting perovskite solar cell is shown in Table 1.

[0071] Comparative Example 1

[0072] The only difference between Comparative Example 1 and Example 1 is that TBP was not added to the precursor solution, and perovskite solar cells were prepared using the same method as in Example 1. The performance of the obtained perovskite solar cells is shown in Table 1.

[0073] Comparative Example 2

[0074] The only difference between Comparative Example 1 and Example 1 is that the TBP concentration is 0.5%, and the rest is the same as in Example 1. The performance of the resulting perovskite solar cells is shown in Table 1.

[0075] Comparative Example 3

[0076] The only difference between Comparative Example 3 and Example 1 is that the TBP concentration is 25%, while the rest is the same as in Example 1. The performance of the resulting perovskite solar cells is shown in Table 1.

[0077] Comparative Example 4

[0078] The only difference between Comparative Example 4 and Example 1 is that after spin-coating the precursor solution onto the electron transport layer, it was annealed at 280°C for 10 min. The rest of the process was the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0079] Comparative Example 5

[0080] The only difference between Comparative Example 5 and Example 1 is that after spin-coating the precursor solution onto the electron transport layer, it was first annealed at 25°C for 1 min, and then annealed at 380°C for 10 min. The rest of the process was the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0081] Comparative Example 6

[0082] The only difference between Comparative Example 6 and Example 1 is that the spin coating process is to first spin coat at 1000 rpm for 30 seconds, and then spin coat at 3000 rpm for 60 seconds. The rest is the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0083] Comparative Example 7

[0084] The only difference between Comparative Example 6 and Example 1 is that the spin coating process is to first spin coat at 1000 rpm for 30 s and then spin coat at 3000 rpm for 120 s. The rest is the same as in Example 1. The performance of the resulting perovskite solar cell is shown in Table 1.

[0085] To verify the quality of the perovskite thin film obtained in this invention and the performance of devices containing the perovskite thin film, the performance of the perovskite solar cells prepared in Examples 1-6 and Comparative Examples 1-5 was tested, and the test results are shown in Table 1.

[0086] Table 1. Performance of perovskite solar cells in Examples 1-7 and Comparative Examples 1-7

[0087]

[0088] To illustrate the improvement in the quality of perovskite thin films by the preparation method provided by the present invention, the perovskite thin films and perovskite solar cells prepared in Example 1 and Comparative Example 1 were characterized as follows.

[0089] Electron microscopy was performed on the perovskite films prepared in Example 1 and Comparative 1. Figure 2 , 3 The surface and cross-sectional morphology of the perovskite thin film prepared in Example 1 are shown. Figure 4 , 5 The surface and cross-sectional morphology of the perovskite film prepared in Comparative Example 1 are shown. The comparison reveals that the film prepared in Comparative Example 1 has a rougher surface and deeper cracks at the grain boundaries, with pores at the interface between ITO and perovskite. In contrast, the film prepared in Example 1 of this invention is more dense and has no obvious defects.

[0090] In addition, in comparison Figure 2 and Figure 4 As can be seen from the surface morphology of the perovskite, the grain size of the perovskite prepared in Example 1 (average grain size of 1.01 μm) is significantly larger than that of the perovskite prepared in Comparative Example 1 (average grain size of 0.71 μm). This is because the crystallization process in Comparative Example 1 is a uniform nucleation and growth process, and its crystallization rate depends on the influence of the adduct formed by lead halide and solvent (e.g., DMSO). In the preparation method of the present invention, the lead halide-TBP adduct with weak interaction is preferentially decomposed during the first annealing process, and the released lead halide acts as heterogeneous nucleation sites, promoting the formation of perovskite seeds. Subsequently, during the second annealing process, the lead halide-DMSO with strong binding force participates in film formation and continues to grow on the seed crystal to form larger grains.

[0091] To evaluate the impact of the preparation method in this invention on improving film quality, the trap density (n) of the perovskite films in Example 1 and Comparative Example 1 was calculated using the following method. t ):

[0092]

[0093] Where, ε r (8.5) represents the relative permittivity of inorganic perovskite, ε0(8.85×10⁻⁶). -12 Fm -1 ) represents the vacuum permittivity, e(1.6×10 -19 C) represents the elementary charge, and L (300 nm) is the thickness of the perovskite layer. According to calculations, the defect densities of the devices in Comparative Example 1 and Example 1 are 2.07 × 10⁻⁶. 16 cm -3 and 1.68×10 16 cm -3 As can be seen, the thin film trap density in Example 1 is lower, proving that the method provided by the present invention can improve crystallization and thin film quality, thereby reducing energy loss by reducing non-radiative recombination.

