Development of High Efficiency, Stability Electrolyte for Dye-Sensitive Solar Cells Using Ionic-Liquid

Dye-Sensitized Solar Cell (DSSC) has some unique properties such as transparency with various colors, easy fabrication processes, and relatively high and steady energy conversion efficiencies, compared to other type of solar cells. Energy conversion efficiencies above 11 % and 13 % have been achieved for cells with volatile liquid- based organic solvents. However, the utilization of liquid electrolytes is often considered as a major causes of significant leakage problems during operation. To overcome disadvantages of liquid- based electrolytes, we used Ionic-liquid which has low viscosity and volatility. Here we report a ionic-liquid-based electrolyte containing 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (EMIM-TFSI), 1-Ethyl-2-methylimidazolium tetrafluoroborate (EMIM-BF4), which satisfies both the high efficiency, stability and high transmittance against leakage. An ionic liquid electrolyte composed of EMIM-TFSI and EMIM-BF4 was combined with and electrolyte solvent (acetonitrile, 3-methoxypropionitrile, valeronitrile) to obtain a solar cell based on a liquid electrolyte. The power conversion efficiency of the DSSCs employing ionic liquid blend electrolytes (PMII, Iodine, GuSCN, tBP, sovent ;3-methyloxypropionitrile; EMIM-TFSI = 7:3) and the transmittance of ionic liquid blen electrolytes were 5.74 % (open-ciruit voltage Voc = 0.74 V , short-circuit current density Jsc = 12.08 mA/cm2 and fill factor FF = 0.64) 75.8 %, which was similar to DSSCs with organic liquid-based electrolytes ( PMII, Iodine, GuSCN, tBP, sovent ;3-methyloxypropionitrile) (η = 5.76%, Voc = 0.75 V, Jsc = 12.30 mA/cm2 and FF = 0.63, Transmittance = 74.3%), However, the vapor pressure of these ionic liquid blend electrolytes (PMII, Iodine, GuSCN, tBP, sovent ;3-methyloxypropionitrile; EMIM-TFSI = 7:3) was 1.25 Hg at 80℃ which was similar to the cells with the electrolytes employing ionic liquid only (PMII, Iodine, GuSCN, tBP, EMIM-TFSI (vapor pressure = 1.21 at 80℃).