Luminescence Mechanism of ns2 Ions in Cs2(Sn/Hf)Cl6 Revealed by First-Principles Calculations

Abstract

A great variety of halide perovskites doped with ns2 ions have been explored for optical functional materials, and a couple of different phenomenological models have been proposed to interpret their luminescence. First-principles calculations are carried out for Cs2SnCl6 and Cs2HfCl6 to explore self-trapped excitons, potentially important intrinsic and extrinsic defects, and different defect-related luminescent centers. A uniform picture of competing processes consistent with a previous study on Cs2ZrCl6 is obtained to interpret the experimental phenomena. Remarkable differences in details between Cs2SnCl6 and Cs2(Hf/Zr)Cl6 are also revealed: the high-symmetry self-trapped exciton not stable in Cs2(Hf/Zr)Cl6 is predicted to be stable in Cs2SnCl6, and the activation energy of the high-symmetry Sb3+ at the M site of Cs2MCl6 is much smaller for M = Sn than Hf/Zr. The elucidation of the defects and transition mechanisms with first-principles calculations will benefit the design and optimization of metal halide perovskites with ns2 ion doping.