Oxygen induced p-doping of α-nickel phthalocyanine vacuum sublimed films: Implication for its use in organic photovoltaics

The effects of oxygen doping on the charge transport and photovoltaic properties of α-nickel phthalocyanine (α-NiPc) based devices are investigated using in situ and ex situ $\mathrm{I–V}$ measurements. $\mathrm{I–V}$ characteristics for devices employing gold contacts indicate ohmic conduction at low voltages, followed by space-charge-limited conduction in higher fields. Upon exposure of NiPc to dry air an increase in the hole concentration ${\mathrm{(p}}_0)$ from ${\text{8.5×10}}^{10}$ to ${\text{2.6×10}}^{15}\hspace{0.5em}{\mathrm{m}}^{\text{−3}}$ is observed. When the top gold ohmic cathode is replaced by lead, Schottky type behavior is evident with the junction exhibiting photovoltaic effect. The energy conversion efficiency of the cell increases following exposure to oxygen. These results suggest that fabrication of air stable electronic devices based on NiPc is feasible.