Formation of MIS Structure in Organic Cell Al/Pb-Phthalocyanine/ITO

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Abstract
The effects of ambient oxygen and air on the current vs voltage characteristic of the sandwich-type cell Al/Pb-Phthalocyanine/ITO (indium tin oxide) were investigated. While the effect of pure oxygen was small, exposure to air caused drastic changes in the characteristic: the linear relation with extremely low resistance observed in vacuum changed into a nonlinear characteristic with enhanced resistivity suggesting a tunnelling conduction, followed by a rectifying and photovoltaic characteristic. The extremely low resistance is a result of the formation of Al spikes penetrating though the PbPc to the ITO during preparation. The rectification and photovoltaic properties are considered to be due to a Schottky barrier with an oxide layer sandwiched between the Al and the PbPc, that is, an MIS-like barrier.