Evidence for the atmospheric p-type doping of titanyl phthalocyanine thin film by oxygen observed as the change of interfacial electronic structure

The effect of O2 doping on titanyl phthalocyanine (TiOPc) thin films was investigated by ultraviolet photoelectron spectroscopy (UPS). The results revealed a clear change in the film thickness dependence of the energy of the electronic levels on exposure to O2. The film deposited in ultrahigh vacuum showed downward band bending characteristic of a n-type semiconductor, probably due to unintentional doping by residual impurity. On the other hand, the film deposited in O2 atmosphere showed upward band bending characteristic of a p-type semiconductor. This conversion is ascribed to the hole doping by O2. These results correspond well with the reported change of the electrical behavior for TiOPc-based field effect transistors.