The transient photovoltage of ITO/CuPc/AI is studied. The transient photovoltage under the Al side illumination is much greater than that under ITO side illumination. It is not negligible while light is almost completely absorbed by the Al layer. It seems that the light absorption of the Al layer could enhance the generation of the photoinduced carriers in the organic layer, which is further shown by the transient photovoltage study of ITO/Al/NPB/Au. A possible mechanism proposed is that the holes generated in the Al are because of light absorption that is injected from the AI to organic materials. This results in further charge separation by the internal built-in electric field.
Non-monotonic, asymmetrical electric field dependence of photoluminescence （PL） intensity is observed in a mono- layer sample of tris-（8-hydroxyquinoline） aluminum （A1Q） doped N,N＇-bis（3-methylphenyl）-N,N＇-bis（phenyl）-benzidine （TPD）. A possible model is proposed： the charge separation from the dissociated photoexcited excitons causes energy band bending in the organic films and improves the hole injection from the electrode, which brings about the extra fluorescence. This mechanism is further verified by a series of experiments using a series of samples, variously featuring symmetrical electrodes, block layers, and hosts with lower hole mobilities.
