Role of defects in MAPbI₃ to modulate optical absorption, and solar efficiency

Methylammonium lead halide (MAPbI₃) perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead-toxicity, the role of Sn-substitution and Pb-vacancy (Pb-■) is addressed in regulating the stability and solar cell efficiency of MAPb_1-X-YSn_X■_YI₃ perovskite using hybrid density functional theory (DFT). We find, to reduce the Pb-content from pristine MAPbI₃, Sn-substitution has favorable thermodynamic stability than Pb-■. High optical absorption coefficient (red shifted) and maximum solar cell efficiency are obtained in
MAPb_1-X-YSn_X■_YI₃ for 0 ≤ X ≤ 0.5. The role of spin-orbit coupling (SOC) and electron self-interaction error are examined carefully. Despite SOC has a significant role in artificially shifting the electronic bands, it doesn't affect the relative hierarchy of formation energies of different defected configurations. However, electron self-interaction plays an important role in determining the same. We find a local/semi-local functional (e.g. PBE) gives a completely opposite trend to determine thermodynamic stability w.r.t HSE06+SOC.