Evaluation of the limiting factors affecting large-sized, flexible, platinum-free dye-sensitized solar cells performance: a combined experimental and equivalent circuit analysis

Abstract

Reducing further the cost, increasing the application range, and scaling up of dye-sensitized solar cells (DSSCs) are important issues for their wide commercialization. The present paper constitutes a comprehensive analysis of the limiting factors affecting large-sized, flexible, platinum-free DSSCs performance. The results are interpreted using a series of materials characterization techniques, including scanning electron microscopy, atomic force microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, ultraviolet–visible spectroscopy, diffuse reflectance spectroscopy, photoluminescence analysis, and cyclic voltammetry. Equivalent circuit analysis of DSSCs was applied, in all cases, to derive the key electrical circuit elements values, determining solar cells performance. Α satisfactory energy conversion efficiency was achieved by the implementation of the novel fabricated carbon-based counter electrodes to DSSCs, equal to the corresponding obtained by the photo-electrochemical cells employing commercially available platinum-based counter electrodes. The flexible, platinum-free DSSCs demonstrated a decreased photo-generated current and electron transport kinetics, while the charge recombination rate at TiO2/electrolyte and conductive substrate/electrolyte interfaces was increased, compared to the rigid ones. The scaling up effect was intense in the flexible devices, while the area-specific total series parasitic resistance increased, at high rates, by the solar cell active area. Equivalent circuit model successfully reproduced all experimental current–voltage characteristic curves of DSSCs, revealing that it is a powerful tool for routine analysis when designing novel photo-electrochemical cells.