Preparation method of perovskite photoactive layer based on formate double additives

Abstract

The invention relates to the technical field of photoelectric functional materials, and discloses a preparation method of a perovskite photoactive layer based on formate double additives, which comprises the following steps: adding cesium formate and formamidine formate into a perovskite precursor solution to prepare a doped precursor solution, and then carrying out spin coating and annealing on the doped precursor solution on a substrate to obtain the perovskite photoactive layer based on the formate double additives. Preparing a perovskite light active layer; the molar ratio of the cesium formate additive to the formamidine formate additive is controlled to be consistent with the ratio of the cation component of the perovskite, so that the influence of the additives on the cation component of the perovskite is avoided. The double-doping strategy adopted by the invention effectively increases the grain size of perovskite, reduces the number of grain boundaries, and significantly improves the quality of the perovskite thin film, thereby effectively improving the photoelectric performance of the perovskite solar cell, improving the fill factor and photoelectric conversion efficiency of a photovoltaic device, and improving the long-term stability of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic functional materials, and in particular to a method for preparing a perovskite photoactive layer based on a formate double additive. Background Art

[0002] Perovskite solar cells stand out for their high photoelectric conversion efficiency and low-cost production process. In recent years, their laboratory photoelectric conversion efficiency has rapidly increased from an initial 3.8% to 26.7%, making perovskite materials a strong competitor to traditional silicon cells. Furthermore, the preparation process for perovskite cells is relatively simple, and they can be produced using a variety of techniques, including solution and vapor phase processes. This significantly reduces production costs and lays the foundation for their large-scale application.

[0003] Wide-bandgap perovskite solar cells (WBGs) can be combined with other narrow-bandgap subcells to create tandem solar cells, demonstrating remarkable potential. The perovskite bandgap can be tuned by varying the halogen composition at the X position within the perovskite ABX3 structure. Wide-bandgap perovskites are typically obtained by introducing Cs at the A position and Br at the X position. Despite their numerous advantages, WBGs also face numerous challenges and issues. High Br content significantly reduces the crystalline quality of WBG perovskite films. During perovskite crystallization, the preferential self-aggregation of Br-rich phases leads to an uneven distribution of halides in the resulting films, resulting in more defect states than conventional bandgap perovskites, thus compromising the photoelectric performance and stability of photovoltaic devices. Furthermore, WBGs typically have smaller grain sizes, which means more grain boundaries within the films serve as non-radiative recombination centers. This increases the density of defect states and ion migration channels, making them susceptible to environmental degradation and significantly reducing the efficiency and lifetime of solar cells. Therefore, improving the crystalline quality of WBGs has become an urgent challenge for the industry. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the present invention provides a method for preparing a perovskite photoactive layer based on a formate double additive.

[0005] A method for preparing a perovskite photoactive layer based on formate double additives, a) dissolving a bromine source, an iodine source, a lead source, a cesium source, and a formamidine source in an organic solvent to form a perovskite precursor solution; b) adding a dual additive of cesium formate and formamidine formate to the perovskite precursor solution, wherein the molar ratio of cesium formate to formamidine formate is consistent with the molar ratio of cesium to formamidine in the perovskite precursor solution, and stirring until completely dissolved to form a doping precursor solution; c) spin coating the doping precursor solution on a substrate to form a thin film; d) performing annealing treatment on the film to obtain a perovskite photoactive layer.

[0006] Furthermore, the formate in the cesium formate and formamidine formate forms a coordination complex with lead ions through the C=O group, thereby regulating the perovskite crystallization process, reducing nucleation sites, promoting the growth of large-sized grains, reducing the number of grain boundaries, and improving the photoelectric performance and stability of the perovskite film.

[0007] Furthermore, the bromine source, iodine source, lead source, cesium source and formamidine source are lead bromide, lead iodide, cesium iodide and formamidine hydroiodide, and the chemical ratio of each element is Cs:FA:Pb:I:Br=0.25:0.75:1:1.8:1.2.

[0008] Furthermore, the organic solvent is one of N,N-dimethylformamide and dimethyl sulfoxide or a mixture of the two.

[0009] Furthermore, in step c), the spin coating speed is 6000 rpm and the spin coating time is 35 seconds. In step d), the annealing temperature is 100° C. and the annealing time is 15 minutes.

[0010] Furthermore, the substrate is a transparent conductive oxide substrate with a hole transport layer, and the hole transport layer includes nickel oxide or a composite layer of nickel oxide and 2PACz.

[0011] Furthermore, in step b), the molar ratio of cesium formate to formamidine formate is 1:3, and the molar ratio of formate to lead is controlled within the range of 0.01 to 0.20.

[0012] Furthermore, the perovskite photoactive layer is used to prepare a perovskite solar cell, and the structure of the solar cell includes or .

