Phonon-driven femtosecond dynamics of excitons in crystalline pentacene from first principles

Kavli Affiliate: Jeffrey B. Neaton

| First 5 Authors: Galit Cohen, Jonah B. Haber, Jeffrey B. Neaton, Diana Y. Qiu, Sivan Refaely-Abramson

| Summary:

Non-radiative exciton relaxation processes are critical for energy
transduction efficiencies in optoelectronic materials, but how these processes
are connected to the underlying crystal structure and its associated electron,
exciton, and phonon band structures is poorly understood. Here, we present a
first-principles approach to explore exciton relaxation pathways in pentacene,
a paradigmatic molecular crystal and optoelectronic semiconductor. We compute
the momentum- and band-resolved exciton-phonon interactions, and use them to
analyse key scattering channels. We find that exciton intraband transitions on
femtosecond timescales leading to dark-state occupation is a dominant
nonradiative relaxation channel in pentacene. We further show how the nature of
real-time propagation of the exciton wavepacket is connected with the
longitudinal-transverse exciton splitting, stemming from crystal anisotropy,
and concomitant anisotropic exciton and phonon dispersions. Our results provide
a framework for understanding time-resolved exciton propagation and energy
transfer in molecular crystals and beyond.

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