Nearly 10% performance for metal-free multibranched DSSC dyes
Norberto Manfredi a, Vanira Trifiletti a, Alessandro Abbotto a, Paolo Biagini b, Giorgio Giannotta b, Fabio Melchiorre b
a Research Center for Non Conventional Energy, Istituto eni-Donegani, eni S.p.A, via Fauser 4, Novara, 28100, Italy
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Poster, Norberto Manfredi, 335
Publication date: 1st March 2014

In recent years, metal free organic sensitizers for dye-sensitized solar cells (DSSC) have attracted great attention because of some advantages they have respect to the metal based ones. The development of new architectures to improve both optical and photovoltaic properties is, at present, a “hot topic” in chemistry field of research.  One of the most promising design for metal free sensitizer in order to achieve broader UV-Vis absorption spectrum and to reduce detrimental effect such as intermolecular charge recombination seems to be the multi-branched multi-anchoring D(-π-A)2 approach. This architecture introduced for the first time in 2009 by some of us1-3 and now widely reported in many papers shows better light harvesting properties and higher stability compared to the corresponding linear D-π-A sensitizers.

Here we present a systematic study upon the influence of the peripheral functionalization of the same D(-π-A)2 core to better understand the correlation between structure and photovoltaic performance. A new family of dibranched dyes as DSSC sensitizers where the donor triphenylamine conventional core has been functionalized with both linear and branched alkyl chains, alkoxychains, and aromatic groups in order to affect the electrolyte-TiO2 interaction is described. We have selected thieno[3,2-b]thiophene as a spacer previously used in efficient DSSC sensitizers, and the corresponding hexyl-substituted core, in combination with the conventional cyanoacrylic acid as double anchoring points. Figure 1 depicts the general design of the series. In conventional liquid iodine-based cells PCE were up to 6.9 %. In an alternative device fabrication geometry based on very small cell areas and large platinum areas at the counter electrodes, we were able to obtain PCE up to nearly 10%.


Figure 1. General design of investigated dibranched dyes.
(1) Abbotto, A.; Manfredi, N.; Marinzi, C.; De Angelis, F.; Mosconi, E.; Yum, J. H.; Zhang, X. X.; Nazeeruddin, M. K.; Gratzel, M.: Di-branched di-anchoring organic dyes for dye-sensitized solar cells. Energy Environ. Sci. 2009, 2, 1094-1101. (2) Abbotto, A.; Leandri, V.; Manfredi, N.; De Angelis, F.; Pastore, M.; Yum, J. H.; Nazeeruddin, M. K.; Gratzel, M.: Bis-Donor-Bis-Acceptor Tribranched Organic Sensitizers for Dye-Sensitized Solar Cells. Eur. J. Org. Chem. 2011, 6195-6205. (3) Leandri, V.; Ruffo, R.; Trifiletti, V.; Abbotto, A.: Asymmetric Tribranched Dyes: An Intramolecular Cosensitization Approach for Dye-Sensitized Solar Cells. Eur. J. Org. Chem. 2013, 2013, 6793-6801.
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