Charge Photogeneration in Non‐Fullerene Organic Solar Cells: Influence of Excess Energy and Electrostatic Interactions. (3rd December 2020)

• Record Type: Journal Article
• Authors: Saladina, Maria; Simón Marqués, Pablo; Markina, Anastasia; Karuthedath, Safakath; Wöpke, Christopher; Göhler, Clemens; Chen, Yue; Allain, Magali; Blanchard, Philippe; Cabanetos, Clément; Andrienko, Denis; Laquai, Frédéric; Gorenflot, Julien; Deibel, Carsten
• Is Part Of: Advanced functional materials. Volume 31:Number 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-03
• Subjects: dissociation -- excess energy -- molecular quadrupole moment -- non‐fullerene acceptors -- organic solar cells; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.202007479
• Languages: English
• ISSNs: 1616-301X

Abstract

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. Abstract : The photogeneration pathways in two non‐fullerene acceptor solar cells are investigated using charge extraction measurements. They reveal higher photogeneration yield and weaker electric field dependence for the nonrelaxed charge transfer states in PTB7‐Th:ITIC. The low molecular quadrupole moment of h‐ITIC, the dipolar analogue of ITIC, reduces delocalization of electron–hole pairs at the donor–acceptor interface lowering the yield.