Imidazolium functionalized TEMPO/iodide hybrid redox couple for highly efficient dye-sensitized solar cells

Abstract

The imidazolium functionalized stable organic radical 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO), and 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidoxyl) butyl)imidazolium bis(trifluoromethanesulfonyl) imide ([MeIm-TEMPO][TFSI]), were synthesized and characterized. The prepared [MeIm-TEMPO][TFSI]/1-propyl-3-methylimidazolium iodide (PMII) hybrid redox couple showed negligible absorption in the visible region and higher redox potential as compared with the iodide/triiodide (I⁻/I₃⁻) redox couple. The resulting dye-sensitized solar cells (DSSCs) containing the imidazolium functionalized TEMPO/PMII hybrid redox couple in combination with organic dye (D205) exhibited average overall power conversion efficiencies of 8.2% and 9.1% under simulated air mass 1.5 solar spectrum illumination at 100 mW cm⁻² and 50 mW cm⁻², respectively, which are higher than that of the traditional PMII/I₂ based electrolyte, probably due to the enhancement of the V_oc and J_sc values of the hybrid electrolytes.