Perovskite thin film based on phosphonic small molecules, preparation method thereof and photovoltaic cell application

Abstract

The application belongs to the technical field of perovskite solar cells, and discloses a phosphonic acid group-containing small-molecule additive perovskite thin film and a preparation method thereof and a trans perovskite solar cell, which comprises the following steps: S1, dissolving metal halide and organic ammonium halide in an organic solvent to prepare a perovskite ABX3 precursor solution, wherein A is Cs + , methylamine ion or formamidinium ion, B is Pb 2+ , and X is halogen ion, including Cl ‑ , Br ‑ , and I ‑ ; S2, adding a phosphonic acid group-containing small-molecule additive to the perovskite precursor solution in S1 to prepare a precursor solution containing small-molecule doping; and S3, depositing the precursor solution containing small-molecule doping in S2 on a conductive substrate to obtain a perovskite thin film after annealing. The application uses a phosphonic acid group-containing small-molecule additive to realize the preparation of a trans perovskite solar cell device without a hole transport layer. The solar cell device has excellent photovoltaic performance, and the photoelectric conversion efficiency is more than 25%, and the device shows excellent long-term stability.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cell technology, specifically relating to a perovskite thin film based on phosphate-based small molecules, its preparation method, and its application in photovoltaic cells. Background Technology

[0002] Solar energy is inexhaustible and an important clean and renewable energy source. Solar cells, based on the photovoltaic effect, can directly convert solar energy into electricity needed by modern society, attracting widespread attention from academia and industry. Currently, the development of perovskite solar cells (PSCs) is particularly noteworthy, with single-junction devices achieving a photoelectric conversion efficiency of 25.7%, making them one of the most promising photovoltaic technologies. Typically, the hole transport layer (HTL) is an indispensable and crucial component for obtaining efficient and stable PSCs. Its function includes extracting holes generated by the perovskite light-absorbing layer and transporting them to the corresponding electrodes, thereby improving hole transport efficiency and reducing recombination losses during transport. In inverted PSCs, the HTL serves as the growth substrate for the perovskite thin film and also significantly influences the crystal quality of the perovskite film, ultimately determining the photovoltaic performance of the perovskite solar cell. However, the introduction of the hole transport layer also brings many problems, such as voltage loss due to interfacial energy level mismatch, poor wettability affecting perovskite film crystallization, high-temperature processing, and increased manufacturing costs due to increased process complexity. Therefore, developing efficient and stable perovskite solar cells without a hole transport layer is of great significance. Existing technologies mainly focus on the modulation of perovskite energy levels to achieve energy level matching with ITO conductive glass substrates. However, surface defects at the interface cannot be effectively passivated, which leads to particularly severe energy loss at the interface due to carrier recombination, resulting in stagnant device performance for a long time. Summary of the Invention

[0003] The purpose of this invention is to provide a perovskite thin film based on the extrusion effect of phosphate-based small molecules. Addressing the many problems existing in traditional hole transport layers, this invention utilizes the top-down crystallization extrusion process of the perovskite thin film to form a hole extraction interface at its lower interface, replacing the traditional HTL. The introduced phosphate-based small molecule additives achieve a synergistic passivation effect on bulk and interface defects through coordination interactions during the perovskite crystallization process, thereby obtaining a highly efficient and stable inverted perovskite solar cell device.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing perovskite thin films containing phosphate-based small molecule additives includes the following steps:

[0006] S1. A perovskite ABX3 precursor solution is prepared by dissolving a metal halide and an organic ammonium salt halide in an organic solvent, wherein A is Cs. +, Methylamine ion or formamidinium ion, B is Pb 2+ X is a halide ion, including Cl- - , Br - I - ;

[0007] S2. Add phosphate-based small molecule additives to the perovskite precursor solution of S1 to prepare a precursor solution containing small molecule doping.

[0008] S3. The precursor solution containing small molecule dopant from S2 is deposited on a conductive substrate and annealed to obtain a perovskite film.

[0009] Tin-based perovskites have divalent tin ions that are easily oxidized, which places special requirements on additives. For example, the additives should preferably be passivating agents with reducing properties. Lead-based perovskites do not have this concern, and this solution is applicable to lead-based perovskites.

