Visualizing the Structure‐Property Nexus of Wide‐Bandgap Perovskite Solar Cells under Thermal Stress

Wide‐bandgap perovskite solar cells (PSCs) toward tandem photovoltaic applications are confronted with the challenge of device thermal stability, which motivates to figure out a thorough cognition of wide‐bandgap PSCs under thermal stress, using in situ atomic‐resolved transmission electron microscopy (TEM) tools combing with photovoltaic performance characterizations of these devices. The in situ dynamic process of morphology‐dependent defects formation at initial thermal stage and their proliferations in perovskites as the temperature increased are captured. Meanwhile, considerable iodine enables to diffuse into the hole‐transport‐layer along the damaged perovskite surface, which significantly degrade device performance and stability. With more intense thermal treatment, atomistic phase transition reveals the perovskite transform to PbI2 along the topo‐coherent interface of PbI2/perovskite. In conjunction with density functional theory calculations, a mutual inducement mechanism of perovskite surface damage and iodide diffusion is proposed to account for the structure‐property nexus of wide‐bandgap PSCs under thermal stress. The entire interpretation also guided to develop a thermal‐stable monolithic perovskite/silicon tandem solar cell.