Origins of Singlet Fission in Solid Pentacene from an ab initio Green's Function Approach

Sivan Refaely-Abramson; Felipe H da Jornada; Steven G Louie; Jeffrey B Neaton

doi:10.1103/PhysRevLett.119.267401

Origins of Singlet Fission in Solid Pentacene from an ab initio Green's Function Approach

Phys Rev Lett. 2017 Dec 29;119(26):267401. doi: 10.1103/PhysRevLett.119.267401. Epub 2017 Dec 26.

Authors

Sivan Refaely-Abramson^{1

2}, Felipe H da Jornada^{1

3}, Steven G Louie^{1

3}, Jeffrey B Neaton^{1

2}

Affiliations

¹ Department of Physics, University of California Berkeley, Berkeley, California 94720, USA.
² Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

PMID: 29328724
DOI: 10.1103/PhysRevLett.119.267401

Abstract

We develop a new first-principles approach to predict and understand rates of singlet fission with an ab initio Green's-function formalism based on many-body perturbation theory. Starting with singlet and triplet excitons computed from a GW plus Bethe-Salpeter equation approach, we calculate the exciton-biexciton coupling to lowest order in the Coulomb interaction, assuming a final state consisting of two noninteracting spin-correlated triplets with finite center-of-mass momentum. For crystalline pentacene, symmetries dictate that the only purely Coulombic fission decay process from a bright singlet state requires a final state consisting of two inequivalent nearly degenerate triplets of nonzero, equal and opposite, center-of-mass momenta. For such a process, we predict a singlet lifetime of 30-70 fs, in very good agreement with experimental data, indicating that this process can dominate singlet fission in crystalline pentacene. Our approach is general and provides a framework for predicting and understanding multiexciton interactions in solids.