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Tuneable sputtered films by doping for wearable and flexible thermoelectrics

Tuneable sputtered films by doping for wearable and flexible thermoelectrics
Tuneable sputtered films by doping for wearable and flexible thermoelectrics
An efficient, flexible power supply is in demand for the billion dollar wearable market. Thermoelectrics (TE) are the ideal choice, utilising body heat to produce green, uninterrupted energy.
Screen-printing, a complicated process requiring synthesis, is the common fabrication method for flexible TEs but suffers from limited material choices and low-throughput [1]. Sputtering, however, is able to deposit a large array of materials, is already used in fabrication lines and is easily incorporated into roll-to-roll manufacturing; a flexible device mass-production technique.
The limited efficiency of TE cells remains to be the main challenge and is related to material properties. Previous investigations into sputtered materials for flexible TE cells is sparse. This work will provide a comprehensive study of sputtered materials and doping effects, for efficient flexible TE cells.
An optimal bandgap for a TE material is dependent on the hot side of the application Th, given by Eg = 4kTh [2]. For body temperature regimes, BiTe, SnTe and GeTe exhibit energy gaps close to this optimum and were therefore chosen for this work.
BiTe, GeTe and SnTe were singly and co-sputtered with Ge, Si and Zn. Soda lime and polyamide substrates were used, with the latter demonstrating wearable applications. The Seebeck coefficient and electrical resistivity were measured.
For BiTe films, pure BiTe exhibited the lowest resistivity of 5 mOhm-cm and was found to be n-type. As both n- and ptypes are required for TE cells, and as chalcogenides are naturally p-type, it is beneficial to have identified a high performance n-type material. Doping BiTe with Zn changed it from n-type to p-type but at the compromise of slightly increased resistivity. BiTe-Ge had the highest seebeck coefficient for BiTe films, S=-65.1µV/K.
Pure SnTe exhibited the lowest resistivity of 2 mOhm-cm for the SnTe films, whilst SnTe-Ge had the highest seebeck coefficient, S=50.8µV/K. Doping with Zn however reduced the Seebeck coefficient considerably to S=1.4uV/K.
Only pure GeTe and GeTe-Si were found to be TE compatible, with p-type behaviour and low resistivities ~ 3 mOhmcm.
Doping with Ge resulted in a resistivity increase of 8 orders of magnitude, whilst GeTe-Zn was beyond the measurement limit. This is a surprising as doping SnTe and BiTe with Zn and Ge had no such effect.
The most efficient TE material was identified by the power factor. BiTe had the highest power factor for n-type whilst GeTe had the highest for p-type, with 0.81 and 1.4 mW/mK2 respectively. Whilst BiTe has been relied on previously for TE cells, GeTe exhibited a much larger power factor, demonstrating its potential for use as a highly efficient TE material in the future. Further work will be conducted into the effects of doping seen in this work, whilst a flexible TE cell using BiTe and GeTe will be demonstrated.
[1] Raihan. A, et al., Ren. & Sus. Energy Rev., 73, 730-744 (2017)
[2] Wood. C, Rep. on Prog. In Phys. 51, 459-539 (1988)
Morgan, Katrina
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Ravagli, Andrea
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Craig, Chris
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Zeimpekis, Ioannis
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Yao, Jin
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Alzaidy, Ghadah
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Hewak, Daniel W.
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Morgan, Katrina
2b9605fc-ac61-4ae7-b5f1-b6e3d257701d
Ravagli, Andrea
36bc59df-8134-42d1-9871-bcf7bab6539a
Craig, Chris
2328b42b-552e-4a82-941d-45449e952f10
Zeimpekis, Ioannis
a2c354ec-3891-497c-adac-89b3a5d96af0
Yao, Jin
83dff1cd-6f7c-4b47-968e-18c64ffcb24b
Alzaidy, Ghadah
2d39b828-3eb4-4d96-85e6-d436a2b71435
Hewak, Daniel W.
87c80070-c101-4f7a-914f-4cc3131e3db0

Morgan, Katrina, Ravagli, Andrea, Craig, Chris, Zeimpekis, Ioannis, Yao, Jin, Alzaidy, Ghadah and Hewak, Daniel W. (2017) Tuneable sputtered films by doping for wearable and flexible thermoelectrics. MRS Fall Meeting 2017, Hynes Convention Center, Boston, United States. 26 Nov - 01 Dec 2017. (In Press)

