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

Abstract

We present that 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 WS 2 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 WS 2. 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 portionsmore » of the sample, the density of which can be controlled by the synthesis conditions. Lastly, 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.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [1];  [3];  [4];  [1]; ORCiD logo [5];  [6]; ORCiD logo [6]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [2]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States)
  3. Warren Wilson College, Swannanoa, NC (United States)
  4. Univ. of Colorado, Boulder, CO (United States)
  5. Institute for Basic Science (IBS), Suwon (Korea)
  6. Institute for Basic Science (IBS), Suwon (Korea); Sungkyunkwan Univ., Suwon (Korea)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1580328
Report Number(s):
NREL/JA-5K00-75256
Journal ID: ISSN 1948-7185
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry Letters
Additional Journal Information:
Journal Volume: 11; Journal Issue: 1; Journal ID: ISSN 1948-7185
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; charge generation; transition-metal dichalcogenides; photoconductivity

Citation Formats

Blackburn, Jeffrey L., Zhang, Hanyu, Myers, Alexis R., Dunklin, Jeremy R., Coffey, David C., Hirsch, Rebecca N., Vigil-Fowler, Derek W., Yun, Seok Joon, Cho, Byeong Wook, Lee, Young Hee, Miller, Elisa M., Rumbles, Garry, and Reid, Obadiah G. Measuring Photoexcited Free Charge Carriers in Mono- to Few-Layer Transition-Metal Dichalcogenides with Steady-State Microwave Conductivity. United States: N. p., 2019. Web. doi:10.1021/acs.jpclett.9b03117.
Blackburn, Jeffrey L., Zhang, Hanyu, Myers, Alexis R., Dunklin, Jeremy R., Coffey, David C., Hirsch, Rebecca N., Vigil-Fowler, Derek W., Yun, Seok Joon, Cho, Byeong Wook, Lee, Young Hee, Miller, Elisa M., Rumbles, Garry, & Reid, Obadiah G. Measuring Photoexcited Free Charge Carriers in Mono- to Few-Layer Transition-Metal Dichalcogenides with Steady-State Microwave Conductivity. United States. doi:10.1021/acs.jpclett.9b03117.
Blackburn, Jeffrey L., Zhang, Hanyu, Myers, Alexis R., Dunklin, Jeremy R., Coffey, David C., Hirsch, Rebecca N., Vigil-Fowler, Derek W., Yun, Seok Joon, Cho, Byeong Wook, Lee, Young Hee, Miller, Elisa M., Rumbles, Garry, and Reid, Obadiah G. Mon . "Measuring Photoexcited Free Charge Carriers in Mono- to Few-Layer Transition-Metal Dichalcogenides with Steady-State Microwave Conductivity". United States. doi:10.1021/acs.jpclett.9b03117.
@article{osti_1580328,
title = {Measuring Photoexcited Free Charge Carriers in Mono- to Few-Layer Transition-Metal Dichalcogenides with Steady-State Microwave Conductivity},
author = {Blackburn, Jeffrey L. and Zhang, Hanyu and Myers, Alexis R. and Dunklin, Jeremy R. and Coffey, David C. and Hirsch, Rebecca N. and Vigil-Fowler, Derek W. and Yun, Seok Joon and Cho, Byeong Wook and Lee, Young Hee and Miller, Elisa M. and Rumbles, Garry and Reid, Obadiah G.},
abstractNote = {We present that 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. Lastly, 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.},
doi = {10.1021/acs.jpclett.9b03117},
journal = {Journal of Physical Chemistry Letters},
number = 1,
volume = 11,
place = {United States},
year = {2019},
month = {12}
}

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