Subwavelength Morphology Engineering for Light‐Extraction Enhancement in Near‐Infrared Perovskite Light‐Emitting Diodes

Despite their inherently high internal quantum efficiency, perovskite light‐emitting diodes (PeLEDs) suffer from limited light‐extraction efficiency (LEE < 20%) due to refractive‐index mismatches and waveguide losses within multilayer device structures. Herein, we report a morphology engineering approach that enhances the LEE of PeLEDs by reducing the perovskite grain spacing to values far smaller than the emission wavelength. This subwavelength morphology was achieved via a ZnO surface amination treatment with 2‐aminoethylphosphonic acid (AEPA), which modulates the nucleation and growth dynamics of the perovskite films. Guided by finite‐difference time‐domain simulations, we found that reducing the perovskite inter‐grain spacing below 0.1 µm drives the emissive layer toward an effective medium regime, thereby reducing lateral refractive‐index inhomogeneity and suppressing guided‐mode confinement. Systematic studies using amino‐phosphonic acid molecules with varied chain lengths further confirm this mechanism, demonstrating the critical role of inter‐grain spacing modulation. As a result, the optimized PeLEDs achieve a peak external quantum efficiency of 20.1% at 798 nm, together with enhanced radiance and operational stability. This optical strategy enables intrinsic light‐extraction enhancement without complex external outcoupling structures, offering a scalable route toward high‐performance near‐infrared PeLEDs.