Lattice and Bandgap Modulation in Metal Halide Perovskites by B-Site Ions Substitution

Abstract

Metal halide perovskites have attracted much attention due to their properties and wide applications in optoelectronic devices. B-site ion substitution, especially heterovalency substitution, is proven to be one of the practical approaches to modulate lattice structure and improve physicochemical properties. Here, lattice and bandgap modulation in all-inorganic perovskites CsPbX₃ are achieved by substituting Pb²⁺ with Bi³⁺. A series of CsPb_1-xBi_xBr₃ (0 ≤ x ≤ 1) microplates with the x values precisely tuned are prepared by a chemical vapor deposition (CVD) method. The lattice structure varies from single crystal CsPbBr₃ with a cubic structure to the single crystal Cs₃Bi₂Br₉ with a hexagonal structure. Correspondingly, three photoluminescence (PL) bands gradually emerge during the substituting: green, blue, and broad red-to-near-infrared emission. From micro-area photoluminescence spectra as a function of excitation power and temperature, combined with time-resolved PL characterization, the emission bands are confirmed from band-edge and self-trapped excitons (STEs) emission. From density functional theory (DFT) calculations, the STE emission in CsPb_0.9Bi_0.1Br₃ and CsPb_0.1Bi_0.9Br₃ is highly related to a combined defect contributed by bromide vacancy and the substitution of B-site ions. This study paves a new way for expanding the spectral range of perovskite emitters and even preparing white light-emitting devices.