Vendredi 27 juin 2014 à 10h15
Salle 234, Ecole de Physique

Ab initio electronic structure calculations for organic photovoltaic systems

Carina Faber, Institut Néel, Grenoble

Photovoltaics represents one of the most promising routes towards a sustainable energy generation. Besides thin film technologies, photovoltaics based on organic semiconductors seems to be a promising candidate for low-cost and clean energy production. Representing crystals of loosely bound molecular building blocks, organic semiconductors are at the interface between classical band structure theories and quantum chemistry molecular calculations and therefore highly interesting from a fundamental point of view. First-principles quantum mechanical calculations contribute to this field not only by finding new efficient material combinations, but equally they allow to understand fundamental processes like photon absorption or charge separation in this special class of materials. Initially developed in the mideighties at the ab initio level for inorganic semiconductors, the many-body perturbation theory GW and Bethe-Salpeter (BSE) formalisms have recently been shown to yield electronic and optical properties of organic systems with a remarkable accuracy. After introducing some of the important limitations associated with organic photovoltaic cells, we will show that key features, such as band gaps, electron-phonon coupling strengths and donor-to-acceptor charge- transfer excitations can be described with unprecedented accuracy. The used techniques are parameter-free and allow the study of systems comprising up to a few hundred of atoms. The selected calculations have been performed with a recently developed Gaussian-basis GW and BSE package, the Fiesta code.