Wednesday Colloquium: Dr. Sahar Sharifzadeh
Title: Towards Computational Design of the Optoelectronic Properties of Organic Materials
Abstract: Organic semiconductors are a highly tunable class of optically-active materials that are promising as next-generation photovoltaics. To effectively harness these materials for light-harvesting applications, we need to fundamentally understand their excited-state electronic structure, i.e. how light absorption, charge transfer, and charge transport relate to the properties of their molecular components and are influenced by solid-state morphology. Here I will present recent computational studies, based on first-principles many-body perturbation theory, aimed at understanding the spectroscopic properties of select organic semiconductors, and improving these properties for enhanced photovoltaic performance. For both gas-phase molecules and condensed-phase crystals, our quantitative calculations agree well with transport gaps extracted from photoemission spectroscopy and conductance measurements, as well as with measured optical absorption spectra. Introducing a new analysis technique, we elucidate the nature of low-lying solid-state singlet and triplet optical excitations (excitons). We demonstrate significant exciton binding energies and charge-transfer character in these systems, providing new insight into the complexities of excitonic effects within organic crystals. Collectively, this work reveals new ways in which the nature of the exciton can be controlled through solid-state morphology, enabling the deliberate design of novel functional organic materials.