Thin films of solid-state polymer electrolytes for dye-sensitized solar cells

For the first time, thin films of solid-state polymer electrolytes (SSPEs) are developed for dye-sensitized solar cells (DSCs). Firstly, poly(ethylene oxide) (PEO)/polyethylene glycol (PEG) blend and acetonitrile-based iodide liquid electrolyte are utilized to prepare the gel-electrolytes. The gel-electrolytes are then cast onto a glass substrate, fabricating the solvent-free SSPEs by evaporating the solvent. To assemble the solid-state DSCs, these films are sandwiched between photoelectrodes and counter electrodes with the aid of a heating and pressing process to enhance the penetration of the SSPEs into the photoelectrodes. The infra-red spectroscopy and thermogravimetric analysis confirm the absence of solvent in the electrolyte films. The optimization studies reveal that, at the PEO/PEG ratio of 7/3, the solid-state DSC can achieve a power conversion efficiency (PCE) of 7.23%. The PCE of the solid-state cell can be increased further to 8.13% by introduction of 2 wt% TiO₂ nanofillers in the SSPEs, attributed to the increase in the ion diffusivity, electrolyte conductivity, charge recombination resistance and charge transfer at the counter electrode/SSPEs interface. The solid-state DSCs have high stability, retaining 98% of their original efficiency after a 700-h test period. This study demonstrates the applicability of the novel solid-state electrolyte films for preparing the solid-state DSCs.