Grain Boundaries Are Strong Sinks for Native defects in Methylammonium Lead Iodide Perovskite

The organometal halide perovskites (OMHPs), and in particular methylammonium lead triiodide perovskite (MAPbI₃, MA=CH₃NH₃), are attracting intense interest due to their unprecedented rapid increase in the solar efficiency in the past few years. We use density functional theory (DFT) with corrections due to van der Waals interactions and spin-orbit coupling, in conjunction with a thermodynamic approach to determine the stability and electronic properties of all native point defects, and their interplays with Σ5-(210) grain boundary (GB) in MAPbI₃. The transition levels of charged defects are investigated with the inclusion of electrostatic charge corrections due to fictitious long-range interactions. We find that the GB region is a sink for most of the native defects under different synthesis conditions. For the crystalline MAPbI₃ and the Σ5-(210) GB, we find respectively that only the p-type antisite defects MA_I and Pb_I, where I replaces MA and Pb, introduce midgap transition levels and both are relatively stable under I-rich conditions. Hence, I-poor conditions are more preferable for synthesizing polycrystalline MAPbI₃ layers with defects that have electronically benign character.