Secondary Grain Growth of Perovskite Films Induced by a Phosphonate Derivative for High-Performance Near-Infrared Light–Emitting Diodes

Efficient charge injection and defect passivation remain pivotal challenges in developing high-performance perovskite light–emitting diodes (PeLEDs). This study reports that [4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) used as an interfacial modifier is capable of simultaneously reducing surface defects in FAPbI 3 perovskite films and enhancing hole injection from the polymeric hole-transporting layer (HTL). Additionally, tuning of the surface induces secondary grain growth in the perovskite film, resulting in larger grain sizes and a denser film morphology, which account for strongly suppressed leakage currents and nonradiative recombination in PeLEDs. Consequently, devices with this interface modification achieve a maximum external quantum efficiency (EQE max ) of 21.98% at a near-infrared (NIR) emission wavelength of 800 nm and an operational half-life (T 50 ) of 47.3 h under a constant current density of 50 mA cm −2 . This work underscores the significance of tailored interfacial engineering in optimizing both the performance and operational stability of PeLEDs for their practical applications.