4 years ago

Surface Layering and Supersaturation for Top-Down Nanostructural Development during Spin Coating of Polymer/Fullerene Thin Films

Surface Layering and Supersaturation for Top-Down Nanostructural Development during Spin Coating of Polymer/Fullerene Thin Films
Chih-Ming Liu, Po-Wei Yang, U-Ser Jeng, Kung-Hwa Wei, An-Chung Su, Po-Chang Lin, Yen-Chih Huang, Tsung-Yu Yang, Chun-Yu Chen, Wei-Tsung Chuang, Chun-Jen Su, Wei-Ru Wu
This study provides new evidence on a long postulated mechanism of phase separation in a polymer/fullerene mixture during spin coating for controlled nanodomains of oriented crystallization and heterojunctions that favor applications in polymer solar cells (PSCs). The simultaneous nanoscale phase separation and crystallization during spin coating of the mixture are traced using in situ grazing-incidence small- and wide-angle X-ray scattering. Combined with the complimentary results from time-resolved optical reflectance spectroscopy, transient stratification of the liquid film during the transition from the flow- to evaporation-dominated stage of spin coating is disclosed; the vertical liquid–liquid phase separation incubates a supersaturated skin layer where fullerene aggregation and polymer crystallization occur and develop concomitantly. Shortly after the transition, the near-surface structural development is largely pinned, leaving the solvent-rich bottom layer to diminish via solvent diffusion and evaporation through the thickened skin layer that finally condenses into the spin-coated film upon solvent depletion. The shear-enhanced surface layering and supersaturation for the surface-down nanostructural development are unexpected in all the existing structural models for PSCs. The mechanistic understanding of coupled vertical phase separation and local nanosegregation provides new insights and alternative strategy to the morphology control of spin-cast PSC active layers in particular and various solution-processed polymeric films in general. Surface layering and supersaturation over transition of the flow- to evaporation-dominance of the spin coating of a polymer/fullerene mixture lead to surface-down structural development of coupled vertical liquid–liquid phase separation and local nanosegregation/crystallization. A segregated upper layer enriched with nanostructures transforms into the final spin-coated film, after solvent depletes from the bottom layer.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/aenm.201601842

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.