Triple‐Additive Strategy for Enhanced Material and Device Stability in Perovskite Solar Cells

Abstract The stability of the FAPbI₃ perovskite phase is significantly affected by internal strain. In this report, additives in the perovskite precursor solution are designed to prevent local lattice mismatch of the resulting perovskite layer. Instead of using a conventional methylammonium chloride (Control), triple additives (Target) are introduced by considering ion association and formation energy. The out‐of‐plane orientation for the (100) plane is less pronounced by the triple additives compared to the Control film with a highly enhanced preferred orientation, which reduces the strain gradient and the Pb─I bond distance. Moreover, the anisotropic atomic‐level lattice strain along (111) plane, associated with the α‐to‐δ phase transition, is more uniformly distributed by the triple additives. The triple‐additive strategy demonstrates exceptional phase stability under relative humidity as high as 90% and the International Summit on Organic Photovoltaic Stability (ISOS)‐L‐2 protocol. The device lifetime measured under the ISOS‐D‐1 condition shows that the Target perovskite solar cell (PSC) maintains 95% of its initial power conversion efficiency (PCE) for over 8000 h, and the best PCE of 24.50% is achieved.