[0013] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: The molar ratio of the two additives, cesium formate and formamidine formate, is controlled to be consistent with the ratio of the cationic components of the perovskite, thereby avoiding the influence of the additives on the cationic components of the perovskite.

[0014] C=O in formate and Pb 2+ The complex phase formed by the coordination can effectively slow down the nucleation and crystallization process of perovskite in the precursor. With the release of formate during annealing, the absorption peak related to C=O will disappear, the complex phase disappears, and fewer nucleation sites help to form larger perovskite grains.

[0015] The dual-doping strategy adopted in the present invention effectively increases the grain size of perovskite, reduces the number of grain boundaries, and significantly improves the quality of perovskite films, thereby effectively improving the photoelectric performance of perovskite solar cells, increasing the fill factor and photoelectric conversion efficiency of photovoltaic devices, and enhancing the long-term stability of the devices.

[0016] The raw materials of the present invention are easy to obtain, the process can be implemented without major changes on the existing basis, and the process is highly feasible and low in cost.

[0017] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 is the surface morphology of the corresponding perovskite film at different doping amounts in the present invention; Figure 2 1. Fourier transform infrared spectra of the CsFa & FAFa mixture and different perovskite films before and after annealing in the present invention; Figure 3 The figure shows the device structure of the perovskite solar cell prepared by the present invention and a comparison of the current density-voltage curves of the champion efficiency device before and after CsFa & FAFa doping; Figure 4 The device structure diagram of the solar cell prepared by the present invention with the buried interface and surface interface modified on the perovskite layer and the current density-voltage curve comparison diagram of the champion efficiency device before and after CsFa & FAFa doping; Figure 5 It is a box-type statistical comparison diagram of photovoltaic parameters of the perovskite solar cell of the present invention; Figure 6 This is a comparison chart of the long-term stability of the unpackaged device of the present invention stored in a nitrogen environment. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0021] This invention aims to introduce formate ions into a wide-bandgap perovskite precursor solution using dual additives: CsFa (cesium formate) and FAFa (formamidine formate). This modulates the crystallization process, reduces perovskite nucleation sites, and promotes the formation of perovskite films with large grains. To avoid significant effects of the additives on the original perovskite composition, the molar ratio of CsFa to FAFa is controlled to be consistent with the A-site cation composition of the original perovskite. To demonstrate the feasibility of this dual-doping strategy, wide-bandgap perovskite solar cells with and without buried and surface interface modifications were prepared for comparative testing.

[0022] A method for preparing a perovskite photoactive layer based on formate ion dual additives, Weigh the solute using a precision balance and add it to a mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) or any organic solvent thereof, and stir until completely dissolved to form a perovskite precursor solution; The solutes are lead bromide, cesium iodide, lead iodide and formamidine hydroiodide. The amount of solute added satisfies the chemical ratio of Cs:FA:Pb:I:Br=0.25:0.75:1:1.8:1.2.

[0023] CsFa & FAFa dual doping is carried out in a wide bandgap perovskite precursor solution, wherein the molecular structure of CsFa is ; The molecular structure of the FAFa is ; Wherein Fa is formate.

[0024] CsFa and FAFa were weighed using a precision balance, dissolved in the perovskite precursor solution, and stirred until completely dissolved to form a CsFa & FAFa solution.

[0025] When weighing CsFa and FAFa, the molar ratio is controlled and kept consistent with the ratio of Cs to FA in the perovskite precursor solution. The total addition amount is controlled by the molar ratio of Fa to Pb, and the control range is 0.01~0.20.

[0026] The above perovskite precursor solution and CsFa&FAFa solutions with different concentrations were spin-coated at 6000 rpm for 35 seconds and annealed at 100°C for 15 minutes to prepare a perovskite photoactive layer.

[0027] Example 1 Weigh PbI20.3782g, PbBr20.4404g, CsI 0.1300g, FAI 0.2580g and dissolve them in The perovskite precursor solution is formed after being fully dissolved in 2 ml of DMF or DMSO solvent.

[0028] 0.5 mg of CsFa and 0.76 mg of FAFa (Fa / Pb molar ratio = 0.0225) were weighed using a precision balance, added to 500 μL of the perovskite precursor solution, and stirred until completely dissolved to prepare the CsFa & FAFa solution of Example 1.

[0029] In this embodiment, the spin coating process of the perovskite active layer thin film is as follows: a rotation speed of 6000 rpm, a spin coating time of 35 seconds, an annealing temperature of 100° C., and an annealing time of 15 minutes.

[0030] Example 2 The preparation method of Example 1 was adopted, except that 1 mg of CsFa and 1.52 mg of FAFa (Fa / Pb molar ratio = 0.0449) were weighed using a precision balance, added to 500 μL of the perovskite precursor solution, and stirred until completely dissolved, thereby preparing the CsFa & FAFa solution of Example 2.

