Abstract: A comb-like copolymer based on N-propylvinylimidazolium iodide (VImI) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) was synthesized. The VImI/PEGMA copolymer was used to prepare quasi-solid electrolytes. The charge transport and interfacial charge transfer of the dye-sensitized solar cells (DSSCs) based on the quasi-solid electrolytes were investigated using photocurrent density-voltage (J-V) curves, ionic conductivities, and impedance spectra. It was found that the copolymer plays an active role in decreasing the electron recombination at TiO₂/electrolyte interface and increases the conduction band edge of TiO₂. The photovoltaic characteristics of the DSSCs are therefore not determined entirely by the conductivity of the quasi-solid electrolyte. Based on the dependence of the open-circuit voltage on the VImI/PEGMA molar ratio, the decrease of recombination is primarily ascribed to the contribution of VImI segments. In addition, open-circuit voltage decay (OCVD) and photocurrent transient results indicate that the introduction of the copolymer not only extends the electron lifetime but also tunes the energy distribution of the localized electrons. When the VImI/PEGMA molar ratio reaches 5.0 and the mass fraction of copolymer in the quasi-solid electrolyte is 50%, the DSSC yields an energy conversion efficiency of 4.10% under an illumination intensity of 100 mW·cm^-2.

Key words: Copolymer, Quasi-solid electrolyte, Dye-sensitized solar cells, Electron recombination, Electron lifetime