Lead-free Halide Perovskites via Functionality-directed Materials Screening*

Hybrid organic-inorganic halide perovskites with the prototype material of CH$_3$NH$_3$PbI$_3$ have recently attracted much interest as low-cost and high-performance photovoltaic absorbers but one would like to improve their stability and get rid of toxic Pb. We used photovoltaic-functionality-directed materials screening approach to rationally design via first-principles DFT calculations Pb-free halide perovskites. Screening criteria involve thermodynamic and crystallographic stability, as well as solar band gaps, light carrier effective masses, exciton binding, etc. We considered both single atomic substitutions in AMX$_3$ normal perovskites (altering chemical constituents of A, M and X individually) as well as double substitution of 2M into B+C in A$_2$BCX$_6$ double-perovskites. Chemical trends in phase stabilities and optoelectronic properties are discussed with some promising cases exhibiting solar cell efficiencies comparable to that of CH$_3$NH$_3$PbI$_3$.