Study on transparency and hierarchical structure with TiO₂ quantum dots for efficient back-side illuminated dye-sensitized solar cells

The fabrication of back-side illuminated dye-sensitized solar cells (DSSCs) incorporating anodized TiO₂ nanotubes is described in this paper. Here, we consider two features of the DSSC under back-side illumination, namely, the transparency and formation of a hierarchical structure, both of which can improve performance. In this research, investigation of the electrocatalytic and optical features showed that transparency had a greater influence on the performance of the DSSCs than the catalytic performance of the electrolytes and Pt counter electrodes did. All photovoltaic parameters, namely, short circuit current, open circuit voltage, fill factor and efficiency, were improved greatly by enhanced transmittance and possible enhancement in the light intensity reaching the dye molecules. To further enhance the performance of the DSSCs, hierarchical structures were formed with TiO₂ quantum dots (QDs) in a facile manner. When a single treatment by TiO₂ QDs was combined with the improved transparency, the DSSCs exhibited a 30% increase in photocurrent density and their efficiency was 5.72% under AM 1.5 illumination because of the increased dye loading and possible advantages in the electronic band structure.