Enhancement of efficiency for white-organic light-emitting diode with a thin electron-blocking layer

Abstract

In this study, we have enhanced the emission property of white-organic light-emitting diodes using the method of inserting the ultrathin electron-blocking layer (thin-EBL) between red-green-blue emissive layers. The devices into which three emissive layers are inserted were fabricated with indium tin oxide/CuPc/[N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine] (alpha-NPD/DPVBi/thin-EBL/Alq(3)/Alq(3): 2wt% 4-(dicyano-methylene)-2-methyl-6-(dimethylaminostyryl-4H-pyran (DCM1)/Alq3/LiF:Al. To enhance the white emission property and improve the efficiency of devices, we suggest the alpha-NPD as the thin-EBL. According to knowledge of the energy band diagram, alpha-NPD was inserted between the blue-emitting layer and green-emitting layer. The alpha-NPD layer showed the effective blocking of electron as a function of thickness. From the Experimental, the effective blocking of electrons through controlling the thin-EBL thickness embodied the balanced white emission and improved the efficiency of the device. In our device with 0.3 nm alpha-NPD, it had a maximum power efficiency of 3.80 lm/W at 250 cd/m(2), a luminance efficiency of 5.14 cd/A at 4.83 mA/m(2), a luminance of 1200 cd/m(2) at 100 mA/cm(2), and the CIE coordinates were (0.353, 0.357), respectively. (c) 2005 The Electrochemical Society.