Ab-initio Calculations of Structure and Electronic Properties of the Ternary Halide perovskite CsSnBr3 in Its Three Phases: Comparative Study

Perovskites are very interesting for applications such as optoelectronic devices emitting light, such as OLEDs and lasers. On the other hand, one can consider using these perovskites in a very special architecture: the tandem cells. The principle of these tandem cells is to put in series two types of absorbers to optimize the absorption of the solar spectrum and thus increase the efficiency of the cells: the perovskites could make it possible to increase the collection of the UV part of the solar spectrum. Many perovskite crystals (ABX3) have been discovered to present second order properties for NLO, they undergo phase transitions in which they transform into slightly disordered structures of the original crystals. Perovskite crystal CsSnBr3 undergoes three successive phase transitions at T = 19.1 and 26°C. The crystal symmetry is sequentially transformed from rhombohedral to monoclinic then to cubic with a decreasing temperature, and this phase transition influences the structural properties and consequently the electronic and optical properties of this material. The results found for the perovskite cubic structure have been compared with experimental values ??and other theoretical works and they are in good agreement, but concerning the monoclinic structure, our results consist of a prediction. The calculation of the electronic properties shows the semi-conductor character of this material since there is a small spacing of the valence (Br-4p5) and conduction (Sn-5p2) bands which is estimated at Eg = 0.5375 eV in the cubic structure. This gap energy plays a key role in evaluating the use and yield of this material in solar cells.