Electrical and optical properties of electrospun TiO2-graphene composite nanofibers and its application as DSSC photo-anodes

Abstract

The present study reports the electrospinning of TiO₂-graphene composite nanofibers to develop conductive nano-fiber mats using polyvinylpyrrolidone as a carrier solution. This carrier solution was sublimated at 450 °C to attain a complete conducting continuous nanofibrous network. It was observed during the annealing that as the graphene content was increased to 1 wt% the continuous fiber morphology was lost. Annealing did not have any impact on the fiber diameter (∼150 nm) or morphology as the graphene content was maintained between 0.0–0.7 wt%. The surface porosity of these samples was found be in the range of 45–48%. The presence of graphene in TiO₂ nanofibers was confirmed using Raman spectroscopy. Photoluminescence spectroscopy showed excitonic intensity to be lower in graphene-TiO₂ samples indicating that the recombination of photo-induced electrons and holes in TiO₂ can be effectively inhibited in the composite nanofibers. Fluorescence spectroscopy was used to confirm this phenomenon where blue and quenched emissions were observed for the electrospun TiO₂ nanofibers and composite fibers, respectively. Conductivity measurements showed the mean specific conductance values obtained for TiO₂-graphene composites to be about two times higher values than that of the electrospun TiO₂ fibers. Assembling these TiO₂-graphene fiber composites as photoanodes in dye sensitized solar cells, an efficiency of 7.6% was attained.