The 2,2,6,6‐Tetramethyl‐1‐piperidinyloxy Radical: An Efficient, Iodine‐ Free Redox Mediator for Dye‐Sensitized Solar Cells

Abstract A promising redox system, offering an alternative to the widely used iodide/triiodide couple, based on the stable organic radical 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) has been employed in dye‐sensitized solar cells. The photovoltaic performance of this new redox couple has been evaluated by employing nanocrystalline TiO 2 films with different thickness. Judicious selections of a 5.0 μm photoanode made from TiO 2 mesoscopic particles and an organic sensitizer with a high molar extinction coefficient yield an overall solar‐to‐electric power conversion efficiency of 5.4 % under AM 1.5 illumination at 100 mW cm –2 , which is unprecedented for an iodine‐free mediator system.