Elucidation of Donor:Acceptor Phase Separation in Nonfullerene Organic Solar Cells and Its Implications on Device Performance and Charge Carrier Mobility

Sebastian F. Hoefler, Georg Haberfehlner, Thomas Rath, Andreas Keilbach, Mathias A. Hobisch, Alex Dixon, Egon Pavlica, Gvido Bratina, Gerald Kothleitner, Ferdinand Hofer, Gregor Trimmel

Research output: Contribution to journalArticleResearchpeer-review

Abstract

In bulk-heterojunction solar cells, the device performance strongly depends on the donor and acceptor properties, the phase separation in the absorber layer, and the formation of a bicontinuous network. While this phase separation is well explored for polymer:fullerene solar cells, only little is known for polymer:nonfullerene acceptor solar cells. The main hurdle in this regard is often the chemical similarity of the conjugated polymer donor and the organic nonfullerene acceptor (NFA), which makes the analysis of the phase separation via atomic force microscopic (AFM) phase images or conventional transmission electron microscopy difficult. In this work, we use the donor polymer PTB7-Th and the small molecule acceptor O-IDTBR as the model system and visualized the phase separation in PTB7-Th:O-IDTBR bulk-heterojunctions with different donor:acceptor ratios via scanning transmission electron microscopy (STEM) high-angle annular dark-field (HAADF) images and electron energy loss spectroscopy (EELS) based elemental mapping, which resulted in a good contrast between the donor and the acceptor despite very low differences in the chemical composition. AFM as well as grazing-incidence wide-angle X-ray scattering (GIWAXS) investigations support the electron microscopic data. Furthermore, we elucidate the implications of the phase separation on the device performance as well as charge carrier mobilities in the bulk-heterojunction layers, and a high performance of the solar cells was found over a relatively broad range of polymer domain sizes. This can be related to the larger domain sizes of the acceptor phase with higher amounts of O-IDTBR in the blend, while the polymer donor phase still forms continuous pathways to the electrode, which keeps the hole mobility at a relatively constant level.

Original languageEnglish
Pages (from-to)7535-7545
Number of pages11
JournalACS Applied Energy Materials
Volume2
Issue number10
DOIs
Publication statusPublished - 28 Oct 2019

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Carrier mobility
Charge carriers
Phase separation
Polymers
Solar cells
Heterojunctions
Transmission electron microscopy
Fullerenes
Hole mobility
Electron energy loss spectroscopy
Conjugated polymers
X ray scattering
Organic solar cells
Scanning electron microscopy
Electrodes
Molecules
Electrons
Chemical analysis

Keywords

  • bulk-heterojunction
  • charge carrier mobility
  • nanomorphology
  • organic photovoltaics
  • scanning transmission electron microscopy

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Energy Engineering and Power Technology
  • Electrochemistry
  • Materials Chemistry
  • Electrical and Electronic Engineering

Fields of Expertise

  • Advanced Materials Science

Treatment code (Nähere Zuordnung)

  • Basic - Fundamental (Grundlagenforschung)

Cite this

Elucidation of Donor:Acceptor Phase Separation in Nonfullerene Organic Solar Cells and Its Implications on Device Performance and Charge Carrier Mobility. / Hoefler, Sebastian F.; Haberfehlner, Georg; Rath, Thomas; Keilbach, Andreas; Hobisch, Mathias A.; Dixon, Alex; Pavlica, Egon; Bratina, Gvido; Kothleitner, Gerald; Hofer, Ferdinand; Trimmel, Gregor.

In: ACS Applied Energy Materials, Vol. 2, No. 10, 28.10.2019, p. 7535-7545.

Research output: Contribution to journalArticleResearchpeer-review

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