[0010] Furthermore, the chemical structure of the phosphate-based small molecule additive is GLA, where G is a functional group, including phenoxazine, phenothiazine, acridine and their derivatives, L is a linking group, and A is an anchoring group. The structure of the additive is as follows:

[0011]

[0012] Wherein, R is (C1-C4) alkyl or halogen; L is (C2-C12) alkyl; and A is a phosphate group.

[0013] Furthermore, the phosphate-based small molecule additive is selected from one of the following structures:

[0014]

[0015] The preferred phosphate-based small molecule additive is 2BrDMAcPA (4-[2,7-dibromo-9,9-dimethylacridin-10(9H)yl]butylphosphoric acid).

[0016] Furthermore, the concentration of the phosphate-based small molecule additive in the precursor solution is 0.1–10 mg / mL.

[0017] Furthermore, the phosphate-based small molecule additive added to the perovskite precursor solution of S1 requires heating and shaking to dissolve it, followed by stirring at room temperature overnight to ensure that the small molecule additive has sufficient time to undergo a coordination reaction with lead halide.

[0018] Furthermore, the organic solvent is selected from at least one of DMSO, DMF, NMP, THF, and isopropanol.

[0019] Furthermore, the conductive substrate is indium tin oxide (ITO) conductive glass, fluorine-doped tin dioxide (FTO) conductive glass, flexible conductive substrate PET / ITO, or PEN / ITO.

[0020] Furthermore, the deposition method is an antisolvent-assisted spin coating method, wherein the antisolvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, butanol, isobutanol, 2-butanol, pentanol, isoamyl alcohol, ethylene glycol, glycerol, acetone, butanone, methyl ether, anisole, diethyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol hexyl ether, acetonitrile, acrylonitrile, chloroform, chlorobenzene, dichlorobenzene, toluene, m-xylene, trimethylbenzene, trifluorotoluene, ethyl acetate, carbon tetrachloride, dichloroethane, carbon disulfide, and cyclohexane, with chlorobenzene being the preferred antisolvent.

[0021] Furthermore, the annealing is performed in one step or two steps. The temperature of the one-step annealing is 80-150°C and the annealing time is 1-60 minutes. The two-step annealing is performed by first annealing at 50-100°C for 1-60 minutes and then annealing at 90-150°C for 1-60 minutes.

[0022] A perovskite thin film containing phosphate-based small molecule additives, wherein the perovskite thin film is prepared by the above-described preparation method.

[0023] An inverted perovskite solar cell includes a perovskite thin film, an electron transport layer on the perovskite thin film, and a metal electrode. The perovskite thin film is as described above. The preparation method of the inverted perovskite solar cell is as follows: first, a perovskite thin film doped with phosphate-based small molecule additives is prepared on a conductive substrate by the above method, and then the electron transport layer and the metal electrode are deposited sequentially to assemble an inverted perovskite solar cell device without a hole transport layer.

[0024] The electron transport layer is a fullerene and its derivatives, including one or more of C60, PC61BM, PC71BM and ICBA.

[0025] The metal electrode is a metal material with a high work function, including gold, silver, copper, aluminum, or conductive carbon material; the conductive carbon material includes carbon nanoparticles, carbon black, carbon nanotubes, graphene, graphyne, and mixtures thereof.

[0026] The present invention has the following beneficial effects:

[0027] This invention, considering the passivation of perovskite interfaces, creatively incorporates self-assembled hole-selective contact materials into the perovskite precursor solution. This approach offers multiple benefits: First, the phosphate groups in the phosphate-based small molecule additive can passivate defects at the perovskite interface, especially uncoordinated lead ion defects. Second, during antisolvent-assisted crystallization, due to the varying strengths of coordination, the additive molecules are repelled and squeezed out during top-down crystallization, accumulating at the lower interface of the perovskite film to form a hole extraction interface, replacing the traditional HTL. The squeezed-out organic molecules exhibit a gradient distribution in the vertical direction, enhancing interface hole extraction and synergistically passivating perovskite bulk and surface defects. Third, the preparation step of the hole transport layer is omitted.

