Example of user project: Who cares about energy levels in phthalocyanines?

Who cares about energy levels in phthalocyanines?
We care, because users of the ETSF care, and they have good reasons!

A project submitted in Spring 2009 called “Spectroscopy of Molecules for Biomimetic Solar Cells” convinced ETSF External Evaluation Panel that these are “details” that are very likely to have an impact on the future of energy production in Europe. Indeed, charge transfer processes between donor–acceptor complexes and metallic electrodes are at the heart of novel organic optoelectronic devices such as solar cells. Molecular dyads lead to the development of new architectures  thanks to the varied properties offered by organic semiconductors. On the one hand, the optical sensitivity of the photovoltaic cell can be tuned to the environmental light conditions by appropriate choice of the molecular pair. On the other hand, the intermolecular interactions can be trimmed by chemical functionalization of the respective molecules, in order to optimize the molecular coupling in the supramolecular assembly. The bottleneck of this emerging technology is represented by the interface with the supporting metal contact, where the charge signal is extracted.

Obviously, we are talking about technologically relevant, very complex systems. A crucial question is, therefore:

Will an object composed of several components behave simply as the sum of its components, or will more complicated mechanismes force device designers to take interference between the single objects into account?

The first part of our study focused therefore on binary supramolecular nanostructures on coppercomprising fluorinated Copper-phthalocyanines (F16CuPc) and diindenoperylene (DIP). ETSF users (D. Oteyza and E. Ortega) have studied the electronic and crystalline properties  by means of scanning tunnelling microscopy and synchrotron radiation spectroscopy measurements performed at the synchrotron ELETTRA, and ETSF scientists have performed  state-of-the-art ab-initio calculations. We have found that, with respect to the corresponding single component layers, the new environment of the binary mixture causes the donor molecule (DIP) to decouple electronically from the metal surface, while the acceptor (F16CuPc) suffers strong hybridization with the substrate.

Published by Adv. Funct. Mater. 2009, 19, 3567

What does this mean?

It means that the charge transfer and the chemical properties of metal- organic interfaces based on single component organic layers cannot be naively extrapolated to the new molecular environments of supramolecular architectures, such as donor–acceptor binary assemblies. As a consequence, a detailed atomistic understanding of the hybrid junction between electrode and organic mixture (both from an electronic and structural point of view) is required for a rational design of functional donor–acceptor nanostructures with optimized properties.

This is what ETSF is for – use fundamental theory and state-of-the art computer codes to speed up the design of future!!!