Performance Enhancement of Dye-Sensitized Solar Cells by Utilizing Carbon Nanotubes as an Electrolyte-Treating Agent

A new carbon nanotube (CNT) function is proposed herein for dye-sensitized solar cell (DSSC) applications. In this study, single-wall CNT is used as a treating agent to conventional liquid electrolytes, which differs from the role of a gelator or an additive as reported in the literature. The experimental results show that the electrochemical properties of the electrolytes do not alter significantly after the CNT treatment; however, the conversion efficiencies of the DSSCs are evidently improved (from 8.15% to 8.70%), which is attributed mainly to the enhanced open-circuit voltages. Device characterizations indicate that the higher voltages are due to the suppression of charge recombination at the TiO2/electrolyte interface. Furthermore, based on the Raman and ultraviolet–visible spectra of the electrolytes, the concentrations of triiodide and higher polyiodide species are reduced after the CNT treatment. The Raman and XPS spectral results further verify the adsorption of polyiodides on the CNTs. More importantly, because fewer polyiodides are present in the electrolyte, fewer electrons in the TiO2 can be recombined; therefore, higher voltages are achieved for the corresponding cells. Quasi-solid-state DSSCs fabricated using CNT-treated electrolytes also demonstrate better cell performance. This CNT effect is anticipated to facilitate the progress of DSSCs.