Lattice strain suppresses point defect formation in halide perovskites

We computationally investigate the impact of crystal strain on the formation of native point defects likely to be formed in halide perovskites; A-site cation antisite (I-A), Pb antisite (I-Pb), A-site cation vacany (V-A), I vacancy (V-I), Pb vacancy (V-Pb), and I interstitial (1). We systematically identify compressive and tensile strain to CsPbI3, FAPbI(3), and MAPbI(3) perovskite structures. We observe that while each type of defect has a unique behaviour, overall, the defect formation in FAPbI(3) is much more sensitive to the strain. The compressive strain can enhance the formation energy of neutral I-pb and I-I up to 15% for FAPbI(3), depending on the growth conditions. We show that the strain not only controls the formation of defects but also their transition levels in the band gap: A deep level can be transformed into a shallow level by the strain. We anticipate that tailoring the lattice strain can be used as a defect passivation mechanism for future studies.