Effects of Co-Solvent and Polymer Composition in Gel Electrolytes on the Performance of Paper Dye-Sensitized Solar Cells

In this study, we investigated how co-solvent and polymer combinations affect the performance of dye-sensitized solar cells (DSSCs) using TiO2- and ZnO-modified carbon nanotube (CNT) composite papers as photoelectrodes. Co-solvents such as N,N-dimethylformamide (DMF) and ethylene glycol (EG) were incorporated into polyethylene glycol (PEG)- and poly(ethylene oxide) (PEO)-based gel electrolytes to increase the amount of dissolved I2/KI redox species and evaluate their influence on the wettability of the electrolyte on CNT composite paper electrodes. PEG-based electrolytes containing DMF or EG improved the fill factor (FF) and power conversion efficiency (PCE) relative to the baseline formulation, with the EG–PEG electrolyte achieving the best single-device PCE of 15.58 × 10−3% using the CNT/ZnO composite paper. Replacing PEG with PEO or using PEG + PEO blends led to reduced performance, possibly because the modified polymer composition affected electrolyte wetting, spreading behavior, and penetration into the porous electrode. These results suggest that the wettability and viscosity-related behavior of gel electrolytes are important empirical factors associated with the performance of flexible paper DSSCs, and provide practical guidance for the design of paper-based photovoltaic devices.