Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607586
Title: Block copolymer patterning of functional materials
Author: Crossland, Edward
ISNI:       0000 0004 5364 5523
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2014
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Abstract:
The objective of this work is to develop and apply the use of block copolymer self assembly as a precision patterning tool on the 10 nm length scale for functional materials in thin films. These methods and resulting structures are interesting for a wide range of applications in nanotechnology, however the specific motivation for this work is the patterning of thin film mesoscale semiconductor composites for next generation solar cells. The proof of principle is demonstrated by fabricating dyesensitized solar cells incorporating structured arrays of TiO2. The first part of this thesis introduces the operating principles of the solar cell as a means of producing electrical energy from sunlight and outlines some of the most promising approaches to low-cost solar technologies, particularly those incorporating organic components. The search thus far has led to the concept of excitonic solar cells, which rely on specific cooperative semiconductor material architectures in order to produce efficient solar energy conversion. Chapter 2 contains the principles of self assembly in block copolymers and important aspects of their use as sacrificial or partially sacrificial templates for selected functional materials. Here, block copolymers containing a minority poly(lactide) component, which is selectively degradable under mild chemical conditions, are used to form mesoporous polymer films with well-defined internal porosity. In Chapter 5, an electric field is used to align standing cylindrical copolymer domains that are removed to leave a template for electrochemical deposition of ordered standing nanowire arrays with 12 nm diameter and packing densities of over 1011 cm-2. A simple in situ electrochemical technique for monitoring the removal of the poly(lactide) component from thin films with a range of morphologies is described in Chapter 6. The thin film behaviour and electrochemical replication of the bicontinuous gyroid block copolymer phase is summarized in Chapter 7. Dye-sensitized solar cells incorporating a TiO2 gyroid network are characterized in Chapter 8. These results are the first reported application of a gyroid structure in a functioning electronic device. In Chapter 9, the performance of nanowire and gyroid networks are compared directly to 'traditional' disordered state-of-the-art mesoporous TiO2 materials. The stability of the freestanding nanostructures is found to be a key requirement in fabricating real composite devices. The network-based gyroid and nanoparticle structures therefore considerably outperform the standing nanowire arrays in solar cells despite their impressive electronic properties. Chapter 10 presents preliminary results achieved using a functional copolymer of poly(lactide) in which the template material itself demonstrates charge transport characteristics. The PLA component again provides a means of introducing a well defined internal porosity to a charge transport medium, enabling a more direct approach to the fabrication of intimate, distributed semiconductor junctions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.607586  DOI: Not available
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