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Title: An investigation of novel coatings for the protection of organic coated iron based substrates and the industrialisation of dye-sensitised solar cell technology
Author: Reynolds, Gavin James
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2013
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A high-throughput method of investigating organic coating delamination from iron substrates incorporating interfacial thin metallic films of varying thickness is presented. Physical vapour deposited aluminium is demonstrated as a means of limiting underfilm oxygen reduction and slowing rates of corrosion-driven cathodic disbondment. A wedge of graded thickness is deposited on an iron surface and overcoated with a model organic layer. After initiating corrosion by applying corrosive electrolyte to a penetrative defect, rates of corrosion-driven delamination are determined by in-situ scanning Kelvin probe measurements, enabling the influence of a range of Al thicknesses to be studied on a single sample. A novel method of monitoring corrosion activity when an iodide/ triiodide dye- sensitized solar cell redox electrolyte is placed in contact with a range of metallic substrates is also described. Corrosion of the metallic substrate results from anodic dissolution of the metallic surface coupled with cathodic reduction of triiodide (I3-) to colorless iodide ions in solution. In the work described here, UV/Vis spectrophotometry in reflectance mode is used in conjunction with encapsulation cells that incorporate a 25 mum thick electrolyte layer, prepared using a range of polished metallic substrates. The corrosion rate is quantified by monitoring changes in the absorption spectra with respect to time. Of the metals evaluated, only titanium was wholly resistant to corrosion and did not show evidence of reaction with the electrolyte for periods of up to 3 months. Other metals such as zinc reacted within seconds and complete and irreversible loss of I3- was observed after only a few minutes. Dye sensitized solar cells (DSCs) have been assembled directly onto a pre-painted construction steel substrate. This has been achieved by chemically isolating the underlying substrate through the application of a high temperature resistant organic polymer rendered conducting by applying a 1.2 mum collection electrode of magnetron sputtered titanium. The resultant DSC achieved 2.9% energy conversion efficiency under one sun illumination compared to 3.2% for identical cells manufactured on 1mm thick Ti coupons. The slight reduction in efficiency reflects the increasing resistance of the substrate 1.2 mum Ti layer that results from microcracking during the titania sintering step. Dye sensitized solar cells (DSCs) have also been assembled directly onto an electrochromium coated steel substrate that has been both chemically and electrically isolated through the application of a high temperature resistant organic polymer (polyimide) coating. The surface of the coated product has been rendered conducting through the application of 0.5 mum aluminium and titanium films deposited directly by DC magnetron sputtering. The resultant DSCs achieved very poor energy conversion efficiencies under one sun illumination as did cells produced on bulk Al substrates. Cells manufactured on 1mm thick Ti coupons gave efficiencies of around 3.2%. The poor efficiencies for the sputtered Ti and Al films can be related to the increasing resistance of the Ti film due to the formation of micro cracking during the titania sintering step, and the inadequate corrosion performance of Al when in contact with an iodine triiodide redox electrolyte. An Al-Ti bilayer has been proposed where the Ti film has been used as a barrier layer to corrosion, cells fabricated on this substrate have showed much promise, and efficiencies of 2.2 % have been achieved.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available