Negative photoconductivity in Cs₄PbBr₆ single crystal

Abstract

Zero-dimensional (0D) inorganic perovskites, particularly Cs₄PbBr₆, have been attracting wide attention due to their excellent photoluminescence (PL) efficiency and spectral color purity. The PL origin of Cs₄PbBr₆ and the underlying photophysics, however, draw intense debate and remain controversial. Revealing the photo-excited carrier generation, separation, and recombination, as well as the roles that mobile ions play, is crucial and helpful to deeply understand the photo-physical property. Photoconductivity is one of the effective approaches to closely explore the photophysics. In this study, high-purity Cs₄PbBr₆ single crystals were grown from Cs-enriched solutions. Negative photoconductivity was first observed in Cs₄PbBr₆ through Au-crystal-Au photo-detectors, and the photocurrents under high illumination power are similar to those of the diode. It is considered that the built-in electric field produced by the charged excitons combined by the neutral excitons and vacancies of Br (V_Br⁺) are responsible for the eccentric negative photoconductivity phenomena because of strong Coulomb interactions and low V_Br⁺ formation energy in Cs₄PbBr₆.