Development of new hybrid solid electrolytes for dye sensitized solar cells

Full text: Dye-sensitized solar cells (DSCs), firstly developed in 1991[1], have received much attention due to their high energy conversion efficiency and low production cost. Recently, efforts have been made in developing solid electrolytes for use in DSCs to avoid leakage and evaporation associated to liquid electrolytes. In this work Siloxane-Polyethers electrolytes containing KI and I2 have been prepared and the effect of incorporation of an organic dye with large absorption in visible light range investigated. For both types of polyethers (Polyoxyethylene (PEO) of molar mass 1900 g/mol or Polyoxypropylene (PPO) of molar mass 4000 g/mol) the ionic conductivity of dye-free and dye-containing electrolytes exhibits a maximum around 10-5 S.cm-1 when [O]/[KI]=15 (the oxygens being of the ether-type). Impedance spectroscopy (EIS) evidences two species involved in the conduction process in Siloxane-PPO hybrids, while only one is detected in Siloxane-PEO electrolytes. The local structure of the Siloxane-PPO samples with [O]/[KI]=15 was investigated by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) whereas their thermal properties were studied by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). XRD and TGA show that dye incorporation promotes KI dissolution in the hybrid, which is promising for future incorporation of larger amounts of KI and dye, aiming improvement of electrical and optical performance. Chemical interaction of iodide species with dye molecules are suggested by FTIR. DSC reveals that glass transition temperature (Tg) of Siloxane-PPO is around -60 °C, promoting conductivity. Further investigation will be performed to understand the conduction mechanisms in Siloxane-PPO and Siloxane-PEO electrolytes and to understand how KI, I2 and dye incorporation affects the hybrids nanostructure. Reference: [1] O'Regan B, Grätzel M (1991) Nature 353:737-740. (author)