Fabrication of transparent TiO2-GO nanocomposites deposited on vertically aligned ZnO nanowire arrays as hybrid nanostructured photo-anode for dye-sensitized solar cells

Abstract

In this article, we report the fabrication of hybrid nanostructures comprised of vertically aligned Zinc Oxide (ZnO) nanowires (NWs) coated with titanium dioxide-graphene oxide (TiO2-GO) nanocomposites by easy, cost-effective, chemical method and demonstrate their utilization as photo-anode for dye-sensitized solar cells (DSSCs). A thin layer of transparent TiO2 with varying GO amount is deposited on top of vertical ZnO NW arrays by sol-gel spin coating method. A conventional DSSC structure is fabricated by using hybrid structure as photo-anode, ruthenium based N3 dye as photosensitizers, iodine solution (I−/I3+) as electrolyte and fluorine-doped tin oxide (FTO) coated glass substrate as counter electrode. The fabricated hybrid nanostructure based DSSC exhibits enhanced power conversion efficiency (η) compared to that of pristine ZnO NW photo-anode. Also, other characteristic parameters of DSSCs like open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF) are estimated from the current density-voltage (J-V) relation measured under illumination of 1 sun (100 mW/cm2) solar spectrum for ZnO NW/TiO2-GO hybrid nanostructures. Improvement in these obtained parameters is observed with increasing GO amount in the TiO2-GO nanocomposite layers deposited on top of ZnO NW arrays. Best performance is delivered by the hybrid nanostructure consists of ZnO NW/TiO2-GO (10%)with optimized value of η ∼0.72% along with Voc ∼491 mV, Jsc ∼2.19 mA/cm2 and FF ∼0.66. This betterment in performance is attributed to the combined effects of improvement in charge transport through the axis of ZnO NWs, increment in contact area and modulation of conductivity of TiO2 by inclusion of conducting GO network. The modulation in charge transport properties of hybrid nanostructures with varying GO amount is studied by complex impedance spectroscopic analyses. The study indicates that particular amount of GO significantly modifies the interfacial effects in fabricated hybrid nanostructures to facilitate better charge transportation.