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The effects of oxygen doping on the charge transport and photovoltaic properties of ␣-nickel phthalocyanine ͑␣-NiPc͒ based devices are investigated using in situ and ex situ I -V measurements. 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 (p 0 ) from 8.5ϫ1010 to 2.6ϫ10 15 m Ϫ3 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.

Sandwich structures of Au/NiPc/Au were fabricated by sequential vacuum thermal sublimation onto borosilicate glass substrates. dc electrical measurements were performed for several NiPc thin films of different thickness in the range (d 0:25±1.09 mm). The relative permittivity was measured at a low frequency of 100 Hz, yielding a value of e r 2:74. This value is considerably lower in comparison with previously published data for various phthalocyanine materials. Current density±voltage characteristics at room temperature reveal an Ohmic conduction in the lower voltage range, followed by SCLC in the higher range, where the latter was found to be controlled by an exponential trap distribution. The plot of current density versus thickness provides further evidence of this effect. The results are analyzed in terms of exponential trap distribution yielding the following values: The temperature parameter characterizing the exponential trap distribution T t 1165 K, the concentration of thermally generated holes p 0 1:40 Â 10 16 m ± ±3 , trap concentration per unit energy range P 0 4:71 Â 10 43 J ± ±1 m ± ±3 and total concentration of traps N t e 7:57 Â 10 23 m ± ±3 .

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