Effect of Surface Treatment on the Efficiency of Dye-Sensitized Solar Cells

Dye Sensitized Solar Cells (DSSC) based on Nanocrystalline TiO₂ Films has potential to be developed as low-cost environmentally friendly, large-area photovoltaic devices. Choice of electrodes, electrolytes, dye etc. are some of the important factors for the efficiency of these cells. One of such methods for improving performance of DSSC is TiCl₄ post-treatment. This surface treatment by TiCl₄ causes an improved electron transport and dye anchoring which results in efficiency increase for the solar cells. Here we report, the fabrication and characterization of quasi solid state DSSCs based on pre/post treated (with TiCl₄) nanoporous TiO₂ electrodes, dye as photosensitizer and PEDOT:PSS as counter electrode. In this study we have investigated the effect of TiCl₄ post-treatment of nanocrystalline TiO₂ films on the performance of solar cell. This surface treatment causes an increase in the surface area of the TiO₂ layer through the deposition of additional TiO₂ particles on the existing nanoporous layer which in turn increases the amount of adsorbed dye molecules. This increase in dye adsorption may be attributed to availability of more specific binding sites on the TiO₂ surface upon TiCl₄ treatment. Increased dye adsorption and enhanced dye loading being significant factors causes an increase in short circuit current. We have also carried out kelvin probe scanning to study the variation in surface potential and improved dye diffusion after chemical bath deposition of TiO₂ from TiCl₄. We have explained a shift in the conduction band edge of the TiO₂ upon TiCl₄ treatment. This shift in conduction band edge causes enhanced current resulting in improved charge injection into the TiO₂. Impedance analysis was also carried out to understand the effects of TiCl₄ post treatment.