Plastic–polymer composite electrolytes for solid state dye-sensitized solar cells

Three types of alkyl-substituted poly(N-alkyl-1-vinyl-imidazolium) iodides were synthesized and plasticized using succinonitrile as a solid plasticizer to develop a series of novel solvent-free plastic–polymer composite electrolytes. All these electrolytes appeared as a soft solid at room temperature and became sticky gel state at high temperature of 100 °C. Among the as-prepared plastic–polymer electrolytes, the SCN–PMVII (succinonitrile–poly(1-vinyl-3-methylimidazolium) iodide) electrolytes with a SCN content of 40–60 wt.% showed a room temperature conductivity of 1.0–1.6 mS cm−1and a photoconversion efficiency of >4.1%, which are comparable to those observed from liquid organic carbonate electrolyte and the DSSCs using the liquid electrolyte at the same experimental conditions. Also, the DSSCs assembled with the SCN–PMVII electrolytes maintained their photoconversion efficiency very steadily during aging test of 50 days despite of being placed at 40 °C under 1 sun illumination or stored at 60 °C in an oven. Since these plastic–polymer electrolytes are solvent-free, highly conductive and electrochemically compatible, it is possible to use this type electrolyte for development of practical DSSCs.