The Effect of Hydrophobicity of Ammonium Salts on Stability of Quasi‐2D Perovskite Materials in Moist Condition

Abstract With the potential of achieving high efficiency and low production costs, perovskite solar cells (PSCs) have attracted great attention. However, their unstableness under moist condition has retarded the commercial development. Recently, 2D perovskites have received a lot of attention due to their high moisture resistance. In this work, four quasi 2D quasi perovskites are prepared, then their stability under moist condition is investigated. The surface morphology, crystal structure, optical properties, and photovoltaic performance are measured. Among the four quasi‐2D perovskites, (C 6 H 5 CH 2 NH 3 ) 2 (FA) 8 Pb 9 I 28 has the best performance: uniform and dense film, extremely well‐oriented crystal structure, strong absorption, and a high power conversion efficiency (PCE) of 17.40%. The aging tests show that quasi‐2D perovskites are more stable under moist conditions than FAPbI 3 is. The (C 6 H 5 CH 2 NH 3 ) 2 (FA) 8 Pb 9 I 28 quasi‐2D perovskite devices exhibit high humidity stability, maintaining 80% of the starting PCE after 500 h under 80% relative humidity. Compared with other quasi‐2D perovskites, (C 6 H 5 CH 2 NH 3 ) 2 (FA) 8 Pb 9 I 28 has the highest humidity stability, due to their strongest hydrophobicity from C 6 H 5 CH 2 NH 3 + . This work demonstrates that the properties of perovskite materials can be modified by adding different ammonium salts into FAPbI 3 . Thus, by introducing ammonium salts with high hydrophobic properties the fabrication of highly efficient and stable 2D PSCs may be possible.