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Title: Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films

Abstract

Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor–acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiopheneco- thieno[3,2- b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π–π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacialmore » morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. As a result, we further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front.« less

Authors:
 [1];  [2];  [3];  [1];  [1];  [4];  [3]; ORCiD logo [2]; ORCiD logo [1]
  1. Univ. of Illinois Urbana-Champaign, Urbana, IL (United States)
  2. Purdue Univ., West Lafayette, IN (United States)
  3. Univ. of Washington, Seattle, WA (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1376901
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 9; Journal Issue: 33; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; morphology; polymer crystallization; alignment; charge transport; conjugated polymer; interfacial; solution printing

Citation Formats

Qu, Ge, Zhao, Xikang, Newbloom, Gregory M., Zhang, Fengjiao, Mohammadi, Erfan, Strzalka, Joseph W., Pozzo, Lilo D., Mei, Jianguo, and Diao, Ying. Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films. United States: N. p., 2017. Web. doi:10.1021/acsami.7b08133.
Qu, Ge, Zhao, Xikang, Newbloom, Gregory M., Zhang, Fengjiao, Mohammadi, Erfan, Strzalka, Joseph W., Pozzo, Lilo D., Mei, Jianguo, & Diao, Ying. Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films. United States. doi:10.1021/acsami.7b08133.
Qu, Ge, Zhao, Xikang, Newbloom, Gregory M., Zhang, Fengjiao, Mohammadi, Erfan, Strzalka, Joseph W., Pozzo, Lilo D., Mei, Jianguo, and Diao, Ying. Tue . "Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films". United States. doi:10.1021/acsami.7b08133. https://www.osti.gov/servlets/purl/1376901.
@article{osti_1376901,
title = {Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films},
author = {Qu, Ge and Zhao, Xikang and Newbloom, Gregory M. and Zhang, Fengjiao and Mohammadi, Erfan and Strzalka, Joseph W. and Pozzo, Lilo D. and Mei, Jianguo and Diao, Ying},
abstractNote = {Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor–acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiopheneco- thieno[3,2-b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π–π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacial morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. As a result, we further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front.},
doi = {10.1021/acsami.7b08133},
journal = {ACS Applied Materials and Interfaces},
number = 33,
volume = 9,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 2017},
month = {Tue Aug 01 00:00:00 EDT 2017}
}

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