Cathodic electrodeposition of oxide semiconductor thin films and their application to dye-sensitized solar cells

Cathodic electrodeposition of titanium dioxide (TiO2) and zinc oxide (ZnO) thin films has been studied in the aim of developing cost-effective alternative routes to the photoelectrode materials for dye-sensitized solar cells (DSCs). Preparation of porous anatase TiO2 thin film modified by cis-dithiocyanato bis(4,4′-dicarboxylic acid-2,2′-bipyridine)ruthenium(II) (N3) dye has been achieved by a three-step process: cathodic electrodeposition of a Ti hydroxide thin film from an acidic aqueous solution containing TiOSO4, H2O2 and KNO3, heat treatment of the film at 400 °C and chemical adsorption of dyes from solution. The photocurrent action spectrum measured at the N3-modified TiO2 thin film electrode in contact with I−/I3− redox electrolyte solution revealed incident photon to current conversion efficiency (IPCE) of 37% in the visible range. While TiO2 needed heat treatment for crystallization, direct electrodeposition of crystalline ZnO was possible from an aqueous solution of Zn(NO3)2. Addition of N3 to the deposition bath made it possible to synthesize porous ZnO/N3 hybrid thin film in one step. IPCE of 24% has been achieved for this film. A sandwich cell using the electrodeposited ZnO/N3 hybrid thin film photoelectrode measured Isc=0.61 mA/cm2, Voc=0.46 V, F.F.=0.46 and η=0.13% under illumination by an artificial light source (500-W Xe lamp equipped with a <420-nm and an IR cutoff filters, intensity=100 mW cm−2), being the first example of a real working DSC fabricated without any heat treatment.