Effect of Organic Chloride Additives on the Photovoltaic Performance of MA‐Free Cs0.1FA0.9PbI3 Perovskite Solar Cells

The use of chloride additives to achieve high performance in perovskite solar cells (PSCs) is extensively reported in perovskite research. However, few studies are dedicated to understanding and comparing the underlying effects of ammonium cations in organic chloride additives. Herein, the effect of ACl additives (A: ethylammonium [EA], propylammonium [PA], butylammonium [BA]), with increasing ammonium size, on the performance of MA‐free Cs 0.1 FA 0.9 PbI 3 PSCs is investigated. The obtained results indicate that Cl promotes the growth of large grains, while organic cations facilitate grain favorable orientation. Moreover, it is observed that EACl evaporates during thermal annealing despite the similar ionic size of EA to that of FA, which would lead to A‐site incorporation. However, PACl and BACl remain in final films, passivating grain boundaries. Moreover, by using double BACl–EACl additive, the films show considerably increased grain dimensions, passivated grain boundaries, and longer carrier lifetime. As a result, planar PSCs based on engineered Cs 0.1 FA 0.9 PbI 3 layers achieve higher power conversion efficiency of 20.98%, 20.07%, 19.64%, and 19.03% for BACl–EACl, BACl, PACl, and EACl, respectively, compared to 17.58%‐efficiency for control PSCs. Moreover, this additive‐based approach also increases moisture resistance of the Cs 0.1 FA 0.9 PbI 3 films, which consequently enhances the device ambient stability.