Lattice vibrational effects on single- and multiexciton phenomena in organic crystals from a first principles Green’s function approach*

Singlet fission, a process in which a photoexcited singlet exciton rapidly decays to a bi-triplet exciton, is of recent interest for achieving beyond Shockley-Queissier limit solar cells. Although this process was experimentally observed over 50 years ago in molecular crystals, mechanisms of singlet fission are still hotly debated. Here, we use a recently developed ab initio Green’s function method [1], based on many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation approach in conjunction with density functional perturbation theory to examine the role of lattice vibrations in linear absorption and singlet fission processes in molecular crystals, including tetracene and TIPS-pentacene. More specifically, inspired by recent work on “one shot” temperature calculations [2], we explore the coupling of specific modes to singlet and triplet excitons and how these might alter rates of singlet fission within the adiabatic and harmonic approximations.

1. S. Refaely-Abramson et al., cond-mat/arXiv:1706.01564 (2017)
2. M. Zacharias and F. Giustino, Phys. Rev. B 94, 075125 (2016)