Time-resolved transient electroluminescence measurements of emission from DCM-doped Alq3 layers

Organic light-emitting devices (OLEDs) using NPB (α-naphthylphenylbiphenyl diamine) as the hole-transport layer and DCM [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran] doped Alq3[tris-(8-hydroxyquinoline)] as the emission layer were studied using a time-resolved transient electroluminescence method. Upon application of a pseudo-rectangular voltage pulse, the luminance increased and overshot to maxima. Using suitable spectrum filters the overshoot luminance peaks were identified to originate solely from the DCM emission. When two consecutive voltage pulses are applied, the overshoot vanished during the second pulse when time gap is shorter than 1 ms. It was considered to be related to carrier traps in the DCM molecules.