Photoelectrochemical properties of hybrid junctions based on zinc phthalocyanine and semiconducting colloidal nanocrystals

In this paper, a photoelectrochemical study of hetero-junctions formed by zinc phthalocyanine (ZnPc) and semiconductor oxide nanocrystals (NCs), is reported. To this purpose, thin films composed of either size- and shape-controlled ZnO or TiO 2 NCs, synthesized by both hydrolytic and non-hydrolytic colloidal methods, were investigated as photo-anodes with ZnPc as the sensitizer. The effects of the oxide nature, of the nanocrystal shape and surface chemistry, and of the modality of photo-anode preparation on the resulting photoelectrochemical response were evaluated. In general, the photoactivity was found to be significantly enhanced when ZnO NCs were used as compared to TiO 2 NCs. In the latter case, the hetero-junctions based on non-hydrolytically prepared TiO 2 provided remarkably lower photocurrents with respect to those formed by its hydrolytically synthesized analogous. Moreover, a slight improvement of photoactivity was observed if spherical TiO 2 NCs were replaced by rod-like particles. Finally, as opposed to expectations, photo-anodes deposited from NC-ZnPc blended solutions exhibited a photoelectrochemical response comparable to that of sensitized films prepared by layer-by-layer procedure.