Nano Energy Research

Structural control of small molecular semiconductor in organic solar cells

Principal Investigator: Jun-Prof. Dr. Manuela Schiek
Collaboration: Prof. Dr. Rüdiger Beckhaus, Prof. Dr. Matthias Wollenhaupt, Dr. Petra Groß

Typical organic so called bulk-heterojunction (BHJ) solar cells consist of a randomly intermixed donor-acceptor blend sandwiched between two electrodes. The performance of the solar cells depends on the choice of the materials (charge generation and transfer), the nano-morphological intermixing of the donor-acceptor system (charge transport), and also interfacial layers at the electrodes (charge extraction). Small molecular semiconductors are advantageous compared to standard polymeric materials, because they allow a more direct control of the structure on the molecular level and consequently solid state properties. The implementation of, e.g., chiral side chains introduces new functionalities arising from supra-molecular order such as circular dichroism.

The project aims at understanding how (molecular) structure and morphology controls the performance of solar cells. The material classes of choice as light harvesting donor are novel squaraines and commercial fullerenes as acceptor [1]. The project involves preparation of the solar cells, opto-electrical characterization of the devices, structural investigations by, e.g. electron microscopy (REM, TEM including selected area diffraction and electron energy loss spectroscopy), atomic force microscopy and X-ray diffraction. Time-resolved spectroscopy can give valuable insight in fundamental dynamics pf the system.

[1] S. Brück, C. Krause, R. Turrisi, L. Beverina, S. Wilken, W. Saak, A. Lützen, H. Borchert, M. Schiek, J. Parisi, Structure–property relationship of anilino-squaraines in organic solar cells, Phys. Chem. Chem. Phys. 16 (2014) 1067.