Lead-free double perovskites Cs 2 InCuCl 6 and (CH 3 NH 3 ) 2 InCuCl 6 : electronic, optical, and electrical properties.

Searching for alternatives to lead-containing metal halide perovskites, we explored the properties of indium-based inorganic double perovskites Cs ₂ InMX ₆ with M = Cu, Ag, Au and X = Cl, Br, I, and of its organic-inorganic hybrid derivative MA ₂ InCuCl ₆ (MA = CH ₃ NH ₃ ⁺ ) using computation within Kohn-Sham density functional theory. Among these compounds, Cs ₂ InCuCl ₆ and MA ₂ InCuCl ₆ were found to be potentially promising candidates for solar cells. Calculations with different functionals provided the direct band gap of Cs ₂ InCuCl ₆ between 1.05 and 1.73 eV. In contrast, MA ₂ InCuCl ₆ exhibits an indirect band gap between 1.31 and 2.09 eV depending on the choice of exchange-correlation functional. Cs ₂ InCuCl ₆ exhibits a much higher absorption coefficient than that calculated for c-Si and CdTe, common semiconductors for solar cells. Even MA ₂ InCuCl ₆ is predicted to have a higher absorption coefficient than c-Si and CdTe across the visible spectrum despite the fact that it is an indirect band gap material. The intrinsic charge carrier mobilities for Cs ₂ InCuCl ₆ along the L-Γ path are predicted to be comparable to those for MAPbI ₃ . Finally, we carried out calculations of the band edge positions for MA ₂ InCuCl ₆ and Cs ₂ InCuCl ₆ to offer guidance for solar cell heterojunction design and optimization. We conclude that Cs ₂ InCuCl ₆ and MA ₂ InCuCl ₆ are promising semiconductors for photovoltaic and optoelectronic applications.