First Domino in the Structural Collapse of Perovskite CsPbI3 and Its Stabilizing Strategies

The retention of the photoactive phase is vital for inorganic CsPbI3 perovskite solar cells; however, the atomic‐level knowledge is currently elusive, leading to trial‐and‐error methods in experiments. In this study, proves that the kinetic process dominates the lifetime of CsPbI3, while the energetic difference, which is conventionally thought to be a dominant factor, only plays a secondary role. The defect—iodine vacancy (VI) can significantly lower the kinetic barriers and act as the seed of structural collapse in the corner‐sharing octahedral structure. Inspired by this, the success of B‐ and X‐site doping as well as strain engineering for stabilizing CsPbI3 arising from the suppression of VI are explained. Through comprehensively investigating thirty‐two and fifteen kinds of passivators substituting on the Pb and I site, respectively, on reducing the VI concentration and inhibiting its diffusion, proposed that the trivalent lanthanide cations, especially La3+ on Pb site, and highly electronegative anions with a small size on I site are proper doping candidates to enhance the stability of perovskite CsPbI3. The results provide a universal picture and guidance for engineering all‐inorganic perovskite CsPbI3 for elevated stability with the focus on inhibiting iodine vacancies. The defect—iodine vacancy significantly lowers the kinetic barrier and easily pushes down the first domino in the structural collapse of perovskite CsPbI3, serving as the seed for the undesired phase degradation, which process can be efficiently slowed down by applying strain and B/X‐site doping engineering to CsPbI3, with the suppression of iodine vacancies.