|Posted: Oct 31, 2017|
Mission not so impossible now: Control complex molecular organization(Nanowerk News) To build better solar cells, scientists need to design materials from the bottom up, placing chains of molecules just where they are needed. Scientists devised a new way to grow neatly arranged, densely packed bundles of molecular chains, specifically semiconducting polymer chains (Chemistry of Materials, "Polythiophene thin films by surface-initiated polymerization: Mechanistic and structural studies").
|The chains folded on themselves to make bundles that stretched from the growth plate to the film’s surface. The bundles were packed side-by-side with neighboring bundles. This bottom-up approach, starting with the building blocks and creating the larger structure, was used to make large-area films with tiny patterns. The films have controlled architecture, uniform assembly and excellent stability.|
|Thin films of semiconducting polymers were made with a surface-initiated growth, resulting in a unique molecular organization. As shown in the schematic, polymer chains grew from the surface and then folded to form bundles through the film’s thickness. The bundles were crystalline and about 3 nanometers (nm) wide. The neighboring lateral bundles were densely packed side-by-side, creating a complex molecular organization. This controlled architecture could be used to enhance light-emitting devices and solar cells. (Image: Evgueni Nesterov, Louisiana State University)|
|The thin films of semiconducting polymers have a unique structure and are highly stable. The films could increase the efficiency and lifetime of organic light-emitting devices and solar cells.|
|Traditional methods using “top-down” solution-based processing typically only allow modest control over the molecular organization and chain alignment of semiconducting polymers.|
|Now a team led by scientists at Louisiana State University have developed a “bottom-up” approach using surface-initiated growth of a semiconducting polymer called polythiophene to prepare thin films. Polythiophene is a promising organic electronic material.|
|Extensive structural studies of the thin films using x-ray and neutron scattering revealed detailed information on the unique molecular organization and the bulk morphology of the films. The studies also further our fundamental understanding of the polymerization.|
|Remarkably, the polymer chains formed densely packed lateral crystalline domains spanning about 3 nanometers, with predominant in-plane alignment of the folded polymer chains within each domain. Achieving such a complex intermediate-scale organization is virtually impossible with traditional methods relying on solution processing of pre-synthesized polymers.|
|This unique morphology would be particularly suited for applications requiring efficient charge transport across the films, such as in photovoltaic and light-emitting devices. In general, surface-initiated polymerization is not limited to polythiophene but can also be expanded for other classes of semiconducting polymers and copolymers.|
|Source: U.S. Department of Energy, Office of Science|
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