TiO₂ composing with pristine, metallic or semiconducting single-walled carbon nanotubes: Which gives the best performance for a dye-sensitized solar cell

Different types of single-walled carbon nanotubes (SWCNTs), pristine (p-), metallic (m-) and semiconducting (s-) are incorporated into TiO₂ photoanodes to improve the dye-sensitized solar-cell (DSSC) performance and their effects on the device performance are further investigated. Although all three types of SWCNTs are found to have comparable structural morphologies and a reduced charge transport resistivity for the photoanodes, only the semiconducting one was able to suppress charge-recombination events, resulting in even greater improvement of DSSC performances. This is very likely to be ascribed to the higher energy barrier of s-SWCNTs compared to both m- and p-SWCNTs to block the back flowing of dye-injected electrons for I ₃^- reduction in the charge recombination process. Photoanodes based on TiO₂ with either pristine (p-), metallic (m-), or semiconducting (s-) single-walled carbon nanotubes (SWCNTs) are prepared and characterized. The mobility of s-SWCNTs and their suppression of charge recombination towards I₃^- redox species (see picture) allow a more positive synergistic influence over the charge separation/ collection within TiO₂ films while p- and m-SWCNTs tend to accelerate charge recombinations.