LAUSR

Abstract In this paper, we report a highly efficient two-stack warm white organic light emitting diodes (WOLEDs) with three spectral peaks using all phosphorescent organic emitters. A multi-stack OLED architecture enhances the color stability along electric field variation by separating emissive layer despite its complex structure. Performances of two- and three-stack WOLEDs having three spectral peaks are theoretically evaluated using our optical structure design method. The theoretically designed two- and three-stack structures show power efficiency of 51.5 and 33.7 lm/W at a constant current density of 1 mA/cm2 with color rendering index (CRI) of 84 and 88, respectively. Two-stack WOLED is expected to have higher power efficiency due to its lower driving voltage and smaller blue portion than that of three-stack WOLED. An optically optimized and fabricated two-stack WOLED with red and co-doped green-blue emissive layers exhibits a power efficiency as high as 58.1 lm/W and CRI of 85. The driving voltage of fabricated WOLED is (5.9 V) well correlated with the expected value of connected unit devices. In addition, our two-stack WOLED with diffusive film and hemispherical structure shows an enhanced power efficiency of 71.0 and 101.3 lm/W, respectively.