A highly efficient quasi-solid polymer electrolyte for dye-sensitized solar cells prepared in only 7 minutes

As a feasible option for photovoltaic technology to meet the growing energy demand, dye-sensitized solar cells (DSSCs) have attracted much attention due to their low cost, ease of fabrication and good performance. Their relevant technological drawbacks are poor long-term stability, difficulty in hermetic sealing, electrolyte evaporation, and permeability to H2O/O2. These problems can be solved replacing the traditional liquid electrolyte with gel-polymer electrolytes or liquids solidified with gelators/nanoparticles. In recent years, it has been verified that the best solution is to trap the liquid electrolyte in a polymer network, thus developing quasi-solid electrolytes capable of providing light-to-electricity conversion efficiencies around 3-5%. The advantage of these electrolytes is that they possess simultaneously the diffusive transport property, the high ionic conductivity and the interfacial contact property of a liquid and the cohesive property of a solid. However the preparation of the polymer network requires solubilization of monomers with solvents, long reaction times (6-12 h), use of catalysts, separation/purification steps: this is antithetical to the environmentally friendly nature of DSSCs and with the timing of a possible technological implementation. In this work, we highlight the great potential of free-radical photopolymerization as a method of preparation of quasi-solid polymer electrolytes. This process is very rapid, cheap, consistent with the main canons of green-chemistry (solvents and catalysts are not required), and could be easily transferred to industrial scale. Polyethylene glycol diacrylate (PEGDA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were reacted under UV light in an appropriate ratio in order to obtain crosslinked, flexible and transparent membranes, subsequently activated with a I-/I3-/CH3CN solution. The entire process of preparation of these quasi-solid electrolytes lasted only 7 minutes, and a light-to-electricity conversion efficiency of 4.41% was obtained. An accurate characterization of the UV-cured membranes and the photo-electrochemical device was performed and will be here thoroughly discussed.