Revealing the limiting factors that are responsible for the working performance of quasi-solid state DSSCs using an ionic liquid and organosiloxane-based polymer gel electrolyte

We report a study on quasi-solid-state-dye-sensitized solar cells (QSS-DSSCs) with polymer gel electrolytes (PGEs) that are composed of an organosiloxane hybrid polymer gel and imidazolium ionic liquid. The ionic diffusion coefficients of these PGEs are smaller than those of the pure ionic liquid, which may explain the observation of decreased cell performances in the DSSCs using these PGEs. However, from more detailed electrochemical impedance spectroscopy (EIS) studies, there is a strong evidence that the cell performance is also limited by inefficient charge transfer and charge transport inside the mesoporous TiO2 layer. This is indicated by the absence of transmission line characteristics in the observed Nyquist plots. The present experimental results then indicate that the lack of electrolyte penetration into the mesoporous TiO2 layer, due to the PGE rheology behavior caused by the siloxane-based polymer gel used here, is another crucial limiting factor for the photovoltaic performance of DSSCs using this kind of PGE. We consider that this kind of gel phase effect may be also observed in DSSCs using other types of gel electrolytes, including polyionic liquids.