Graphitic carbon nitride (g-C3N4), a metal-free and visible light responsive photocatalyst, has garnered much attention due to its wide range of applications. In order to elucidate the role of dimensionality on the properties of photo-generated charge carriers, we apply nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory to investigate nonradiative relaxation of hot electrons and holes, and electron–hole recombination in monolayer and bulk g-C3N4. The nonradiative charge recombination occurs on a nanosecond timescale and is faster in bulk than the nanosheet, in agreement with the experiment. The difference arises due to the smaller energy gap and participation of additional vibrations in the bulk system. The long carrier lifetimes are favored by small NA coupling and rapid phonon-induced loss of quantum coherence between the excited and ground electronic states. Decoherence is fast because g-C3N4 is soft and undergoes large scale vibrations. The NA coupling is small since electrons and holes are localized on different atoms, and the electron–hole overlap is relatively small. Phonon-driven relaxation of hot electrons and holes takes 100–200 fs and is slightly slower at higher initial energies due to participation of fewer vibrational modes. This feature of two-dimensional g-C3N4 contrasts traditional three-dimensional semiconductors, which exhibit faster relaxation at higher energies due to larger density of states, and can be used to extract hot carriers to perform useful functions. The ab initio quantum dynamics simulations present a comprehensive picture of the photo-induced charge carrier dynamics in g-C3N4, guiding design of photovoltaic and photocatalytic devices.
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7 August 2020
Research Article|
August 03 2020
Ab initio quantum dynamics of charge carriers in graphitic carbon nitride nanosheets Available to Purchase
Special Collection:
2D Materials
Sraddha Agrawal
;
Sraddha Agrawal
1
Department of Chemistry, University of Southern California
, Los Angeles, California 90089, USA
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Wei Lin;
Wei Lin
2
State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University
, Fuzhou 350108, People’s Republic of China
3
Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry
, Xiamen, Fujian 361005, China
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Oleg V. Prezhdo
;
Oleg V. Prezhdo
1
Department of Chemistry, University of Southern California
, Los Angeles, California 90089, USA
4
Department of Physics and Astronomy, University of Southern California
, Los Angeles, California 90089, USA
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Dhara J. Trivedi
Dhara J. Trivedi
a)
5
Department of Physics, Clarkson University
, Potsdam, New York 13699, USA
a)Author to whom correspondence should be addressed: [email protected]
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Sraddha Agrawal
1
Wei Lin
2,3
Oleg V. Prezhdo
1,4
Dhara J. Trivedi
5,a)
1
Department of Chemistry, University of Southern California
, Los Angeles, California 90089, USA
2
State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University
, Fuzhou 350108, People’s Republic of China
3
Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry
, Xiamen, Fujian 361005, China
4
Department of Physics and Astronomy, University of Southern California
, Los Angeles, California 90089, USA
5
Department of Physics, Clarkson University
, Potsdam, New York 13699, USA
a)Author to whom correspondence should be addressed: [email protected]
Note: This paper is part of the JCP Special Topic on 2D Materials.
J. Chem. Phys. 153, 054701 (2020)
Article history
Received:
April 13 2020
Accepted:
June 11 2020
Citation
Sraddha Agrawal, Wei Lin, Oleg V. Prezhdo, Dhara J. Trivedi; Ab initio quantum dynamics of charge carriers in graphitic carbon nitride nanosheets. J. Chem. Phys. 7 August 2020; 153 (5): 054701. https://doi.org/10.1063/5.0010628
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