(704c) Band-Edge Engineered Hybrid SnO2 Nanowires Electrodes for Dye Sensitized Solar Cells

Dye sensitized solar cells (DSSC's) based on wide band gap semiconducting oxide nanomaterials have gained increased importance in the last few years due to their high solar to electric conversion efficiencies at low costs. Of the different types of nanostructures, highly crystalline nanowires offer unique advantages over nanoparticle networks by providing a direct and fast pathway for electron transport. In this work, we show that SnO2 nanowire based dye sensitized solar cells exhibit an open circuit voltage of 560 mV, which is 200 mV higher than that using SnO2 nanoparticle based cells. The nanowires were employed in hybrid structures consisting of highly interconnected SnO2 nanowire matrix coated with TiO2 nanoparticles, which showed an open circuit voltage of 720 mV and an efficiency of 4.1% compared to 2.5% obtained with pure SnO2 nanowire matrix. Transient photovoltage and photocurrent measurements of hybrid electrodes show that the recombination time constant is ~100 times higher and transport time constants is ~10 times lower than that of TiO2 nanoparticles. The higher efficiency observed for DSSC's based on hybrid structure is attributed to the band edge positions of SnO2 relative to that of TiO2 and faster electron transport in SnO2 nanowires.