Structural, electrical, optical properties and stability of Cs2InBr5-yXy·H2O (X = Cl, I, y = 0, 1, 2, 3, 4, 5) perovskites: the first principles investigation

Abstract

Structural, electrical, and optical properties, as well as the thermal stability, of lead free mixed halide perovskites, Cs2InBr5-yXy·H2O (X = Cl, I; y = 0, 1, 2, 3, 4, 5) and Cs2InBr6-x·xH2O (x = 1, 2, 3, 4) were investigated using first principles calculation. The structural stability of all studied pervoskites has been estimated by the calculation of structural parameters, Goldschmidt tolerance factor, and the octahedral factor. The obtained band gap of I-doped Cs2InBr5-yIy·H2O systems are 2.049, 1.726, 1.581, 1.475 and 1.272 eV with y =1, 2, 3, 4, 5, lower than 2.391 eV of Cs2InBr5·H2O. The absorption spectra were also calculated to evaluate optical properties of Cs2InBr5-yXy·H2O, which presents an obvious red-shift for I-doped perovskites in the visible region, while a blue-shift for Cl-doped perovskites. The formation energies of Cs2InBr5-yXy·H2O were calculated and the obtained negative values determined their good thermodynamic stability, except Cs2InBrI4·H2O and Cs2InI5·H2O with the extremely small positive values. In addition, the influence of the amount of crystal water on the properties of Cs2InBr6-x·xH2O was also considered. The defect formation energies of Cs2InBr6-x·xH2O were calculated and the obtained negative values indicate their appropriate stability. In brief, Cs2InBr3I2·H2O and Cs2InBr4·2H2O are two optimal candidates among all the studied systems for the photovoltaic application. These results provide some ideas for understanding various properties of mixed halide perovskites.