A series of vinyl copolymers (P1-P6) containing pendant hole-transporting triphenylamine (11-88 mol%) and carbazole chromophores were synthesized by radical copolymerization to investigate the influence of triphenylamine groups upon optoelectronic properties. The copolymers were readily soluble in common organic solvents and their weight-average molecular weights (Mws) were between 1.41 × 104 and 2.24 × 104. They exhibited moderate thermal stability with Td = 402-432 °C at 5% weight loss. The emission spectra (both PL and EL) of the blends [P1-P6 with 4 wt% Ir(ppy)3] showed dominant green emission (517 nm) attributed to Ir(ppy)3 due to efficient energy transfer from P1-P6 to Ir(ppy)3. The HOMO levels of P1-P6, estimated from onset oxidation potentials in cyclic voltammeter, were -5.42 to -5.18 eV, which are much higher than -5.8 eV of conventional poly(9-vinylcarbazole) (PVK) host owing to high hole-affinity of the triphenylamine groups. The optoelectronic performances of phosphorescent EL devices, using P1-P6 as hosts and Ir(ppy)3 as dopant (ITO/PEDOT:PSS/P1-P6:Ir(ppy)3 (4 wt%):PBD (40 wt%)/BCP/Ca/Al), were greatly improved relative to that of PVK. The best performance was obtained with P4 device, in which the maximum luminance and luminance efficiency were 11 501 cd/m2 and 10.6 cd/A, respectively.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry