Manipulation of parity and polarization through structural distortion in light-emitting halide double perovskites

Abstract Halide perovskite materials recently attracted wide attention for light-emitting applications. The intense white light emission and excited state lifetimes greater than 1 μs are the hallmarks of a good light-emitting material. Here, we provide a clear design strategy to achieve both of these aforementioned properties in a single material via the introduction of octahedral asymmetry in halide double perovskites Cs 2 AgMCl 6 through iso-trivalent substitution at the M site. In the substituted Cs 2 AgMCl 6 , the presence of mixed M 3+ sites distorts the [AgCl 6 ] 5- octahedra, affecting the parity of the valence and conduction band edges and thereby altering the optical transitions. The distortion also creates a local polarization that leads to an effective photogenerated carrier separation. Considering perovskite series with three M 3+ cations, namely Bi 3+ , In 3+ and Sb 3+ , the mixed trivalent cationic compounds with specific ratios of In 3+ and Bi 3+ show white light emission with intensity nearly 150 times larger than that of the parent compounds, and are characterised by excited state lifetimes nearing 1 μs. Using single crystal X-ray diffraction, far-infrared absorption, steady-state and time-resolved photoluminescence, bias-dependent photoluminescence, P-E loop traces and density-functional theory calculations, we hence demonstrate the role of octahedral distortion in enhancing white light emission and excited state lifetimes of halide double perovskites.