High Efficiency White Organic Light-Emitting Devices Incorporating Yellow Phosphorescent Platinum(II) Complex and Composite Blue Host

A new class of charge neutral, strongly luminescent cyclometalated platinum(II) complexes supported by dianionic tetradentate ligand are synthesized. One of these platinum(II) complexes, Y-Pt, displays a high photoluminescence quantum yield of 86% and electroluminescence efficacy ((power)) of up to 52 lm W-1, and is utilized as a yellow phosphorescent dopant in the fabrication of white organic light-emitting devices (WOLEDs). WOLEDs based on conventional structures with yellow emission from Y-Pt in combination with blue emission from bis(4,6-difluorophenyl-pyridinato-N,C-2) (picolinate) iridium(III) (FIrpic) show a total (power) of up to 31 lm W-1. A two-fold increase in (power) by utilizing a modified WOLED structure comprising of a composite blue host is realized. With this modified device structure, the total (power) and driving voltage at a luminance of 1000 cd m(-2) can be improved to 61 lm W-1 and 7.5 V (i.e., 10 V for control devices). The performance improvement is attributed to an effectively broaden exciton formation-recombination zone and alleviation of localized exciton accumulation within the FIrpic-doped composite host for reduced triplet-triplet annihilation, yielding blue light-emission with enhanced intensity. The modified device structure can also adopt a higher concentration of Y-Pt towards its optimal value, leading to WOLEDs with high efficiency.