Efficient and Super‐Stable 990 Nm Light‑Emitting Diodes Based on Quantum Cutting Emission of Trivalent Ytterbium in Pure‐Br Quasi‑2D Perovskites

Abstract Quasi 2D layered metal halide perovskites (2D‐LMHPs) with natural quantum wells (QWs) structure have garnered significant attention due to their excellent optoelectronic properties. Doping rare earth (RE) ions with 4 f n inner shell emission levels can largely expand their optical and optoelectronic properties and realize diverse applications, but has not been reported yet. Herein, an efficient Yb 3+ ‐doped PEA 2 Cs 2 Pb 3 Br 10 quasi 2D‐LMHPs is fabricated and directly identified the Yb 3+ ions in the quasi 2D‐LMHPs at the atomic scale using aberration electron microscopy. The interaction between different n phases and Yb 3+ ions is elucidated using ultrafast transient absorption spectroscopy and luminescent dynamics, which demonstrated efficient, different time scales and multi‐channel energy transfer processes. Finally, through phase distribution manipulation and surface passivation, the optimized film exhibits a photoluminescence quantum yield of 144%. This is the first demonstration of quantum cutting emission in pure Br‐based perovskite material, suppressing defect states and ion migration. The efficient and stable near‐infrared light‐emitting diodes (NIR LED) is fabricated with a peak external quantum efficiency (EQE) of 8.8% at 990 nm and the record lifetime of 1274 min. This work provides fresh insight into the interaction between RE ions and quasi 2D‐LMHPs and extend the function and application of quasi 2D‐LMHPs materials.