PEO electrolytes containing dioctyl phthalate (DOP) for dye-sensitized nanocrystalline TiO2 solar cells

Abstract

In this paper, we aim to prepare polymer electrolytes consisting of NaI and I2 dissolved in poly(ethylene oxide) (PEO) and dioctyl phthalate (DOP) as an additive and apply the electrolytes to dye-sensitized solar cells (DSSC). Upon the incorporation of salt, the phthalic-stretching C=O bands of DOP in Fourier transform infrared spectra shifted to a lower wave number (Δf = 93 cm−1), confirming the unusual strong complex formation between sodium ions and phthalic oxygen. Coordinative interactions and structural changes of PEO/NaI/I2/DOP electrolytes have also been characterized by wide angle X-ray scattering, presenting an almost amorphous structure of the polymer electrolytes. The ionic conductivity of the polymer electrolytes reached ∼10–4 S/cm at room temperature at the mole ratio of [EO]:[Na]:[DOP] = 10:1:0.5, as determined by the four-probe method. DSSC using the polymer electrolytes and conductive indium tin oxide glasses exhibited 2.9% of overall energy conversion efficiency (=Pmax/Pin × 100) at one sun condition (100 mW/cm2). The good interfacial contact between the electrolytes and the dye-attached nanocrystalline TiO2 layers were verified by field-emission scanning electron microscopy.