Charge Transport Properties in Nanostructured Electrodes of Metal Oxides

Abstract: In the last decade research in the field of nanostructured metal oxide thin film electrodes for various applications, e.g., solar cells and hydrogen production, has been of great interest. In this thesis, interfacial and bulk electrochemical properties and charge transport properties of nanostructured thin films have been investigated. Studies of the dependence on such properties on the morphology and chemical composition of the nanocrystalline metal oxide particles are reported.Different techniques were used to manufacture the thin film electrodes, e.g., sputtering, forced hydrolysis and a compressing method. The resulting films were investigated using time resolved photocurrent measurements and steady state solar cell measurements.Initial studies were performed with nanorods of iron(III)oxide as a semiconductor material for both photoelectrochemical solar energy conversion and splitting of water. Incident photon-to-current conversion efficiencies reached values that are about 7 and 100 times higher, depending on illumination direction, compared to spherical particles. In the same spirit, investigations on sputtered TiO2 material exhibiting columnar structure with a very large internal surface area were performed. Compared to colloidally prepared films, where the electron transport is driven by diffusion, the transport in the sputtered films is in addition driven by an electric field.Two combinations of incorporated TiO2 (Nb:TiO2 and Zr:TiO2) were investigated. Recordings from time resolved photocurrent measurements showed that the charge transport was slower for electrodes containing Zr and Nb compared to pure TiO2 sample, probably due to additional trap states. However, an increase in the overall light-to-electric-conversion efficiency was observed for a Zr content of 1–2 mol% compared to pure TiO2.