Interface Engineering of Perovskite/Hole‐Transport Layers Toward Efficient Pure‐Red Quasi‐2D PeLEDs

High‑efficiency perovskite light‑emitting diodes (PeLEDs) with pure‑red emission are crucial for next‑generation ultra‑high‑definition displays. However, the widely used hole transport layer poly(9‑vinylcarbazole) (PVK) in iodine‐based PeLEDs suffers from poor wettability, interfacial defects, and energy‑level misalignment with the perovskite layer, which hinder the formation of high‑quality perovskite films, induce non‐radiative recombination loss, and limit efficient hole injection. Herein, we report an interfacial engineering strategy that simultaneously addresses these challenges by incorporating a multifunctional small molecule, thiophene‑2‑sulfonamide (2‑ThSA), into the perovskite precursor. 2‑ThSA acts as a molecular bridge: its sulfonamide moiety interacts with the carbazole units of PVK, while its thiophene ring facilitates π‐π stacking with the PVK layer, thereby improving interfacial contact. Simultaneously, the sulfonamide group provides multivalent coordination sites, where ─S═O bonds coordinate with undercoordinated Pb 2+ ions and ─NH 2 groups interact with I − ions, effectively passivating interfacial defects and suppressing non‑radiative recombination. As a result, the 2‑ThSA‑modified pure‑red PeLEDs exhibit stable electroluminescence at 634 nm with a peak external quantum efficiency (EQE) of 27.2% and CIE coordinates (0.701, 0.299) that align perfectly with the Rec. 2020 standard.