Effect of Additives AX (A = FA, MA, Cs, Rb, NH4, X = Cl, Br, I) in FAPbI3 on Photovoltaic Parameters of Perovskite Solar Cells

Herein, the dependence of photovoltaic performance on the additives of FAX (X = Cl, Br, and I, FA = formamidinium) and ACl [A = methylammonium (MA), Cs, Rb, and NH 4 ] in FAPbI 3 ‐based perovskite solar cells (PSCs) is reported. Effect of concentration on photovoltaic parameters is first screened for each additive, from which optimal concentration is determined with respect to the pristine without additive. Power conversion efficiency (PCE) is significantly improved from 16.55% to 22.51% after adding 20 mol% FACl in the perovskite precursor solution, whereas moderate increase in PCE to 20.08% and 19.97% is observed for FABr and FAI, respectively, indicating an important role of chloride. MACl and CsCl improved PCE to 20.81% and 20.59%, respectively, which is, however, inferior to FACl. A significantly increased carrier lifetime by treating FACl is responsible for the best performance. Energy dispersive X‐ray spectroscopy shows that chloride in the additive FACl is not incorporated in grain but placed on the grain boundary, which plays an important role in passivating iodide‐deficient grain boundary. The FACl additive has benefits over other additives because it cannot change the bandgap of FAPbI 3 .