In order to cope with the issue, the team has investigated the use of anodized TiO2 nanotubes on Ti foil in combination with the standard TiO2 nanoparticle paste coated anode structure. The presence of nanotubes in the anode structure enabled a significant mitigation of the size-dependent deterioration of the DSSC performance. Devices exhibited a much milder decrease in efficiency as a function of cell dimension up to 9 cm2.

The observed improvement in performance is partly attributed to the elimination of fluorine-doped tin oxide glass in the anode structure, as well as the enhanced charge collection via the nanotube-coated Ti substrate, resulting from enhanced mechanical and electrical connections and possibly improved light trapping.

Moving towards a simpler design

Typically, fluorine-doped tin oxide (FTO) glass has been used in DSSC assemblies as the transparent conducting oxide because of the advantages in terms of sunlight transmittance and electrical conductivity. However, the FTO glass substrates are expensive and also cause a noticeable decrease in the efficiency in the larger solar cell due to the Ohmic loss. To get around this, FTO-glass-based DSSCs are constructed with a stop-gap approach that involves solder-bond stitching 1 cm wide parallel strips of material together. A larger single-cell design that avoids the stitching of narrower cells would be highly desirable for design simplicity and lower cost.

Full details can be found in the journal Nanotechnology.