Understanding the impact of polymer self-organization on the microstructure and charge transport in poly(3-hexylthiophene)
Aiyar, Avishek R.
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Conjugated polymers represent the next generation of conducting materials that will enable technological devices incorporating thin film transistors, photovoltaic cells etc., in a cost-effective roll-to-roll manner. Given the importance of microstructure on charge transport, ordered self-assembly in polymeric semiconductors assumes paramount relevance. This thesis thus focuses on a fundamental investigation of the correlations between the morphology and microstructure of the first high mobility solution processable semiconducting polymer, poly(3-hexylthiophene)(P3HT), and its corresponding charge transport properties. The evolution of polymer chain conformations is first studied, leading up to the formation of the conducting channel. An intermediate lyotropic liquid crystalline phase is identified, characterized by anisotropic ordering of the polymer chains. Methods for tuning the microstructure of P3HT thin films are also discussed, with an emphasis on understanding the role of molecular parameters, such as regioregularity and process parameters such as the film formation method. An ultrasound based technique for inducing the formation of ordered π-stacked molecular aggregates is also introduced. The results presented here not only provide understanding of microstructure-charge transport correlations, but also the very process of film formation in solution processable organic semiconductors, which could in turn hold the key to approaching the mobility benchmark represented by single crystals.