Lead-free double perovskites Cs2InCuCl6 and (CH3NH3)2InCuCl6: Electronic, optical, and electrical properties

Searching for alternatives to lead-containing metal halide perovskites, we explored the properties of indium-based inorganic double perovskites Cs2InMX6 with M = Cu, Ag, Au and X = Cl, Br, I, and of its organic-inorganic hybrid derivative MA2InCuCl6 (MA = CH3NH3+) using computation within Kohn-Sham density functional theory. Among these compounds, Cs2InCuCl6 and MA2InCuCl6 were found to be potentially promising candidates for solar cells. Calculations with different functionals provided the direct band gap of Cs2InCuCl6 between 1.05 and 1.73 eV. In contrast, MA2InCuCl6 exhibits an indirect band gap between 1.31 and 2.09 eV depending on the choice of exchange-correlation functional. Cs2InCuCl6 exhibits a much higher absorption coefficient than that calculated for c-Si and CdTe, common semiconductors for solar cells. Even MA2InCuCl6 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 Cs2InCuCl6 along the L-Γ path are predicted to be comparable to those for MAPbI3. Finally, we carried out calculations of the band edge positions for MA2InCuCl6 and Cs2InCuCl6 to offer guidance for solar cell heterojunction design and optimization. We conclude that Cs2InCuCl6 and MA2InCuCl6 are promising semiconductors for photovoltaic and optoelectronic applications.