The carrier transport properties of the blends of the hole transport material poly(N-vinylcarbazole) (PVK) and the electron transport material tris (8-hydroxyquinolinolato) aluminum III (Alq3) are investigated at room temperature using steady-state and time-resolved transient photocurrent measurements as a function of doping concentration of Alq3. Due to lower LUMO and higher HOMO energy level of Alq3 than those of PVK

Alq3 molecules may act as carrier trap states in PVK films at low concentration. However

at high concentration of Alq3

phase separation reduces trap states to some extent

which leads to the rise of photocurrent. It is concluded that strong excitation transfer from PVK to Alq3 does harm to photocurrent

because strong fluorescence effect of Alq3 inhibits photogeneration of charge carriers. In time-resolved transient photocurrent measurements

it is found that the decay time is obviously shortened because the recombination rate increases and the electron mobility of Alq3 is higher than the hole mobility of PVK.