Correlation between ionic conductivity and cell performance in solid-state dye-sensitized solar cells employing polymer electrolyte

Poly(ethylene glycol) dimethyl ether (PEGDME)/fumed silica/1-methyl-3-propyl imidazolium iodide (MPII)/I2 mixtures were used as polymer electrolytes in solid-state dye-sensitized solar cells (DSSCs). Correlation between the ionic conductivity and cell performance by varying the composition of polymer electrolytes was investigated to elucidate the importance of the ionic conductivity in determining the energy conversion efficiency of solid-state DSSCs. If the ionic conductivity is a rate determining step among many transport processes, the maximum ionic conductivity would match with the best cell efficiency in the solid-state DSSCs. However, the composition with the highest ionic conductivity did not show the maximum solar cell performance, indicating a mismatch between the ionic conductivity and cell performance in these experimental conditions. This suggests that other than the ionic conductivity such as the electron recombination may also play an important role in determining the energy conversion efficiency. Thus, the surface of the TiO2 particles was modified by coating a thin metal oxide such as Nb2O5 layer to prevent electron recombination. As a result, the electrolyte composition of the best cell efficiency was shifted to coincide with that of the maximum ionic conductivity, suggesting that the electron recombination is also important in determining the energy conversion efficiency in addition to the ionic conductivity in solid-state DSSCs.