Transient photovoltage (TPV) was performed on the ITO/tris-(8-hydroxyquinolinato)aluminum (AlQ)/silver device to study the dynamics of carriers. It has been previously reported that typical TPV results in organic semiconductors show no more than one turning point of voltage polarity, where interfacial exciton dissociation and carrier drift are responsible as suggested by the conventional model. By contrast, two polarity turning points were observed in our TPV studies, for which the conventional model fails to explain and thus a more detailed model is proposed to add the diffusion of carriers. The new model is further supported by the TPV evolution study where the effect induced by insertion of a thin LiF layer between AlQ and silver was examined. Our new findings may give a better understanding of optoelectronic dynamics in organic semiconductors.

Devices with copper phthalocyanine (CuPc):molybdenum trioxide (MoO3) co-evaporated layer were fabricated and the current–voltage (I–V) and capacitance–voltage (C–V) characteristics were measured. It has been found that for a given voltage, the current of the device with a co-evaporated layer is higher than those without the co-evaporated layer and it reaches the highest value if the ratio of MoO3 to CuPc is 1:1. Meanwhile, the C–V characteristics showed that only free holes exist in the function layer consisting of pure CuPc. However, charge transfer (CT) complexes exist in the function layer of a CuPc:MoO3 mixture. The charge transfer complexes do not contribute to the transport of the device efficiently under low applied fields but are disassociated into free carriers rapidly at applied fields higher than 1.7 × 105 V/cm, which greatly increases the conductivity.

Understanding of the dynamic optoelectronic processes at the organic/ metal electrode interface is crucial to the interface engineering of organic electronics. Here we present the systematic studies of exciton dissociation of p-type organic semiconductor at the organic/Ag interface. The interfacial dissociation of photogenerated excitons at the N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB)/Ag interface was systematically investigated using the transient photovoltage technique as a proof-ofconcept. The results indicate that two types of exciton dissociationtransfer of either electrons or holes to the metal electrodecoexist at the organic/metal electrode interface. This conclusion is further confirmed by two additional experimentsthe current response of the NPB/Ag interface to light illumination under constant biases and the successive light current−voltage measurements under constant illumination. Moreover, the proportion of two types of dissociations was found to be tunable upon the oxidation of the silver electrode or the insertion of a lithium fluoride interlayer to the NPB/Ag interface. These results may be useful for interface engineering of organic photovoltaic cells.