通过具有高表面能和延长共轭链段的耐溶剂空穴传输材料实现高效喷墨打印QLED

Quantum-dot light-emitting diodes (QLEDs) prepared using the solution method have great potential in printed displays, particularly when combined with inkjet printing. The surface energy of the lower film plays a crucial role in the spreading of the upper film in QLEDs. High surface energy promotes close contact between different functional film layers and reduces leakage currents. However, cross-linkable hole transport materials (HTMs) with low surface energies are unsuitable for inkjet printing. Herein, a cross-linkable HTM and its polymer derivative were fabricated using a molecular design. The new polymer poly 9-(4-(ethoxymethyl)phenyl)-3-(7-(9-(4-((hexa-2,4-diyn-1-yloxy)methyl)-phenyl)-9H-carbazol-3-yl)-9,9-dimethyl-9H-fluoren-2-yl)-9H-carbazole (PDA-FLCZ) is synthesized via the polymerization of 3,3′-(9,9-dimethyl-9H-fluorene-2,7-diyl)bis[9-(4-(prop-2-yn-1-yloxy)methyl)phenyl]-9H-carbazole (DA-FLCZ). For the new HTM, stable network structures can be formed at low cross-linking temperatures using two cross-linking strategies, in-situ photothermal cross-linking and thermal cross-linking after prepolymerization, exhibiting excellent solvent resistance and high surface energy. By optimizing the cross-linking process, the cross-linked PDA-FLCZ achieves higher hole mobility and lower trap density, resulting in a maximum external quantum efficiency (EQE) of 17.59% for spin-coated QLEDs, which is 23% higher than that of the device based on DA-FLCZ (14.25%). Moreover, the inkjet-printed QLEDs based on the cross-linked PDA-FLCZ demonstrate a maximum EQE of 15.28%, which is close to 90% of the value of its spin-coated devices.