Charge Photogeneration in Non-Fullerene Organic Solar Cells: Influence of Excess Energy and Electrostatic Interactions |
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Authors: | Maria Saladina Pablo Simón Marqués Anastasia Markina Safakath Karuthedath Christopher Wöpke Clemens Göhler Yue Chen Magali Allain Philippe Blanchard Clément Cabanetos Denis Andrienko Frédéric Laquai Julien Gorenflot Carsten Deibel |
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Affiliation: | 1. Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz, Germany;2. MOLTECH-Anjou CNRS UMR 6200, University of Angers, 49045 Angers, France;3. Max Planck Institute for Polymer Research, 55128 Mainz, Germany;4. King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC), Physical Sciences and Engineering Division (PSE), Material Science and Engineering Program (MSE), Thuwal, 23955-6900 Kingdom of Saudi Arabia |
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Abstract: | In organic solar cells, photogenerated singlet excitons form charge transfer (CT) complexes, which subsequently split into free charge carriers. Here, the contributions of excess energy and molecular quadrupole moments to the charge separation process are considered. The charge photogeneration in two separate bulk heterojunction systems consisting of the polymer donor PTB7-Th and two non-fullerene acceptors, ITIC and h-ITIC, is investigated. CT state dissociation in these donor–acceptor systems is monitored by charge density decay dynamics obtained from transient absorption experiments. The electric field dependence of charge carrier generation is studied at different excitation energies by time delayed collection field (TDCF) and sensitive steady-state photocurrent measurements. Upon excitation below the optical gap, free charge carrier generation becomes less field dependent with increasing photon energy, which challenges the view of charge photogeneration proceeding through energetically lowest CT states. The average distance between electron–hole pairs at the donor–acceptor interface is determined from empirical fits to the TDCF data. The delocalization of CT states is larger in PTB7-Th:ITIC, the system with larger molecular quadrupole moment, indicating the sizeable effect of the electrostatic potential at the donor–acceptor interface on the dissociation of CT complexes. |
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Keywords: | dissociation excess energy molecular quadrupole moment non-fullerene acceptors organic solar cells |
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