Unexpected bowing band evolution in an all-inorganic CsSn 1- x Pb x Br 3 perovskite.

We theoretically investigated the structural and electronic properties of the all-inorganic perovskite CsSn 1- x Pb x Br 3 , compared with the mixed perovskite compound MA y Cs 1- y Sn 1- x Pb x Br 3 , based on first-principle calculations. It has been demonstrated that Pb and Sn atoms are inclined to occupy the lattice sites uniformly in the all-inorganic perovskite, and this is distinguished from the most stable configurations observed in the mixed Cs-MA system. It is interesting that small Sn atoms prefer to stay close to the large MA + cations, leading to smaller local structural distortion. Through spin-orbital coupling calculations, we found non-linear bowing band evolution in the all-inorganic mixed Sn-Pb system with a small bowing parameter ( b = 0.35), while the band gap of MA y Cs 1- y Sn 1- x Pb x Br 3 was clearly reduced as the ratio of MA was around 0.5 ( y ≥ 0.25). We determined the bowing band evolution in the mixed cation perovskites and the intrinsic electronic deficiency of the all-inorganic perovskite to obtain the optimal band gap.