[0028] Depositing an electron transport layer and metal electrodes on a perovskite thin film and assembling them into an inverted perovskite solar cell device is a simple and low-cost process that yields a highly efficient and stable inverted perovskite solar cell with a photoelectric conversion efficiency exceeding 25% without a hole transport layer.

[0029] This invention involves directly adding a phosphate-based small-molecule additive to a perovskite precursor solution, followed by thorough shaking to dissolve the additive before use. During this process, the additive preferentially coordinates with lead halide in the precursor solution. The molecularly coordinated lead halide concentrates at grain boundaries during perovskite crystallization and diffuses downwards into the ITO substrate. Based on this molecular extrusion mechanism, a hole extraction interface is ultimately formed at the perovskite substrate interface, achieving multiple functions including defect passivation and enhanced hole extraction. Simultaneously, the crystallinity of the perovskite film is enhanced, with almost no grain boundaries in the vertical orientation. This helps reduce carrier transport losses at grain boundaries, resulting in higher device current. This method of directly adding a phosphate-based small-molecule additive to the precursor solution can further improve the photoelectric conversion efficiency of solar cells.

[0030] This invention selects lead-based perovskite thin films and uses phosphate-based small molecule additives with phenothiazine, phenotoxazine, and acridine skeletons. Compared with traditional carbazole-based small molecule additives, the additive molecules used in this invention are more compatible with lead-based perovskite in terms of energy level structure. At the same time, the introduction of S atoms, O atoms, and sterically hindered methyl groups enables fine-tuning of the interaction between functional groups and lead ions, achieving better results than carbazole-based additives. Attached Figure Description

[0031] Figure 1 XRD patterns of the perovskite films prepared in Example 1 before and after additive doping;

[0032] Figure 2 SEM images of the upper surface, cross-section, and lower surface of the perovskite film prepared in Example 1 before and after additive doping;

[0033] Figure 3The steady-state fluorescence (PL) spectra of the perovskite films prepared in Example 1 before and after additive doping are shown.

[0034] Figure 4 The image shows the time-resolved fluorescence (TRPL) spectra of the perovskite films prepared in Example 1 before and after additive doping.

[0035] Figure 5 The infrared absorption spectrum of the 2BrDMAcPA and PbI2-2BrDMAcPA complex is shown below.

[0036] Figure 6 AFM images and infrared AFM images of the upper surface, lower surface, and ITO substrate after removing the perovskite film of the additive-doped perovskite film prepared in Example 1.

[0037] Figure 7 This is a structural diagram of an inverted perovskite solar cell device without a hole transport layer, as shown in Example 2.

[0038] Figure 8 The JV curve of the inverted perovskite solar cell without a hole transport layer in Example 2 is shown.

[0039] Figure 9 The long-term stability curve of the inverted perovskite solar cell without a hole transport layer in Example 2 is shown.

[0040] Figure 10 The JV curve of the inverted perovskite solar cell without a hole transport layer based on 2MePTZPA in Example 3 is shown.

[0041] Figure 11 The JV curve is shown for the inverted perovskite solar cell without a hole transport layer based on 2ClPXZPA in Example 4. Detailed Implementation

[0042] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0043] Example 1

[0044] Phosphate-based small molecule additive 2BrDMAcPA-doped perovskite thin films

[0045] (1) Dissolve lead iodide, lead bromide, formamidine iodide, and methyl bromide in a DMF / DMSO (v / v, 4 / 1) mixed solvent, keeping the lead iodide concentration at 1.1 mol / L and the iodine / bromine and formamidine / methyl bromide ratios at 0.85 / 0.15 mol / L; heat and stir at 60°C for 1 hour, then add 35 μL of cesium iodide (2 mol / L, DMSO) solution and continue stirring for 1 hour to obtain perovskite precursor solution 1;

[0046] (2) Then, the phosphoric acid-based small molecule additive 2BrDMAcPA was added to the above perovskite precursor solution 1 to make its concentration 4mg / mL. After heating and shaking to dissolve, it was stirred at room temperature overnight to obtain the doped perovskite precursor solution 2.

[0047] (3) Perovskite films were prepared on a conductive ITO glass substrate by antisolvent-assisted spin coating of precursor solutions 1 and 2 respectively. The spin coating parameters were 4000 rpm and 35 seconds. Chlorobenzene was added as an antisolvent 25 seconds before the end of spin coating. The films were then annealed at 100°C for 60 minutes to obtain perovskite films.