[0094] This invention utilizes steady-state emission spectra (PL, such as...) Figure 7 (as shown) and time-resolved emission spectra (TRPL, as shown) Figure 8 (As shown) The charge characteristics of the mineralized thin film on the ITO substrate were further tested. Compared with the film of Comparative Example 1, the film in Example 1 showed a higher PL intensity and no peak shift, indicating that charge recombination at the grain boundaries was suppressed. The corresponding carrier lifetime can be extracted by fitting the TRPL curve using the following bi-exponential function.

[0095] y=A1·exp(-x / t1)+A2·exp(-x / t2)+y0

[0096] The rapid decay process is related to carrier recombination caused by surface defects, while the slow decay reflects the carrier lifetime confined by defects in the calcite body. The average lifetime of the film in Comparative Example 1 is 1.52 ns, while the average lifetime of the film in Example 1 increases to 1.80 ns, and the longer lifetime indicates higher crystal quality.

[0097] The fabrication method provided by this invention has a certain impact on the band structure. This invention calculated the valence band top of the thin films in Example 1 and Comparative Example 1, and found that the valence band top of the thin film in Example 1 is significantly higher than that in Comparative Example 1, increasing from -5.71 eV to -5.65 eV. This indicates that the valence band top of the perovskite thin film prepared by the method of this invention is closer to the HOMO level of Spiro-OMeTAD, which is beneficial for hole extraction and thus reduces the energy loss of the device. The increased Fermi level of the perovskite enhances the built-in electric field between the n-type perovskite and the p-type Spiro-OMeTAD, facilitating charge transport. Furthermore, the wider band gap, in conjunction with the above effects, can improve the photovoltage output of the device.

[0098] This invention uses transient photovoltage (TPV, such as...) Figure 9 (as shown) and transient photocurrent (TPC, such as) Figure 10 The tests (shown) were used to evaluate the charge extraction time and charge recombination lifetime of the battery devices in Comparative Example 1 and Example 1. TPC results showed that the two devices had similar charge extraction times, while TPV fitting results showed that the charge lifetime of the device in Comparative Example 1 was 315.7 μs, while the battery in Example 1 exhibited a longer charge recombination lifetime of 583.0 μs. This test demonstrates that the charge extraction process of the transport layer is similar in both groups of devices. However, due to the reduction of defects in the perovskite layer after the addition of TBP, the reverse transport and recombination processes after the extraction of electrons and holes were significantly suppressed in the device of Example 1. From the perspective of device operation, this improvement in carrier dynamics contributes to enhanced photovoltaic performance. Furthermore, the electroluminescence (EL) spectra of the two groups of devices were also tested. Compared with the device in Comparative Example 1, the device in Example 1 exhibited a stronger EL peak, indicating less non-radiative recombination. In addition, the device in Example 1 showed an emission peak at a relatively high voltage, indicating a higher built-in potential.

[0099] This invention also tested the stability of the device stored in a nitrogen atmosphere under ambient light conditions, and the test results are as follows: Figure 11 As shown, the device of Example 1 maintained a high efficiency exceeding its initial efficiency after storage for over 400 hours, while the device of Comparative Example 1 only maintained 90% of its initial PCE. The better stability of the device of Example 1 may be due to the suppression of ion migration caused by internal defects. This indicates that the introduction of TBP not only improves the device performance but also delays device degradation.

[0100] In summary, the perovskite films prepared by this invention exhibit a dense morphology and a lower defect state density compared to traditional methods. The technical solution provided by this invention eliminates the need for anti-solvents. Current mainstream perovskite preparation processes involve using specific solvents to drip onto the rotating perovskite film surface during spin coating, which increases the complexity of perovskite preparation. The perovskite film preparation method provided by this invention does not involve an anti-solvent process; high-quality films can be obtained by sequentially heating and annealing after spin coating. Furthermore, this invention introduces a volatile TBP solution to optimize the crystallization process. The TBP completely evaporates during the final high-temperature annealing process, leaving no residue that could affect the long-term stability of the device.

[0101] The concentration range of 4-tert-butylpyridine disclosed in this invention can further improve the morphology of perovskite films, give the grains a suitable size range, and reduce the defect state density; and the number and size of crystal particles can be controlled by controlling the concentration of 4-tert-butylpyridine, so as to achieve controllable growth of perovskite crystals without the need for antisolvents.

[0102] The temperature range of the first annealing treatment in this invention not only needs to desorb the lead halide complexed with 4-tert-butylpyridine, but also needs to ensure that the lead halide bound to the solvent does not participate in film formation at this temperature. Based on the above requirements and considering the interaction characteristics between 4-tert-butylpyridine, lead halide and solvent, this invention proposes a preferred temperature range for the first annealing treatment. The temperature range of the second annealing treatment needs to promote crystal growth while ensuring that the 4-tert-butylpyridine in the system completely volatilizes and does not remain in the film. Based on the above considerations, this invention proposes a preferred temperature range for the second annealing treatment.

[0103] The present invention further discloses that the solvents for the precursor solution are preferably dimethyl sulfoxide and N,N-dimethylformamide, which have suitable binding forces with lead halide; and lead halide and cesium halide have suitable solubility in these two solvents.

