Enhancing Performance of CsSnBr ₃ Light‐Emitting Diodes via Synergistic Ion Doping and in Situ Interfacial Reaction

ABSTRACT Tin‐based perovskites are among the most promising lead‐free emitters for perovskite light‐emitting diodes (PeLEDs), but their performance is severely hindered by the uncontrolled rapid crystallization and facile oxidation. Here, we report a synergistic bulk–interface strategy for enhancing performance of CsSnBr 3 PeLEDs by combining Zn 2+ bulk doping with an in situ interfacial reaction. Incorporation of ZnBr 2 suppresses Sn vacancies and residual SnBr 2 while regulating crystallization to improve film morphology. Concurrently, sodium citrate‐modified PEDOT:PSS promotes deprotonation of 6‐phosphonylhexyl acid, forming robust coordination bonds that delay crystallization and passivate defects. Benefiting from these dual effects, the optimized devices achieve a record external quantum efficiency for CsSnBr 3 PeLEDs. This work highlights the effectiveness of synergistic bulk–interface regulation in tuning crystallization kinetics, providing constructive insights for the development of efficient lead‐free perovskite optoelectronics.