PEO-imidazole ionic liquid-based electrolyte and the influence of NMBI on dye-sensitized solar cells

Highlights: → Ionic liquid oligomer (PEOImI) is applied as electrolyte for DSSC to improve its efficiency. → 1-Alkyl-3-methylimidazolium iodide is mixed with PEOImI to form electrolyte. → The efficiency is further improved by adding N-methylimidazole (NMBI). → NMBI enhances the Grotthus type diffusion of triiodide. → A highest energy conversion efficiency of 6.14% has been attached at 100 mW cm-2. - Abstract: 1-Oligo(ethylene oxide)-3-methylimidazolium iodide (PEOMImI) was synthesized and applied to dye-sensitized solar cells (DSSCs) by blending it with different 1-alkyl-3-methylimidazolium iodides used as ionic liquid electrolytes. The 1-propyl-3-methylimidazolium iodide (PMII) blend enabled the DSSC to attain a higher solar energy conversion efficiency of 4.52% under a light intensity of 100 mW cm-2. The addition of N-methylimidazole (NMBI) to the electrolytes increased the conversion efficiency as compared to DSSCs based on NMBI-free electrolytes. The addition of both 1-allyl-3-methylimidazolium iodide (AMII) and NMBI enabled DSSCs to reach their highest solar energy conversion efficiency of 6.14% under a light intensity of 100 mW cm-2. The ionic conductivity and diffusion coefficient of the triiodide were found to be augmented dramatically after adding NMBI, which leads to an increase in the photocurrent density. The enhancement mechanism of NMBI in the electrolyte was investigated by Raman spectroscopy and differential scanning calorimetry, and it was mainly due to the enhancement of electron exchange in electrolytes.