By employing several lattice model systems, we investigate the free energy barrier and real-time dynamics of charge separation in organic photovoltaic (OPV) cells. It is found that the combined effects of the external electric field, entropy, and charge delocalization reduce the free energy barrier significantly. The dynamic disorder reduces charge carrier delocalization and results in the increased charge separation barrier, while the effect of static disorder is more complicated. Simulation of the real-time dynamics indicates that the free charge generation process involves multiple time scales, including an ultrafast component within hundreds of femtoseconds, an intermediate component related to the relaxation of the hot charge transfer (CT) state, and a slow component on the time scale of tens of picoseconds from the thermally equilibrated CT state. Effects of hot exciton dissociation as well as its dependence on the energy offset between the Frenkel exciton and the CT state are also analyzed. The current results indicate that only a small energy offset between the band gap and the lowest energy CT state is needed to achieve efficient free charge generation in OPV devices, which agrees with recent experimental findings.
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28 February 2018
Research Article|
February 27 2018
Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells
Yaming Yan;
Yaming Yan
Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun
, Beijing 100190, China
and University of Chinese Academy of Sciences
, Beijing 100049, China
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Linze Song;
Linze Song
Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun
, Beijing 100190, China
and University of Chinese Academy of Sciences
, Beijing 100049, China
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Qiang Shi
Qiang Shi
a)
Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun
, Beijing 100190, China
and University of Chinese Academy of Sciences
, Beijing 100049, China
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J. Chem. Phys. 148, 084109 (2018)
Article history
Received:
November 30 2017
Accepted:
February 07 2018
Citation
Yaming Yan, Linze Song, Qiang Shi; Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells. J. Chem. Phys. 28 February 2018; 148 (8): 084109. https://doi.org/10.1063/1.5017866
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