Influence of O2 on rectification properties of nickel phthalocyanine thin film devices

Thin sandwich film structure devices of Gold/Nickel Phthalocyanine/Lead (Au/NiPc/Pb) were fabricated employing a novel in-situ method. Electrical measurements were performed prior to, and after exposure of the samples to dry air. Under forward bias and for low applied voltages an ohmic conduction was evident, followed by SCLC in the higher voltage range. In the reverse bias, devices were found to exhibit weak rectifying properties originated mainly from the bulk of the NiPc layer. After exposure of the sample to dry air for five days a strong rectifying effect at the NiPc/Pb interface was evident. The phenomenon is believed to be associated with a change of NiPc work function as result of O-2 adsorption on the NiPc layer. To verify this a second sample of the type Au/NiPcO2/Pb, was fabricated. Electrical characterization of the sample showed stronger rectifying properties providing further experimental evidence on the influence of O-2 adsorption on the organic layer. Potential barrier height and diode ideality factor for both NiPc/Pb, and NiPcO2/Pb interfaces after exposure to dry air, were also calculated.