Exploring interchain polaron pair formation in neat conjugated polymers
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THE EUROPEAN PHYSICAL JOURNAL B
Regular Article
Exploring interchain polaron pair formation in neat conjugated polymers Zhen Sun 1,2,a , Sheng Li 1 , Shijie Xie 3 , and Zhong An 4 1 2
3 4
Department of Physics, Zhejiang Normal University, Jinhua, Zhejiang 321004, P.R. China Collaborative Innovation Center of Light Manipulations and Applications, Shandong Normal University, Jinan 250358, P.R. China School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P.R. China College of Physics, Hebei Normal University, Shijiazhuang 050024, P.R. China Received 26 November 2019 / Received in final form 6 April 2020 Published online 15 July 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. We present theoretical studies to explore interchain polaron pair (PP) formation in conjugated polymers. Based on the Pariser-Parr-Pople (PPP) Hamiltonian combined with the configuration interaction singles (CIS), we perform excited-state geometry optimization on a poly-p-phenylenevinylene (PPV) dimer, and identify interchain PPs in this system by analyzing the real-space distributions of electron and hole in different excited states. We find that interchain PP states can not form in highly symmetric cofacial PPVdimer, but can form in this PPV-dimer when applying an external electric field, rotating one of two chains, or doping an impurity. Considering that highly symmetric systems are hardly present in real polymer films, PPs should commonly exist as high-lying excited states of real polymer systems.
1 Introduction The formation of interchain species in neat conjugated polymer films has important implications for the performance of devices based on conjugated polymers [1]. Recent years, polaron pair (PP) formation in conjugated polymers has been aroused interest [2–11]. Compared with excitons, PPs might split into free charge carriers more easily, since they exhibit a weak Coulomb attraction between electron and hole. This may be used to optimize the organic solar cells. Experimentally, Park et al. [3] investigated how disorder within conjugated polymer aggregates influences the polaron generation process, and found that the efficient polaron generation was attributed to the excess energy and enhanced interchain delocalization of precursor states provided by the interchain torsional disorder and the close packing structure. Nuzzo et al. [8] show that light absorption from interchain aggregates is highly beneficial for charge photogeneration in semiconducting polymers. Theoretically, Hong et al. [4] performed density functional theory calculations to investigate PP photogeneration in poly (4,7-benzo[2,1,3]thiadiazole-2,6-(4,4-bis(2 -ethylhexyl)-4H-cyclopenta[1,2-b;3,4-b’]dithiophene-4,7benzo[2,1,3]thiadiazole) (CPDTBT) dimer. They found that effective PP state can happen when the group in one monomer deviate against the conjugated plane. Donati a
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et al. [6] use a combined approach of first-princip
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