Electrical characterisation of phthalocyanine-fullerene photovoltaic devices

The morphology of the active layer of molecular and polymer photovoltaic devices is important for the device performance. The vacuum thermal (co-)evaporation of molecular materials enables a better control over the film formation. We fabricated and studied two-layer- and co-evaporated photovoltaic cells made of zinc-phthalocyanines (ZnPc) and fullerenes (C60). The photovoltaic efficiency of the cells was studied by the current-voltage (I-V) technique. Moreover, admittance spectroscopy was applied to study electrically active defects. In this method, the conductance and capacitance are measured as a function of the frequency of the applied sc-bias and temperature. In the C(omega ,T) spectrum, we observed one step which is due to trapping/detrapping of the shallow traps. External quantum yields of 3% and 7% were measured for the two-layer and the co-evaporated cell, respectively.