NIR-sensitization of p-type DSSCs with multibranched squaraine sensitizers

Dirk M. Guldi^a, Rubén D. Costa^a, Oliver Langmar^a, Guido Viscardi^b, Claudia Barolo^b, Davide Saccone^b

^aFriedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany

^bUniversity of Torino, Department of Chemistry and NIS Interdepartmental Centre, Via Pietro Giuria 7, 10125, Torino

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, Oliver Langmar, 322
Publication date: 5th February 2015

In order to maximize the energy, which is being harvested by solar cell technologies, new concepts for the future are needed. One of these novel ideas is the use of a dye sensitized tandem solar cell based on TiO₂ and NiO as photoanodes and photocathodes, respectively. Here, each electrode is decorated with different photosensitizers featuring complementary absorption features.^[1] One of the most efficient sensitizers for n-type DSSCs is N719. Notable, the latter absorbs in the high energy region of the spectrum. In this regard a matching photoabsorber for p-type cathodes needs to absorb in the low energy region of the spectrum. Promising candidates to fulfil such a requirement are squaraines, which show additional assets, like intense absorption and excellent photo and thermal stabilities.^[2] In this work, a novel family of multibranched squaraines has been tested in p-type DSSCs with NiO as photocathode. In particular, several dyes, which differ in the number of carboxyl anchoring groups, as well as the influence of an electron-withdrawing cyano-group, have been tested. It was proven that these novel sensitizers show different attachments onto the surface of the semiconductor electrode, resulting in a dramatic impact on the device efficiency. To support our results, devices have been probed with electrochemical impedance spectroscopy (EIS) assays. EIS assays corroborated that the above-mentioned changes regarding the molecular structure have only a minor impact on the charge injection, but sizeable consequences on the recombination with the electrolyte due to different surface coverages.

[1] Nattestad, A.; Mozer, A. J.; Fischer, M. K. R.; Cheng, Y.; Mishra, A.; Bäuerle, P.; Bach, U. Highly efficient photocathodes for dye-sensitized tandem solar cells, Nat. Mater.,2010, 9, 31-35. [2] Beverina, L.; Salice, P. Squaraine Compounds: Tailored Design and Synthesis towards a Variety of Material Science Applications, Eur. J. Org. Chem., 2010, 7, 1207-1225.

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