Understanding Film-To-Stripe Transition of Conjugated Polymers Driven by Meniscus Instability

Journal Article · 29 October 2018 · ACS Applied Materials and Interfaces

DOI: https://doi.org/10.1021/acsami.8b13790 · OSTI ID:1484808

Qu, Ge ^[1]; Kwok, Justin J. ^[1]; Mohammadi, Erfan ^[1]; Zhang, Fengjiao ^[1]; Diao, Ying  ^[1]

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1. Univ. of Illinois at Urbana-Champaign, IL (United States)

Meniscus instability during meniscus-guided solution coating and printing of conjugated polymers has a significant impact on the deposit morphology and the charge-transport characteristics. The lack of quantitative investigation on meniscus-instability–induced morphology transition for conjugated polymers hindered the ability to precisely control conjugated polymer deposition for desired applications. In this paper, we report a film-to-stripe morphology transition caused by stick-and-slip meniscus instability during solution coating seen in multiple donor–acceptor polymer systems. We observe the coexistence of film and stripe morphologies at the critical coating speed. Surprisingly, higher charge-carrier mobility is measured in transistors fabricated from stripes despite their same deposition condition as the films at the critical speed. To understand the origin of the morphology transition, we further construct a generalizable surface free energy model to validate the hypothesis that the morphology transition occurs to minimize the system surface free energy. As the system surface free energy varies during a stick-and-slip cycle, we focus on evaluating the maximum surface free energy at a given condition, which corresponds to the sticking state right before slipping. Indeed, we observe the increase of the maximum system surface free energy with the increase in coating speed prior to film-to-stripe morphology transition and an abrupt drop in the maximum system surface free energy post-transition when the coating speed is further increased, which is associated with the reduced meniscus length during stripe deposition. Such an energetic change originates from the competition between pinning and depinning forces on a partial wetting substrate which underpins the film-to-stripe transition. This work establishes a quantitative approach for understanding meniscus-instability–induced morphology transition during solution coating. The mechanistic understanding may further facilitate the use of meniscus instability for lithography-free patterning or to suppress instability for highly homogeneous thin film deposition.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1484808
• Journal Information: ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 47 Vol. 10; ISSN 1944-8244
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: ENGLISH