Synergistic stabilization of lead halide perovskites by univalent cations under electric field stress

Abstract

The low operational stability of perovskite solar cells, primarily caused by ion migration under photogenerated electric fields, remains one of the key barriers to their practical deployment. In the present paper, we report the results of a comparative study of the field-induced aging dynamics in lead iodide perovskite films with different univalent cation compositions: MAPbI₃, FAPbI₃, Cs_0.15FA_0.85PbI₃ and Cs_0.1MA_0.15FA_0.75PbI₃. By employing a complementary suite of techniques including IR s-SNOM, PL microscopy, SEM/EDX, and ToF-SIMS mapping, alongside AIMD simulations of hydrogen on the surface of FAPbI₃, we visualized the dynamic behavior of cations and anions during aging and identified the corresponding reaction products. The simulations revealed that surface-based hydrogen can destabilize the lattice by abstracting surface iodine, in agreement with experimentally observed degradation of FAPbI₃, where volatile species are produced. It is shown that the formamidinium cations have a significantly higher resistance to electric fields when compared to the methylammonium cations. Univalent cation induced phase segregation has been observed for multication perovskite films upon electric field exposure. The results obtained provide a deep insight into the mechanistic pathways of the electrodegradation of differently composed lead halide perovskites and pave the way for the rational design of a new generation of perovskite absorber materials that can resist electric field-induced damage.