Photopolymerization of acrylic/methacrylic polymer electrolyte membranes for dye-sensitized solar cells: effect of crosslinking density and addition of iodine salts

Dye-sensitized solar cells (DSSCs) are one of the promising candidates for the next generation of solar cells because of their simple structure, relatively high conversion efficiencies, inexpensive fabrication procedures and availability of many materials for their assembly. The main limitation of these devices is that undesirable intrinsic properties of liquid electrolyte significantly affect the operational stability and long-term durability of the cells. Evaporation and leakage, difficulty in robust and hermetic sealing, alteration of the attached dye, water and oxygen permeability are the main criticalities encountered in the presence of organic solvents-based liquid electrolytes. Replacing liquid electrolytes with solid or quasi-solid state ones is expected to solve most of these problems, especially in view of outdoors applications. In this context, polymer-based electrolytes are the best candidates due to their non-volatility, flexibility on the structure design, chemical and electrochemical stabilities. In this work we propose five gel-polymer electrolyte membranes, prepared by a rapid, cheap and eco-friendly process of free-radical photopolymerization. These acrylic/methacrylic membranes are prepared by co-photopolymerising difunctional and monofunctional oligomers, thus modulating the architecture of the polymeric matrix, mainly the crosslinking density. The membranes are activated by soaking them into a liquid electrolyte swelling solution (I-/I3-/CH3CN). The obtained gel-polymer electrolytes are free-standing, non-tacky, and extremely flexible. The characterization of these gel-polymer electrolytes and of the corresponding DSSCs has been carried out. In particular, we introduce here a correlation between the crosslinking density of the polymer networks and the light-to-electricity conversion efficiency of the cells. Moreover, we investigate the possibility of preparing membranes photopolymerising the reactive oligomers and the iodine salts-based electrolyte directly on the photoanode.