Defect evolution of iodine vacancy and related strain modulation in all-inorganic halide perovskites

Vacancy related defects play a crucial role in optoelectronic properties and carrier transport for photovoltaic materials, especially for its structural evolution becoming non-radiative defects induced by strain. Thus far, the evolution phenomena of vacancy defects in halide perovskite triggered by energy or strain have not been systematically investigated. Herein, we study the change in defect levels occurred in different inorganic perovskite systems and the situation caused by strain in varied strength based on density functional theory calculations. We discover that VI deep levels are easily transformed from shallow levels due to the formation of Pb–Pb dimers and octahedral distortion in all-inorganic perovskites, especially in CsPbI3. Moreover, strain can be quantitatively applied to control the suppression or enhancement of the formation of dimer in CsBI3 (B = Pb/Ge) perovskites. Eventually, our calculation results unravel that the defect physics of VI defect and the formation mechanism of non-radiative center in all inorganic perovskites, which depends on the strain strength and the accompanying octahedral distortion. The strain modulation and its quantitation effect on defect evolution of dominant vacancy map a pioneering route toward fabricating high performance inorganic photovoltaics.