Investigating optical adsorption properties of lead‐free double perovskite semiconductors Cs2SnI6−xBrx (x = 0–6) via first principles calculation

In this work, the properties of the Br− ion‐doped Cs2SnI6 system (Cs2SnI6−xBrx, x = 0–6) are systematically explored via the first principle calculation. The evolution of Cs2SnI6−xBrx crystal structure in the doping process is obtained by regulating the doping positions where I− ions are replaced with Br− ions, and the changing curve of the bandgap is drawn on the basis of the setting of the U value in I 5p and Br 5p orbits and the accurate description of the bandgap of Cs2SnI6−xBrx with HSE06 hybrid functional. Br− ions doping not only improves the stability of the Cs2SnI6−xBrx structure, but also can adjust its bandgap width. In light of the analysis of gain and loss of electrons among ions and electron density difference during the doping process, the introduction of Br− ions enable Cs2SnI6−xBrx to have a stronger ionic crystal character than Cs2SnI6, which indicates that the Cs2SnI6−xBrx is suitable to be applied to photoelectric devices as a carrier transport layer. The further analysis of the distribution of electronic states density of Cs2SnI6−xBrx and the variation trend of its absorption spectra confirms the transition process of electrons among energy bands, which also reveals the main reason why the performance of current photovoltaic devices based on Cs2SnI6 are unsatisfactory. It is notable that we find Cs2SnI6−xBrx, especially Cs2SnI3Br3 is an ideal material for solar‐blind detection.