New Electronic Mediators Based on Negative Cobalt Complexes in Dye Sensitized Solar Cells

Stefano Carli^a, Carlo Alberto Bignozzi^a, Eva Busatto^a, Stefano Caramori^a, Laura Casarin^a

^aUniversity of Ferrara, Italy, Via Fossato di Mortara, 17, Ferrara, Italy

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Laura Casarin, 306
Publication date: 5th February 2015

Several strategies have been investigated in order to improve the electron collection efficiency in Dye Sensitized Solar Cells based on common Ru(II) complexes like Z907 and kinetically fast redox mediators based on the [Co(bpy)₃]^2+/3+ couple^{[1, 2]}. With the aim of increasing the dye regeneration efficiency, reducing at the same time charge recombination processes, which characterize this type of systems, we have explored the use of negatively charged cobalt complexes as a new type of redox mediators. The basic idea is that the reduced form of the complexes, negatively charged, would have an increased tendency to reduce the oxidized dye, while the oxidized, neutral form should be less available for recombination with conduction band electrons confined in the titanium dioxide semiconductor. The use of the redox couple [CoTTT(NCS)₃]^-/0 in DSSCs with Z907 and PEDOT, compared to the classic [Co(bpy)₃]^2+/3+, was effective in suppressing the dark current at the TiO₂ interface but the cell was limited by a slow electron transfer kinetics at the PEDOT counter electrode. This approach uses the electrostatic effect with the purpose of reducing electronic recombination, rather than the steric factor, exploited in the case of certain dyes specifically designed to work in conjunction with kinetically fast metal based mediators.
Fig. Effects of the negative and neutral forms of the cobalt based mediator in accelerating dye regeneration and retarding electron recombination
[1] Feldt,S.M.; Gibson,E.A.; Gabrielsson,E.; Sun,L.; Boschloo,G.; Hagfeldt,A.Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efﬁciency Dye-Sensitized Solar Cells. J.Am.Chem.Soc. 2010, 123, 16714-16724 [2] Carli,S.; Casarin,L.; Caramori,S.; Boaretto,R.; Busatto,E.; Argazzi,R.; Bignozzi,C.A.; Polyhedron 2014,82, 173-180

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