The bandgap regulation and optical properties of alloyed Cs2NaSbX6 (X=Cl, Br, I) systems with first principle method

Lead-free halide double perovskite materials have the advantages of optical absorption efficiency, carrier mobility, adjustable bandgap, defect tolerance, wide variety of raw materials, low price, etc. which were used as many environmental substitutes for lead-based halide perovskite materials. In this work, we investigated the Cs2NaSbX6 (X = Cl, Br, I) systems with elements (K, In and Au) alloying and the photoelectric properties of the materials with the first principle method. The research results show that when the alloying concentration was 50%, all bandgaps of given double perovskite materials turned from indirect to direct bandgap. Especially, the alloying Cs2Na0.5K0.5SbI6's and the Cs2NaSb0.5In0.5I6's bandgaps were 1.92eVand 1.46eV, respectively. The energy values are well match within the range of applications as light absorbing materials. Optical properties show that the peak position of the absorption spectrum of the alloying elements of the Cs2NaSbX6 (X = Cl, Br, I) system is associated with the types of halogen elements at the X site, for X = Cl element, alloying elements to a certain proportion makes the absorption spectrum of the material red shift; for X = Br, There is no obvious change in the position of the peak of the absorption spectrum of the material; for X = I, after alloying elements to a certain proportion, the position of the peak of the absorption spectrum of the material has an obvious blueshifts. This work provides a reliable theoretical basis for the bandgap regulation of perovskite materials and a reference for the development of new non-toxic and environmentally friendly solar materials.