Deep insight into electron transport and photovoltaic parameters in DSSCs

Dye-sensitized solar cells (DSSCs) based on titanium (IV) oxide (TiO2) nanoparticles and nanotubes (NTs) with different weight ratios and phase compositions were fabricated. The obtained nanostructures were investigated using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and ultraviolet-visible spectroscopy. Current-voltage measurements and electrochemical impedance spectroscopy were used to investigate the electron transport and photovoltaic performance of DSSCs. An increase of 14% in cell efficiency was achieved by introducing 10 wt% NTs. In this configuration, high dye loading is ensured and substantial improvement in electron transport efficiency is achieved by a more effective stack of the particles. Moreover, a 21 wt% rutile content is beneficial to the overall solar energy conversion by prompting highly efficient electron migration from the rutile conduction band to anatase trapping sites. When 20-100% NTs are incorporated in the structure, the photocurrent and thus the cell efficiency decrease progressively. The diminution of photocurrent is associated with a lesser amount of adsorbed dye, owing to the small surface area of titanium (IV) oxide films with high NT content. The photocurrent decrease also correlates with the decrease in the electron lifetime, indicating that electron transport through titanium (IV) oxide film is becoming less efficient due to the diminution of the extent of interparticle connectivity.