Highly-efficient solution-processed green phosphorescent organic light-emitting diodes with reduced efficiency roll-off using ternary blend hosts
We have investigated the effect of various materials 1,3-bis(carbazol-9-yl)benzene (mCP), 10-(4-(5,5-dimethylbenzofuro[3,2-c]acridin-13(5H)-yl)phenyl)-10-phenylanthracen-9(10H)-one (DpAn-5BzAc), poly(9-vinylcarbazole) and 4,4′,4′′-tris(N-carbazolyl)-triphenylamine (TCTA) as the hosts on the performance of solution-processed green phosphorescent organic light-emitting diodes (PhOLEDs). Compared with the corresponding single and binary host systems, the device with the ternary blend hosts (mCP:DpAn-5BzAc:TCTA) blended with bis(2-phenylpyridine)iridium(III) acetylacetonate as a green dopant is highly efficient with the following performance parameters: a maximum brightness of 40 320 cd m−2 and a maximum current efficiency (CE) of 40.9 cd A−1 with the Commission Internationale de L’Eclairage coordinates of (0.30, 0.63). More importantly, the PhOLED device has an extremely low efficiency roll-off: at the brightness values of 1000 and 5000 cd m−2, its CEs are close, being 40.6 and 36.5 cd A−1, with the corresponding efficiency roll-off of only 0.7% and 10.8%, respectively. The superior electroluminescence performance for ternary blend host-based green PhOLEDs was attributed to the enhanced charge carrier balance, improved structural order in the film as verified by using the grazing-incidence small-angle scattering technique, along with excellent multi-component miscibility, which has a dramatic influence on the morphology of the emissive layer and the final device performance. These results demonstrate the great potential of the multi-hosts in solution-processed organic optoelectronic devices.