Dye-Sensitized Solar Cells Based on MWCNT/TiO2 Counter Electrode and Thiolate/Disulfide Non-Iodine Redox Couple

Multi-walled carbon nanotube (MWCNT)/TiO2 composites were prepared using acid-treated MWCNT and titanium (IV) isopropoxide by a facile hydrothermal method. The morphology and structure of composites were characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis with differential scanning calorinnetry (TGA-DSC), Raman and X-ray photoelectron spectroscopy (XPS). The results show that the cohesion effect of MWCNT/TiO2 was due to the interaction between -COOH group of acid-treated MWCNT and -OH group of the anatase TiO2 surface, which might form a similar chemical bonding (O=C-O-Ti or C-O-Ti) interaction. The photoelectrochemical performance of dye-sensitized solar cell (DSSC) based on both MWCNT/TiO2 counter electrode and thiolate/disulfide (T-/T-2) non-iodine redox couple was investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Tafel and voltage-photocurrent density curves. The results indicate that the reduction of T-2 to T- at MWCNT/TiO2 counter electrode was more effective than that of Pt counter electrode. Under optimized conditions (m(MWCNT)/m(TiO2), mass ratio), DSSC achieved an optimal performance, such as open-circuit voltage of 0.63 V, short-circuit photocurrent density of 15.81 mA.cm(-2), fill factor of 0.65, and photon-to-electron conversion efficiency of 6.47%.