Highly Bright and Stable Lead‐Free Double Perovskite White Light‐Emitting Diodes

Abstract Lead‐free double perovskites (DPs) are emerging highly stable emitters with efficient broadband self‐trapped exciton (STE) photoluminescence (PL), but their low electroluminescent (EL) efficiency is a critical shortcoming. This work promotes the external quantum efficiency (EQE) and luminance of DP‐based white light‐emitting diode (wLED) with a normal device structure to 0.76% and 2793 cd m −2 via two modifications: This work prevents the formation of adverse metallic silver, spatially confined STE, and lowers local site symmetry in Cs 2 Na 0.4 Ag 0.6 In 0.97 Bi 0.03 Cl 6 DP by terbium doping; and this work develops a guest–host strategy to improve film morphology, reduce defect density, and increase carrier mobility. These alterations cause substantial increase in STE radiative recombination and charge injection efficiency of perovskite layer. Finally, pure white EL with ideal color coordinates of (0.328, 0.329) and a record‐breaking optoelectronic performance is achieved by introducing additional green carbon dots in LED to fill the deficient green component.