Dissociation of excitons in the C60 film studied by transient photovoltage measurements

The dissociation of excitons at indium tin oxide (ITO)∕C60 interface is studied by means of transient photovoltage measurements. An abnormal polarity change of transient photovoltage from positive to negative upon pulsed laser irradiation is observed, indicating that the exciton dissociation at ITO∕C60 interface results in holes injected into ITO and electrons left in the C60 film, opposite to that occurring at ITO/NPB and ITO/CuPc interfaces. It is confirmed that C60 has a moderately strong ability of donating holes to ITO during the dissociation process of the excitons at the ITO∕C60 interface. Moreover the long term transient photovoltage (t>10ns) and its polarity can be tuned by applying external bias on the device, which further proves the validity of the model proposed to explain the polarity change of the transient photovoltage.