SPP1355:Electronic properties of interfaces with conjugated polymers III

The project focuses on polymer interfaces that are of direct relevance for organic photovoltaic
cells (OPVCs), their function and efficiency. Our goal is to provide a complete understanding
of the energy levels at all interfaces that occur in polymer/polymer heterojunction
photovoltaic cells (i.e., donor polymer/anode, donor/acceptor and acceptor polymer/cathode
interfaces) and how these energy levels influence the OPVC energy conversion efficiency. In
the third project phase, these interfaces comprise new naphthalene diimide-based acceptor
copolymers and also conjugated polyelectrolytes for a novel scheme of improved electron
extraction, available through collaboration with the Scherf group (Uni Wuppertal) within this
priority program.
Using ultraviolet and X-ray photoemission spectroscopy as key experimental methods we will
determine all relevant interfacial energy levels with the goal of revealing (i) the influence of
polymer donor/acceptor interfacial electric fields due to energy level pinning and (ii) the
energy level alignment mechanisms at acceptor polymer and polyelectrolyte interfaces. Our
results will be used, in combination with OPVC characterization, to test existing device
models, and to provide a reliable parameter base for improved understanding of device
function. This work is performed in close cooperation with the project of Neher/Scherf (Uni
Potsdam/Uni Wuppertal) which employs the same donor and acceptor polymers, as well as
the conjugated polyelectrolytes, for OPVC fabrication and characterization. These concerted
efforts will provide knowledge of the elementary physical properties of polymer interfaces and
will thus lead to a significant advance in the understanding of elementary processes of
organic photovoltaics.