Photoinduced charge injection in the metal/organic interface studied by transient photovoltage measurements with bias

Transient photovoltage of ITO/organic/Al cells is studied under different bias polarities and voltages. It is found that for an ITO/NPB/Al cell, light incidence on the Al side induces more bias-dependent transient photovoltage variation when the photovoltage is positive than when it is negative. However, for an ITO/C₆₀/Al cell, the variation characteristics of transient photovoltage is reversed. These results support the previously proposed mechanism that Al could inject charges into the organic layer upon photon excitation, indicating that the absorption of electrode can also contribute to photovoltaic effect.