Green organic light-emitting diodes with improved stability and efficiency utilizing a wide band gap material as the host

We propose an emitting co-doped system for obtaining high efficient and stable green organic light-emitting diodes (OLEDs) based on the host material 9,10-di (2-naphthyl) anthracene (ADN). In these diodes, 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl) quinolizino-[9,9a,1gh] coumarin (C545T) and N,N'-dimethyl-quinacridone (DMQA) are co-doped into the ADN emitting layer. In the co-doped emitting layer, ADN act as the exciting energy donor, C545T as the sensitizer and DMQA as green fluorescent dye. The green emission comes from exciton emission in DMQA molecules via a two-step excitation energy transfer from ADN to C545T and then from C545T to DMQA. The co-doped cell 0.6:1.2(wt% C545T: wt% DMQA) has showed the best performance. When the current density was 20 mA/cm(2), the brightness of the device exceeded 1400 cd/m(2) and maximum luminance reached to 15000 cd/m2 at 12 V with CIEx,y = 0.30, 0.62. The maximum current efficiency of the device reached 10.8 cd/A. Compared with devices where the emitting layer is made of Alqcl and DMQA, the emission efficiency and stability of the co-doped ADN-based devices are greatly improved. We attribute this significant improvement to effective Utilization Of the host energy and depression of concentration quenching. (C) 2008 Elsevier B.V. All rights reserved.