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IRTG / Soft Matter Science
Freiburger Materialforschungszentrum
Stefan-Meier-Str. 21
79104 Freiburg, Germany

Contact: Jana Husse

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You are here: Home Events CANCELLED: Dr. Amparo Ruiz Carretero "Advancing organic photovoltaics from the supramolecular level"

CANCELLED: Dr. Amparo Ruiz Carretero "Advancing organic photovoltaics from the supramolecular level"

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Institut Charles Sadron, University of Strasbourg, France

What
  • Seminar
When Nov 30, 2016
from 02:15 PM to 03:00 PM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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Securing the global energy supply in a renewable way is one of the biggest challenges of our generation. Solar energy is one of the best alternatives, since it is a safe and unlimited clean energy source. One of the best alternatives is the use of organic solar cells that can be highly efficient and fabricated low (energy) cost. Several organic and hybrid devices have been described, such as perovskite- based, dye-sensitized solar cells (DSSCs) and bulk heterojunction solar cells (BHJSCs). While perovskite-based cells and DSSCs have reached efficiency values close to the ones found for inorganic cells, BHJSCs are still far from reaching the maximum theoretical value described up to date (22%).[1]

Nevertheless, BHJSCs are very interesting since they are easily scalable to large device areas, and compatible with flexible substrates. In addition, they are not toxic as perovskite-based devices and do not have a liquid electrolyte as DSSCs. In short, BHJSCs would be the solar harvesting of choice if only they could have higher efficiencies. The main crux is the morphology of donor (D) and acceptor (A) molecules in the active layer of the BHJSCs, where light is absorbed and converted to charge carriers. Most common materials used are π-conjugated D polymers[2] or small organic D molecules[3] that match their electronic properties with those of acceptor molecules (A). Both components are blended and sandwiched in between two electrodes, resulting in D and A domains that are randomly distributed and oriented, some of them being isolated and not contributing to the final power conversion. The optimal BHJSC morphology has been described as the “checkerboard morphology,”[4] which consists of electrode to electrode percolating domains of D and A components, where the molecules in each domain are oriented face-on with respect to the electrodes. With such morphology, once excitons are created upon light absorption they can easily reach the interface between D and A materials where they split into charge carriers. Percolating domains and good connectivity among molecules then leads to efficient charge transport, and thus increased efficiency.

So far, many processing protocols have been used to achieve such desired morphology. However, the ideal “checkerboard” morphology for a BHJ OPV is impossible to achieve just relying on phase separation. Here I will show the use of supramolecular strategies based on the use of hydrogen-bonded semiconductors[5, 6] to achieve the desired morphology as well as surface initiated methods to program the desired molecular orientation for efficient device performance.


References
(1)    Janssen, R. A. J.; Nelson, J. Adv. Mater. 2013, 25 (13), 1847.
(2)    Bijleveld, J. C.; Zoombelt, A. P.; Mathijssen, S. G. .; Wienk, M. M.; Turbiez, M.; de Leeuw, D. M.; Janssen, R. A. . J. Am. Chem. Soc. 2009, 131 (46), 16616.
(3)    Sun, Y.; Welch, G. C.; Leong, W. L.; Takacs, C. J.; Bazan, G. C.; Heeger, A. J. Nat. Mater. 2011, 11 (1), 44.
(4)    Watkins, P. K.; Walker, A. B.; Verschoor, G. L. B. Nano Lett. 2005, 5 (9), 1814.
(5)    Ruiz-Carretero, A.; Aytun, T.; Bruns, C. J.; Newcomb, C. J.; Tsai, W.-W.; Stupp, S. I. J. Mater. Chem. A 2013, 1 (38), 11674.
(6)    Aytun, T.; Barreda, L.; Ruiz-Carretero, A.; Lehrman, J. A.; Stupp, S. I. Chem. Mater. 2015, 27 (4), 1201.

 

invited by Jörg Baschnagel

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