Reconciling the Driving Force and the Barrier to Charge Separation in Donor-Nonfullerene Acceptor Films

Taylor Allen, Panagiota Kafourou, Bryon Larson, Martin Heeney, Obadiah Reid, Garry Rumbles

Research output: Contribution to journalArticlepeer-review

9 Scopus Citations


We investigate the dependence of charge yields on the driving force for photoinduced electron transfer in a series of all-small-molecule, semiconducting films made from indacenodithiophene nonfullerene acceptors (IDT NFAs). In contrast to reports of efficient, barrierless charge separation at near zero driving force for NFA-containing organic photovoltaics, we find that barrierless charge separation occurs only if the driving force is sufficient to overcome the Coulomb potential, ≥300 meV, based on time-resolved microwave conductivity and PL quenching measurements of 5 mmolal sensitized and 700 mmolal blended films comprising IDT NFAs paired with three different donors. This discrepancy with recent literature is caused by a difference in the way that we calculate driving force. Far from being semantic, the driving force calculation is crucial because its value controls the mechanisms needed to explain experimental observations. We provide a candid assessment of the uncertainties for our methods and popular ones used in the literature and emphasize the importance of standardizing methods across this field.

Original languageAmerican English
Pages (from-to)3572-3581
Number of pages10
JournalACS Energy Letters
Issue number10
StatePublished - 8 Oct 2021

Bibliographical note

Publisher Copyright:
© 2021 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-80584


  • nonfullerene acceptors
  • organic photovoltaics
  • organic semiconductors
  • photoinduced electron transfer
  • solar-photochemistry
  • time-resolved microwave conductivity


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