Exciton Localization Engineering in Thermally Evaporated Yb‐Doped CsPbCl₃ Near‐Infrared Light‐Emitting Diodes

Near‐infrared (NIR) emission underpins biomedical imaging, night vision, and optical communication. Yb 3+ ‐doped CsPbCl 3 have demonstrated ultrahigh photoluminescence quantum yields via quantum cutting, primarily enabled by a singular defect‐assisted energy transfer pathway arising from the substitution of Pb 2+ by Yb 3+ . However, whether additional pathways exist to facilitate visible (VIS)‐to‐NIR conversion, thereby further enhancing the performance of NIR‐emissive devices, remains an open and compelling question. Here, strategic engineering of localized bound excitons (BEs) is proposed in the thermally evaporated CsPbCl 3 :Yb system. Assisted BEs significantly promote energy transfer from CsPbCl 3 matrix to Yb dopants, unveiling a previously unknown excitonic energy transfer channel. Atomic‐scale characterization combined with first‐principles calculations uncovers a BE‐driven excitonic transfer mechanism, specifically implicating Cs‐vacancy‐induced defects in mediating exciton behavior. These insights lead to the fabrication of high‐performance NIR‐LEDs with an 8.9% external quantum efficiency and 410 mW·Sr −1 ·m −2 radiance, marking a breakthrough in thermally evaporated NIR (>950 nm) light‐emitting diodes.