Dye-sensitized TiO₂ solar cells based on nanocomposite photoanode containing plasma-modified multi-walled carbon nanotubes

A series of anatase TiO₂-based nanocomposite incorporated with plasma-modified multi-walled carbon nanotubes (MWNTs) was prepared by physical blending and shows its capability for efficient electron transport when used as photoanode in dye-sensitized solar cells (DSSCs). These MWNTs characterized with good dispersal performance were obtained by functionalization technique via in situ plasma treatment and subsequent grafting with maleic anhydride (MA) onto the external walls reported previously. Compared with the conventional DSSCs, the TiO₂ film with 1D carbon nanotubes possesses more outstanding ability to transport electrons injected from the excited dye within the device under illumination. As a result, at an optimum addition of 0.3 wt% MWNTs-MA in TiO₂ matrix, the photocurrent-voltage (J-V) characteristics showed a significant increase in the short-circuit photocurrent (J_sc) of 50%, leading to an increase in overall solar conversion efficiency by a factor of 1.5. Electrochemical impedance spectroscopy analyses reveal that the MWNTs-MA/TiO₂ incur smaller resistances at the photoanode in assembled DSSCs when compared with those in the anatase titania DSSCs. These features suggest that the conducting properties of the MWNTs-MA within the anodes are crucial for achieving a higher transport rate for photo-induced electrons in TiO₂ layer by exhibiting lower resistance in the porous network and hence retard charge recombination that could result in poor conversion efficiency.