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Abstract:

During the past year, halide double perovskites attracted attention as potential lead-free alternatives to Pb-based halide perovskites. However, none of the compounds discovered so far can match the optoelectronic properties of MAPbI3 (MA = CH3NH3). Here we argue that, from the electronic structure viewpoint, the only option to make Pb-free double perovskites retaining the remarkable properties of MAPbI3 is to combine In and Bi as B(+) and B(3+) cations, respectively. While inorganic double perovskites such as Cs2InBiX6 were found to be unstable due to In(+) oxidizing into In(3+), we show that the +1 oxidation state of In becomes progressively more stable as the A-site cation changes from K to Cs. Hence, we propose the use of MA and FA [FA = CH(NH2)2] to stabilize A2InBiBr6 double perovskites. We show that the optoelectronic properties of A2InBiBr6 are remarkably similar to those of MAPbI3, and explore the mixed-cation (Cs/MA/FA)2InBiBr6 halide double perovskites.