Exciton Localization Engineering in Thermally Evaporated Yb‐Doped CsPbCl 3 Near‐Infrared Light‐Emitting Diodes

Near-infrared (NIR) emission underpins biomedical imaging, night vision, and optical communication. Yb³⁺-doped CsPbCl₃ have demonstrated ultrahigh photoluminescence quantum yields via quantum cutting, primarily enabled by a singular defect-assisted energy transfer pathway arising from the substitution of Pb²⁺ by Yb³⁺. 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 CsPbCl₃:Yb system. Assisted BEs significantly promote energy transfer from CsPbCl₃ 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.