Comparative spectroscopic approach for the dye loading optimization of sheet-like ZnO photoanodes for dye-sensitized solar cells

The peculiarly critical sensitization of zinc oxide with Ru-based dyes is the serious problem that prevents this semiconductor oxide from achieving photoconversion efficiencies in dye-sensitized solar cells (DSCs) comparable to those obtained with TiO2. Within this framework, methodologies for the optimization of the sensitization procedure of this material in acidic environments prove to be essential. In this paper, in view of streamlining the critical sensitization procedure of sheet-like zinc oxide-based DSC photoanodes with Ru-based dye, a comparative study on active and passive evaluations of N719 dye loading on sheet-like ZnO nanostructures are reported. For the active in-situ spectroscopic approach, a home-made set-up has been appropriately designed and developed for real time monitoring the dye adsorption on the ZnO-based photoanodes, whereas the standard passive dye loading measurements were performed after the electrodes had been sensitized for different time periods in the dye solutions of different concentrations. The dye adsorption results are carefully analyzed and correlated to the photovoltaic conversion efficiency and the incident photon-to-electron conversion efficiency (IPCE) of the corresponding ZnO-based DSCs, fabricated by employing our customized microfluidic architecture. The obtained results show that the real time monitoring of the dye absorption can be successfully employed for optimizing the sensitization conditions of ZnO-based photoanodes for DSCs. When applied online in a large scale production system for dye-sensitized solar cells, the proposed active method will permit to save both time and materials.