Fundamentals of Molecular Electrical Doping of Organic Semiconductors (FoMEDOS)

• Applicants: Professorin Dr. Caterina Cocchi, since 10/2017; Professor Dr. Norbert Koch, since 10/2017; Professor Dr. Dieter Neher
• Subject Area: Experimental and Theoretical Physics of Polymers ; Experimental Condensed Matter Physics ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 286798544

Today's information society depends on our ability to controllably dope inorganic semiconductors, such as silicon, thereby tuning their electrical properties to application-specific demands. For opto-electronic devices, however, organic semiconductors have emerged as superior alternative owing to the ease of tuning their optical gap through chemical variability and their potential for low-cost, large-area processing on flexible substrates. There, the potential of molecular electrical doping for improving the performance of, e.g., organic light-emitting devices or organic solar cells, has only recently been established. The doping efficiency, however, remains conspicuously low, highlighting the fact that the underlying, fundamental mechanisms of molecular electrical doping in organic semiconductors are only little understood compared to their inorganic counterparts. In particular, this is reflected in the observation that two important classes of organic semiconductors, small conjugated molecules and conjugated polymers, exhibit a vastly different phenomenology upon doping with no satisfactory explanation put forward to date. This project proposes to solve this important problem and, thereby, to enable the truly knowledge-based improvement of existing organic opto-electronic devices as well as the realization of entirely new functionalities. By combining the unique and complementary capabilities of three experienced PIs, a comprehensive set of experimental techniques will be applied to a meticulously constructed and systematic set of prototypical dopant/organic-semiconductor material combinations, covering both the small-molecule and the polymer variety. With particular emphasis on sample preparation, structural characterization (both in real and in reciprocal space), spectroscopic investigation (optical, vibrational, photoelectron and spin), and various electrical measurements, the proposed project aims at unifying the phenomenology of small-molecule and polymer organic semiconductors to derive an equally unified picture of molecular electrical doping. Challenges arising from the intrinsically disordered nature of organic semiconductors and the dominance of strong intra-molecular interactions over weak inter-molecular interactions will be met by seamlessly interweaving experimental work with advanced theoretical modeling on multiple length scales (from density functional theory to model Hamiltonians) into a single, concerted research effort. Results will not only shed light on the little-explored physics in such systems on a fundamental level, but must also be expected to provide viable guidelines for future technological advances, both in chemical synthesis and in device manufacturing, especially with regard to light-harvesting energy applications.

• DFG Programme: Research Grants
• Ehemalige Antragsteller: Dr. Georg Heimel, until 10/2017; Professor Dr. Ingo Salzmann, until 10/2017