A performance enhancement of dye-sensitized solar cells using pyrazolium-based ionic liquids electrolytes vs imidazolium-based ionic liquids electrolytes

Abstract

Pyrazolium-based ionic liquids (ILs) having similar heteroaromatic ring structure as imidazolium are distinguishable by the position of the heteroatom (nitrogens) but are less delved into their properties and their capability in dye-sensitized solar cells (DSSCs). Herein, alkylpyrazolium and alkylimidazolium-based ionic liquids having iodide and triiodide anions were compared in terms of their properties namely viscosity, ionic conductivity, and performance as electrolytes in dye-sensitized solar cells (DSSCs). Furthermore, the effect of varying the concentration of the iodide and triiodide anions was also scrutinized. The DSSCs having pyrazolium-based ILs electrolytes showed considerably higher fill factor (FF) and short circuit current (Jsc) than the cells containing imidazolium-based ILs electrolytes attributable to the high ionic conductivities. The cells with butylpyrazolium [4-1-pz][I] and [4-1-pz][I3] ILs showed the highest power conversion efficiency of 4.76 % with an improvement of 62.4 % compared to corresponding imidazolium ILs electrolytes, owing to the high current density (Jsc). The concentration of the iodide and triiodide redox couple was found to affect the dye regeneration and recombination process as elucidated by electrochemical impedance spectra. The high concentration of triiodide has caused cell efficiency to decrease by more than 50 % with low Jsc, electron diffusion (Deff), and triiodide ions diffusion (DI3-) indicating poor mass transport. The best concentrations for iodide and triiodide found in this study are 0.45 M and 0.064 M, respectively. Hence, pyrazolium-based ILs have high potential to be used as electrolytes for DSSCs applications.