Organic donor-acceptor systems: Charge generation and morphology

Plastic electronics are currently finding their way into mass scale applications. Bringing this technology to the next level requires a profound understanding of the key physical processes occurring in the underlying materials: the organic semiconductors. Organic donor-acceptor materials designed for photovoltaic applications are central to this Thesis. The main focus is on the crucial initial processes occurring immediately after absorption of light in these materials leading to the generation of free charges which can be harvested to provide energy.
Chapter 2 discusses one of the crucial steps in the light-to-electricity production line: the ultrafast transfer of charge between the widely used acceptor known as PC71BM and donor polymer materials. The diffusion of neutral excitons prior to their dissociation into charges is the topic of Chapter 3, where we show that ultrafast spectroscopy is a very convenient method to obtain key information on the nanostructure of blended organic semiconductors. It is vital to have an understanding of the spectroscopic signatures of the various excitations in organic in order to study and understand the photovoltaic charge generation chain on an ultrafast time scale. This is the topic of the last chapter of this Thesis.
The insights presented and discussed in this Thesis are not only relevant to the specific photo-voltaic blends used here, but are also expected to have broader implications in the field of the photo-physics of organic electronics and organic materials.