LAUSR

Recently, all‐inorganic halide double perovskites (DPs) with a chemical formula of Cs2BIBIIIX6 have been emerging as a shinning star to be used in modern optoelectronic devices, due to their unique advantages such as environmentally friendly, high absorption coefficient, low trap densities, tunable bandgap, variable constituent elements and valences states through BI or BIII sites engineering. In this review, first, the impact of BI and BIII cation doping on the electronic structure and optical properties of Cs2BIBIIIX6 DPs are systematically overviewed, which cover several key issues including the interconversion between direct and indirect band gaps, the enhancement of light absorption, promotion of exciton localization, elucidation of energy transfer mechanisms, regulation of defect density and improvement in both stability and luminescence efficiency. Subsequently, state‐of‐the‐art research activities regarding their interesting optoelectronic device applications are systematically discussed, such as light‐emitting diodes, anticounterfeiting encryption, X‐ray scintillators, and optical thermometry. Finally, the existing difficulties, prospects, and research directions in this field are proposed.