Synthesis and characterization of bipolar copolymers containing oxadiazole and carbazole pendant groups and their application to electroluminescent devices

A series of random copolymers POC10{Poly(2,5-bis[(5-decyloxy-phenyl)-1,3,4- oxadiazole]styrene)}-co-Poly(N-vinylcarbazole) (PVK) with different nvk content were synthesized through common radical polymerization and were incorporated into light emitting diodes as emitting layers. The structures and properties of the copolymers were characterized and evaluated by GPC, TGA, DSC, UV, PL, CV, and EL analyses. All the polymers enjoy high thermal stability. Cyclic voltammetry revealed that, with the incorporation of N-vinylcarbazole to the copolymer, these copolymers had high-lying HOMO energy values, which facilitated hole injection. PL peaks in the film show blue-shift compared with those in solutions and fluorescent quantum efficiency decreased with the nvk content increasing, which supported the efficient energy transfer from nvk units to the oxadiazole units. Single-layer LEDs with the configuration of ITO/PEDOT/PC10-nvk/Mg:Ag/Ag were fabricated, which emit a blue light around 440 and 490 nm with a maximum brightness of 675.3 cd/m² and luminous efficiency of 0.108 cd/A. Moreover, we fabricated electrophosphorescent device from bipolar transport copolymer PC10-nvk4 as host material and an orange-light-emitting iridium phosphor IrMDPP as guest. The maximum luminous efficiency of 0.548 cd/A was obtained.