Color-stable non-doped white phosphorescent organic light-emitting diodes based on ultrathin emissive layers

Color-stable white organic light-emitting diode (WOLED) with bipolar mixed spacer based on ultrathin non-doped phosphorescent emitting layers was investigated. We find that the location and thickness of Bis(3,5-difluoro-2-(2-pyridyl) phenyl-(2-carboxypyridyl)iridium(III) (FIrPic) play a critical role on the spectral stability. Transient PL lifetime results show that the spectral variations with the driving voltage can be effectively controlled by enhanced energy transfer or weakened energy transfer respectively depending on different location of FIrPic. Meanwhile, green layer, located between blue layer and orange layer, acts an indispensable role in keeping the color stability by alleviating triplet–triplet annihilation and maintaining sequential energy transfer. The most stable spectrum of WOLED can be obtained with the change in Commission Internationale de L'Eclairage coordinates less than (0.001, 0.002) as the luminance increase from 697 cd m⁻² to about 16 550 cd m⁻² when FIrPic is on anode side. This discovery provides a significant method for achieving high-quality WOLEDs with superior color stability. (paper)