Chemical modification of GaPc-Cl thin film photoelectrodes

Modification of chlorogallium phthalocyanine (GaPC-Cl) thin film photoelectrodes with thin films of polyvinylferrocene (PVF), thin films of PVF with incorporated ferricyanide, and thin films of a coprecipitated ferricenium-ferricyanide salt is demonstrated. The analysis of the coprecipitated ferriceniuin-ferricyanide salt demonstrates the formation of a Prussian Blue (PB)-like electroactive film. PVF films on bare gold were first characterized to demonstrate incorporation of ferricyanide during formation of ferricenium ions. This was followed by demonstration of the direct interaction of ferrocenium and ferricyanide, without the polymer, on bare gold, and on the Pc surface. GaPc-Cl films overlayed with PB thin films formed from ferricenium/ferricyanide can produce either negative or positive photopotentials, depending upon the dopant condition of the Pc layer, relying only upon the photoelectrochemical redox activity of the PB layer. On the PVF-modified GaPc-Cl electrodes, the ferrocene redox activity could be depleted in the dark through oxidation at potentials positive of the apparent flat band potential of the p-type molecular semiconductor. Following this, reduction of the ferricenium centers was suppressed by the rectifying nature of the Pc layer, until solution contact was made with a reductant such as ascorbate. Redox activity of the ferrocene (oxidation of ferrocene in PVF) could be restored in relation to the solution concentration of the ascorbate.