Graphene cryogel-based counter electrode materials freeze-dried using different solution media for dye-sensitized solar cells

Cryogels are typically synthesized using a freeze-drying method based on hydrogels. However, we have found that the volume changes of water during the freeze-drying process can destroy the gel structure. In this paper, t-butanol was selected as an excellent freeze-drying medium because of its favorable properties and retention of the massive gel structure. The graphene/single-walled carbon nanotube (SWCNT) cryogel exhibited a higher specific surface area (SSA) using t-butanol as a solvent (GCT) compared with using water (GCW) in the hydrogel for freeze-drying. GCT retained the most porous structure with the highest SSA (402.19 m2·g−1) after the freeze-drying process. Then, GCW and GCT were tested as counter electrode materials as a substitute for platinized FTO in dye-sensitized solar cells (DSSCs). The DSSC based on the GCT counter electrode exhibited a remarkable photovoltaic conversion efficiency (8.70%) compared with the GCW-based CE (7.05%) and Pt (7.57%). Hence, our results demonstrate that graphene/SWCNT cryogels freeze-dried with t-butanol as the solvent are promising candidates for use in Pt-free DSSCs.