White organic light-emitting devices with a bipolar transport layer between blue fluorescent and yellow phosphor-sensitized-fluorescent emitting layers

We report white organic light-emitting devices (WOLEDs) based on 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) and phosphorescence sensitized 5,6,11,12-tetraphenylnaphthacene (rubrene). By introducing a bipolar transport 4,4′-N,N′-dicarbazole-biphenyl (CBP) layer between the fluorescent and the phosphor-sensitized-fluorescent layers, additional light emission from the phosphorescence sensitized layer is observed. This can be attributed to the elimination of the Dexter energy transfer between these two emitters. White emission with Commission International de L’Eclairage coordinates of (0.22,0.33) and a maximum luminance of 22,360 cd/m2 were obtained. The maximum current efficiency can reach 10.7 cd/A.