First-Principles Design of Excited-State Properties of Organic Materials

Dr. Sahar Sharifzadeh
Lawrence Berkeley National Laboratory
Molecular Foundry

Abstract
Organic semiconductors are a highly tunable and diverse class of optically active materials that are promising for next-generation optoelectronic devices. 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. In this talk, I will present our recent theoretical studies aimed at understanding and tuning the spectroscopic properties of organic semiconductors. We use a first-principles many-body perturbation theory approach to calculate densities of states and optical-excitation spectra for prototypical organic semiconductors – pentacene, its functionalized derivatives, and PTCDA. These studies provide a quantitative perspective on a recent controversy regarding the magnitude of transport gaps extracted from photoemission and inverse photoemission spectra, and the energy required to dissociate optically-excited states (excitons) into free carriers. Moreover, for experimentally-synthesized bulk crystals, I will discuss how the energy of low-lying excitons can be understood through an electrostatic model, and their nature tuned through structural control. Additionally, I will describe how this relationship between solid-state structure and excited-state properties can lead to new insight into spatially resolved transient absorption measurements.

Biography
Sahar Sharifzadeh is a project scientist in the Materials Science Division at Lawrence Berkeley National Laboratory. She obtained her PhD in Electrical Engineering from Princeton University before joining Lawrence Berkeley Laboratory as a postdoctoral fellow and subsequently project scientist. Her research interests are in understanding and predicting material properties using first-principles electronic structure theories. Her current focus is on characterization and manipulation of the spectroscopic properties of organic photovoltaic materials, using density functional theory and many-body perturbation theory.