Quasi-solid-state dye-sensitized solar cells on plastic substrates

Interest has recently grown around flexible dye-sensitized solar cells (DSCs) for their potential low cost roll-to-roll production process and their wide range of applications. However, flexible DSCs do not perform as well as their glass substrate equivalents, and standard devices using liquid electrolytes are challenged with long-term stability issues. Consequently, constructing stable flexible solar cells presents a major challenge. This article focuses on flexible quasi-solid-state DSCs (QS-DSCs), constructed with poly(vinylidenefluoride-co-hexafluoropropylene)-based gel electrolytes and submicrometer mesoporous TiO2 beads on plastic substrates. The influence of the gel electrolyte composition was investigated and optimized by varying the polymer content and introducing inorganic fillers. The diffusion behavior of the gel electrolytes was studied by means of voltammetric measurements. Electrochemical impedance spectroscopy gave an understanding of the role of polymer and inorganic fillers with regard to the charge recombination process. Transient photocurrent measurements and scanning electron microscopy coupled with energy X-ray dispersive spectrometry revealed that infiltration of the electrolyte through the photoanode was advantageous for films made with TiO2 beads over TiO2 P25 particles. A record power conversion efficiency of 6.4% for flexible QS-DSCs was obtained with an optimized gel electrolyte, constituting a promising step toward the fabrication of stable flexible DSCs.