Temperature-induced orbital polarizations and tunable charge dynamics in layered double perovskite thin films

The realization of lead-free all-inorganic perovskites in emergent materials requires an in-depth understanding of strongly correlated systems toward optoelectronics or spintronics applications. Herein, we report the electronic and optical variation of the < 111 >-oriented layered double perovskites (LDP) family with the formula of (Cs4MBi2Br12)-Bi-II thin films (where MII: Cu, Mn, Pb, or Sr). The element and shell-specific orbital polarization based on soft X-ray linear dichroism spectroscopy probes the Cs M-4,M-5- and Mn L-2,L-3-edges of Cs4MnBi2Br12 thin films as a function of temperature. A strong reversal orbital polarization at the respective edges at 150 K indicates a thermally induced orbital-selective rearrangement at low temperature. In addition, the valence band analysis indicates different orbital admixtures of Br 4p and M-II d states, corroborated by the density functional theory calculations. In terms of the transient charge dynamics, we observe the photoluminescence peak maxima position trend line is shifted toward a longer wavelength. In addition, the longest average lifetime is recorded for Cs4CuBi2Br12 at 27.40 +/- 1 mu s. As the LDP structural integrity is lead-free, therefore, these all-inorganic perovskites hold promising potentials as sustainable and green materials for photophysics applications. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study reports the electronic and optical variation of lead-free all-inorganic perovskites, which hold promising potentials for optoelectronics and spintronics applications.