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Title: Charge transport mechanisms of microcrystalline conjugated polymer thin film transistors
Author: Chang, Jui-Fen
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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This thesis is concerned with a prototype microcrystalline semiconducting polymer, poly(3-hexylthiophene) (P3HT), incorporated into a thin-film transistor structure in a bottom gate configuration with n-doped silicon as gate contacts and SiO2 as gate dielectric. The mechanisms to influence the charge transport in P3HT thin films are investigated in detail from experiments and theoretical analyses. Crystallisation of P3HT polymer during the spin-coating process is limited by the drying time of solvent. Compared with the most commonly used solvent, chloroform, it is demonstrated that choosing appropriate solvents with good solubility and higher boiling point for sufficiently high molecular weight (MW) P3HT could help improve its crystallinity and in-plane orientation of π-π stacking, leading to an enhanced field-effect mobility. In high crystalline P3HT films the microcrystals in nanoribbon shape are also observed. More comprehensively, the field-effect mobility of P3HT related to the macroscopic morphology and microstructures is studied as a function of MW of polymers and thin film processing conditions. From comparative studies of transistor characteristics, film morphology, and spectroscopic properties, it is shown that the crystalline quality of P3HT nanoribbons which depends on the chain folding kinetics and polymer chain lengths plays a decisive role to determine the MW dependence of mobility. The highest mobilities above 0.1 cm2/Vs can be achieved in highly-crystalline, sufficiently high-MW polymers. However, the mobility is found to saturate at high-MW regime due to the residual conformational disorder in polymer microcrystals probably arising from the intrinsic properties or crystallization kinetics of long chains, which need to be addressed to improve mobility further.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available