Ternary blend hostes for solution processed green phosphorescent organic light-emitting diodes

In this paper a series of solution processed green phosphorescent organic light-emitting diodes (PhOLEDs) based on blend hosts-guest configuration have been fabricated and the effect of various hole transport materials, e.g. 1,3-Di-9- carbazolylbenzene (mCP), poly(9-vinylcarbazole) (PVK) and 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) and their combination as the hosts on the performance of PhOLEDs have investigated. It is found that the device with the ternary blend host (mCP:PVK:TCTA) doped with tris(2-(p-tolyl)pyridine-C2,N)iridium(III) (Ir(mppy)3) as a green guest material can achieve a luminance of 10213 cd m-2 at a driven voltage of 7 volts, the uppermost external quantum efficiency (EQE) of 16.91%, and a small roll over and maintain EQE of 12.95% at 1000 cd m-2 with the CIE coordinates of (0.31,0.61). Compared with the corresponding single and binary host systems (mCP, 4600.49 cd m-2, 14.62%, 24.90%; PVK, 5116.74 cd m-2, 15.77%, 19.78%; mCP:PVK, 5275.05 cd m-2, 16.99%, 22.07%), the PhOLED based on ternary-host materials has the optimal performance. The superior electroluminescence (EL) performance for ternary blend host-based green PhOLEDs was attributed to the efficient energy transfer from the host to dopant, the appropriate highest occupied molecular orbital (HOMO) level and the enhanced charge carrier transport balance.