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Title: Control and characterisation of metal oxide/polymer morphologies for hybrid photovoltaic devices
Author: Downing, Jonathan Mark
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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The ready formation of nanostructures, combined with excellent optoelectronic properties has shown zinc oxide (ZnO) to be a promising material for use in photovoltaic devices. Hybrid photovoltaic (h-PV) devices composed of metal oxide-organic pairings are currently limited by ineffective charge transfer between the materials and by poor transport of free charge out of the active layer. Control of interfacial properties, and the structure and morphology of each component is key to device optimisation. In this thesis, ZnO nanorods are paired with the photoactive polymer, poly 3-hexlythiophene (P3HT) with two areas studied: i) nanorod alignment to aid polymer infiltration, and ii) elucidating optimum polymer processing conditions to prepare efficient devices. Aligned nanorods are synthesised from ZnO coated substrates by a hydrothermal method. To understand the influence of ionic additives on morphological control, the addition of potassium chloride (KCl) to growth solutions is investigated. Films have been studied by SEM and XRD, with the correlation of these results (nanorod length, width, density vs (002) diffraction peak area) used to examine alignment, which increases at higher concentrations. This ordering is explained via a geometrical selection argument. Effective polymer infiltration into nanorod arrays is found to be possible by spin coating and annealing above the polymer melting point. Extended annealing (> 60 seconds) is seen to reduce device performance. Small angle X-ray scattering and X-ray diffraction as a function of temperature was conducted to investigate polymer orientation and the kinetics of crystallisation within nanostructured films. These results are combined with device measurements to aid in understanding the relationship between morphological characteristics of the constituent materials and h-PV performance.
Supervisor: Ryan, Mary ; McLachlan, Martyn Sponsor: Engineering and Physical Sciences Research Council ; Amrourers & Brassiers ; Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available