Electrospun TiO₂-MWCNTs nanofibers as photoanode in dye-sensitized solar cell (DSSC)

Electrospinning process was used to fabricate hybrid TiO₂ nanofibrous membrane containing multi-walled carbon nanotubes (MWCNTs). The MWCNTs treated with plasma modification as established in our previous studies are dispersed in the mixture of titanium (IV) isopropoxide and poly(methyl methacrylate) in N,N-dimethylformamide prior to electrospinning. Diameter of the calcined TiO₂-MWCNTs nanofibers (NFs) ranged from 100 to 200 nm, and transmission electron microscopy shows that the MWCNTs are both embedded and lying externally on the NFs. Photoanodes for dye-sensitized solar cells are prepared by first conglutinating the nanofibrous membranes onto conducting glass substrate under methanol vapor treatment followed by calcination and dye sensitization. The NFs exhibit improved conducting behavior (from 10⁻⁸ to 10⁻⁶ S/m) with small quantity (0.5–1.5 wt%) of MWCNTs. An optimum addition of 1.0 wt% MWCNTs into the TiO₂ nanofibrous membrane improves the overall solar conversion efficiency by 47 % with significant increase in the short-circuit photocurrent. Electrochemical impedance spectroscopy and intensity-modulated photocurrent/photovoltage spectroscopy analyses reveal that the enhanced electron transport with smaller resistance is responsible for the improved cell performance. The results suggest that the conducting properties of the MWCNTs are crucial for faster transport of photogenerated electrons, hence retarding charge recombination that could result in poor conversion efficiency.