Study on Cs2AgIn(Cl1−xBrx)6 perovskite based on the balance of stability and optical absorption properties

Abstract

The Cs2AgIn(Cl1−xBrx)6 (x = 0, 1/6, 1/3, 1/2, 2/3, 5/6, 1) lead-free perovskites show great advantages as a stable and non-toxic alternative to lead halide perovskite. In this study, Cs2AgIn(Cl1−xBrx)6 are treated by replacing Cl with Br in a stepwise manner to balance its stability and optical properties. Density functional theory is used to investigate the structural, electronic, and optical properties of Cs2AgIn(Cl1−xBrx)6. The results show that the doping of Br make the average bond length of metal-halides longer, resulting in an increase in volume. The value of the bandgap decreases from 3.168 eV to 2.095 eV. The decomposition energy (−92.3365 to −70.4435 meV/atom) of the material gradually increases, the stability decreases gently (−92.3365 to −90.934 meV/atom, Δ0–1/2 = 0.4675) when the amount of Br doping is less than 1/2, and it decreases significantly (−90.934 to −70.4435 meV/atom, Δ1/2–1 = 6.83) when it exceeds 1/2. The partial density of states reveal that the electronic contribution is mainly related to the [AgX6]5- (X = Cl, Br) octahedral. The analysis of charge density indicates that partially or completely replacing Cl with Br is beneficial for the generation of free electrons, which may improve its photoelectric performance. The analysis of the complex dielectric function and the optical absorption coefficient shows a more significant increase in the absorption coefficient when half of the Br is incorporated compared to full substitution. According to our results, adjusting x in Cs2AgIn(Cl1−xBrx)6 can expand the material's range of spectroscopic applications. Based on the trade-off between stability and light absorbance, Cs2AgInCl3Br3 exhibits the best overall performance.