Stable Sky‐Blue Perovskite LEDs Achieved by Efficient Sub‐Bandgap Emission With 24.5% PCE

Abstract As an emerging light‐source technology, blue perovskite light‐emitting diodes (PeLEDs) have demonstrated remarkable progress in external quantum efficiency. However, their poor operational stability remains a critical bottleneck hindering further commercialization. Simultaneously achieving high power conversion efficiency (PCE) and brightness in the ultralow‐voltage regime represents a promising strategy for realizing long‐lived PeLEDs. Here, efficient defect passivation in perovskite emissive layers is demonstrated through the incorporation of a 0D perovskite phase, while simultaneously modulating the semiconductor characteristics from n‐type to p‐type via strategic bulky cation engineering. The resulting PeLED operates below the bandgap voltage, achieving a high PCE of 24.5%. Notably, the drastically reduced driving voltage suppresses Joule heating and ion migration, extending the operational lifetime to a record T 50 of 318.8 min at 1000 cd m −2 . This work provides a strategic roadmap for developing blue PeLEDs that simultaneously achieve high efficiency, high brightness, and long operational lifetime.