Design and Synthesis of Conjugated Polymers for Organic Photovoltaics: Tuning the Conjugated Backbone and the Substituents

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  • March 20, 2019
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  • Zhang, Qianqian
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Developing new conjugated polymer materials has been one of the most important driving forces for improving the performance of organic photovoltaics. This dissertation has been focused on structural design of polymers, including fine-tuning the backbone and the substituents of the polymers in order to adjust specific properties and improve the efficiency of organic photovoltaics. This dissertation details new methodologies to prepare the designed polymers and explores the structure-property relationship. We first developed regio-regular and regio-random terpolymers based on two parent copolymers with complementary absorption range. We found that adequate aggregation of these terpolymers is necessary for high performance photovoltaics. We then incorporated fluorine substituents into π linker thiophene units between the donor and the acceptor units and succeeded in controlling the positions and amount of fluorine substituents on the polymer backbone. The efficiency of the photovoltaics was remarkably improved by the fluorinated thiophene units. More importantly, we demonstrated the beneficial effects of fluorinated thiophene on improving the hole mobility and the importance of high hole mobility in improving fill factors of photovoltaics using eight structurally related polymers. Finally, in order to lower the bandgap of the polymers, we introduced strong electron withdrawing cyano group to the acceptor units. We systematically study the effect of cyano substitution on the properties of the polymers and the polymer solar cells by controlling the amount of cyano substituents. With single cyano substitution, a high device efficiency of ~ 8.6% was achieved for the monoCNTAZ polymer. All the works highlight the importance of optimizing the polymer structure to reach high solar cell performance.
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  • In Copyright
Advisor
  • Cahoon, James
  • You, Wei
  • Gagne, Michel
  • Meek, Simon
  • Leibfarth, Frank
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2017
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