Spectral Characteristics of White Organic Light-Emitting Devices Based on a Novel Nitrile Fluorescence Dye
WEN Wen,YU Jun-sheng*,LI Lu,MA Tao,JIANG Ya-dong
State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China
Abstract：A white organic light-emitting device with a blend polymeric emissive system consisting of a novel nitrile fluorescence (2Z, 2’Z)-3, 3’-(1,4-phenylene)bis(2-phenylacrylonitrile) (BPhAN) as dopant and poly(N-vinylcarbazole) (PVK) as host was fabricated. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was introduced into bilayer device as an electron transporting layer (HTL) and a hole blocking layer (HBL), respectively. By adjusting the doping ratio of BPhAN, a series of devices with different concentration proportion of PVK∶BPhAN were constructed. The photoluminescence (PL) and electroluminescence (EL) characteristics of the devices were systemically studied. The Frster energy transfer mechanisms and direct carrier trapping mechanisms were specially investigated. The results showed that effective Frster energy transfer from PVK to BPhAN existed in the blending system as well as carrier trapping. However, at the identical bias voltage, the performance of devices was affected mainly by the carrier trapping mechanisms. Nevertheless, at different bias voltages, the performance of devices was affected by both of the two mechanisms. When the doping ratio of BPhAN reached 4 wt%, bright white light was obtained. The peaks of EL spectra were located at 425 and 556 nm corresponding to the Commissions Internationale De L’Eclairage (CIE) coordinates of (0.33, 0.37) at 6 V and (0.32, 0.33) at 16 V, respectively. The slight shift of CIE coordinates was attributed to that energy transfer probability from PVK to BPhAN and BPhAN charge carrier trapping efficiency both decreased with the increase in voltages.
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