Computational Screening of Homovalent Lead Substitution in Organic-Inorganic Halide Perovskites

Perovskite solar cells are gaining increasing popularity due to their unprecedented rise in power conversion efficiency. However, concerns over the potential environmental impact of CH3NH3PbI3 are stimulating experimental and theoretical searches for the replacement of lead by nontoxic elements. In this study we explore all homovalent metal ions which could substitute lead in a perovskite halide configuration by performing a systematic combinatorial search over the entire periodic table. Our screening process selects compounds based on two concurrent criteria: the stability of the compound in a perovskite structure and the band gap. Using these search criteria, we are able to reduce the number of possible compounds from 248 to 25, including 15 compounds which have not yet been proposed as semiconductors for optoelectronics. We identify Mg as a potential candidate for partial replacement of Pb and show that the band gap of hypothetical magnesium iodide perovskites is tunable over a range of 0.8 eV via the size of the A-site cation.