[0048] The perovskite films before and after doping with phosphate-based small molecule additives were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), such as... Figure 1 and Figure 2 As shown in the figure, PVK represents perovskite.

[0049] Compared with pure perovskite, 2BrDMAcPA-doped perovskite has higher diffraction peak intensity and the lead iodide signal disappears, indicating that the perovskite crystal quality is significantly improved after molecular doping.

[0050] SEM images of the top surface and cross-section of the perovskite film show that the grain size increases and the grain boundaries decrease in the vertical orientation after molecular doping. SEM images of the bottom interface show that, compared to pure perovskite, the molecularly doped perovskite exhibits molecular coating at the bottom interface. This demonstrates that the small phosphate molecules doped in the precursor solution are squeezed out to the lower interface during the top-down crystallization process of the perovskite film, thus forming a molecular coating layer that serves multiple functions, including interface defect passivation and hole extraction.

[0051] The above perovskite films were characterized and analyzed using steady-state fluorescence spectroscopy (PL) and time-resolved fluorescence spectroscopy (TRPL), such as... Figure 3 and Figure 4 As shown, the intensity and lifetime of the PL peak in the perovskite film doped with phosphate-based small molecule additives were significantly enhanced, indicating that the perovskite bulk phase and interface defects were effectively passivated.

[0052] Compare the infrared absorption spectra of 2BrDMAcPA and perovskite precursor solution 2, as follows: Figure 5As shown, 2BrDMAcPA preferentially coordinates with lead iodide in the precursor solution; the above perovskite film was analyzed by AFM and infrared AFM, as shown... Figure 6 As shown, (a), (b), and (c) are AFM images of the upper surface, lower surface, and ITO substrate after removing the perovskite film, and (d), (e), and (f) are infrared AFM images of the upper surface, lower surface, and ITO substrate after removing the perovskite film. After molecular coordination, lead iodide concentrates at the grain boundaries during the crystallization process of perovskite and diffuses from top to bottom into the ITO substrate. Based on this molecular extrusion mechanism, a hole extraction interface is finally formed at the bottom interface of the perovskite.

[0053] Example 2

[0054] Application of phosphate-based small molecule additive 2BrDMAcPA-doped perovskite thin films in inverted perovskite solar cell devices without hole transport layer

[0055] The structure of an inverse perovskite solar cell device without a hole transport layer is as follows: Figure 7 As shown, from bottom to top, the structure consists of ITO conductive glass, the 2BrDMAcPA-doped perovskite thin film prepared in Example 1, an electron transport layer (PCBM, BCP), and a silver electrode. The specific preparation method is as follows:

[0056] (1) Clean the ITO conductive glass in detergent, deionized water, acetone and isopropanol in sequence for 15 minutes, and dry it with nitrogen and ozone for 30 minutes before use.

[0057] (2) The perovskite precursor solution containing 2BrDMAcPA prepared in Example 1 was spin-coated onto an ITO glass substrate by antisolvent-assisted spin coating. The spin coating parameters were: 4000 rpm, 40 seconds, and antisolvent chlorobenzene was added dropwise in a suitable time window (10-20 seconds). Then, the perovskite film was obtained by heat annealing at 100°C for 60 minutes.

[0058] (3) Dissolve PCBM in chlorobenzene at 20 mg / mL, spin-coat to prepare an electron transport layer. Spin-coating parameters are 3000 rpm for 40 seconds, and then anneal at 100°C for 10 minutes.

[0059] (4) At a vacuum degree of 4×10 -4 Under Pa conditions, an 8 nm thick BCP and a 100 nm thick silver electrode were deposited on the surface of the PCBM to obtain an inverted perovskite solar cell device without a hole transport layer.

[0060] The fabricated inverse perovskite solar cell device without a hole transport layer was characterized and tested. The JV curve is shown below. Figure 8 As shown, the short-circuit current of the device during reverse scanning is 25.69 mA cm⁻¹.-2 The open-circuit voltage is 1.187V, the fill factor is 84.61%, and the photoelectric conversion efficiency reaches 25.80%. Furthermore, this inverted perovskite solar cell without a hole transport layer also exhibits excellent device stability, such as... Figure 9 As shown, after 1000 hours of continuous illumination, it still retains 96% of its initial efficiency.

