Accelerated formation of iodine vacancies in CH₃NH₃PbI₃ perovskites: The impact of oxygen and charges

Defects in CH₃NH₃PbI₃ perovskites, oxygen species in the air, and local charges play a significant role in the long-term stability of perovskites. However, the interplay of these factors are complex and their role in the degradation of perovskites at the atomistic level is not well understood. By using density functional theory calculations and chemical bonding analysis, we study the effect of oxygen and local charges on the degradation of perovskites. We find that the easier formation of I vacancies upon oxygen and the accelerated degradation of CH₃NH₃PbI₃ by excess electrons via the formation of peroxide species. The creation of peroxide disintegrates the lattice of perovskites on the surfaces and possibly induces a cascade of degradation reactions that eventually destruct the perovskite lattices. We further demonstrate that the addition of holes are beneficial to prevent the formation of the peroxide, therefore can potentially improve the stability of the perovskites. (Figure presented.).