Linking Optical Spectra to Free Charges in Donor/Acceptor Heterojunctions: Cross-Correlation of Transient Microwave and Optical Spectroscopy

Hyun Suk Kang, Samuel Peurifoy, Boyuan Zhang, Andrew Ferguson, Obadiah Reid, Colin Nuckolls, Jeffrey Blackburn

Research output: Contribution to journalArticlepeer-review

3 Scopus Citations

Abstract

The primary photoexcited species in excitonic semiconductors is a bound electron-hole pair, or exciton. An important strategy for producing separated electrons and holes in photoexcited excitonic semiconductors is the use of donor/acceptor heterojunctions, but the degree to which the carriers can escape their mutual Coulomb attraction is still debated for many systems. Here, we employ a combined pump-probe ultrafast transient absorption (TA) spectroscopy and time-resolved microwave conductivity (TRMC) study on a suite of model excitonic heterojunctions consisting of mono-chiral semiconducting single-walled carbon nanotube (s-SWCNT) electron donors and small-molecule electron acceptors. Comparison of the charge-separated state dynamics between TA and TRMC photoconductance reveals a quantitative match over the 0.5 microsecond time scale. Charge separation yields derived from TA allow extraction of s-SWCNT hole mobilities of ca. 1.5 cm2 V-1 s-1 (at 9 GHz) by TRMC. The correlation between the techniques conclusively demonstrates that photoinduced charge carriers separated across these heterojunctions do not form bound charge transfer states, but instead form free/mobile charge carriers.

Original languageAmerican English
Pages (from-to)1509-1517
Number of pages9
JournalMaterials Horizons
Volume8
Issue number5
DOIs
StatePublished - May 2021

Bibliographical note

Publisher Copyright:
© The Royal Society of Chemistry.

NREL Publication Number

  • NREL/JA-5K00-78538

Keywords

  • carbon nanotubes
  • organic photovoltaics
  • photoinduced charge transfer
  • solar-photochemistry
  • time-resolved spectroscopy

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