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emerging opportunities in solar cell technologies
Thermoelectric “Fabrics” based on carbon nanotube composites
David L. Carroll Center for Nanotechnology and Molecular Materials Department of Physics. Wake Forest University Winston-Salem NC 27109
NANOTECH Center for Nanotechnology and Molecular Materials
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This work was performed by Wake Forest University at the Center for Nanotechnology and Molecular Materials in collaboration with…
Alan Kaiser University of Wellington Siegmar Roth Korea University Richard Czerw NanotechLabs This work was funded through internal NANOTECH funds
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Focus of Research Increasing the figure of merit of thermoelectric materials drives the majority of the research on thermoelectrics. Benchmarks Bismuth Telluride (Bi2Te3) is the most common commercially used TEP material, and has a ZT~1. However, it is speculated that a ZT ≥ 3 is required before TEP materials can become competitive with current sources of electricity. Although there have been reports of ZT values around 2, these values have not been verified. Manufacturing and Commercialization Importantly, their use of exotic nanostructured crystalline materials makes them both expensive and difficult to reproduce on a large scale. Therefore, it is useful to explore more economical sources of thermoelectric power.
A “macro-electronics’ approach to Thermoelectrics
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Composite Thermoelectrics are not very good
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Our Thermoelectrics Measurement
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Resistivity of Composites
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Seeback Coeff. vs. Loading
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Seeback Coeff. vs. Loading
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15
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25
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35
0 20 40 60 80 100
α (μ
V/K
)
SWNT Concentration (%)
SWNT/PVDF Film Seebeck Coefficient vs NT Concentration
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Power Factor vs. Loading
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SWNT vs. MWNTs
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Dispersion
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Module Design
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Thermally/electrically insulating layers
Electrical connection points
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n
n
n
p
p
p
p
assembly
Nanotube Modules
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0 50 100 150 200 250 300 3501.0
1.5
2.0
2.5
N-dopedB-doped
pure
ln R
[Ω]
103/T [K-1]
R(Ω
)/R(3
20K
)
T(K)
3.0 3.5 4.05.50
5.55
5.60
5.655.70
5.75
5.80
N-doped
B-doped
A two-probe measurement of the temperature dependence of R, normallized to 320 K, after degassing in vacuum at 320 K for three days, is shown. All three mats exhibited non-metallic behavior over the entire temperature range (dR/dT < 0). Activation energy from Arrhenius plot: ρ = ρ0exp(Ea/kT)
B-doped ~ 12 meV N-doped ~ 2 meV
Module Design
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0 50 100 150 200 250 300
-10
0
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50
Undoped MWNT Mat B-doped MWNT Mat N-doped MWNT Mat
S[V
/K]
T [K]
Module Design
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Nanotube Modules
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Nanotube Modules
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Demonstration
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Summary
We have demonstrated: 1) Composites of Carbon Nanotubes within polymers can approach thermoelectric response of Carbon Nanotubes mats which is advantageous for products. 2) A novel and simple module design that allows for these very thin materials to be integrated into a basic device. These devices can be made in large areas and are about as thick as a fabric. The thermoelectric fabrics can be applied in a wide range of applications not currently accessible to BiTe.
