A promising all-inorganic double perovskite Rb2TiBr6 for photovoltaic applications: Insight from first-principles calculations

Abstract

Lead halide perovskites have been considered as the most promising materials for solar cell applications. However, the issues of the instability and the toxic lead are still major drawbacks to hinder their wide usage. In this study, the structural stability, electronic and optical properties of A2TiX6 (A ​= ​In, K, Rb, Cs; X ​= ​Cl, Br, I) and Rb2TiI6-xYx (Y = Cl, Br; x ​= ​2, 4) are investigated by using first-principles calculations. The calculated lattice constants of Ti-based halide perovskites are consistent well with the available experimental values. According to our calculated results, Rb2TiBr6 shows high stability, and it is also a ductile material. The calculated band gap of Rb2TiBr6 is 1.59 ​eV, which is suitable for single-junction solar cells. An ideal band gap can be obtained by doping Cl or Br and applying pressure. Although Rb2TiI2Cl4 and Rb2TiI2Br4 have also suitable band gaps, the poor stability of these materials are found. At the pressure of 8.66 ​GPa, an ideal band gap value (1.31 ​eV) is obtained for Rb2TiBr6, and this material is also dynamically stable. Rb2TiBr6 exhibits high optical absorption coefficient in the whole visible light range. We expect that this findings can provide theoretical guidance for further experimental research to explore the photovoltaic performance of Rb2TiBr6 in the field of perovskite solar cells.