Charge Transport Regulation in Solution-Processed OLEDs by Indenocarbazole-Triazine Bipolar Host Copolymers

This work reports the synthesis of a series of bipolar host polymers, specifically PPPIC-co-PPDPT (9:1), PPPIC-co-PPDPT (8:2), and PPPIC-co-PPDPT (7:3), which incorporate a hole-transporting unit, 7,7-dimethyl-5-phenyl-2-(4-vinylphenyl)-5,7-dihydroindeno[2,1-b]carbazole (PPIC), and an electron-transporting unit, 2,4-diphenyl-6-(4-vinylphenoxy)-1,3,5-triazine (PDPT). These polymers are meticulously designed to achieve efficient bipolar charge transport while exhibiting high triplet energy levels (T₁), robust thermal stability, and smooth surface morphology. The tunability of the recombination zone position was achieved by adjusting the relative ratio of the hole and electron transport units in the emissive layer, leading to optimized charge balance and enhanced device performance. The maximum current efficiency of 40.71 cd/A and an EQE of 11.19% were achieved through a simple device structure. Overall, this study highlights the potential of these bipolar host materials for advancing the OLED technology by enabling superior charge transport and reducing efficiency roll-off.