Electron Localization and Transport in SnO/TiO Mesoporous Thin Films: Evidence for a SnO/SnTiO/TiO Structure.

A study of SnO/TiO core/shell films was undertaken to investigate the influences of shell thickness and post deposition sintering on electron localization and transport properties. Electrochemical reduction of the materials resulted in the appearance of a broad visible-near IR absorbance that provided insights into the electronic state(s) within the core/shell structures. As the shell thickness was increased from 0.5 to 5 nm, evidence for the presence of a SnTiO interfacial state emerged that was physically located between the core and the shell. The lifetime of photoinjected electrons increased with the shell thickness. Electron transport occurred through the SnO core; however, when materials with shell thicknesses ≥2 nm were annealed at 450 °C, a new electron transport pathway through the shell was evident. The data indicate that these materials are best described as SnO/SnTiO/TiO where electrons preferentially localize in a SnTiO interfacial state and transport through SnO and annealed TiO (if present). The implications of these results for applications in solar energy conversion are discussed.