Abstract
Highly efficient single-stack hybrid cool white organic light-emitting diodes (OLEDs) having blue-yellow-blue multiple emitting layers (EMLs) are designed and constructed by utilizing blue thermally activated delayed fluorescent (TADF) and yellow phosphorescent emitters. The out-coupling efficiencies of yellow and blue emissions are maximized by tuning the ITO and total device thickness that satisfies both of antinode positions for yellow and blue emissions in a limited multiple EML thickness. To obtain a cool white emission, the exciton formation ratio in the blue-yellow-blue multiple EML system is controlled by manipulating the recombination zone through charge conductivity variation of host medium in the blue TADF EML. The resulting device exhibits cool white emission with very high maximum external quantum efficiency of 23.1% and CIE color coordinates of (0.324, 0.337). We anticipate that the studied approach will raise the viability of single-stack hybrid cool white OLEDs for high performance display applications.
Highlights
White organic light-emitting diode (WOLED) is a core technology for large-area active matrix organic light-emitting diodes (OLEDs) (AMOLED) displays and a promising candidate for generation lighting applications[1,2]
Single-stack cool WOLEDs (CWOLEDs) with blue-yellow-blue hybrid multiple emitting layers (EMLs) structure was developed by utilizing blue thermally activated delayed fluorescent (TADF) and yellow phosphorescent emitters
The device structure was optimized to achieve balanced and highly efficient blue and yellow emission by using constructive interference condition of the blue and yellow emission as well as exciton dynamics in the multiple EML system. Both of constructive interference condition for yellow and blue emissions are satisfied even in the single-stack OLED using 150 nm thick indium tin oxide (ITO) and second antinode condition, which results in high out-coupling efficiency and very high external quantum efficiency (EQE) of 23.1%
Summary
White organic light-emitting diode (WOLED) is a core technology for large-area active matrix OLED (AMOLED) displays and a promising candidate for generation lighting applications[1,2]. Only three-stack tandem structure is adopted for display applications due to its high efficiency and long device life In this tandem structure, two blue emitting layers (EML) are used to compensate low intensity of blue fluorescence, and thereby highly efficient cool white emission and long device life can be achieved. Two blue emitting layers (EML) are used to compensate low intensity of blue fluorescence, and thereby highly efficient cool white emission and long device life can be achieved Such a complicate structure increases manufacturing cost and driving voltage and degrades viewing angle characteristics. By utilizing the optimum device thickness and the multiple EML system, very high external quantum efficiency (EQE) of 23.1% and cool white emission with CIE color coordinate of (0.324, 0.337) are achieved in single-stack hybrid CWOLED
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