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 TiO 2 nanoparticulate layer in the photoanode, and hence most efforts have been directed on the improvement and deliberate optimization of the quality the TiO 2 nanocrystalline layer. In this work, we aim to reduce the electron collection distance between the place of origin in the TiO 2 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 TiO 2 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 μm-thick TiO 2 NP film.