The effects of cation and halide anion on the stability, electronic and optical properties of double perovskite Cs2NaMX6 (M = In, Tl, Sb, bi; X = Cl, Br, I)

In recent years, the application of inorganic lead-free double perovskite halides in optoelectronic devices has attracted extensive attention because they can solve the toxicity problems of traditional perovskite materials and exhibit excellent environmental stability. The photoluminescence properties of the structure can be significantly improved by doping Cs2NaInCl6 with VA group elements. The geometrical and optoelectronic characteristics of the double perovskite Cs2NaMX6 (M = In, Tl, Sb, Bi; X = Cl, Br, I) were studied using first-principles calculations in this work. It is found by calculation that the doping substitution of M-site cations can change the energy band characteristics due to the change of the M -p orbital. The X-site anion substitution can adjust the structural band gap while maintaining the energy band structure shape. Our study shows that by compositional modulation of the M3+ site of Cs2NaInCl6 by 1:1 substitution of VA groups, the maximum light absorption in the near-ultraviolet region can be increased up to three times compared to undoped Cs2NaInCl6. Therefore, Cs2NaInCl6 can be widely used in the fields of luminescent and ultraviolet detectors through compositional modulation.