Design of Inorganic Pb-free Double-perovskite<i> </i>Halides for Optoelectronic Applications

Pb-based halide perovskites AMX₃ (prototype CH₃NH₃PbI₃) have recently attracted much interest for optoelectronic applications, yet two key impediments need to be resolved: the intrinsic material instability (e.g., towards decomposition) and the toxicity due to water soluble Pb²⁺. We address these issues by exploiting the idea of “cation-transmutation” in tetrahedral semiconductors to design stable inorganic Pb-free halide perovskites with appropriate direct band gaps. The idea is to convert two divalent Pb²⁺ ions in A₂Pb₂X₆ into one monovalent M⁺ and one trivalent M³⁺ ions, thus forming a rich class of quaternary halide double-perovskites A₂[M⁺M³⁺]X₆ structures [JACS 139, 2630 (2017), JACS 139, 6718 (2017)]. With optoelectronic-functionality-directed materials screening, we identify a series of optimal materials with intrinsic thermodynamic stability, and favorable optoelectronic properties (e.g., band gaps, carrier effective masses, and excitons binding energies) as promising candidates to replace Pb-based halide perovskites. Several of our proposed compounds have been verified by experimental synthesis.