Improved electroluminescent efficiency of organic light emitting devices by co-doping N, N′-Dimethyl-quinacridone and Coumarin6 in tris-(8-hydroxyquinoline) aluminum

Electroluminescent (EL) efficiency of organic light emitting devices was improved by co-doping N, N′-dimethyl-quinacridone (DMQA) and Coumarin6 (C6) in tris-(8-hydroxyquinoline) aluminum (Alq3). At 20mA∕cm2, superior EL efficiency of 9.33cd∕A was obtained from 1.6% co-doped (0.8% DMQA and 0.8% C6) device, much higher than those of single-doped devices based on 1.6% DMQA (∼5.0cd∕A) or 1.6% C6 (∼6.0cd∕A). EL efficiency of the single-doped devices with optimal dopant concentration, 0.8% in both cases, are merely 7.13cd∕A for DMQA and 6.43cd∕A for 0.8% C6, respectively. The significant improvement could be attributed to effective utilization of the host energy and depression of concentration quenching. The co-doping technique provides an effective way to overcome the notorious concentration quenching and hence to improve the EL efficiency.