Molecular engineering of organic sensitizers for highly efficient gel-state dye-sensitized solar cells

Three novel organic sensitizers incorporating a planar 4,4-dimethyl-4H-indeno[1,2-b]thiophene or 4,4-dimethyl-4H-indeno[1,2-b] thienothiophene in the bridged group have been designed and synthesized for use in gel-state dye-sensitized solar cells. The photovoltaic performance is quite sensitive to the bridged unit. The optimized cell in JK-276 using a gel electrolyte gave a short circuit photocurrent density of 16.61 mA cm(-2), an open circuit voltage of 0.69 V and a fill factor of 0.72, affording an overall conversion efficiency of 8.31% under standard global AM 1.5 solar cell conditions. The efficiency is close to the value of the liquid-state cell (8.40%). The gel-electrolyte cell of JK-276 showed an excellent long-term stability, which remained almost unchanged during the 300 h light soaking test at 70 degrees C.