Lead-free halide double perovskites are stable and versatile materials for a wide range of applications, particularly for lighting, thanks to their very efficient emission of warm white light. Element substitution in halide double perovskite is recognized as a powerful method for tuning the emission wavelength and improve the efficiency. This review provides an overview on composition and recent progress in halide double perovskite with main focus on the synthesis and emission properties of chloride-based compounds
