Direct Evidence of Ion Diffusion for the Silver‐Electrode‐Induced Thermal Degradation of Inverted Perovskite Solar Cells

Perovskite solar cells (PSCs) have recently demonstrated high efficiencies of over 22%, but the thermal stability is still a major challenge for commercialization. In this work, the thermal degradation process of the inverted structured PSCs induced by the silver electrode is thoroughly investigated. Elemental depth profiles indicate that iodide and methylammonium ions diffuse through the electron‐trasnporting layer and accumulate at the Ag inner surface. The driving force of forming AgI then facilitates the ions extraction. Variations on the morphology and current mapping of the MAPbI₃ thin films upon thermal treatment reveal that the loss of ions occurs at the grain boundaries and leads to the reconstruction of grain domains. Consequently, the deteriorated MAPbI₃ thin film, the poor electron extraction, and the generation of AgI barrier result in the degradation of efficiencies. These direct evidences provide in‐depth understanding of the effect of thermal stress on the devices, offering both experimental support and theoretical guidance for the improvement on the thermal stability of the inverted PSCs.