Dual-descriptor molecular design of cross-linkable hole transport materials for efficient and stable quantum dot light-emitting diodes

Abstract

Cross-linkable small-molecule (SM) hole-transport materials (HTMs) are attractive for solution-processed quantum dot light-emitting diodes (QLEDs) because they provide solvent-resistant multilayer architectures while retaining structural precision and high synthetic reproducibility. However, cross-linking often introduces a fundamental trade-off: although network formation improves solvent resistance, it can simultaneously disrupt molecular packing, increase energetic disorder, and impair charge transport. Molecular design principles to overcome this trade-off remain largely unexplored. Herein, toward the development of cross-linkable HTMs, we introduce a dual-descriptor molecular design strategy based on two key parameters, i.e., reorganization energy and bond dissociation energy (BDE), which govern intermolecular hole transfer efficiency and molecular robustness against electrically induced degradation, respectively. Guided by this framework, we developed a symmetric dibenzofuran-dimer-based cross-linkable HTM, 4,4 '-([2,2 '-bidibenzo[b,d]furan]-6,6 '-diyl)bis(N,N-bis(4-vinylphenyl)aniline) (Sy-DdTPA), which simultaneously exhibits low reorganization energy and high BDE. Unlike conventional cross-linkable HTMs, Sy-DdTPA forms a solvent-resistant network while preserving electronic structure and promoting local molecular ordering, leading to reduced energetic disorder, enhanced hole mobility, suppressed interfacial charge-transfer loss, and lowered trap-state density at the quantum dot/hole-transport layer interface. Green QLEDs based on cross-linked Sy-DdTPA achieve a maximum external quantum efficiency of 25.69%, which is among the highest values reported for solution-processed QLEDs using cross-linkable SM HTMs, together with a projected operational half-lifetime exceeding 510 000 h at 100 cd m-2. This work establishes reorganization energy and BDE as predictive molecular descriptors for designing cross-linkable organic semiconductors, providing a general framework for simultaneously achieving charge transport efficiency and operational stability in solution-processed optoelectronic devices.