In this report, we show for the first time 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. This is attributed to the more negative flat band potential of nanowires compared to the nanoparticles as determined by open circuit photo voltage measurements made at high light intensities. 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 2.1% obtained with pure SnO2 nanowire matrix. The electron transport time constants for SnO2 nanowire matrix were an order of magnitude lower and the recombination time constants are about 100 times higher than that of TiO2 nanoparticles. The higher efficiency observed for DSSCs 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.

Our recent studies showed that nanowire based DSSCs exhibited over 250 mV higher open circuit potentials (V OC ) compared to those using nanoparticles. In this study, the electron transport and surface properties of nanowires and nanoparticles are investigated to understand the reasons for the observed higher photovoltages with NW based solar cells. It was seen that, in addition to slow recombination kinetics, the lower work function of SnO 2 nanowires compared to the nanoparticle counterparts also significantly contributes to the high V OC observed for the nanowire based DSSCs.

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