Role of defects in MAPbI₃ to modulate optical absorption and solar cell 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-■) are addressed in regulating the stability and solar cell efficiency of MAPb_1−X−YSn_X■_YI₃ perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron's self-interaction error are examined carefully. We find to reduce the Pb content from pristine MAPbI₃, Sn substitution has a more favorable thermodynamic stability than creating Pb-■. Moreover, on substituting Sn, due to strong s−p and p−p couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the bandgap (direct). This further helps us to get a high optical absorption coefficient (redshifted) and maximum solar cell efficiency in MAPb_1−XSn_XI₃ for 0<X≤0.5.