Interfacial electrostatic phenomena in phthalocyanine Langmuir–Blodgett films

Surface potentials of Cu-tetra-tert-butyl-phthalocyanine (CuttbPc) Langmuir–Blodgett (LB) films on metal electrodes were measured under photoillumination in a vacuum vessel. The surface potential of CuttbPc LB films on Al and Cr electrodes, positively charged as deposited. Decreases very little but not zero by photoillumination, whereas the potential of films on Al and Cr electrodes increases. A linear relationship between the work function of metal electrodes and the saturated surface potential of CuttbPc LB films was obtained in dark and under photoillumination, indicating that electronic charges are exchanged at the interface between metal electrodes and film. The space charge distribution in CuttbPc LB films was determined on the order of nanometer film-thickness scale. It was concluded that about 1% of CuttbPc molecules make a contribution to the charge exchange and 9–27% of the contributed charges lose the charge exchange by photoillumination.