Stability, electronic, and optical properties of lead-free halide double perovskites ( CH 3 NH 3 ) 2 InBi X 6 ( X = halogen)

Recently developed halide double perovskites ${A}_{2}{M}^{+}{M}^{3+}{X}_{6}$ have attracted attention as potential lead-free perovskite solar cell absorbers. Here, the stability, electronic, and optical properties of the lead-free inorganic-organic hybrid double perovskites ${({\mathrm{CH}}_{3}{\mathrm{NH}}_{3})}_{2}\mathrm{InBi}{X}_{6}$ ($X$ = halogen) are studied based on density functional theory. By investigating the thermodynamic stability against decomposition, the ${({\mathrm{CH}}_{3}{\mathrm{NH}}_{3})}_{2}\mathrm{InBi}{X}_{6}$ double perovskites are shown to be stable. Furthermore, the use of a small magnitude of hydrostatic pressure is proposed to improve the thermodynamic stability of double perovskites ${({\mathrm{CH}}_{3}{\mathrm{NH}}_{3})}_{2}\mathrm{InBi}{X}_{6}$. Meanwhile, the calculated electronic band structures of ${({\mathrm{CH}}_{3}{\mathrm{NH}}_{3})}_{2}\mathrm{InBi}{X}_{6}$ double perovskites exhibit suitable direct band gaps, small carrier effective masses, and three-dimensional electronic dimensionality. This, in turn, leads to strong optical absorption. Both the electronic and optical features make double perovskites ${({\mathrm{CH}}_{3}{\mathrm{NH}}_{3})}_{2}\mathrm{InBi}{X}_{6}$ suitable for applications in optoelectronics.