Enhancing the performance of transparent conductive oxide-less back contact dye-sensitized solar cells by facile diffusion of cobalt species through TiO2 nanopores

Abstract

We report a back contact (BC) transparent conductive oxide (TCO)-less dye-sensitized solar cell (DSSC) fabricated utilizing a Co^2+/3+ redox shuttle based electrolyte. A new strategy has been proposed for the reduction of the electrolyte layer by coating with a TiO₂ nanoparticle spacer (TN spacer) with controlled thickness. The negatively charged TN spacer was found to decrease the diffusion of cobalt species through the TN spacer due to electrostatic interactions leading to a hampered photoconversion efficiency of 4.41%. This sluggish diffusion of bulky cobalt ions was amicably facilitated by passivating the negatively charged TN spacer surface with dye molecules. Facile transport of electrolyte ions in the nanopores of the passivated TN spacer was further confirmed by electrochemical impedance spectroscopy and estimation of the diffusion of Co³⁺ species in the nanopores of the passivated TN spacer using cyclic voltammetry. The TCO-less BC-DSSC in combination with the cobalt electrolyte fabricated in this novel device architecture exhibits a significantly improved photoconversion efficiency of 6.42% after the TN spacer was passivated with the porphyrin-based dye YD2-o-C8.