Charge Recombination Dynamics in Sensitized SnO2/TiO2 Core/Shell Photoanodes

• Published in: Journal of physical chemistry. C 2015-12, Vol.119 (51), p.28353-28360
• Main Authors: Knauf, Robin R, Kalanyan, Berç, Parsons, Gregory N, Dempsey, Jillian L
• Format: Article
• Language: English
• Subjects: catalysis (heterogeneous); catalysis (homogeneous); charge transport; electrodes - solar; hydrogen and fuel cells; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; materials and chemistry by design; photosynthesis (natural and artificial); solar (fuels); solar (photovoltaic); synthesis (novel materials); synthesis (self-assembly)
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.5b10574

Studies have been conducted to examine the mechanisms of charge recombination in dye-sensitized SnO2/TiO2 core/shell films. Nanostructured SnO2/TiO2 core/shell films varying in TiO2 shell thicknesses were prepared via atomic layer deposition and sensitized with a phosphonate-derivatized ruthenium chromophore [Ru­(bpy)2(4,4′-(PO3H2)2bpy)]2+. Transient absorption spectroscopy was used to study the interfacial charge recombination dynamics for these core/shell materials. Charge recombination for sensitized, as-deposited SnO2/TiO2 core/shell systems is dominated by a tunneling mechanism for shell thicknesses between 0 and 3.2 nm, with β = 0.25 Å–1. For shell thicknesses greater than 3.2 nm, recombination primarily proceeds directly via electrons localized in the relatively thick TiO2 shell. Annealing the SnO2/TiO2 core/shell structure at 450 °C affects the recombination dynamics substantially; charge recombination dynamics for the annealed films do not show a dependence on shell thickness and are comparable to ZrO2/TiO2 control samples, suggesting the annealing process perturbs the core/shell interface. This analysis of charge recombination dynamics indicates that there is an optimum shell thickness to maximize charge separation lifetimes in dye-sensitized core/shell photoanodes and that the nature of the core/shell interface influences the efficacy of these materials.