Seidler, N; (2014) Polythiophene nanofibres for optoelectronic applications. Doctoral thesis , UCL (University College London).

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Abstract

This thesis reports on the fabrication and characterisation of self-assembled nanofibres of poly(3-hexylthiophene) (P3HT), and demonstrates how these nanofibres can be used in applications like thin-film transistors and solar cells. The first results chapter describes a preparation method of P3HT nanofibres in a solution of chlorobenzene by using di-tert butyl peroxide (DTBP) as an additive. This method allows the fabrication of films of P3HT with high molecular order and gives control over the film retention. The films are characterised using a range of experimental techniques, including optical absorption, X-ray diffraction and atomic force microscopy, which also allows to determine the dimensions of individual, separated nanofibres. A more detailed investigation into the temperature dependence of the photoluminescence (PL) of nanofibre films in comparison to P3HT thin-films is presented in the second results chapter. The line-shape of the measured PL of the nanofibres shows significant differences to the thin-film, which is most distinctive at a temperature of around 150K. At this temperature, the measurements show a change of the emission characteristics for the nanofibres which is absent in the thin-film. The cause for the observed transition can be related to the increased planarisation of the polymer backbone inside the nanofibres with increasing temperature. This gives rise to more dominant intrachain coupling for the fibres, in contrast to predominantly interchain coupling in P3HT thin-films. The third results chapter demonstrates the application of the nanofibre films in thin-film transistors and solar cells. It is shown how the high molecular order of the nanofibres in combination with the formation of fibre networks can be used to control the field-effect mobility of P3HT films. Solar cells are fabricated by successive deposition of a nanofibre film and an electron acceptor layer, resulting in power conversion efficiencies comparable to bulk heterojunction solar cells.

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