University of Southampton Research Repository Eprints Soton
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University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk University of Southampton Printable Thermoelectric Devices for Energy Harvesting By Zhuo Cao A thesis submitted in partial fulfilment for the degree of Doctor of Philosophy In the Faculty of Physical Science and Engineering Electronics and Computer Science October, 2014 Abstract This thesis describes the approaches of fabricating and testing thermoelectric generators (TEG) using screen printing. It includes the formation of the pastes, optimizing of the manufacture processes and the measurement of the thermoelectric properties. A nickel/copper based high temperature TEG was made to demonstrating the screen printing can be applied to fabricate thermoelectric materials. A bismuth/antimony based low temperature TEG was fabricated to identify the proper polymer binder for low temperature TEG application. A flexible bismuth tellurium/antimony tellurium low temperature TEG with 4 thermocouples was presented with a generated voltage of 23 mV and an output power of 194 nW when ∆T=20°C . Moreover, a dispenser printed structured TEG was also demonstrated for its ability to achieve 3D structured thermocouples with a thickness of 500 μm. The objective of this work involves developing screen printable thermoelectric material pastes and suitable processes; a proper approach to transfer the printed TEGs from rigid substrate onto flexible substrate (Kapton). The flexibility allows the printed TEGs to be applied on heat sources with curved surface, such as, human body. An additional research on the interface material of textile is also presented. i Contents Chapter 1. Introduction ............................................................................................ 1 1.1 Overview of research ............................................................................................... 1 1.2 Objective and scope of the research ......................................................................... 2 1.3 Document structure .................................................................................................. 3 1.4 Novelty statement .................................................................................................... 4 Chapter 2. Theoretical background .......................................................................... 5 2.1 Introduction .............................................................................................................. 5 2.2 Principles of thermoelectric devices ........................................................................ 5 2.2.1 The Seebeck effect ........................................................................................... 5 2.2.2 The Peltier effect .............................................................................................. 8 2.2.3 The Kelvin relationship .................................................................................... 9 2.3 Evaluation of thermoelectric properties ................................................................. 10 2.3.1 Electrical resistivity and Hall coefficient measurement ................................. 11 2.3.2 Thermal conductivity measurement ............................................................... 12 2.3.3 Seebeck coefficient measurement .................................................................. 13 2.3.4 Summary of the properties of some commonly used materials for TEGs ..... 14 2.3.5 Power output, conversion efficiency and figure of merit ............................... 15 2.4 Structure of thermoelectric devices ........................................................................ 18 2.5 Summary ................................................................................................................ 20 Chapter 3. Literatures of TEGs, printed TEGs and its application ........................ 22 3.1 Introduction ............................................................................................................ 22 3.2 Micro-fabricated thermoelectric generators ........................................................... 22 3.2.1 Micro-fabricated TEGs in literature ............................................................... 24 3.2.2 Discussion ...................................................................................................... 29 3.3 Thick film technologies ......................................................................................... 30 3.3.1 Screen printing technology ............................................................................ 30 3.3.2 Dispenser printing technology ....................................................................... 34 3.4 Printed thermoelectric generator devices ............................................................... 36 3.4.1 Printed TEGs in literature .............................................................................. 36 3.4.2 Discussion ...................................................................................................... 44 3.5 Applications of thermoelectric generators on the human body .............................. 46 3.5.1 Human body TEGs in literature ..................................................................... 46 3.5.2 Discussion ...................................................................................................... 49 ii 3.6 Summary and discussion ........................................................................................ 50 Chapter 4. High temperature curing copper and nickel based thermocouples ...... 52 4.1 Introduction ............................................................................................................ 52 4.2 Experimental analysis of screen printed nickel thick films .................................... 52 4.2.1 Experiment procedure .................................................................................... 52 4.2.2 Nickel thick film paste formation and adhesion improvements ..................... 53 4.2.3 Nickel thick film characterisation .................................................................. 60 4.3 Experimental analysis of copper paste ................................................................... 63 4.3.1 Copper thick-film pattern formation .............................................................. 63 4.3.2 Copper thick film characterisation ................................................................. 66 4.4 Screen printed Ni/Cu thermocouples...................................................................... 69 4.5 Summary and discussion ........................................................................................ 76 Chapter 5. Low temperature curing copper and nickel based thermocouples and evaluation of the interface material of the textile ....................................................... 78 5.1 Introduction ............................................................................................................ 78 5.2 Low temperature curing copper paste .................................................................... 79 5.2.1 Polyurethane binder based copper paste ......................................................... 80 5.2.2 Silicone binder based copper paste ................................................................. 81 5.2.3 Epoxy binder based copper paste ................................................................... 83 5.3 Low temperature curing nickel paste ..................................................................... 85 5.4 Low temperature curing nickel/copper based thermocouples ................................ 87 5.5 Failure analysis of low temperature Ni/Cu thermocouples .................................... 89 5.6 Approaches to textile surface treatment for depositing electronics ........................ 90 5.7 Quality of adhesion of silicone interface layer improvement ................................. 92 5.8 Summary and discussion ........................................................................................ 98 Chapter 6. Screen printing bismuth and antimony based thermocouples .............. 99 6.1 Introduction ............................................................................................................ 99 6.2 Experimental analysis of screen printed Bi thick films .......................................... 99 6.3 Experimental analysis of screen printed Sb thick films ....................................... 104 6.4 Bismuth and Antimony based thermocouples ...................................................... 107 6.5 Safety handling and processing in experiment ..................................................... 111 6.6 Summary and discussion .....................................................................................