This document discusses organic-based hybrid materials for thermoelectric applications. It begins by introducing thermoelectrics and their importance in recovering waste heat. It then covers the key effects involved in thermoelectrics like the Seebeck, Peltier and Thomson effects. Next, it discusses the factors that influence thermoelectric efficiency like the Seebeck coefficient, electrical conductivity, and thermal conductivity. The document notes that while metals were initially studied, semiconductors are more effective due to their higher Seebeck coefficients and ratio of electrical to thermal conductivity. It covers approaches to improving performance like quantum confinement and reducing phonon thermal conductivity. Finally, it discusses the potential of organic-based hybrid materials which offer low-cost solution processing

1. Organic Based Hybrid Materials for
Thermoelectric Applications
Vijitha I.
SRF, CSIR-NIIST

2. Waste Heat
Useful
Energy
2
"All India Installed Capacity of Utility Power Stations".
Retrieved 11 January 2017
Thermoelectrics
Installed capacity by source in India as of 31 December 2016

3. Reduce Weight
Improve efficiency
Reliable
3
today… … tomorrow
POWER SOURCE
Batteries
CLIMATE CONTROL
None
POWER SOURCE
Thermoelectric
CLIMATE CONTROL
Thermoelectric
Defense Advance Research
Projects Agency, USA
NASA: Voyager
Photo courtesy of BMW

4. THE SEEBECK EFFECT:
• EMF caused by temperature
gradient across two dissimilar
conducting metals, which
form a closed loop.
THE PELTIER EFFECT:
• Temperature differential
caused at the junctions of
dissimilar conductors, with
the passing of current.
THE THOMSON EFFECT:
• Electrical current caused
by a temperature gradient
in a single homogeneous
conductor.
4

5. α
Seebeck Coefficient
Measure of voltage
produced by a
temperature
gradient in the
material
κ
Total thermal
conductivity of
the material
σ
Electrical
conductivity of the
material
5
Thermoelectric Efficiency

6.  High Seebeck coefficient
 High electrical conductivity
 Low thermal conductivity
6
Semiconductor
Semimetals & highly
doped semiconductors
Metals
κ:0-10W/m.Kα:0-500µV/Kσ:0-5,000S/cm
ZT

7. From transport calculations in nanoscale
α σ
EC
EV
EF
N-type
α σ
L.D. Hicks, M.S. Dresselhaus, Physical Revew B, 1993,47, 12727-12731 7
L
T
e


 (Wiedemann Franz Law)








 n
TK
EE
e
K
B
FCB

 Quantum confined structures (α, k )
 Unusual band structures (α )
 Control over the disorder (α , k )

8. Metals were initially the center point for research into thermoelectrics, but metals are
limited with respect to this application for the following reason.
Wiedemann Franz Law
A metals electrical conductivity and
thermal conductivity are related at a given
temperature; therefore, metals best suited
for thermoelectric applications must
posses a high Seebeck coefficients.
8
L
T
e




9. Semiconductors were found to be
much more effective
thermoelectric materials with
Seebeck coefficients in the range of
100μV/K (for metals, typically 10
μV/K ). In addition,
semiconductors have a higher ratio
of electrical conductivity to
thermal conductivity when
compared to metals. These factors
contribute to a greater figure-of-
merit for thermoelectric
applications.
9

10. L.D. Hicks, M.S. Dresselhaus, Physical Review B,
1993,47, 12727-12731
Two methods for increasing α:
1. Increasing μ(E), by a scattering mechanism.
2. Increasing n(E), by a local increase in the Density of States (DOS).
   2
1 1
3
F
B
B
E E
dn E d Ek
k T
q n dE dE


 
 
  
 
n(E) = carrier density at energy E
μ(E) = mobility at energy E
10

11. • κe cannot be reduced without reducing σ (Wiedemann-Franz Law)
• ZT enhancement can be done by reducing the κL of materials,
λ is the wavelength, cλ is the specific heat per unit wavelength, ν is the
group velocity, L is the mean-free path.
• cλ(λ,T) ν(λ) can be reduced through phonon confinement in
nanomaterials and superlattices with extremely small dimensions.
• L(λ,T) can be reduced through enhancing phonon scattering in
boundaries and interfaces in nanomaterials and composites.
11

12. • Thin film superlattice structures grown from methods like chemical
vapor deposition and molecular beam epitaxy.
•Thin films of p-type Bi2Te3 / Sb2Te3 superlattices with quantum well
periodicity of 6 nm have been produced with ZT ≈ 2.4 at room
temperature. The highest value for bulk alloys of the same composition
is 1.1. 12
Venkatasubramanian, R., et al., Nature, 2001,
413, 597-602
• Using quantum-confinement.
• Phonon blocking electron
transmitting superlattices.
• Thermionic effects in
heterostructures.

13. ‣ Costly and contain toxic, rare
materials.
‣ Restrictions on the supply of
even relatively abundant
materials (rare-earth metals) has
led to instability in pricing and
availability.
‣ High temperature special
processing is required.
13
• Low intrinsic thermal conductivity.
• Cheap solution processing at low
temperatures.
• Good for large area applications -
Roll to roll printable.
• Lighter materials.
• Non-toxic.
• Applicable in flexible technology.

14. 14
Boris Russ, Anne Glaudell, Jeffrey J. Urban, Michael L.
Chabinyc, Rachel A. Segalman, Nat. Review Mater.,
2016,1, 1-14
• Existing inorganic
materials consists of
heavy elements; shows
a maximum ZT = 1.2
• Organic materials has
low intrinsic thermal
conductivity; ZT =0.42
• By incorporating both a
large ZT may achieved.
• Highest ZT for hybrid
materials 0.1

15. 15
ZT = 0.42 for PEDOT:PSS doped with DMSO
G. H. Kim, L. Shao, K. Zhang, K. P. Pipe, Nat. Mater. 2013, 12, 719 – 723
D. Kim, Y. Kim, K. Choi, J. C. Grunlan, C. Yu, ACS Nano 2010,4, 513– 523
K.C. See, J.P. Feser, C. E. Chen, A. Majumdar, J. J. Urban,
R. A. Segalman, Nano Lett., 2010, 10, 4664-4667

16. Conductive polymer matrices with particle additives
Material Filler
Filler
form
Loading
[wt%]
σ [S/cm] α [µV/K]
PF
[µW/m.K2]
PEDOT:PSS PbTe spherical 30 0.003 2500 1.45
PEDOT:PSS Te nanowire - 19 163 70
PEDOT:PSS Bi0.5Sb1.5Te3 platelet 4.1 1295 16 32
PEDOT:PSS Au spherical 0.01 241 27 18
PEDOT:PSS SWCNT nanotube 35 400 23 24
PEDOT:PSS SWCNT nanotube 85 4000 16 102
PANI-HCl Bi2Te3 nanowire 30 11.6 40 200
PANI-HCl MoS2 platelet 85 0.8 8 0.0000512
PANI-HCl MWCNT nanotube 1 14 80 0.0896
PANI-HCl Graphene platelet 50 123 34 14
PANI-HCl
Graphene
oxide
platelet 10 7.5 28 0.601
PPy MoS2 platelet 85 0.8 82 0.00537
16

17.  For a material to be useful for thermoelectrics, a high electrical
conductivity, a high Seebeck coefficient and a low thermal
conductivity is required.
 Literature suggests that hybrid materials are a potential candidate.
17

18. Thank You
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