A solvent-free composite polymer/inorganic oxide electrolyte for high efficiency solid-state dye-sensitized solar cells

A new solvent-free composite polymer electrolyte consisting of high-molecular mass polyethylene oxide (PEO) filled with titanium oxide and containing LiI and I2 was developed. The introduction of the inorganic filler (TiO2 Degussa P25) into the polymer matrix produces dramatic morphological changes to the host polymer structure. Upon addition of the inorganic oxide, the surface roughness increases, with respect to the original polymer and in parallel, the fractal dimension decreases. Both the thermograms and the atomic force microscope (AFM) pictures confirm the amorphicity of the composite electrolyte. The polymer sub-units are held together in a parallel orientation, forming straight long chains of about 500 nm in width, along which TiO2 spherical particles of about 20-25 nm in diameter are distributed. The polymer chains separated by the titania particles are arranged in a three-dimensional, mechanically stable network, that creates free space and voids into which the iodide/triodide anions can easily migrate. All solid-state dye-sensitized solar cells fabricated using this composite electrolyte present high efficiencies (typical maximum incident photon to current efficiency (IPCE) as high as 40% at 520 nm and overall conversion efficiency (η) of 0.96% (Voc = 0.67 V, Jsc = 2.050 mA/cm2, FF = 39%) under direct solar irradiation. Further improvement of the photovoltaic performance is expected by optimization of the electrolyte parameters and of the cell assembly.