Electrolyte infiltration in phosphazene-based dye-sensitized solar cells

We report here a study of phosphazene polymer and oligomer electrolyte infiltration into high surface area titanium dioxide electrodes and its effect on the performance of dye-sensitized solar cells. The effects of different cell assembly procedures on the electrochemical properties are examined, as well as the infiltration of electrolytes based on poly[bis(2-(2-methoxyethoxy)ethoxy) phosphazene] (MEEP), hexakis(2-(2-methoxyethoxy)ethoxy)cyclotriphosphazene (MEE trimer), and a linear short chain analogue into conventional titanium dioxide electrode mesoporous (nanosphere) films, microcolumns and nanowires. The effects of temperature, co-solvents, and the order of addition of the electroactive components are found to affect both the conductivity of the electrolytes and the electrochemical performance of the cells. Cross-sectional scanning electron microscopy (SEM) imaging is employed to examine the degree of electrolyte infiltration into the nanostructured electrodes as a function of filling conditions. Using these techniques, conditions are identified for achieving a high degree of pore filling by the three electrolyte systems. Increased power conversion efficiency is obtained when iodine is introduced after the heating and evacuation procedures required for maximum infiltration.