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 Cs2AgMCl6 through iso-trivalent substitution at the M site. In the substituted Cs2AgMCl6, the presence of mixed M3+ sites distorts the [AgCl6]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 M3+ cations, namely Bi3+, In3+ and Sb3+, the mixed trivalent cationic compounds with specific ratios of In3+ and Bi3+ 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.
Highlights
Halide perovskite materials recently attracted wide attention for light-emitting applications
There are several literature reports with octahedral distortion in their structures, but no clear correlation between the structural distortion and optical/optoelectronic properties is established. In this combined experimental and first-principle study, we systematically induced the distortion in MX6 octahedra in halide double perovskites and analysed the electronic structure to develop a correlation between the distortion and optical transitions
The end members Cs2AgBiCl6, Cs2AgInCl6, and Cs2AgSbCl6 are denoted as CABC, CAIC, and CASC, respectively
Summary
Halide perovskite materials recently attracted wide attention for light-emitting applications. Among various double-perovskite materials, special attention has been paid to chloride-based compounds; Cs2AgBiCl6 (CABC), Cs2AgInCl6 (CAIC), and Cs2AgSbCl6 (CASC) that are crystallizing in the cubic structure Each of these materials has different optical properties due to direct/indirect bandgap or parity allowed/forbidden transitions that make them distinguishable[5,10,11,12]. Semiconductor materials having broad emission spectra can be effectively used in white light-emitting diodes though a broad emission is rarely observed from the single-source material This rare family includes some semiconducting quantum dots, a few organic–inorganic 2D halide perovskite compounds, and single molecular crystals[14,15,16,17,18]. The strength and nature of distortion in [AgCl6]5− octahedron due to the mixture of Bi3+/In3+, Bi3+/Sb3+, and In3+/Sb3+, and subsequently its effect on the optical properties is investigated[33,35]
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