Synthetic Metals 160 (2010) 829–831 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Short communication White organic light-emitting devices with a bipolar transport layer between blue fluorescent and yellow phosphor-sensitized-fluorescent emitting layers Qin Xue, Guohua Xie, Ping Chen, Jianhua Lu, Dandan Zhang, Yanna Tang, Yi Zhao ∗ , Jingying Hou, Shiyong Liu State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Qianjin Street, Changchun 130012, People’s Republic of China article info Article history: Received 2 September 2009 Accepted 15 December 2009 Available online 12 January 2010 Keywords: White organic light-emitting diodes Bipolar transport layer Phosphorescence sensitized abstract 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/m 2 were obtained. The maximum current efficiency can reach 10.7 cd/A. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent years, organic light-emitting devices (OLEDs) have attracted more and more attention due to their potential appli- cations in flat panel displays. The needs for white organic light-emitting devices (WOLEDs), as one of the major methods to fabricate full-color display combined with color filters, as flat panel display backlights and as general solid-state lighting sources, have spurred much effort in the research of them [1–8]. Although phos- phorescent materials can harvest both singlet and triplet excitons which lead to the potential for achieving 100% internal quantum efficiency [9,10], the instability and the low efficiency of the blue phosphorescent dyes, as well as their demand for wide band-gap host materials, will hamper their application in field of display or lighting. In general, the electroluminescence (EL) efficiencies of all-fluorescent devices are relatively low unless phosphores- cent complexes are added to sensitize the Förster energy transfer between the phosphor triplet excitons and the singlet excitons in the fluorophore [9]. As for organic materials, their emission spec- tra are generally broader than that of inorganic materials, and thus two complementary colors can produce white light emission. So the combination of fluorescent blue and phosphor-sensitized- fluorescent yellow emitting layers may solve these problems and obtain efficient and stable WOLEDs. Recently, efficient WOLEDs were reported to comprise the fluorescent blue emitter and the phosphorescent green and red emitters [11,12]. However, an ∗ Corresponding author. E-mail address: xueqin19851202@163.com (Y. Zhao). interlayer was also inserted to separate the fluorescent and the phosphorescent emitting layers, thereby preventing the mutual quenching between the fluorescent blue and the phosphorescent red and green emitters [12]. Here we reported an efficient WOLED by introducing a bipolar transport 4,4 ′ -N,N ′ -dicarbazole-biphenyl (CBP) layer between fluo- rescent blue and phosphor-sensitized-fluorescent yellow emitting layers (EMLs), where 4,4 ′ -bis(2,2 ′ -diphenylvinyl)-1,1 ′ -biphenyl (DPVBi) and CBP codoped with 5,6,11,12-tetraphenylnaphthacene (rubrene) and fac tris (2-phenyl-pyridine) iridium [Ir(ppy) 3 ] are used as blue and yellow EMLs, respectively. The presence of CBP may prevent the quenching between the fluorescent blue and the phosphor-sensitized-fluorescent yellow emitters. This quenching may occur through the nonradiative triplet energy level of the flu- orescent blue emitters, which is positioned lower than the radiative triplet energy level of the phosphorescent green emitters. 2. Experimental details ITO-coated glass was used as the substrate for OLEDs. Organic layers were deposited by high-vacuum (10 -6 Torr) thermal evaporation with a rate of 0.1–0.2 nm/s. 4,4 ′ ,4 ′′ -tris(3- methylphenylphenylamino)-triphenylamine (m-MTDATA) and N,N ′ -bis-(1-naphthyl)-N,N ′ -diphenyl-1,1 ′ -biphenyl-4,4 ′ -diamine (NPB) were used as hole-transporting layers (HTLs). 4,7-diphenyl- 1,10-phenanthroline (Bphen) was used as hole-blocking (HBL) and electron-transporting layer (ETL). A bilayer cathode of LiF/Al was subsequently vapor-deposited onto the organic films. The layer thickness and the deposition rate of the organic and inor- ganic materials were monitored in situ by an oscillating quartz 0379-6779/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2009.12.011