Highly efficient red phosphorescent light-emitting diodes based on ruthenium(II)-complex-doped semiconductive polymers

Abstract

Red electrophosphorescence from light-emitting devices based on ruthenium(II)-complex [Ru(4,7-Ph2-phen)3]2+-doped wide-band-gap semiconductive polymers, i.e., poly(vinylcarbazole) (PVK), polydihexylfluorene (PDHF), and ladderlike polyphenylene (LPPP), as the emitting layers are reported. However, only highly efficient energy transfer was investigated in a PVK system, not only because of the relatively longer lifetime of its excited state compared with PDHF and LPPP, but also because of the good chemical compatibility of [Ru(4,7-Ph2-phen)3]2+ with PVK. The EL spectra show the characteristic spectrum of [Ru(4,7-Ph2-phen)3]2+, at a peak of 612 nm and Commission Internationale del’Eclairage of (0.62, 0.37). The optimized device indium tin oxide/PVK: 5 wt % [Ru(4,7-Ph2-phen)3]2+/PBD/Alq3/LiF/Al shows the maximum luminance efficiency and power efficiency as 8.6 cd/A and 2.1 lm/W, respectively.