Interfacial Passivation for Perovskite Solar Cells: The Effects of the Functional Group in Phenethylammonium Iodide

Defect passivation is an effective method to improve the performance of perovskite solar cells. In this study, four phenethylammonium iodides featuring different functional groups directly linking to the benzene ring are introduced on the surface of perovskite films ((FAPbI3)1–x(MAPbBr3–yCly)x) to investigate their passivation effects. It is found that the electron density of the benzene ring has significant influence on the interfacial passivation: phenethylammonium iodide with electron-donating groups (methoxyl and methyl) present favorable passivation effects, while the salt with electron-withdrawing group (nitro) delivers undesirable impacts. The passivation is attributed to the electrostatic interaction between the benzene ring and the undercoordinated Pb2+ ions. The salt-treated films are employed to fabricate solar cells, and an efficiency of 22.98% is achieved. In addition, the treated device shows good long-term stability for 1000 h of storage in a dark, ambient environment.