(682d) Nanowire Based Dye Sensitized Solar Cells and Electrochromic Devices

The performance of nanowires based dye sensitized solar cells (DSCs) and electrochromic devices (EC's) were compared with those made out of nanoparticles. Two material systems, tin oxide and tungsten trioxide were used for DSCs and ECs, respectively. DSCs based on wide bandgap semiconducting oxide nanomaterials have gained increased importance in the last few years due to the large surface areas for efficient light absorption. Of these nanomaterials, nanowires represent a different kind compared to nanoparticles due to their aspect ratio, charge transport ability and unique surfaces. Mats of high densities of nanowires in a network fashion could offer interesting possibilities for solar cell and electrochromic device applications.

Tin oxide and tungsten trioxide, unbranched and branched nanowires, with diameters ranging from 40nm to 100 nm and high aspect ratios were synthesized by chemical vapor transport method. The obtained nanowire powders were dispersed in a solvent and then deposited on to FTO glass substrates. DSCs were made using different active photoelectrode areas of about 0.25, 0.5, and 1 cm². Similar cells were also made using commercially-available nanoparticles of tin oxide and tungsten trioxide, with the same quantity of material in each photoelectrode.

The DSCs were characterized under a calibrated light source for the short circuit current density (Isc), open circuit voltage (Voc), fill factor (ff) and efficiency (η) for different nanowire morphologies, thicknesses of the nanowire layer, dye loading and sintering times used. The electrochromic behavior of both the nanowire and nanoparticle films of tungsten trioxide were characterized for their optical absorbance and response times with applied potential. Initial studies performed on DSCs and ECs based on nanowires have shown performances comparable or better than the devices made with nanoparticles.

Authors acknowledge Institute for Advanced Materials at UofL, support from the US Department of Energy through contract DE-FG02-05ER64071 and a grant from Western KY Energy Consortium.