Exchanged: The organic radical 2‐azaadamantan‐N‐oxyl (AZA; see picture) is found to be a stable and highly reactive redox mediator in dye‐sensitized solar cell (DSSC) electrolytes. This radical has an appropriate redox potential and significantly high values for the diffusivity, heterogeneous electron‐transfer rate, and electron self‐exchange reaction rate. In a DSSC the AZA‐based electrolyte achieves an excellent photovoltaic performance.

A robust nitroxide radical, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its 4-subsituted derivatives (R-TEMPO) exhibit electrochemically reversible redox properties with tunable half-wave potentials (E1/2) based on the substituent effect. Dye-sensitized solar cells using R-TEMPO as mediators with electron-withdrawing R groups showed significantly enhanced photovoltages compared with those obtained using iodides. The linearity between the open-circuit voltage (Voc) and E1/2 revealed that Voc was dominated by the energy gap between the Fermi level of TiO2 and the SOMO level of R-TEMPO.

Electrochemical reversibility and fast bimolecular exchange reaction found for VO(salen) gave rise to a highly efficient redox mediation to enhance the photocurrent of a dye-sensitized solar cell, leading to an excellent photovoltaic performance with a conversion efficiency of 5.4%. A heterogeneous electron-transfer rate constant at an electrode (k0) and a second-order rate constant for an electron self-exchange reaction (k(ex)) were proposed as key parameters that dominate the charge transport property, which afforded a novel design concept for the mediators based on their kinetic aspects.

Ausgetauscht: Das 2‐Azaadamantan‐N‐oxyl‐Radikal (siehe Bild) erweist sich als stabiler und hochreaktiver Redoxmediator in Farbstoffsolarzellen‐Elektrolyten. Das Radikal hat ein geeignetes Redoxpotential und zeigt signifikant hohe Diffusionsgeschwindigkeitskonstanten sowie heterogene Elektronentransfer‐ und Elektronenaustauschgeschwindigkeiten. Mit dem Elektrolyt werden exzellente photovoltaische Leistungen erzielt.

A durable nitroxide radical combined with a triarylamine moiety exhibited a hole-drift mobility of 6 x 10(-3) cm(2) V(-1) s(-1), to which the aminophenyl nitroxide structure contributed.