Rubbery copolymer electrolytes containing polymerized ionic liquid for dye-sensitized solar cells

A novel type of random copolymer comprised of a polymerized ionic liquid, poly(1-((4-ethenylphenyl)methyl)-3-butyl-imidazolium iodide) (PEBII), and amorphous rubbery poly(oxyethylene methacrylate) (POEM) was synthesized and employed as a solid electrolyte in an I2-free dye-sensitized solar cell (DSSC). The copolymer electrolytes deeply infiltrated into the nanopores of mesoporous TiO ₂ films, resulting in improved interfacial contact of electrode/electrolyte. The glass transition temperature (T _g) of the PEBII-POEM(-23 °C) was lower than that of PEBII homopolymer (-4 °C), indicating greater chain flexibility in the former. However, the DSSC efficiency of PEBII-POEM (4.5 % at 100 mW/cm2) was lower than that of PEBII (5.9 %), indicating that ion concentration is more important than chain flexibility. Interestingly, upon the introduction of ionic liquid, i.e., 1-methyl-3 propylimidazolium iodide, the efficiency of PEBII remained almost constant (5.8 %), whereas that of PEBII-POEM was significantly improved up to 7.0 % due to increased I ^- ion concentration, which is one of the highest values for I ₂-free DSSCs.