Photovoltaic improvement and charge recombination reduction by aluminum oxide impregnated MWCNTs/TiO₂ based photoanode for dye-sensitized solar cells

The photovoltaic performance of dye-sensitized solar cells was investigated by incorporation of Al₂O₃ impregnated multi-walled carbon nanotubes (MWCNTs) and without impregnated MWCNTs in TiO₂. The composites of Al₂O₃-MWCNTs and MWCNTs with TiO₂ were prepared by a direct mixing technique. The dispersions of Al₂O₃-MWCNTs and MWCNTs in TiO₂ were confirmed by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) analysis confirms the interstitial incorporation of carbon atoms in the TiO₂ lattice via O-Ti-C and Ti-O-C surface states. The solar cells assembled by using composite photoanodes were characterized by UV-Visible absorption spectroscopy measurement, photocurrent-voltage characteristics, and electrochemical impedance spectroscopy. The results showed that upon optimization the device made of Al₂O₃-0.10%CNTs/TiO₂, 0.10%CNTs/TiO₂ and pristine TiO₂ showed an overall conversion efficiency of 7.02, 5.94 and 5.02 respectively. The improvement in the efficiency of Al₂O₃-MWCNTs/TiO₂ based DSSC can be attributed to an enhanced short-circuit current and reduction in charge recombination. We also employed density functional theory (DFT) to find the band gaps of Al₂O₃-CNTs/TiO₂, CNTs/TiO₂ and pristine TiO₂.