Low-temperature photothermally cross-linked hole transport layer enabled by Thiol-Ene click chemistry for high-performance quantum dot light-emitting diodes

Abstract

Small-molecule cross-linkable hole-transport materials (HTMs) possess well-defined molecular structures and can be readily purified, making them attractive for the commercialization of quantum-dot light-emitting diodes (QLEDs). However, their device performance often lags behind that of conventional polymeric HTMs due to deteriorated film morphology arising from high cross-linking temperatures and prolonged thermal curing. Here, we demonstrate that incorporating a small amount (1 wt%) of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) into 4-(dibenzo[b, d]furan-3-yl)-N, N-bis(4-vinylphenyl)aniline (3-DTPA) enables the formation of a high-quality hole transport layer (HTL) with excellent film morphology under low-temperature photothermal cross-linking conditions. The cross-linking temperature is reduced from 150 to 70 degrees C, accompanied by a marked improvement in film morphology. The resulting photothermally cross-linked HTL, denoted 3-CPDTPA, forms within 1 min under simultaneous 365 nm UV irradiation and heating at 70 degrees C, exhibiting excellent solvent resistance, superior film morphology, enhanced hole-transport capability, and suppressed interfacial exciton quenching. Green QLEDs based on 3-CPDTPA exhibit a maximum external quantum efficiency (EQE max) of 24.83%, a maximum current efficiency of 96.45 cd A-1, and a maximum power efficiency of 80.38 lm W-1, significantly outperforming devices employing thermally cross-linked 3-CDTPA and poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB). Notably, the EQE max of 3-CPDTPA-based green QLEDs ranks among the highest reported for devices using cross-linkable HTLs. Moreover, the operational half-lifetime is extended by 2.43- and 5.64-fold compared to those of 3-CDTPA- and TFB-based devices, respectively. These results demonstrate that incorporating a small amount of PETMP into the vinyl-functionalized small-molecule HTM enables the low-temperature formation of a solvent-resistant HTL with superior film morphology, providing an effective approach for efficient and operationally stable QLEDs.