[0061] Example 3

[0062] Perovskite thin films and inverted perovskite solar cells doped with phosphate-based small molecule additive 2MePTZPA

[0063] The specific preparation method is the same as in Example 1, except that the phosphate-based small molecule additive used in this example is 2MePTZPA. The prepared perovskite film containing 2MePTZPA exhibits higher crystal quality compared to the reference film.

[0064] A hole-transport layer-less inverted perovskite solar cell device using 2MePTZPA was fabricated according to Example 2. The device was characterized and tested; the JV curve is shown below. Figure 10 As shown. Under AM 1.5G simulated sunlight illumination, the short-circuit current of the device during reverse scanning is 23.61 mA cm⁻¹. -2 The open-circuit voltage is 1.19V, the fill factor is 81.61%, and the photoelectric conversion efficiency is 22.93%.

[0065] Example 4

[0066] Perovskite thin films and inverted perovskite solar cells doped with phosphate-based small molecule additive 2ClPXZPA

[0067] The specific preparation method is the same as in Example 1, except that the phosphoric acid-based small molecule additive used in this example is 2ClPXZPA.

[0068] An inverted perovskite solar cell device without a hole transport layer using 2ClPXZPA was fabricated according to Example 2. The device was characterized and tested; the JV curve is shown below. Figure 11 As shown. Under AM 1.5G simulated sunlight illumination, the short-circuit current of the device during reverse scanning is 23.36 mA cm⁻¹. -2 The open-circuit voltage is 1.18V, the fill factor is 80.48%, and the photoelectric conversion efficiency is 22.06%.

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing perovskite thin films containing phosphate-based small molecule additives, characterized in that, Includes the following steps: S1. A perovskite ABX3 precursor solution is prepared by dissolving a metal halide and an organic ammonium salt halide in an organic solvent, wherein A is Cs. + , Methylamine ion or formamidinium ion, B is Pb 2+ X is a halide ion; S2. Add phosphate-based small molecule additives to the perovskite precursor solution of S1 to prepare a precursor solution containing small molecule doping. S3. Deposit the precursor solution containing small molecule dopant from S2 onto a conductive substrate, and obtain a perovskite film after annealing. The phosphate-based small molecule additive is selected from one of the following structures: 。 2. The preparation method according to claim 1, characterized in that, The concentration of the phosphate-based small molecule additive in the precursor solution is 0.1~10 mg / mL.

3. The preparation method according to claim 1, characterized in that, The organic solvent is selected from at least one of DMSO, DMF, NMP, THF, and isopropanol.

4. The preparation method according to claim 1, characterized in that, The conductive substrate is indium tin oxide conductive glass, fluorine-doped tin dioxide conductive glass, flexible conductive substrate PET / ITO, or PEN / ITO.

5. The preparation method according to claim 1, characterized in that, The deposition method is an antisolvent-assisted spin coating method, wherein the antisolvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, butanol, isobutanol, 2-butanol, pentanol, isoamyl alcohol, ethylene glycol, glycerol, acetone, butanone, methyl ether, anisole, diethyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol hexyl ether, acetonitrile, acrylonitrile, chloroform, chlorobenzene, dichlorobenzene, toluene, m-xylene, trimethylbenzene, trifluorotoluene, ethyl acetate, carbon tetrachloride, dichloroethane, carbon disulfide, and cyclohexane.

6. The preparation method according to claim 1, characterized in that, The annealing is performed in one step or two steps. The temperature of the one-step annealing is 80~150℃ and the annealing time is 1~60 minutes. The two-step annealing is performed by first annealing at 50~100℃ for 1~60 minutes, and then annealing at 90~150℃ for 1~60 minutes.

7. A perovskite film containing a phosphate-based small molecule additive, wherein the perovskite film is prepared by the preparation method according to any one of claims 1 to 6.

8. An inverted perovskite solar cell, comprising a perovskite thin film, an electron transport layer on the perovskite thin film, and a metal electrode, wherein the perovskite thin film is as described in claim 7.

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