The impact of halogens on the structural, electronic, and optical properties of vacancy-ordered double perovskites Rb2SeX6 (X=I, Br, Cl)

Lead-based perovskite materials have become one of the most widely used materials in the field of photovoltaics due to their excellent properties. However, concerns over lead toxicity and the stability of materials have prompted the search for alternative, eco-friendly, and stable perovskite materials. To address this need, our study conducts an in-depth analysis of the electronic and optical properties of the lead-free double perovskite materials Rb₂SeX₆ (X = Cl, Br, I) using first-principles calculations. The results indicate that Rb₂SeX₆ perovskites possess an indirect bandgap, with values of 3.26 eV, 2.52 eV and 1.39 eV for Rb₂SeCl₆/Br₆/I₆, respectively. Rb₂SeI₆ has larger dielectric function and superior absorption spectrum across the visible range than the other two materials. Thus, Rb₂SeI₆ has a promising future as a photoelectric material for solar cells. Rb₂SeCl₆ and Rb₂SeBr₆ also have the potential for use in photodetectors, light-emitting diodes and other optoelectronic devices.