Abstract
Organic-based semiconductors are a highly tunable, diverse class of cheap-to-process materials promising for next-generation optoelectronics, for example solar cells. Further development of new organic materials requires new intuition that links molecular-scale morphology to underlying excited-state properties and related phenomena. Here, I will discuss the use of first-principles van der Waals-corrected density functional theory and many-body perturbation theory – within the GW approximation and the Bethe-Salpeter equation approach – for computing and understanding spectroscopic properties of selected organic semiconductor crystals, including acenes, from benzene to hexacene; TIPS-pentacene; and halide perovskites. Our quantitative calculations for these systems are in agreement with transport gaps extracted from experiment, and with measured polarization-dependent optical absorption spectra, provided an adequate starting point for GW is used. For acene crystals, we further elucidate the nature of low-lying solid-state singlet and triplet excitons, which have significant binding energies and charge-transfer character in these systems, and rationalize trends in predicted singlet and triplet excitation energies in the context of recently proposed mechanisms for singlet fission. Implications for spectroscopic and transport measurements are discussed.
© 2015 Optical Society of America
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