Polymer light-emitting diodes based on cationic iridium(III) complexes with a 1,10-phenanthroline derivative containing a bipolar carbazole–oxadiazole unit as the auxiliary ligand

Abstract A 1,10-phenanthroline derivative (co-phen) containing a bipolar carbazole–oxadiazole unit was synthesized and used as the auxiliary ligand in cationic iridium(III) complexes [(ppy)2Ir(co-phen)]PF6 (ppy: 2-phenylpyridine) and [(npy)2Ir(co-phen)]PF6 (npy: 2-(naphthalen-1-yl)pyridine). Two complexes have high thermal stability with the glass-transition temperatures (Tg) of 207 °C and 241 °C, and the same 5% weight-reduction temperatures (ΔT5%) of 402 °C. Both of them were used as phosphorescent dopants in solution-processed polymer light-emitting diodes (PLEDs): ITO/PEDOT: PSS/PVK: PBD: complex (mass ratios 100: 40: x, x = 1.0, 2.0, and 4.0)/CsF/Al. The maximum luminances of the PLEDs using [(ppy)2Ir(co-phen)]PF6 and [(npy)2Ir(co-phen)]PF6 were 12567 cd m−2 and 11032 cd m−2, the maximum luminance efficiencies were 17.3 cd A−1 and 20.4 cd A−1, the maximum power efficiencies were 9.8 lm W−1 and 10.3 lm W−1, and the maximum external quantum efficiencies were 9.3% and 11.4% respectively. The CIE color coordinates were around (0.37, 0.57) and (0.44, 0.54) respectively, corresponding to the yellow green region.