Conductivity-enhanced thick hole-transporting layers via doping–crosslink synergy for efficient and stable NIR QLEDs

Abstract

Scalable manufacturing of quantum-dot light-emitting diodes (QLEDs) is often hindered by challenges in forming uniform charge-transporting layers on uneven indium tin oxide substrates. These irregularities lead to localized leakage currents and reduced production yields. To address this, we employ an UV/thermally crosslinkable material, 4,4′-bis (3-vinyl-9H-carbazol-9-yl)1,1′-biphenyl (CBP-V), to create thick (∼100 nm) hole-transporting layers (HTLs) that improve surface coverage and suppress shunting paths. To compensate the intrinsically low mobility of crosslinked polymers, we further introduce a doped HTL design by embedding a high-mobility small molecule, 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), into the crosslinked CBP-V matrix. The crosslinked CBP-V network provides smooth morphology and excellent solvent resistance, while the dispersed TAPC molecules create auxiliary hopping pathways that facilitate hole transport through the thick polymer layer. This approach enables the formation of thick HTLs without significantly increasing the driving voltage and maintains balanced carrier injection in the light-emitting layer. Consequently, FAPbI₃-based near-infrared QLEDs achieve a peak external quantum efficiency of 17.3% and a T₅₀ lifetime of 262 min using TAPC-doped CBP-V HTLs, far surpassing devices with either thin or undoped HTLs. Moreover, the doped thick HTL effectively compensates for substrate roughness and enables uniform emission in large-area blade-coated devices, offering a scalable and reliable route toward high-performance near-infrared QLEDs.