Towards Computational Design of the Optoelectronic Properties of Organic Materials

Note: Pizza served at 11:45 AM
Speaker: Sahar Sharifzadeh, ECE, Boston University

When: November 7, 2014 (Fri), 12:00PM to 01:00PM (add to my calendar)
Location: SCI 352
Hosted by: Ophelia Tsui

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract: Low-­‐cost earth-­‐abundant materials such as organic molecules are currently being pursued as integrated components within next-­‐generation optoelectronics. The design and optimization of these materials requires understanding of their structural features and spectroscopic properties at the nanometer scale. 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. I will demonstrate that while the energy of low-­‐energy excitations in the solid-­‐state can be understood through an electrostatic model, inter-­‐molecular interactions lead to significant excited-­‐state delocalization. Furthermore, I will introduce a general analysis of two-­‐particle electron-­‐ hole wavefunctions that elucidates the nature of low-­‐lying solid-­‐state singlet and triplet optical excitations (excitons), leading to new insight into the complexities of excitonic effects within organic crystals. Collectively, this work reveals new ways in which the nature and energy of the exciton can be controlled through solid-­‐state morphology, enabling the deliberate design of novel functional organic materials.