Azide-induced crosslinking of electrolytes and its application in solid-state dye-sensitized solar cells

Poly(ethylene glycol) containing terminal azide groups, i.e. PEG-N3, was synthesized by reacting poly(ethylene glycol diglycidyl ether) (PEGDGE) with NaN3, as confirmed by 1H NMR and FT-IR spectroscopy. The resultant PEG-N3 was complexed with LiI or ionic liquid (1-methyl-3-propylimidazolium iodide, MPII) and then crosslinked under UV irradiation to enhance the mechanical properties of the electrolytes. The ionic conductivity of electrolytes with MPII reached 1.6×10−5 S/cm at 25 °C, which is ten-fold higher than that of electrolytes with LI (1.5×10−6 S/cm), due to different chain mobility. A worm-like morphology of the TiO2 nanoporous layer was observed in the FE-SEM micrographs, which resulted from the interfacial contact between the TiO2 nanoparticles and the electrolytes. Dye-sensitized solar cells (DSSCs) employing electrolytes with MPII and LiI exhibited an energy conversion efficiency at 100 mW/cm2 of 1.6% and 0.8%, respectively. Solar cell performances were further improved by up to 4.2% with careful optimization.