Band energies of nanoparticle semiconductor electrodes determined by spectroelectrochemical measurements of free electrons.

Nanostructured semiconductor electrodes have garnered intense recent interest for use in various solar energy conversion systems since they offer the possibilities of circumventing low efficiencies associated with short diffusion length bulk materials as well as optimizing light absorption in dye-sensitized solar cells. In such context, knowledge of the conduction (ECB) and valence band (EVB) edge positions are the most important electronic properties in order to optimize performance and obtain a detailed understanding of relevant electron-transfer processes. However, there is no reliable direct method to measure the band edges in nanostructured semiconductor electrodes. Spectroeletrochemical methods have been utilized, but the nature of the absorbing species and interpretation of results are unsettled issues. Herein we describe a new simple spectroelectrochemical method which simultaneously produces the conduction band energy and the extinction coefficient, ε, of free conduction band electrons in nanoparticle TiO2 electrodes.