Novel Dibenzofuran-Based Cross-Linked Hole Transport Materials for High-Performance Blue Quantum Dot Light Emitting Diodes

Inefficient hole injection represents a major challenge in achieving stable and cost-effective solution-processed blue quantum dot light-emitting diodes (QLEDs). The development of hole transport materials (HTMs) suitable for high-performance blue QLEDs has proven particularly difficult, mainly due to their inherently low hole mobility and mismatched energy levels. In this study, we designed and synthesized two vinyl-based cross-linkable HTMs: 4,4'-bis(3-vinyl-9H-carbazol-9-yl)-1,1'-biphenyl (CBP-V) and 2,8-bis(3-vinyl-9H-carbazol-9-yl)dibenzo[b,d]furan (KFP-V). Compared to CBP-V, the replacement of biphenyl groups with dibenzofuran groups in KFP-V results in a relatively lower cross-linking temperature of 200 °C and complete solvent resistance. Moreover, KFP-V exhibits exceptional hole transport properties, with a notable high hole mobility of 2 × 10^-3 cm² V^-1 s^-1. The HOMO level of KFP is reduced to -5.95 eV, effectively lowering the injection barrier between the HTL and QDs layer. When applied in solution-processed blue QLEDs, devices based on KFP-V show outstanding performance, achieving a maximum luminance of 31432 cd m^-2 and an external quantum efficiency of 16.67%. Moreover, the cross-linked KFP-V enhances deep-blue emission characteristics, with Commission Internationale de l'Eclairage coordinates of (0.15, 0.03). This work offers valuable insights for the rational design of cross-linkable HTMs aimed at advancing solution-processed blue QLEDs.