Ruthenium(II) Complex as Phosphorescent Dopant for Highly Efficient Red Polymers Light-Emitting Diodes

Abstract

Red electrophosphorescence from light-emitting devices based on a ruthenium(II) complex [Ru(4,7-Ph2-phen)3]2+-doped wide-band-gap semiconductive polymers, e.g., poly(vinylcarbazole) (PVK), polydihexylfluorene (PF), and ladder-like polyphenylene (LPPP), as the emitting layer are reported. These polymers show the short-wavelength electroluminescence emission peaking ranged from 410 to 490 nm, which overlaps well with the absorption band of [Ru(4,7-Ph2-phen)3]2+; however, very efficient energy transfer was investigated in the PVK system, likely due to relative long excited-state lifetimes of PVK than that of PF and LPPP and 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+, with a peak at 612 nm and CIE of (0.62, 0.37) which is comparable with standard red color. The optimized device ITO/PVK 5 wt % [Ru(4,7-Ph2-phen)3]2+/PBD/Alq3/LiF/Al shows the maximum luminance efficiency and power efficiency of 8.6 cd/A and 2.1 lm/W, respectively.