Organic materials are highly tunable, chemically diverse cheap-to-process materials with promise for next-generation optoelectronics. They also harbor interesting excited-state phenomena such as singlet fission, whereby a singlet exciton decays into two spin-correlated triplets, a mechanism of significant interest for achieving efficiencies beyond the Shockley-Queisser limit of conventional solar cells. Further development of new organic materials requires new intuition that links atomic- and molecular-scale morphology to underlying excited-state properties and phenomena, and integrated studies involving theory and experiments. In this talk, I will review and discuss applications of ab initio many-body perturbation theory for calculating excited-state properties of organic molecules and crystalline solids. First, I will briefly review recent efforts to benchmark ab initio MBPT against wavefunction-based methods for charged and neutral excitation energies of gas-phase molecules. Second, I will summarize prior work on the application of ab initio MBPT to crystals; and then describe the use of a new predictive, first-principles Bethe-Salpeter framework for understanding the morphology dependence of multiexciton effects, in particular singlet fission, in acene crystals, such as pentacene and TIPS-pentacene. Direct connections with experiments will also be drawn in all cases.

Single- and multi-exciton phenomena in organic systems from first principles

254th National Meeting (2017)

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