Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf
1 PublikationAlkyl Branching Position in Diketopyrrolopyrrole Polymers: Interplay between Fibrillar Morphology and Crystallinity and Their Effect on Photogeneration and Recombination in Bulk-Heterojunction Solar Cells
Shivhare, R.; Erdmann, T.; Hörmann, U.; Collado-Fregoso, E.; Zeiske, S.; Benduhn, J.; Ullbrich, S.; Hübner, R.; Hambsch, M.; Kiriy, A.; Voit, B.; Neher, D.; Vandewal, K.; Mannsfeld, S. C. B.
Abstract
Diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers have gained a significant amount of research interest in the organic electronics community because of their high charge carrier mobilities in organic field-effect transistors (OFETs) and their ability to harvest near-infrared (NIR) photons in solar cells. In this study, we have synthesized four DPP-based donor-acceptor copolymers with variations in the donor unit and the branching point of the solubilizing alkyl chains (at the second or sixth carbon position). Grazing incidence wide-angle X-ray scattering (GIWAXS) results suggest that moving the branching point further away from the polymer backbone increases the tendency for aggregation and yields polymer phases with a higher degree of crystallinity (DoC). The polymers were blended with PC70BM and used as active layers in solar cells. A careful analysis of the energetics of the neat polymer and blend films reveals that the charge-transfer state energy (ECT) of the blend films lies exceptionally close to the singlet energy of the donor (ED*), indicating near zero electron transfer losses. The difference between the optical gap and open-circuit voltage (VOC) is therefore determined to be due to rather high nonradiative (≈ 418 ± 13 mV) and unavoidable radiative voltage losses (≈ 255 ± 8 mV). Even though the four materials have similar optical gaps, the short-circuit current density (JSC) covers a vast span from 7 to 18 mA cm-2 for the best performing system. Using photoluminescence (PL) quenching and transient charge extraction techniques, we quantify geminate and nongeminate losses and find that fewer excitons reach the donor-acceptor interface in polymers with further away branching points due to larger aggregate sizes. In these material systems, the photogeneration is therefore mainly limited by exciton harvesting efficiency.
Beteiligte Forschungsanlagen
- Ionenstrahlzentrum DOI: 10.17815/jlsrf-3-159
Verknüpfte Publikationen
- DOI: 10.17815/jlsrf-3-159 is cited by this (Id 28035) publication
-
Chemistry of Materials 30(2018), 6801-6809
DOI: 10.1021/acs.chemmater.8b02739
Cited 13 times in Scopus
Permalink: https://www.hzdr.de/publications/Publ-28035
Jahre: 2023 2022 2021 2020 2019 2018 2017 2016 2015