Influence of Different Iodide Salts on the Performance of Dye-Sensitized Solar Cells Containing Phosphazene-Based Nonvolatile Electrolytes

Polyphosphazene-based electrolytes containing different iodide salts were studied as components of dyesensitized solar cells (DSSCs). Electrolytes based on hexa[methoxyethoxyethoxycyclotriphosphazene] (MEE trimer) with dissolved LiI, NaI, NH4I, and 1-methyl-3-propylimidazolium (PMII) and I2 were examined by ac conductivity and steady-state voltammetry. These measurements gave the individual conductivities of I-, I3, and cations in each electrolyte as a function of salt concentration. The anionic conductivities were highest in the PMII system and decreased in the order PMII > NH4I > NaI > LiI. Photovoltaic measurements of DSSCs containing these electrolytes showed the same order of performance, and electrochemical impedance spectra (EIS) under open circuit and forward bias conditions were used to study the separate impedance components of the cells. High polymeric polyphosphazene-plasticizer blends with a dissolved PMII/I2 electrolyte gave better performance in DSSCs than equivalent poly(ethylene oxide)-plasticizer electrolytes. Although the efficiencies of these DSSCs were low (1.9%), this study identified the primary loss mechanisms and suggested possible avenues for designing more efficient polyphosphazene-based cells.