Sulfonium-Ligand-Regulated Crystallization Interfacial Dynamics Enables Near-Infrared Perovskite Light-Emitting Diodes with 27% EQE

Despite the rapid evolution of perovskite light-emitting diodes (PeLEDs), achieving high brightness while mitigating efficiency roll-off remains a significant challenge, primarily arising from grain-size-induced Auger recombination and imbalanced carrier injection. Here, we demonstrate an interfacial engineering strategy by using dimethylphenethylsulfonium iodide (DMPESI) to concurrently regulate crystal growth and interfacial electronic states. The sulfonium cation, devoid of N–H protons and thus incapable of forming hydrogen bonds, engages in electrostatic anchoring with both FA + and undercoordinated Pb 2+ sites. This not only suppresses the formation of deep non-radiative traps but also facilitates an intermediate phase that promotes secondary grain growth. The DMPESI-modified interfacial layer minimizes leakage current and optimizes charge injection balance under high-injection conditions. The DMPESI-modified PeLED delivers a peak EQE of 27.0%, a high radiance of 782.5 W sr –1 m –2 and a T 50 of 627.8 h (20 mA cm –2 ), maintaining an EQE above 20% even at a current density of 1000 mA cm –2 .