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

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 A(2)TiX(6) (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.

Automated summary

Lead halide perovskites are considered highly promising materials for solar cell applications, but issues related to stability and toxicity of lead remain major drawbacks. In this study, Rb2TiBr6 was found to exhibit high stability, ductility, and a suitable band gap for single-junction solar cells. Doping and applying pressure can help achieve an ideal band gap value for this material.