[0031] Example 3 The preparation method of Example 1 was adopted, except that 2 mg of CsFa and 3.04 mg of FAFa (Fa / Pb molar ratio = 0.0898) were weighed using a precision balance, added to 500 μL of the perovskite precursor solution, and stirred until completely dissolved, thereby preparing the CsFa & FAFa solution of Example 3.

[0032] Example 4 The preparation method of Example 1 was adopted, except that 3 mg of CsFa and 4.56 mg of FAFa (Fa / Pb molar ratio = 0.1347) were weighed using a precision balance, added to 500 μL of the perovskite precursor solution, and stirred until completely dissolved, to prepare the CsFa & FAFa solution of Example 4.

[0033] Comparative Example The perovskite photoactive layer of the comparative example was prepared by directly using the perovskite precursor solution without adding CsFa and FAFa.

[0034] In this embodiment, the spin coating process of the perovskite active layer thin film is as follows: a rotation speed of 6000 rpm, a spin coating time of 35 seconds, an annealing temperature of 100° C., and an annealing time of 15 minutes.

[0035] The wide bandgap perovskite component prepared in each embodiment is Cs 0.25 FA 0.75 Pb(I 0.6 Br 0.4 )3, the band gap is about 1.79eV, and the molar ratio of Cs to FA is maintained at 1:3 in the embodiment.

[0036] The CsFa & FAFa dual doping can change the surface morphology of the perovskite film. The perovskite film before and after the dual doping treatment with different concentrations was tested by scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown, the undoped perovskite film exhibits smaller grain size and poor density. After dual doping with CsFa and FAFa at different Fa / Pb molar ratios, the perovskite grain size increases. The film in Example 3 exhibits the best density, and the reduced number of grain boundaries effectively reduces non-radiative recombination at the grain boundaries.

[0037] The C=O in the CsFa&FAFa dual additive can react with Pb 2+ The present invention conducted Fourier transform infrared spectroscopy tests on the CsFa & FAFa dual additives, the perovskite film before and after annealing, and the perovskite film before and after annealing with dual doping treatment. The results are as follows Figure 2 As shown. CsFa & FAFa dual additives at 1588.69 cm -1 There is a vibration peak near the 1560.86 cm-1. The spectral trends of the undoped perovskite film before and after annealing are similar. The double-doped perovskite film before annealing has a peak at 1560.86 cm-1. -1 The absorption peak appears near the PbO2, which disappears after annealing. It can be seen that after the perovskite precursor solution is doped with double, the lone pair electrons provided by the C=O on the formate group react with the PbO2. 2+ Coordination, forming a complex phase, changes the electron distribution around the O atom, resulting in the red shift of the stretching vibration peak of the C=O group. 2+ The complex phase formed by the coordination can effectively slow down the nucleation and crystallization process of perovskite in the precursor. With the release of formate during annealing, the absorption peak related to C=O will disappear, the complex phase disappears, and fewer nucleation sites help to form larger perovskite grains.

[0038] The CsFa & FAFa dual-doping strategy is helpful to improve the device performance of perovskite solar cells. x / Perovskite / PC 61BM / BCP / Ag structured perovskite solar cells were tested for current density-voltage. Figure 3 Compared with the control example device, the example 3 device achieved the highest efficiency of 12.38%, and the corresponding fill factor, open circuit voltage, and short circuit current were significantly improved.

[0039] Figure 3 (a) shows the device structure of the prepared perovskite solar cell. Figure 3 (b) shows the relationship between the current density and voltage curves of the champion efficiency device before and after doping with different concentrations of CsFa & FAFa.

[0040] Figure 4 (a) shows the device structure of a solar cell with modified bottom and surface interfaces of the perovskite layer; Figure 4 (b) shows the relationship between the current density and voltage curves of the champion efficiency device before and after doping with different concentrations of CsFa & FAFa.

[0041] Figure 5 Box plots of photovoltaic parameters of perovskite solar cells are shown, namely: (a) short-circuit current; (b) open-circuit voltage; (c) fill factor; and (d) photoelectric conversion efficiency.

[0042] Applying CsFa&FAFa dual-doping strategy to ITO / NiO x / 2PACz / Perovskite / PEAI / PC 61 BM / BCP / Ag structured perovskite solar cells and current density-voltage tests, such as Figure 4 As shown, the device of Example 3 achieved a champion efficiency of 17.83%, corresponding to a fill factor of 82.21%, an open circuit voltage of 1283 mV, and a current of 16.90 mA / cm 2 In comparison, the top efficiency of the control example device is only 17.09%, the corresponding fill factor is 81.15%, the open circuit voltage is 1283mV, and the short circuit current is 16.40mA / cm 2 The photovoltaic parameters of perovskite solar cells before and after the CsFa&FAFa dual-doping strategy were statistically analyzed, such as Figure 5 As shown, the device of Example 3 exhibits a higher fill factor and short-circuit current, and its larger grain size and fewer grain boundaries play a crucial role.

