Defect Manipulation in Pi-Conjugated Semiconducting Polymers and their Effect on Microstructure and Transport Properties

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TECHNICAL SUMMARY: Pi-conjugated semiconducting polymers are under intense development for use in organic light-emitting diodes, thin-film transistors, and solar cells. However, the understanding of their performance in many applications is limited because of the difficulty in establishing a detailed correlation of structure-property relationships. This in turn requires deeper understanding of structure development and formation of these classes of materials, which is currently hampered by the synthetic chemists' inability to precisely control defects in pi-conjugated semiconducting polymers. The goal of this proposal is to develop model pi-conjugated polymers with precisely controlled defects, so that a more complete description of their microstructure can be developed and therefore elucidate how the microstructure affects optoelectronic properties. The model polymer will be poly(3-hextylthiophene) (P3HT) to begin with, and as the project moves on other polymer systems will be investigated. To simplify the model, polymer nanowires will be characterized rather than the semi-crystalline thin film so that the crystalline domains can be studied extensively. As the work progresses, the degree of disorder in the films will be systematically increased in order to explore the interplay between the crystalline and amorphous domains, and the role of disorder in optoelectronic properties of pi-conjugated semiconducting polymers.NON-TECHNICAL SUMMARY: This proposal aims to further the understanding of an increasingly important class of materials, namely pi-conjugated semiconducting polymers. These polymers have been attracting a lot of interest in the general area of flexible electronics, where the aim is to develop portable electronic devices in a more cost-effective and energy-efficient manner. These polymers are increasingly being used in commercial applications, for example in organic light-emitting diodes (OLEDs). Furthermore, they are actively being developed for use in renewable energy as the light absorber material in solar cells. Despite their widespread usage, there is much that remains unknown about how defects (for example, kinks in the polymer chain) affect the polymers' properties. In this proposal, the defects in the polymers will be systematically altered so that a more detailed understanding of these materials can be developed. The proposed research will be enhanced by community outreach activities through the Pacific Science Center, the Science Cafe, and through mentoring activities for underrepresented minorities (URMs) and for women. The project also includes educational activities for undergraduate and high-school students.