Ionic Liquid-Sulfolane Composite Electrolytes for High-Performance and Stable Dye-Sensitized Solar Cells

Ionic liquid electrolytes are prepared using sulfolane as a plasticizer for eutectic melts to realize highly stable and efficiently performing dye-sensitized solar cells (DSCs) in hot climate conditions. Variations in the viscosity of the formulations with sulfolane content are measured and performance in DSCs is investigated using the ruthenium dye C106 as a sensitizer. A power conversion efficiency (PCE) of 8.2% is achieved under standard reporting conditions. Apart from lowering the viscosity, the addition of sulfolane induces a negative shift of the TiO2 conduction band edge. Strikingly the device performance increases to 8.4% at 50 degrees C due to higher short circuit photocurrent and fill factor, over-compensating the loss in open circuit voltage with increasing temperature. The PCE increases also upon decreasing the light intensity of the solar simulator, reaching up to 9% at 50 mW cm(-2). Devices based on these new electrolyte formulations show excellent stability during light soaking for 2320 h under full sunlight at 60 degrees C and also during a 1065 h long heat stress at 80 degrees C in the dark. A detailed investigation provides important information about the factors affecting the principal photovoltaic parameters during the aging process and the first results from a series of outdoor measurements are reported.