Controlling Electronic Transitions in Fullerene van der Waals Aggregates via Supramolecular Assembly

Saunak Das; Felix Herrmann-Westendorf; Felix H Schacher; Eric Täuscher; Uwe Ritter; Benjamin Dietzek; Martin Presselt

doi:10.1021/acsami.6b06800

Controlling Electronic Transitions in Fullerene van der Waals Aggregates via Supramolecular Assembly

ACS Appl Mater Interfaces. 2016 Aug 24;8(33):21512-21. doi: 10.1021/acsami.6b06800. Epub 2016 Aug 15.

Authors

Saunak Das^{1

2}, Felix Herrmann-Westendorf^{1

2}, Felix H Schacher^{3

4}, Eric Täuscher⁵, Uwe Ritter⁵, Benjamin Dietzek^{1

2}, Martin Presselt^{1

2}

Affiliations

¹ Institute of Physical Chemistry (IPC), Friedrich Schiller University Jena , Helmholtzweg 4, 07743 Jena, Germany.
² Leibniz Institute of Photonic Technology (IPHT) , Albert-Einstein-Str. 9, 07745 Jena, Germany.
³ Institute of Organic Chemistry and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena , Humboldtstraße 10, Jena, 07743, Germany.
⁴ Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena , Philosophenweg 7, Jena, 07743, Germany.
⁵ Institute for Chemistry and Biotechnology, Ilmenau University of Technology , D-98684 Ilmenau, Germany.

PMID: 27482718
DOI: 10.1021/acsami.6b06800

Abstract

Morphologies crucially determine the optoelectronic properties of organic semiconductors. Therefore, hierarchical and supramolecular approaches have been developed for targeted design of supramolecular ensembles of organic semiconducting molecules and performance improvement of, e.g., organic solar cells (OSCs), organic light emitting diodes (OLEDs), and organic field-effect transistors (OFETs). We demonstrate how the photonic properties of fullerenes change with the formation of van der Waals aggregates. We identified supramolecular structures with broadly tunable absorption in the visible spectral range and demonstrated how to form aggregates with targeted visible (vis) absorption. To control supramolecular structure formation, we functionalized the C60-backbone with polar (bis-polyethylene glycol malonate-MPEG) tails, thus yielding an amphiphilic fullerene derivative that self-assembles at interfaces. Aggregates of systematically tuned size were obtained from concentrating MPEGC60 in stearic acid matrices, while different supramolecular geometries were provoked via different thin film preparation methods, namely spin-casting and Langmuir-Blodgett (LB) deposition from an air-water interface. We demonstrated that differences in molecular orientation in LB films (C2v type point group aggregates) and spin-casting (stochastic aggregates) lead to huge changes in electronic absorption spectra due to symmetry and orientation reasons. These differences in the supramolecular structures, causing the different photonic properties of spin-cast and LB films, could be identified by means of quantum chemical calculations. Employing supramolecular assembly, we propounded that molecular symmetry in fullerene aggregates is extremely important in controlling vis absorption to harvest photons efficiently, when mixed with a donor molecule, thus improving active layer design and performance of OSCs.

Keywords: Langmuir−Blodgett isotherms; TDDFT modeling; fullerene acceptor; organic solar cells; supramolecular assembly; van der Waals aggregates.