Missing Excitons: How Energy Transfer Competes with Free Charge Generation in Dilute-Donor/Acceptor Systems

Joshua Carr, Melissa Gish, Obadiah Reid, Garry Rumbles

Research output: Contribution to journalArticlepeer-review

Abstract

Energy transfer across the donor-acceptor interface in organic photovoltaics is usually beneficial to device performance, as it assists energy transport to the site of free charge generation. Here, we present a case where the opposite is true: dilute donor molecules in an acceptor host matrix exhibit ultrafast excitation energy transfer (EET) to the host, which suppresses the free charge yield. We observe an optimal photochemical driving force for free charge generation, as detected via time-resolved microwave conductivity (TRMC), but with a low yield when the sensitizer is excited. Meanwhile, transient absorption shows that transferred excitons efficiently produce charge-transfer states. This behavior is well described by a competition for the excited state between long-range electron transfer that produces free charge and EET that ultimately produces only localized charge-transfer states. It cannot be explained if the most localized CT states are the intermediate between excitons and the free charge in this system.
Original languageAmerican English
Pages (from-to)896-907
Number of pages12
JournalACS Energy Letters
Volume9
Issue number3
DOIs
StatePublished - 2024

NREL Publication Number

  • NREL/JA-5900-87537

Keywords

  • acceptor
  • charge transfer
  • charge transfer state
  • donor
  • energy transfer
  • free charges
  • fullerene
  • microwave conductivity
  • organic semiconductors

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