Composite Perovskites of Cesium Lead Bromide for Optimized Photoluminescence

The halide perovskite CsPbBr₃ has shown its promise for green light-emitting diodes. The optimal conditions of photoluminescence and the underlying photophysics, however, remain controversial. To address the inconsistency seen in the previous reports and to offer high-quality luminescent materials that can be readily integrated into functional devices with layered architecture, we created thin films of CsPbBr₃/Cs₄PbBr₆ composites based on a dual-source vapor-deposition method. With the capability of tuning the material composition in a broad range, CsPbBr₃ is identified as the only light emitter in the composites. Interestingly, the presence of the photoluminescence-inactive Cs₄PbBr₆ can significantly enhance the light emitting efficiency of the composites. The unique negative thermal quenching observed near the liquid nitrogen temperature indicates that a type of shallow state generated at the CsPbBr₃/Cs₄PbBr₆ interfaces is responsible for the enhancement of photoluminescence.