Interplay of Coulomb and Exciton-Phonon Coupling Controls Singlet Fission Dynamics in Two Pentacene Polymorphs: Article No. 091101

Dylan Arias, Galit Cohen, Niels Damrauer, Sivan Refaely-Abramson, Justin Johnson

Research output: Contribution to journalArticlepeer-review

Abstract

Pentacene is an important model organic semiconductor in both the singlet exciton fission (SF) and organic electronics communities. We have investigated the effect of changing crystal structure on the SF process, generating multiple triplet excitons from an initial singlet exciton, and subsequent triplet recombination. Unlike for similar organic semiconductors that have strong SF sensitive to polymorphism, we find almost no quantitative difference between the kinetics of triplet pair (TT) formation in the two dominant polymorphs of pentacene. Both pairwise dimer coupling and momentum-space crystal models predict much faster TT formation from the bright singlet excited state of the Bulk vs ThinFilm polymorph, contrasting with the experiment. GW and Bethe-Salpeter equation calculations, including exciton-phonon coupling, reveal that ultrafast phonon-driven transitions in the ThinFilm polymorph compensate the intrinsically slower purely Coulomb-mediated TT formation channel, rationalizing the similarity in observed rates. Taking into account the influence of subtle structural distinctions on both the direct and phonon-mediated SF pathways reveals a predictive capability to these methods, expected to be applicable to a wide variety of molecular crystals.
Original languageAmerican English
Number of pages9
JournalThe Journal of Chemical Physics
Volume161
Issue number9
DOIs
StatePublished - 2024

NREL Publication Number

  • NREL/JA-5900-90283

Keywords

  • dark states
  • electronic coupling
  • excitons
  • organic semiconductors
  • phonons
  • polymorphism
  • potential energy surfaces
  • solar cell efficiency
  • thin films
  • triplet state

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