[0043] Figure 6 The figure shows the long-term stability test results of unpackaged devices stored in a nitrogen environment.

[0044] The CsFa&FAFa dual-doping strategy is helpful to improve the stability of perovskite solar cells. Figure 6 As shown, stability testing of unpackaged photovoltaic devices in a nitrogen environment revealed that after approximately 1600 hours of storage, the efficiency of the device in Example 3 remained at 84% of its initial value, while the efficiency of the device in the control example was only 72% of its initial value. The dual-doping improves the quality of the perovskite film and reduces the number of grain boundaries, effectively reducing the ion migration channels associated with grain boundary defects and the number of reactive sites that can cause device aging, resulting in better long-term device stability.

[0045] The present invention introduces a formate dual additive (CsFa & FAFa) with the same ratio as the wide bandgap perovskite cation component into the perovskite precursor solution to achieve CsFa & FAFa dual doping and regulate the crystallization process of the perovskite. 2+ The formation of complex phases delays the crystallization process of perovskite and reduces the nucleation sites. In the subsequent annealing process, formate escapes and eventually forms larger perovskite grains, effectively reducing the number of grain boundaries. The present invention overcomes the disadvantage of wide bandgap perovskites with small grains. The larger grain size means fewer grain boundaries in the film, so the grain boundary-induced non-radiative recombination and ion migration are greatly reduced, which helps the device achieve long-term stability. By preparing ITO / NiO x / Perovskite / PC 61 BM / BCP / Ag structure and ITO / NiO x / 2PACz / Perovskite / PEAI / PC 61 The feasibility of wide-bandgap perovskite solar cells with a BM / BCP / Ag structure was verified. Comparative experimental results showed that the dual-doping strategy significantly improved the device's photoelectric conversion efficiency. Stability tracking tests on unpackaged devices revealed that the dual-doping strategy exhibited better long-term stability.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a perovskite photoactive layer based on a formate double additive, characterized in that: a) dissolving a bromine source, an iodine source, a lead source, a cesium source, and a formamidine source in an organic solvent to form a perovskite precursor solution; b) adding a dual additive of cesium formate and formamidine formate to the perovskite precursor solution, wherein the molar ratio of cesium formate to formamidine formate is consistent with the molar ratio of cesium to formamidine in the perovskite precursor solution, and stirring until completely dissolved to form a doping precursor solution; c) spin coating the doping precursor solution on a substrate to form a thin film; d) performing annealing treatment on the film to obtain a perovskite photoactive layer.

2. The method for preparing a perovskite photoactive layer based on a formate double additive according to claim 1, characterized in that: The formate in the cesium formate and formamidine formate forms a coordination complex with lead ions through the C=O group, thereby regulating the perovskite crystallization process, reducing nucleation sites, promoting the growth of large-sized grains, reducing the number of grain boundaries, and improving the photoelectric performance and stability of the perovskite film.

3. The method for preparing a perovskite photoactive layer based on a formate double additive according to claim 1, characterized in that: The bromine source, iodine source, lead source, cesium source and formamidine source are lead bromide, lead iodide, cesium iodide and formamidine hydroiodide, and the chemical ratio of each element is Cs:FA:Pb:I:Br=0.25:0.75:1:1.8:1.

2.

4. The method for preparing a perovskite photoactive layer based on a formate double additive according to claim 1, characterized in that: The organic solvent is one of N,N-dimethylformamide and dimethyl sulfoxide or a mixture of the two.

5. The method for preparing a perovskite photoactive layer based on formate double additives according to claim 1, characterized in that: The spin coating speed in step c) is 6000 rpm, and the spin coating time is 35 seconds. In step d), the annealing temperature is 100° C. and the annealing time is 15 minutes.

6. The method for preparing a perovskite photoactive layer based on formate double additives according to claim 1, characterized in that: The substrate is a transparent conductive oxide substrate with a hole transport layer, and the hole transport layer includes nickel oxide or a composite layer of nickel oxide and 2PACz.

7. The method for preparing a perovskite photoactive layer based on formate double additives according to claim 1, characterized in that: The molar ratio of cesium formate to formamidine formate in step b) is 1:3, and the molar ratio of formate to lead is controlled at 0.01 to 0.

20.

8. The method for preparing a perovskite photoactive layer based on formate double additives according to claim 1, characterized in that: The perovskite photoactive layer is used to prepare a perovskite solar cell, and the structure of the solar cell includes or .

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