Record type: Conference or Workshop Item (Poster)

Abstract

An efficient, flexible power supply is in demand for the billion dollar wearable market. Thermoelectrics (TE) are the ideal choice, utilising body heat to produce green, uninterrupted energy.
Screen-printing, a complicated process requiring synthesis, is the common fabrication method for flexible TEs but suffers from limited material choices and low-throughput [1]. Sputtering, however, is able to deposit a large array of materials, is already used in fabrication lines and is easily incorporated into roll-to-roll manufacturing; a flexible device mass-production technique.
The limited efficiency of TE cells remains to be the main challenge and is related to material properties. Previous investigations into sputtered materials for flexible TE cells is sparse. This work will provide a comprehensive study of sputtered materials and doping effects, for efficient flexible TE cells.
An optimal bandgap for a TE material is dependent on the hot side of the application Th, given by Eg = 4kTh [2]. For body temperature regimes, BiTe, SnTe and GeTe exhibit energy gaps close to this optimum and were therefore chosen for this work.
BiTe, GeTe and SnTe were singly and co-sputtered with Ge, Si and Zn. Soda lime and polyamide substrates were used, with the latter demonstrating wearable applications. The Seebeck coefficient and electrical resistivity were measured.
For BiTe films, pure BiTe exhibited the lowest resistivity of 5 mOhm-cm and was found to be n-type. As both n- and ptypes are required for TE cells, and as chalcogenides are naturally p-type, it is beneficial to have identified a high performance n-type material. Doping BiTe with Zn changed it from n-type to p-type but at the compromise of slightly increased resistivity. BiTe-Ge had the highest seebeck coefficient for BiTe films, S=-65.1µV/K.
Pure SnTe exhibited the lowest resistivity of 2 mOhm-cm for the SnTe films, whilst SnTe-Ge had the highest seebeck coefficient, S=50.8µV/K. Doping with Zn however reduced the Seebeck coefficient considerably to S=1.4uV/K.
Only pure GeTe and GeTe-Si were found to be TE compatible, with p-type behaviour and low resistivities ~ 3 mOhmcm.
Doping with Ge resulted in a resistivity increase of 8 orders of magnitude, whilst GeTe-Zn was beyond the measurement limit. This is a surprising as doping SnTe and BiTe with Zn and Ge had no such effect.
The most efficient TE material was identified by the power factor. BiTe had the highest power factor for n-type whilst GeTe had the highest for p-type, with 0.81 and 1.4 mW/mK2 respectively. Whilst BiTe has been relied on previously for TE cells, GeTe exhibited a much larger power factor, demonstrating its potential for use as a highly efficient TE material in the future. Further work will be conducted into the effects of doping seen in this work, whilst a flexible TE cell using BiTe and GeTe will be demonstrated.
[1] Raihan. A, et al., Ren. & Sus. Energy Rev., 73, 730-744 (2017)
[2] Wood. C, Rep. on Prog. In Phys. 51, 459-539 (1988)

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MRS Fall accepted abstract
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Accepted/In Press date: 30 August 2017
Additional Information: Poster - submitted & accepted abstract
Venue - Dates: MRS Fall Meeting 2017, Hynes Convention Center, Boston, United States, 2017-11-26 - 2017-12-01

Identifiers

Local EPrints ID: 414770
URI: http://eprints.soton.ac.uk/id/eprint/414770
PURE UUID: 305f2998-aed5-43dd-9623-27bfc406263d
ORCID for Katrina Morgan: ORCID iD orcid.org/0000-0002-8600-4322
ORCID for Chris Craig: ORCID iD orcid.org/0000-0001-6919-4294
ORCID for Daniel W. Hewak: ORCID iD orcid.org/0000-0002-2093-5773

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Date deposited: 10 Oct 2017 16:31
Last modified: 12 Dec 2021 03:54

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Contributors

Author: Katrina Morgan ORCID iD
Author: Andrea Ravagli
Author: Chris Craig ORCID iD
Author: Jin Yao
Author: Ghadah Alzaidy
Author: Daniel W. Hewak ORCID iD

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