In Situ Evaporated Phosphine Oxide Bifunctional Additive for Efficient Vacuum‐Deposited Near‐Infrared Perovskite Light‐Emitting Diodes

Abstract Vacuum‐deposited perovskite light‐emitting diodes (PeLEDs) have demonstrated great potential for next‐generation light sources. However, vacuum‐deposited perovskites suffer from high defect densities due to the lack of sufficient passivation strategies. Herein, an effective in situ passivation strategy for vacuum‐deposited PeLEDs using bifunctional tris(4‐fluorophenyl)phosphine oxide (TFPPO) additive is introduced. The P═O moieties of TFPPO with lone pair electrons bond with the undercoordinated Pb ²⁺ sites, suppressing the defect formation. Besides, the fluorine functional groups of TFPPO that form hydrogen bonds with the formamidinium cations control their diffusion during the vacuum deposition, thus reducing the crystal grain size. As a result, the uniform and compact TFPPO‐incorporated FACsPbI ₃ thin film enables near‐infrared PeLED with a record external quantum efficiency of 14.33%. This work presents a process‐compatible defect passivation strategy to advance vacuum‐deposited perovskite optoelectronics.