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Long-range exciton transport in conjugated polymer nanofibers prepared by seeded growth

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Science  25 May 2018:
Vol. 360, Issue 6391, pp. 897-900
DOI: 10.1126/science.aar8104

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A longer exciton pathway

Organic semiconductors typically exhibit exciton diffusion lengths on the order of tens of nanometers. Jin et al. prepared nanofibers from block polymers consisting of emissive polyfluorene cores surrounded by coronas of polyethylene glycol and polythiophene (see the Perspective by Holmes). Excitons generated in the polyfluorene cannot enter the polyethylene glycol layer and so diffuse more than 200 nm. This distance can be tuned by varying the length of the polyethylene glycol—a feature that could potentially be exploited in the development of organic devices such as photovoltaics.

Science, this issue p. 897; see also p. 854

Abstract

Easily processed materials with the ability to transport excitons over length scales of more than 100 nanometers are highly desirable for a range of light-harvesting and optoelectronic devices. We describe the preparation of organic semiconducting nanofibers comprising a crystalline poly(di-n-hexylfluorene) core and a solvated, segmented corona consisting of polyethylene glycol in the center and polythiophene at the ends. These nanofibers exhibit exciton transfer from the core to the lower-energy polythiophene coronas in the end blocks, which occurs in the direction of the interchain π-π stacking with very long diffusion lengths (>200 nanometers) and a large diffusion coefficient (0.5 square centimeters per second). This is made possible by the uniform exciton energetic landscape created by the well-ordered, crystalline nanofiber core.

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