Anionic Conjugated Polyelectrolyte as a Multifunctional Interfacial Layer for Defect Suppression in Perovskite LEDs

Nickel oxide (NiOx) is widely used as a hole transport layer in perovskite light-emitting diodes (PeLEDs) due to its suitable energy level alignment, high transparency, and stability. However, its surface typically contains inhomogeneous oxygen vacancies and abundant hydroxyl groups, leading to interfacial energy mismatches and defect formation that hinder efficient charge injection and limit device performance. To address these challenges, we introduce a dual-passivation strategy employing an anionic conjugated polyelectrolyte (CPE), Poly[9,9-bis(4-C-sulfonatobutyl)fluorene-alt-thiophene]-Li (PFS-T-Li), as a multifunctional interfacial layer. The sulfonate groups (SO3−) and Li+ counterions in PFS-T-Li selectively coordinate with oxygen vacancies in NiOx and Pb2+-related trap sites in the perovskite layer, respectively. This dual interfacial passivationeffectively suppresses trap-assisted non-radiative recombination, enhancing charge injection, luminescence efficiency, and operational stability. Devices incorporating PFS-T-Li achieve a maximum external quantum efficiency (EQE) of 8.16 % and luminance of 5,111 cd m−2, demonstrating its critical role in improving PeLED performance.