Quantitative Evaluation of Optical Free Carrier Generation in Semiconducting Single-Walled Carbon Nanotubes

Yusong Bai, George Bullard, Jean-Hubert Olivier, Michael J. Therien

Research output: Contribution to journalArticle

Abstract

Gauging free carrier generation (FCG) in optically excited, charge-neutral single-walled carbon nanotubes (SWNTs) has important implications for SWNT-based optoelectronics that rely upon conversion of photons to electrical current. Earlier investigations have largely provided only qualitative insights into optically triggered SWNT FCG, due to the heterogeneous nature of commonly interrogated SWNT samples and the lack of direct, unambiguous spectroscopic signatures that could be used to quantify charges. Here, employing ultrafast pump-probe spectroscopy in conjunction with chirality-enriched, length-sorted, ionic-polymer-wrapped SWNTs, we develop a straightforward approach for quantitatively evaluating the extent of optically driven FCG in SWNTs. Owing to the previously identified trion transient absorptive hallmark (Tr+ 11 → Tr+ nm) and the rapid nature of trion formation dynamics (<1 ps) relative to established free-carrier decay time scales (>ns), we correlate FCG with trion formation dynamics. Experimental determination of the trion absorptive cross section further enables evaluation of the quantum yields for optically driven FCG [φ(Enn→h++e-)] as a function of optical excitation energy and medium dielectric strength. We show that (i) E33 excitons give rise to dramatically enhanced φ(Enn→h++e-) relative to those derived from E22 and E11 excitons and (ii) φ(E33→h++e-) monotonically increases from ∼5% to 18% as the solvent dielectric constant increases from ∼32 to 80. This work highlights the extent to which the nature of the medium and excitation conditions control FCG quantum yields in SWNTs: such studies have the potential to provide new design insights for SWNT-based compositions for optoelectronic applications that include photodetectors and photovoltaics.

Original languageEnglish (US)
Pages (from-to)14619-14626
Number of pages8
JournalJournal of the American Chemical Society
Volume140
Issue number44
DOIs
StatePublished - Nov 7 2018
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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