Improved Hole Transport Layer Surface by Carbazole Ammonium Treatment for 988 nm Near‐Infrared Tin‐Lead Perovskite LEDs

ABSTRACT Incorporating tin (Sn) and lead (Pb) into metal halide perovskites is an effective strategy for reducing bandgap energy, enabling applications in the near‐infrared (NIR) spectral region. Recently, we demonstrated light‐emitting diodes (LEDs) with long‐wavelength emission peaks exceeding 900 nm. However, non‐radiative recombination at the perovskite/transport layer interface remains a key limitation to device efficiency. In this work, we introduce carbazole ammonium iodide as an interfacial modifier, forming a hydrophilic thin layer atop the PEDOT:PSS hole transport layer. This interlayer enhances surface wettability, promotes improved perovskite crystallization, and facilitates better interface contact. The resulting perovskite films exhibit extended carrier lifetimes, and the corresponding NIR LEDs show reduced leakage current densities. Additionally, we systematically investigate the influence of annealing temperature on Sn–Pb‐based perovskite film formation. X‐ray diffraction (XRD) analysis reveals that high‐temperature annealing accelerates crystallization but promotes PbI 2 formation, leading to rougher surfaces and increased crystal defects. By combining surface modification of the hole transport layer with optimized annealing conditions, we achieve a significant performance enhancement. The NIR LED with an emission peak at 988 nm exhibits a twofold increase in external quantum efficiency (EQE), improving from 0.6% to 1.3%, compared to devices using unmodified PEDOT:PSS.