Slow Charge Transfer from Pentacene Triplet States at the Marcus Optimum

Natalie Pace, Nadezhda Korovina, Gerard Carroll, Justin Johnson, Garry Rumbles, Obadiah Reid, Sanjini Nanayakkara, Tyler Clikeman, Sarah Holliday, Devin Granger, John Anthony, Iain McCulloch, Steven Strauss, Olga Boltalina

Research output: Contribution to journalArticlepeer-review

34 Scopus Citations

Abstract

Singlet fission promises to surpass the Shockley–Queisser limit for single-junction solar cell efficiency through the production of two electron–hole pairs per incident photon. However, this promise has not been fulfilled because singlet fission produces two low-energy triplet excitons that have been unexpectedly difficult to dissociate into free charges. To understand this phenomenon, we study charge separation from triplet excitons in polycrystalline pentacene using an electrochemical series of 12 different guest electron-acceptor molecules with varied reduction potentials. We observe separate optima in the charge yield as a function of driving force for singlet and triplet excitons, including inverted regimes for the dissociation of both states. Molecular acceptors can thus provide a strategic advantage to singlet fission solar cells by suppressing singlet dissociation at optimal driving forces for triplet dissociation. However, even at the optimal driving force, the rate constant for charge transfer from the triplet state is surprisingly small, ~107 s−1, presenting a previously unidentified obstacle to the design of efficient singlet fission solar cells.

Original languageAmerican English
Pages (from-to)63-70
Number of pages8
JournalNature Chemistry
Volume12
Issue number1
DOIs
StatePublished - 1 Jan 2020

Bibliographical note

Publisher Copyright:
© 2019, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.

NREL Publication Number

  • NREL/JA-5900-73057

Keywords

  • electron transfer
  • photochemistry

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