New insights in long-term photovoltaic performance characterization of cellulose-based gel electrolytes for stable dye-sensitized solar cells

The gelation of ionic liquid-based solutions with inorganic or organic fillers is one of the strategies commonly adopted in the Dye-Sensitized Solar Cells (DSSCs) field for preparing quasi-solid electrolytes characterized by good photovoltaic performance and long-term stability. In the present paper, the application of a gel electrolyte based on unmodified microcrystalline cellulose and ionic liquids in a DSSC is reported. The gel electrolyte has been characterized evaluating its conductive, thermogravimetric, viscous and crystalline properties, while the photoelectrochemical behavior of the quasi-solid DSSCs has been investigated measuring current-voltage, Electrochemical Impedance Spectroscopy and Linear Sweep Voltammetry curves. The photovoltaic performance of cellulose gel-based DSSCs has been optimized by monitoring some key parameters, such as ionic liquid volume ratios and cellulose content. A maximum photoconversion efficiency of 3.33% has been obtained with the total absence of organic solvents, and a good stability has been demonstrated during more than 8 hours of exposition (replicated over months) to simulated solar light. Moreover, a peculiar and reversible trend in the short-circuit current density and in the overall efficiency of the cell has been observed during prolonged photovoltaic measurements. The present findings suggest the necessity to adopt a new protocol for the measurement of the photovoltaic parameters of quasi-solid DSSCs.