Control Of Crystallization Behavior Of CH₃NH₃PbI₃ And Its Effect On The Stability Of PSCs

Perovskite solar cells have attracted the attention of many researchers at home and abroad because of their simple preparation process,including low cost,abundant raw materials and high efficiency.At present,perovskite solar cells are developing rapidly,but there are still many problems yet to be solved effectively,and the progress of commercialization is limited.Among them,the preparation of high-efficiency perovskite cellsneeds harsh experimental environment,poor stability,life span is far less than the crystalline silicon solar cells,which are inhibiting the development of perovskite solar cells.The results show that the properties of perovskite solar cells are mainly determined by the quality of perovskite thin films,high film coverage,large grain size and less defects of perovskite films,which are one of the necessary conditions for preparing high performance cells.Based on this,this article from improving perovskite film quality,improving device stability and extending cell life as the starting point,by optimizing the cell preparation process,adding additives and anti-solvent to improve the perovskite film quality,so as to enhance the efficiency,Improve the stability of the cells,and creatively put forward the freezing treatment method to improve efficiency and service life,and study the internal mechanism.The main conclusions are as follows:?1?A two-step perovskite film was prepared in air to study the effect of PbI₂ film preparation on the performance of CH₃NH₃PbI₃ thin films and cells.The results show that the coverage of CH₃NH₃PbI₃ film is not high when the concentration of PbI₂ is too low.When the PbI₂ concentration is too high,the grain size of the film is too small and the grain boundaries are too large.The annealing temperature of PbI₂ is too low and the residual amount of DMF solvent is more than that of CH₃NH₃PbI₃ film,When the annealing temperature of PbI₂ is too high,the CH₃NH₃PbI₃ film is decomposed.With the increase of PbI₂ annealing time,the cell efficiency first increases and then decreases.When the concentration of PbI₂ is 1 M,the annealing temperature is 130^oC and the annealing time is 15 min,the cell efficiency is the highest?8.93%?.?2?Based on the best PbI₂ thin film preparation process,water was added as an additive to the PbI₂ solution to study the effect of water content on the cell performance.The results show that excess water can inhibit the formation of CH₃NH₃PbI₃ and decompose the formed CH₃NH₃PbI₃,resulting in low film coverage,poor crystallinity and poor charge transport properties.Adding trace amounts of water can improve the film formation performance of CH₃NH₃PbI₃ thin films and improve the cell performance and photoelectric properties.When the water content is 2%,the optimal CH₃NH₃PbI₃thin film and the photoelectric properties of the cell are obtained.In this case,the series resistance of the cell is only 73?,and the photoelectric conversion efficiency is 10.2%.?3?In this paper,a two-step method was used to prepare perovskite solar cells.The effects of PEG addition on the quality of perovskite films and device self-repairing performance were studied.The PEG concentration,annealing temperature and annealing time of CH₃NH₃PbI₃ were also optimized.The results show that:PEG as an additive slows down the reaction rate of CH₃NH₃PbI₃ to obtain CH₃NH₃PbI₃ film with high surface coverage,good compactness and uniform grain size.In high humidity environment,the PEG-added cell has the ability of self-healing,the cell efficiency decreased from 9.50%to 6.9%,maintaining the original efficiency of 73%,compared with the non-PEG-based cells have greatly improved.In addition,the cell prepared by adding PEG has a lower cell efficiency decay ability,stored in air for 30 days,can maintain the original efficiency of 75%,much higher than the cell without PEG.When the molar ratio of CH₃NH₃I and PEG was 100:0.5,annealing at 45^oC for 45 min,the perovskite solar cells with the best performance parameters were prepared.The cell efficiency increased from 6.4%to 11.1%.?4?PbI₂ thin films rapidly formed a certain hole structure during the spin-coating process,and promoted the formation of CH₃NH₃PbI₃ thin films and decreased the amount of residual PbI₂.After anti-solvent treatment perovskite solar cells prepared with lower dark current and steady-state fluorescence intensity of different wavelengths of visible light absorption capacity has increased,the number of photo-generated carriers increased electron and hole The degree of recombination decreases,cell efficiency increases from 7.75%to 10.45%and is stored in air,cell efficiency decays more slowly.?5?Revealed the internal factors and external conditions of ice-induced cell efficiency improvement.Efficiency of the two factors is the storage of environmental humidity and freezing temperature,the cell needs to be sealed at a relative humidity of 30%,and placed in a-18^oC refrigerator for 24 h,after removing the cell temperature to be recovered to room temperature,Test the photoelectric properties of the cell.The results show that the interfacial contact between the cells is improved after the freezing process,mainly due to the decrease of the defects at the interface of TiO₂and CH₃NH₃PbI₃,which leads to the enhancement of internal charge transfer performance.The open circuit voltage increases from 0.93 V to 0.96 V and the fill factor from 49%to 53%,efficiency from8.34%to 9.23%,85%of the original efficiency of 10.85%.The same cell can be frozen many times,the cell efficiency decreased from 8%to 6%of the process,the cell life from 16 days to 47 days.