Improvement of Power Efficiency in Phosphorescent White Organic Light-Emitting Diodes Using p-Doped Hole Transport Layer

We investigated the optical and electrical properties of molybdenum trioxide- (MoO3-) doped (1,1-bis[(di-4-tolylamino)phenyl]cyclohexane) (TAPC) films with different doping concentrations. Based on our results, we have fabricated white organic light emitting diodes (WOLEDs) with multi-emitting layer structures that consist of 1,3-bis(9-carbazolyl)benzene as a host and three phosphorescent dopants: iridium(III) bis[4,6-difluorophenyl]-pyridinato-N,C2′] picolinate as a blue dopant, bis(2-phenylbenxothiozolato-N,C2′)iridium(III) (acetylacetonate) as an orange dopant, and bis(1-phenylisoquinoline) (acetylacetonate) iridium(III) as a red dopant. We improved the power efficiency and decreased driving voltage of WOLEDs by employing a MoO3-doped TAPC layer as a hole transport layer. The MoO3-doped TAPC layer lowers the driving voltage by about 1.2 V and increases the power efficiency from 6.2lm⋅W−1 to 7.9lm⋅W−1 at 1,000cd⋅m−2, an approximately 27.4% increase. Furthermore, the WOLED has a high color-rendering index, which is about 86 with the Commission Internationale de l’Eclairage 1931 chromatic coordinates of (0.4303, 0.3893) and correlated color temperature of 3008 K