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

Structural, electrical, and optical properties, as well as the thermal stability, of lead free mixed halide perovskites, Cs2InBr5-yXy center dot H2O (X = Cl, I; y = 0, 1, 2, 3, 4, 5) and Cs2InBr6-x center dot 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 center dot 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 center dot H2O. The absorption spectra were also calculated to evaluate optical properties of Cs2InBr5-yXy center dot H2O, which presents an obvious red-shift for I-doped perovskites in the visible region, while a blueshift for Cl-doped perovskites. The formation energies of Cs2InBr5-yXy center dot H2O were calculated and the obtained negative values determined their good thermodynamic stability, except Cs2InBrI4 center dot H2O and Cs2InI5 center dot H2O with the extremely small positive values. In addition, the influence of the amount of crystal water on the properties of Cs2InBr6-x center dot xH2O was also considered. The defect formation energies of Cs2InBr6-x center dot xH2O were calculated and the obtained negative values indicate their appropriate stability. In brief, Cs2InBr3I2 center dot H2O and Cs2InBr4 center dot 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.

Automated summary

The study investigated the structural, electrical, and optical properties, as well as the thermal stability of lead-free mixed halide perovskites using first principles calculations. It found that I-doped perovskites exhibit a red-shift in the visible region, while Cl-doped perovskites show a blue-shift in absorption spectra. Two optimal candidates for photovoltaic applications were identified.