Intercalation of Ammonium Cationic Ligands Enabled Grain Surface Passivation in Sequential-Deposited Perovskite Solar Cells

Solution-processed formamidinium lead iodide (FAPbI(3)) perovskite typically contains a high number of ionic defects that are intrinsically formed during film formation. To reduce the defects, postsynthetic 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, the use of 4-(trifluoromethyl)benzylammonium iodide (CF(3)BZAI) is demonstrated as a novel passivator additive for sequentially deposited perovskite films. Due to its unique molecular structure and trifluoromethyl (-CF3) moiety, CF(3)BZAI is expected to have enhanced adsorption with defect sites during the film formation. Owing to grain surface passivation, the CF(3)BZAI-intercalated FAPbI(3) (target) film has enhanced morphology and crystallinity as well as significantly fewer defects than the normal FAPbI(3) film. Interestingly, the intercalation of CF(3)BZAI passivators does not lead to the formation of a low-dimensional perovskite phase in FAPbI(3) films. The best perovskite solar cell (PSC) device based on the target film achieves a maximum efficiency of approximate to 22.4%, which is much higher than the efficiency (approximate to 20.7%) of the normal device. CF(3)BZAI-assisted grain surface passivation is a facile yet effective strategy to enhance the performance and stability of FAPbI(3)-based PSCs.

Automated summary

By using a novel passivator additive called 4-(trifluoromethyl)benzylammonium iodide (CF(3)BZAI), the morphology and crystallinity of perovskite films can be enhanced, and defects can be significantly reduced. Interestingly, the use of CF(3)BZAI does not lead to the formation of a low-dimensional perovskite phase.