Direct observation of microscopic photoinduced charge redistribution on TiO2 film sensitized by chloroaluminum phthalocyanine and perylenediimide

The microscopic photoinduced charge redistribution on the surface of an organic dye composite layer was directly observed using Kelvin probe force microscopy (KFM) coupled with a laser source. The organic layer composed of chloroaluminum phthalocyanine and N,N′-dioctadecyl-3,4,9,10-perylene tetracarboxylic-diimide was cast onto the surface of nano-TiO2 film. Under illumination, the surface potential morphologies of the organic layer changed from large fluctuation to relatively uniform features. Such a phenomenon was associated with the photoinduced charge transfer between the dye composite and nano-TiO2, which was rationalized in terms of energy level alignment. Considering that the KFM have been proved to be a visual technique in the characterization of nanomaterials, we have presented a method to visualize the photoinduced charge transfer in microscopic scale.