White Organic Light-Emitting Diodes Based on Three Emissive Layers

Abstract

We report white organic light-emitting diodes (WOLEDs) based on 4,4′-bis(2,2′-diphenyl vinyl)- 1,1′-biphenyl (DPVBi), fac tris(2-phenylpyridine)iridium (Ir(ppy)3) and bis(2-(2′-benzo[4,5-a]thienyl) pyridinato-N,C3′) iridium (acetylacetonate) (Btp2Ir(acac)). White OLEDs with the structure of ITO/NPB/DPVBi/CBP: Ir(ppy)3/BCP: Btp2Ir(acac)/Alq3/Liq/Al were fabricated and characterized, where Ir(ppy)3 and Btp2Ir(acac) were used as a green phosphorescent dye and red phosphorescent dye, respectively. And DPVBi was used as blue emitting layer. The electroluminescent spectra of the device consisted of blue fluorescent, green phosphorescent and red phosphorescent emissions. The optimized device exhibited white light emission between 10 and 15 V. A maximum luminance of 11000 cd/m2 with CIE coordinates of (0.322, 0.344) was reached at 15 V. The white light emission is related to the simultaneous exciton formation on both sides of the CBP/BCP interface. The main exciton formation zone gradually shifts to the CBP side from the BCP side with increase of voltage in the devices. As a result, the intensity of the green and blue emission increased gradually relative to the red emission with increasing voltage.