Development of titania nanostructures for the exploration of electron transport in dye-sensitized solar cells

Dye-sensitized solar cells (DSSC) utilizing titania (TiO2) nanomaterials in conjunction with a light-absorbing dye have been extensively explored for the last few decades. Earlier efforts to surpass the 10% overall light conversion efficiency of these devices emphasized the synthesis of dyes with enhanced light-absorbing capabilities, but slow progress in the increase in efficiency has directed attention to the exploration into the modification of the TiO2 nanostructure. Up to this point, the most efficient electrodes in DSSC devices have consisted of 10 mum-thick mesoporous TiO2 film with an interconnected network of 15-20nm particles. This type of structure has shown to impart a large enough surface area for efficient light absorption and charge formation, but the random distribution of nanometer-sized particles is thought to be the limiting factor for enhanced electron transport, hindering further progress in achieving higher efficiencies. Our research utilizes TiO2 nanorods in an attempt to explore and compare the electron transport pathways associated with 1) a random distribution of nanoparticles and 2) a straightforward arrangement of nanorods within the TiO2 nanostructure. It is assumed that a more ordered structure of nanorods would minimize inefficient electron percolation pathways and improve ion diffusion at the TiO2-dye-electrolyte interface by eliminating the randomization of the particle network, by increasingly contact points for good electrical connection, and by decreasing small necking points that have shown to develop between adjacently-bound particles in the current TiO2 nanoparticle structure after sintering. The current-voltage (I-V) behavior of three solar cell electrode structures consisting of (1) TiO2 nanoparticle film, (2) TiO2 nanoparticle-nanorod film, and (3) TiO2 nanorod film were compared and analyzed to determine whether the nanorod structure provided a more efficient pathway for effective electron conduction. SEM analysis was also done to examine the structural alignment and morphology of each TiO2 electrode.