Electrical characterisation of phthalocyanine-fullerene photovoltaic devices

The morphology of the active layer of molecular and polymer photovoltaic de vices is important for the device performance. The vacuum thermal (co-)evap oration of molecular materials enables a better control over the film forma tion. We fabricated and studied two-layer- and co-evaporated photovoltaic c ells made of zinc-phthalocyanines (ZnPc) and fullerenes (C60). The photovol taic efficiency of the cells was studied by the current-voltage (I-V) techn ique. Moreover, admittance spectroscopy was applied to study electrically a ctive 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/det rapping of the shallow traps. External quantum yields of 3% and 7% were mea sured for the two-layer and the co-evaporated cell, respectively.