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Title:Elucidation of Donor:Acceptor Phase Separation in Nonfullerene Organic Solar Cells and Its Implications on Device Performance and Charge Carrier Mobility
Authors:Hoefler, Sebastian F. (Author)
Haberfehlner, Georg (Author)
Rath, Thomas (Author)
Keilbach, Andreas (Author)
Hobisch, Mathias (Author)
Dixon, Alexander (Author)
Pavlica, Egon (Author)
Bratina, Gvido (Author)
Kothleitner, Gerald (Author)
Hofer, Ferdinand (Author)
Trimmel, Gregor (Author)
Files:.pdf acsaem.9b01534.pdf (6,22 MB)
 
Language:English
Work type:Not categorized (r6)
Tipology:1.01 - Original Scientific Article
Organization:UNG - University of Nova Gorica
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.
Keywords:nanomorphology bulk-heterojunction scanning transmission electron microscopy organic photovoltaics charge carrier mobility
Year of publishing:2019
Number of pages:7535-7545
Numbering:2, 10
COBISS_ID:5544443 Link is opened in a new window
URN:URN:SI:UNG:REP:FLCJGBQB
DOI:10.1021/acsaem.9b01534 Link is opened in a new window
License:CC BY-ND 4.0
This work is available under this license: Creative Commons Attribution No Derivatives 4.0 International
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Record is a part of a journal

Title:ACS Applied Energy Materials
Shortened title:ACS Appl. Energy Mater.
Publisher:ACS Publications
ISSN:2574-0962
Year of publishing:2019

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