Double Emitting Layer Based Solution Processed WOLEDs Simultaneously with High Power Efficiency and Good Color Stability

Abstract

AbstractA double emitting layer (EML) device configuration is successfully demonstrated for power‐efficient and color‐stable white organic light‐emitting diodes (WOLEDs) that are fabricated via orthogonal solvent processing. In this case, a self‐host blue dendrimer B‐G2 is independently used as the bottom EML due to its excellent nondoped device performance and perfect alcohol resistance, and an alcohol‐soluble yellow phosphor Ir(Flpy‐CF3‐EG)3 functionalized with 2‐(2‐methoxyethoxy)ethyl group is newly developed as the upper EML combined with the arylphosphine oxide‐containing electron transporting materials. Unlike single EML based white devices, the unwanted charge trap from long‐wavelength phosphors can be easily and effectively prevented by tuning the energy level alignment in the upper EML, leading to a nearly unchanged white electroluminance with a negligible Commission Internationalede l'Eclairage (CIE) variation of ΔCIE (0.008, 0.005) in a luminance range from 2.2 to 1015 cd m−2. Meanwhile, a promising power efficiency of 51.5 lm W−1 is realized, which can be further optimized to 104.5 lm W−1 at maximum and 62.0 lm W−1 at 1000 cd m−2 after the addition of an out‐coupling half‐sphere. The simultaneous achievement of high power efficiency and good color stability clearly indicates the great potential of double EML in solution processed WOLEDs.