First-principles calculations of structural, electronic, and optical properties of double perovskites Cs2Sn1-B I6 (B = Si, Ge; x = 0, 0.25, 0.50, 0.75, 1)

Abstract

• The effect of Si/Ge doping on the material properties of Cs 2 SnI 6 is studied. • The structural stability of Cs 2 SnI 6 is reduced by doping Si or Ge. • Cs 2 SnI 6 shows strong optical absorption coefficient in the visible light region. In this study, the structural stability, electronic and optical properties of all-inorganic mixed-metal double perovskites Cs 2 Sn 1- x B x I 6 (B = Si, Ge; x = 0, 0.25, 0.50, 0.75, 1) have been explored by using first-principles calculations. Our calculated results show that Cs 2 SnI 6 shows excellent stability, while Cs 2 SiI 6 and Cs 2 GeI 6 are unstable. Moreover, the structural stability of Cs 2 SnI 6 is reduced by doping Si or Ge. The predicted band gaps of the Cs 2 Sn 1- x Si x I 6 systems are in the range of 1.1–1.3 eV. The band gaps of the Cs 2 Sn 1- x Ge x I 6 systems decrease gradually with the increasing concentration of Ge doping. Cs 2 SnI 6 exhibits the highest optical absorption coefficient in the visible light region among the Cs 2 Sn 1- x Si x I 6 systems. The Cs 2 Sn 1- x Ge x I 6 systems show stronger absorption coefficients in the range of 500–1000 nm compared to the pure Cs 2 SnI 6 perovskite. Based on our calculated results, Cs 2 SnI 6 is expected to become the most promising candidate material for perovskite solar cells.