Enhanced Molecular Stacking Enabled by Photo-Induced Crosslinking of Hole Transport Materials for High-Performance QLED

Solution-processed quantum dot light-emitting diodes (QLEDs) are attractive candidates for next-generation displays. A critical component of high-performance QLEDs is a robust hole-transporting layer (HTL) with well-aligned energy levels. However, conventional polymer HTLs often suffer from disordered molecular stacking and severe tail states, leading to insufficient hole transport mobility, imbalanced carrier transport efficiency, and consequently, degraded device performance. To address these challenges, this study proposes a crosslinking-induced structural reforming strategy to optimize the polymer HTLs. As proof of this concept, poly(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec- butylphenyl)) diphenylamine) (TFB), the commonly used HTL material, is modified by adding a photo-crosslinking agent. The crosslinked TFB layers exhibit enhanced molecular ordering and narrowed tail states, suggesting reduced energetic disorder. The red QLED devices using crosslinked TFB as the HTL have shown significant improvement in performance, achieving peak external quantum efficiency (EQE) of 24.62% and current efficiency (CE) of 24.3 cd A⁻¹. Furthermore, the operational stability is also improved, with a nearly three-fold enhancement compared to the control sample. Additionally, the photo-crosslinking process enables the precise patterning of TFB films, supporting the fabrication of pixelated HTLs. These results highlight the potential of crosslinked HTLs for enhancing performance and promoting commercialization in next-generation QLED displays.