Published online by Cambridge University Press: 01 February 2011
A stable organic molecular radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), has been electrochemically studied and employed as a new redox mediator in nanocrystalline TiO2 dye-sensitized solar cells (DSCs) when it is doped with nitrosonium tetrafluoroborate (NOBF4). Reasonable photocurrents can be achieved despite of driving force of only 0.2 eV for the TEMPO/TEMPO+ system as compared to 0.6 eV for the iodide/triiodide redox system. Judicious selections of a 5 µm photoanode made from TiO2 mesoscopic particles (60 nm in diameter) and an organic sensitizer with high molar extinction coefficient yield an overall power conversion of 5.0 % under AM 1.5 illumination at 100 mW cm-2 and an incident photon-to-current conversion efficiencies (IPCE) in excess of 50 %.