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 Pb2+ ions and ─NH2 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.