Impedance investigation of TiO2 nanotubes/nanoparticles-based dye-sensitized solar cells

In this work, we studied the influence of TiO2 morphology on photovoltaic performances, electron transport and charge recombination properties of nanotubes/nanoparticle-based dye-sensitized solar cells. Nanotubes and nanoparticles nanostructures have been synthetized by hydrothermal and sol-gel methods, and then characterized using X-ray diffraction, scanning and transmission electron microscopies. Electrochemical impedance spectroscopy results have shown that the recombination process becomes less significant when nanotubes amount decreases in the cells induced by the low recombination site concentration due to the small surface area of nanotubes regarding to nanoparticles. However, despite the low recombination rate, a drastic decrease of lifetime has been observed indicating a very low charge transport due to the poor interconnectivity of randomly dispersed TiO2 nanotubes in the high nanotubes content cells. Proper content of 10-20% nanotubes pile up effectively with nanoparticles favoring a good connection between the grains, and thus facilitating the charge transport in TiO2 network.