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Title: Effect of moiety choice on structural and electrical properties in organic semiconductors
Author: Moriarty, John
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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This dissertation details work conducted in the Optoelectronics Group at the University of Cambridge. It includes detailed characterisation of two groups of novel polymer semiconductors, one based on fluorinated variants of polyalkylthiophenes and the other on a series of copolymers based on a fused poly-dithieno-thiophene-benzene core. In both cases the goal is to employ highly fused moieties in order to promote a high degree of planarity within the conjugated backbone. Also discussed is the refinement of the zone casting technique in order to produce pristine films from these materials and a novel use of absorption spectroscopy data to produce estimates of polymer conjugation length. Characterisation was conducted along the same lines for both material groups, beginning with measurements of field-effect charge carrier mobility in order to evaluate the materials' relative electrical performance, followed by a variety of characterisation techniques of their photophysical properties in order to understand the reasons for differences observed in the first set of measurements. This experimental work was supported by quantum chemical modelling. Results suggest that, while backbone planarity is an important determinant of charge carrier mobility in polymer organic semiconductors, it can be a detriment if it causes the material’s microstructure to change in such a way that hinders intermolecular charge transport: effectively sacrificing long-range charge carrier mobility for short-range charge carrier mobility. Suggestions for further development of the techniques used and for future work based on the results are included in the conclusion.
Supervisor: Sirringhaus, Henning Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Organic Semiconductors ; Polymers ; Rational Design