[0104] The preparation method of the present invention can improve the band structure of perovskite. When the perovskite thin film prepared is used in perovskite solar cells, the valence band level of the perovskite thin film shifts upward and is closer to the hole transport layer, thereby achieving efficient charge extraction.

[0105] The perovskite solar cell provided by this invention has a photoelectric conversion efficiency of 16.5%, and no significant efficiency degradation was observed after 400 hours of storage in a nitrogen atmosphere, demonstrating good stability.

[0106] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0107] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0108] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A CsPbI x Br 3-x A method for preparing perovskite thin films, where x = 0~3, characterized in that... include: A perovskite precursor solution comprising lead halide, cesium halide, 4-tert-butylpyridine and a solvent is provided, wherein the concentration of 4-tert-butylpyridine in the perovskite precursor solution is 1%-20% v / v; The precursor solution is subjected to a film-forming treatment, followed by a first annealing treatment and a second annealing treatment in sequence, thereby obtaining CsPbI. x Br 3-x Perovskite thin films; The temperature of the first annealing treatment is 30-60℃, and the annealing time is 20s-10min; the temperature of the second annealing treatment is 200-350℃, and the annealing time is 5s-1h.

2. The preparation method according to claim 1, characterized in that: The solvent can combine with lead halide to form a complex.

3. The preparation method according to claim 1, characterized in that: The concentration of 4-tert-butylpyridine in the perovskite precursor solution is 1%-10% v / v.

4. The preparation method according to claim 3, characterized in that: The concentration of 4-tert-butylpyridine in the perovskite precursor solution is 4%-8% v / v.

5. The preparation method according to claim 2, characterized in that: The solvent includes at least one of dimethyl sulfoxide and N,N-dimethylformamide.

6. The preparation method according to claim 5, characterized in that: The solvent includes dimethyl sulfoxide.

7. The preparation method according to claim 1, characterized in that: The lead halide includes PbI2 and / or PbBr2; and / or, the cesium halide includes CsI and / or CsBr.

8. The preparation method according to claim 1, characterized in that: The molar ratio of lead halide to cesium halide is 1:0.9~1.

1.

9. The preparation method according to claim 1, characterized in that: The film-forming process includes uniformly coating the precursor solution onto the substrate surface to form a liquid film.

10. The preparation method according to claim 9, characterized in that: The precursor solution is uniformly coated onto the substrate using a spin coating method, wherein the spin coating includes a first spin coating process and a second spin coating process.

11. The preparation method according to claim 10, characterized in that: The spin coating speed for the first spin coating process is 500~1500 rpm, and the spin coating time is 5~10s.

12. The preparation method according to claim 10, characterized in that: The spin coating speed for the second spin coating process is 2000~4000 rpm, and the spin coating time is 80s~100s.

13. CsPbI obtained by the preparation method according to any one of claims 1 to 12 x Br 3-x Perovskite thin films.

14. The CsPbI according to claim 13 x Br 3-x Perovskite thin films, characterized in that: The CsPbI x Br 3-x The perovskite grain size in the perovskite thin film is 0.5 μm to 3 μm.

15. The CsPbI as described in claim 13 or 14 x Br 3-x Applications of perovskite thin films in the fabrication of perovskite solar cells, photodetectors, lighting devices, or display devices.

16. A perovskite solar cell, comprising conductive glass, an electron transport layer, a perovskite active layer, a hole transport layer, and a metal electrode, characterized in that: The perovskite active layer comprises the CsPbI as described in claim 13 or 14. x Br 3-x Perovskite thin films.

17. The perovskite solar cell according to claim 16, characterized in that: The conductive glass includes ITO and / or FTO.

18. The perovskite solar cell according to claim 16, characterized in that: The electron transport layer includes at least one of TiO2, ZnO, and SnO2.

19. The perovskite solar cell according to claim 16, characterized in that: The hole transport layer includes at least one of Spiro-OMeTAD, PTAA, P3HT, and CuSCN.

20. The perovskite solar cell according to claim 19, characterized in that: The hole transport layer includes Spiro-OMeTAD.

21. The perovskite solar cell according to claim 16, characterized in that: The metal electrode includes at least one of Ag electrode, Al electrode, Au electrode and Cu electrode.

22. The perovskite solar cell according to any one of claims 16-21, characterized in that: The perovskite solar cell has a conversion efficiency of 16.5% or higher.

23. A method for preparing a perovskite solar cell, characterized in that, include: An electron transport layer is formed on the conductive glass; The CsPbI group is formed on the side of the electron transport layer away from the conductive glass using the preparation method according to any one of claims 1 to 12. x Br 3-x Perovskite thin films; In the CsPbI x Br 3-x A hole transport layer is formed on the side of the perovskite thin film away from the electron transport layer; A metal electrode is formed on the hole transport layer.

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