White organic light-emitting diodes with improved performance using phosphorescent sensitizer and ultrathin fluorescent emitter

White organic light-emitting diodes (WOLEDs) have been fabricated by using a novel phosphor of bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)2Ir(acac)] as a sensitizer doped into a carbazole polymer of poly(N-vinylcarbazole) (PVK), and a fluorescent dye of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) as an ultrathin red light-emitting layer. By characterizing the UV–Vis absorption spectra, photoluminescence (PL) spectra of (pbi)2Ir(acac) and DCJTB, and the electroluminescence (EL) properties of the WOLEDs, the effect of ultrathin fluorescent light-emitting layer on the injection and transport characteristics of charge carrier and EL performance of WOLEDs was investigated. The results demonstrated that the device has stable EL spectra and Commissions Internationale de 1’Eclairage (CIE) coordinates in a wide bias range. Both energy transfer and charge trapping play the role on the performance of WOLEDs, and the device luminance was enhanced significantly with a maximum luminance of 9260 cd/m2, which is about 70% higher than the codoped device.