Determination of band edge energies for transparent nanocrystalline TiO2-CdS sandwich electrodes prepared by electrodeposition

We describe preparation of transparent nanocrystalline semiconductor sandwich electrodes. Specifically, TiO2-CdS and CdS-TiO2 sandwich electrodes have been prepared by electrodeposition of CdS on TiO2 and TiO2 on CdS, respectively. Also described are the application of optoelectrochemical techniques for determination of the energy of the conduction band edge at thesemiconductor-liquid electrolyte solution interface (V-cb). Specifically, V-cb has been determined for each semiconductor in nanocrystalline TiO2, CdS, TiO2-CdS and CdS-TiO2 electrodes. For TiO2 and CdS electrodes, V-cb is -0.37 V (SCE) and -0.7 V, respectively, in aqueous solution at pH 2.0. Under similar conditions V-cb for TiO2 and CdS is -0.47 V and -0.4 V, respectively, in the corresponding TiO2-CdS sandwich electrode. Using the results of these and similar experiments, it has been possible to prepare energy level diagrams for nanocrystalline semiconductor sandwich electrodes. Implications for potential applications of these electrodes, particularly in regenerative photoelectrochemical cells, are considered.