Measuring Photoexcited Free Charge Carriers in Mono- to Few-Layer Transition-Metal Dichalcogenides with Steady-State Microwave Conductivity

Jeffrey Blackburn, Hanyu Zhang, Alexis Myers, Derek Vigil-Fowler, Elisa Link, Garry Rumbles, Obadiah Reid, David Coffey, Rebecca Hirsch, Seok Yun, Byeong Cho, Young Lee, Jeremy Dunklin

Research output: Contribution to journalArticlepeer-review

10 Scopus Citations


Photoinduced generation of mobile charge carriers is the fundamental process underlying many applications, such as solar energy harvesting, solar fuel production, and efficient photodetectors. Monolayer transition-metal dichalcogenides (TMDCs) are an attractive model system for studying photoinduced carrier generation mechanisms in low-dimensional materials because they possess strong direct band gap absorption, large exciton binding energies, and are only a few atoms thick. While a number of studies have observed charge generation in neat TMDCs for photoexcitation at, above, or even below the optical band gap, the role of nonlinear processes (resulting from high photon fluences), defect states, excess charges, and layer interactions remains unclear. In this study, we introduce steady-state microwave conductivity (SSMC) spectroscopy for measuring charge generation action spectra in a model WS2 mono- to few-layer TMDC system at fluences that coincide with the terrestrial solar flux. Despite utilizing photon fluences well below those used in previous pump-probe measurements, the SSMC technique is sensitive enough to easily resolve the photoconductivity spectrum arising in mono- to few-layer WS2. By correlating SSMC with other spectroscopy and microscopy experiments, we find that photoconductivity is observed predominantly for excitation wavelengths resonant with the excitonic transition of the multilayer portions of the sample, the density of which can be controlled by the synthesis conditions. These results highlight the potential of layer engineering as a route toward achieving high yields of photoinduced charge carriers in neat TMDCs, with implications for a broad range of optoelectronic applications.

Original languageAmerican English
Pages (from-to)99-107
Number of pages9
JournalJournal of Physical Chemistry Letters
Issue number1
StatePublished - 2 Jan 2020

Bibliographical note

Publisher Copyright:
Copyright © 2019 American Chemical Society.

NREL Publication Number

  • NREL/JA-5K00-75256


  • charge generation
  • photoconductivity
  • solar-photochemistry
  • transition-metal dichalcogenides


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