The modulation of the electrical and optical properties of Cs2TiBr6 by doping

Abstract

As one of the most promising light absorbing-materials, all inorganic lead-free perovskite Cs₂TiBr₆ has obvious advantages, such as outstanding photoelectric properties, an adjustable band gap, and environmental friendliness. However, the wide band gap limits its application in optoelectronic devices. Here, the modulation of its electrical and optical properties by doping is investigated based on first-principles density functional theory (DFT). The elements Si, Ge, and Te are used to substitute Ti, and Br is substituted by Cl and I with different concentrations, respectively. Compared with the pristine material, Cs₂Ti_0.5Ge_0.5Br₆ has better physical stability, and a smaller band gap (1.33 eV). The light absorption is broadened obviously because of the states of 4s from Ge. Similarly, the band gap of Cs₂Ti(Br_0.75I_0.25)₆ is 1.29 eV and its visible light absorption was enhanced due to the 5p electron of the I atom. Furthermore, the quasi-direct band gap of the original material is adjusted to the direct band gap, which approaches the optimum band gap. Our results indicate that doping modulation will greatly improve the prospects of the Cs₂TiBr₆ perovskite for application in solar cells.