Enhanced Photovoltaic Performance of Nanowire Dye-Sensitized Solar Cells Based on Coaxial TiO2@TiO Heterostructures with a Cobalt(II/III) Redox Electrolyte

The growth of a TiO shell at the surface of TiO2 nanowires allowed us to improve the power conversion efficiency of nanowire-based dye-sensitized solar cells by a factor 2.5. TiO2@TiO core-shell nanowires were obtained by a two-step process. First, rutile-phase TiO2 nanowires were hydrothermally grown. Second, a hongquiite-phase TiO shell was electrochem. deposited at the surface of the TiO2 nanowires. Bare TiO2 and heterojunction TiO2@TiO nanowire-based dye-sensitized solar cells were obtained using a cobalt(II/III) redox electrolyte and LEG4 as the dye. With this electrolyte/dye combination, dye-sensitized solar cells with outstanding open-circuit voltage values above 900 mV were systematically obtained. While TiO2@TiO nanowire-based dye-sensitized solar cells had slightly lower open-circuit voltage values than bare TiO2 nanowire-based dye-sensitized solar cells, they provided 3-fold higher photocurrents, overall reaching 2.5-fold higher power conversion efficiencies. The higher photocurrents were assocd. with the larger surface roughness and an enhanced charge-carrier sepn./transfer at the nanowire/dye interface.