39.4: Highly Efficient Fluorescent Blue OLEDs with Efficiency‐enhancement Layer

Abstract We found a new device structure which has an efficiency‐ enhancement layer between emitting layer and electron transporting layer. We applied the structure to a pure blue fluorescent device with a CIE1931 coordinate of (0.14, 0.12) and successfully obtained very high EQE of over 10% with low driving voltage of 3.7 V at 10 mA/cm 2 and long lifetime of 10,000 hrs at an initial luminance of 1,000 cd/m 2 . Results of transient EL measurements indicated the contribution of triplet excitons to the high EQE.