High‐Efficient Blue Emission and Bandgap Engineering from Jahn–Teller Distorted Halide Double Perovskites

Abstract Decreasing the power consumption of light‐emitting diodes (LEDs) and increasing the energy generation of solar cells are crucial tasks toward the mitigation of greenhouse gas emissions and Paris Agreement goals. Lead (Pb)‐free halide double perovskites, identified as environmentally friendly alternatives to Pb‐based perovskites, are not deemed useful thus far due to the absence of high photoluminescence quantum yield (PLQY) examples and large bandgaps. Herein, penta‐cationic antimony (Sb 5+ )‐doping strategy is demonstrated for the benchmark material of Cs 2 NaInCl 6 , achieving blue emission with near‐unity PLQY and the lowest bandgap of 1.24 eV. The excellent PLQY observed in the material is attributed to Sb 5+ doping‐induced Jahn–Teller distortion in Cs 2 NaInCl 6 and a newly emerged band structure, which has remained undisclosed in all previous reports. This groundbreaking discovery represents the first instance in the field of perovskite materials where the incorporation of a single dopant has resulted in a zero‐to‐one enhancement in their emission profile. This breakthrough is expected to have profound implications for advancing research in the utilization of similar dopants, such as manganese cations (Mn 6+ and Mn 7+ ), not only in halide perovskite structures but also in oxide‐based perovskites and other semiconductor systems.