Regulation Of Perovskite Thin-film Quality And Photovoltaic Performance Via Reaction Temperature Optimization And Additive Engineering

Organic-inorganic hybrid perovskite solar cells have attracted much attention due to their excellent optoelectronic properties and low preparation cost.The efficiency of perovskite solar cells is affected by many factors including the quality of perovskite films and charge transfer layers.Among them,perovskite films with grain size,phase purity,crystallinity,defect density and optical properties as quality indicators have a particularly great impact on device performance.Therefore,the major target of the thesis is to regulate perovskite crystallization process,passivate defects in perovskite films,and thereby further enhance device performance.By controlling the reaction temperature and introducing passivators,high-quality perovskite films and high-efficiency PSCs were obtained.The main contents and results are as follows:（1）Improving the quality of perovskite films and cell performance by adjusting the reaction temperature,and the effect of reaction temperature on perovskite films with different compositions comparatively studied.Herein we have systematically investigated the effect of reaction temperature（controlled by changing the temperature of ammonium salt solution in this work）on film quality and cell performance of single and mixed cation/halide perovskite systems,namely（FAPb I₃）_1-x（MAPb Br₃）_x,FA_xMA_1-xPb I₃ and MAPb I₃（FA:formamidine,CH（NH₂）₂）.The results show that an appropriate increase in the reaction temperature is favorable for obtaining high-quality perovskite films and improving cell performance,while an excessively high reaction temperature can cause the generation of non-perovskite phase and the reduction of cell performance.In addition,the mixed-cation/halide perovskite systems are more susceptible to reaction temperature relative to the single cation/halide perovskite with respect to phase purity and grain size.The optimal ammonium salt solution temperatures for preparing（FAPb I₃）_1-x（MAPb Br₃）_x,FA_xMA_1-xPb I₃ and MAPb I₃films and corresponding solar cells were found to be around 30,30 and 55℃,respectively,in our two-step deposition process.The（FAPb I₃）_1-x（MAPb Br₃）_x based device prepared with ammonium precursor solution at 30℃ delivered the highest efficiency of 18.09%,which can be attributed to the reduced defect density in the perovskite film and the accelerated charge extraction at interfaces.（2）Improving the quality of perovskite films and cell performance by passivating defects.Aiming at decreasing defects in the interior and on the surface and grain boundaries of perovskite films and improving film quality and device performance,acetylsalicylic acid（ASA）was introduced into the lead salt solution as a passivation agent to prepare perovskite films and solar cells via a two-step method in the work.The impacts of acetylsalicylic acid on film quality and cell performance were investigated by means of optical spectroscopy,scanning electron microscopy and various electrical measurements.Our results show that the introduction of appropriate amount of ASA can obviously increase the grain size of perovskite films and effectively reduce the defect density of perovskite films via Lewis acid-base interaction.The solar cell prepared with the incorporation of 2.5 mmol/L ASA achieved the highest photoelectric conversion efficiency of 19.83%,appreciably outperforming the control device（17.47%）.This work demonstrates the good passivation effect of acetylsalicylic acid on defects in perovskite films.