Highly efficient white organic light-emitting devices consisting of undoped ultrathin yellow phosphorescent layer

High-efficiency white organic light-emitting devices (WOLEDs) based on an undoped ultrathin yellow light-emitting layer and a doped blue light-emitting layer were demonstrated. While the thickness of blue light-emitting layer, formed by doping a charge-trapping phosphor, iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6) in a wide bandgap host, was kept constant, the thickness of neat yellow emissive layer of novel phosphorescent material, bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′]iridium (acetylacetonate) [(t-bt)2Ir(acac)] was varied to optimize the device performance. The optimized device exhibited maximum luminance, current efficiency and power efficiency of 24,000 cd/m2 (at 15.2 V), 79.0 cd/A (at 1550 cd/m2) and 40.5 lm/W (at 1000 cd/m2), respectively. Besides, the white-light emission covered a wide range of visible spectrum, and the Commission Internationale de lʹEclairage coordinates were (0.32, 0.38) with a color temperature of 5800 K at 8 V. Moreover, high external quantum efficiency was also obtained in the high-efficiency WOLEDs. The performance enhancement was attributed to the proper thickness of (t-bt)2Ir(acac) layer that enabled adequate current density and enough phosphorescent dye to trap electrons.