Reversible solubility allows for optical patterning of small features

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.

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 organisation 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 organisation and the bulk morphology of the films. The studies also further our fundamental understanding of the polymerisation.

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 organisation is virtually impossible with traditional methods relying on solution processing of pre-synthesised 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 polymerisation is not limited to polythiophene but can also be expanded for other classes of semiconducting polymers and copolymers.