Engineering of cheap nanoscale elements based on self-assembled organic molecular materials with spatially distributed p-n interfaces is envisaged as a promising alternative to the expensive inorganic photovoltaic cells. In this frame, we plan to explore nanophotovoltaic interfaces to advance our understanding of the processes of sunlight conversion into usable electrical energy in molecular-scale structures.
Of particular relevance for the working principle of solar cells are the interfaces between n- and p-type semiconductors, as well as those between the semiconductors and metallic contacts. We will address 3 main types of model systems: (i) bicomponent molecular layers comprising both donor and acceptor semiconducting molecules, (ii) single molecules featuring covalently coupled but yet differentiated donor and acceptor moieties, and (iii) donor-acceptor networks resulting from surface supported polymerization of previously assembled appropriate precursors. As substrates we will use the bare surface of atomically clean single crystal metals, as well as an isolating buffer layer grown on top to decouple the molecules from the metal.
The functionality of such interfaces strongly depends on their electronic properties, and also on their crystalline structure and morphology. A combination of STM and STS measurements will provide not only a thorough structural analysis of the systems under study, but also detailed and spatially resolved spectroscopic insight of the relevant interfaces. Furthermore, complementary spatially averaging photoelectron and NEXAFS spectroscopies, as well as DFT calculations, will complete our study.
Such study of the electronic structure of all these systems, put in relation with their simultaneously measured spatial arrangement, is expected to give valuable insight into the underlying physics of nano-photovoltaic interfaces, and thereby allow for the design and synthesis of functional interfaces with optimized optoelectronic response.
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