“…The lead halide perovskite materials with a chemical formula of APbX 3 (A = Cs + , CH 3 NH 3 + , or HC(NH 2 ) 2 + , X = Cl – , Br – , I – ) have attracted widespread interest due to their outstanding optoelectronic properties, such as a long carrier diffusion length, a high photoluminescence (PL) quantum yield (QY), a tunable band gap, and high carrier mobility. − However, the toxicity of Pb is a threat to the human body and the environment. , As an alternative, the lead-free double perovskites based on Bi 3+ , Sb 3+ , and In 3+ have been developed to conquer the toxicity and increase the stability. , Unfortunately, pure double perovskites, such as Cs 2 NaBiCl 6 , Cs 2 NaInCl 6 , and Cs 2 AgInCl 6 , exhibit poor luminescence properties due to the dark transition of the free excitons and self-trapped excitons (STEs), which could hinder their commercialization and industrialization in the lighting field. Because the properties of STEs profoundly depend on the inorganic structure distortion, the STE emission could be improved by chemical tailoring (doping, alloying, and reducing the dimensionality), which could result in moderate lattice distortion. − Notably, the perovskite is sensitive to external stimuli, such as temperature and pressure, due to the soft lattices of metal halides. Accordingly, the inorganic octahedron in the lead-free double perovskite could also be modified by applying external stimuli, especially pressure.…”