Enhanced Electron Collection in TiO2 Nanoparticle-Based Dye-Sensitized Solar Cells by an Array of Metal Micropillars on a Planar Fluorinated Tin Oxide Anode

Charge collection efficiency exhibits a strong influence on the overall efficiency of nanocrystalline dye-sensitized solar cells. It highly depends on the quality of the TiO2 nanoparticulate layer in the photoanode, and hence most efforts have been directed on the improvement and deliberate optimization of the quality the TiO2 nanocrystalline layer. In this work, we aim to reduce the electron collection distance between the place of origin in the TiO2 layer to the electron-collecting TCO anode as an alternative way to enhance the charge collection efficiency. We use an array of metal micropillars on fluorine-doped tin oxide (FTO) as the colleting anode. Under the same conditions, the Ni micropillar-on-FTO-based dye-sensitized solar cells (DSSCs) exhibit a remarkably enhanced current density, which is approximately 1.8 times greater compared with the bare FTO-based DSSCs. Electron transport was investigated using the electrochemical impedance spectroscopy technique. Our results reveal that the electron collection time in Ni micropillar-on-FTO-based DSSCs is much shorter than that of bare FTO-based DSSCs, indicating faster electron collection due to the Ni micropillars buried in TiO2 nanoparticulate layer that serve as electron transport shortcuts. As a result, the charge collection efficiency was enhanced by 15-20% with respect to that of the bare FTO-based DSSCs. Consequently, the overall energy conversion efficiency was found to increase from 2.6% in bare FTO-based DSSCs to 4.8% in Ni micropillar-on-FTO-based DSSCs for a 6 mu m-thick TiO2 NP film.