The Role of Defects and Grain Boundaries in the Electronic Structures of Hybrid and Inorganic Tin Iodide Perovskites: a DFT Study

Perovskite have recently become a topic of intense interest in the field of material science due to their promising applications as light harvesting materials in solar cell devices. The champion perovskite at this time is CH₃NH₃PbI₃ (MAPbI₃), however there is a major concern with the toxicity of the lead atom. Using first principles density functional theory (DFT) calculations, we examine the electronic properties of point defects and grain boundaries (GBs) in two tin-based perovskite alternatives, MASnI₃ and CsSnI₃. We find evidence that defects and GBs in both hybrid and inorganic perovskites are beneficial to electronic performance due to intrinsic p-doping without the generation of deep states. We also show that MASnI₃ is intrinsically less stable than CsSnI₃ according to chemical potential diagram and formation energy comparisons. We also provide evidence to support experimental observations of charge collection and separation at the GB due to band bending at the interface. Furthermore, we find wider bandgaps at the GB, pointing to a synergistic effect between charge collection and increased charge carrier lifetime at the interface.