Solution-processed formamidinium lead iodide (FAPbI3) perovskite typically contains a high number of ionic defects that are intrinsically formed during film formation. To reduce the defects, which undermine the performance and stability of FAPbI3 films, post-synthetic surface passivation treatment is widely practiced. However, the practicality of the surface passivation approach is limited by the poor coverage and incomplete adsorption of passivators into the defective sites. Unprecedentedly, we demonstrate the use of 4-(trifluoromethyl)benzylammonium iodide (CF3BZAI) as a novel passivator additive for sequentially-deposited perovskite films. Due to its unique molecular structure and –CF3 moiety, CF3BZAI is expected to have enhanced adsorption with defect sites during the film formation. Owing to grain surface passivation, the CF3BZAI-intercalated FAPbI3 (target) film has enhanced morphology and crystallinity as well as significantly fewer defects than the normal FAPbI3 film. Interestingly, the intercalation of CF3BZAI passivators does not lead to the formation of a low-dimensional perovskite phase in FAPbI3 films. The best perovskite solar cell (PSC) device based on the target film achieved a maximum efficiency of ~22.4%, which is much higher than the efficiency (~20.7%) of the normal device. CF3BZAI-assisted grain surface passivation is a facile yet effective strategy to enhance the performance and stability of FAPbI3-based PSCs.
January 2023