This document summarizes the history and development of thermoelectric materials. It discusses key figures who discovered thermoelectric effects from the 1820s to present. Major applications of thermoelectrics include radios, refrigerators, pacemakers, and watches. The document then focuses on organic-based thermoelectric materials like PEDOT:PSS and their composites with tellurium. Treatment of Te-PEDOT:PSS composites with sulfuric acid improves thermoelectric properties by rearranging the PEDOT:PSS structure. Flexible thermoelectric generators fabricated with the treated composite demonstrate power generation from human body heat.

1. Vijitha I
JRF, CSIR-NIIST
THERMOELECTRIC MATERIALS

2. 1821
Thomas Johann Seebeck
1834
Jean-Charles-Athanase Peltier
1854
William Thomson( Lord Kelvin)
1928
Abram F. Ioffe
1947
Maria Telkes
1954
H. Julian Goldsmid

3. 1930
Radio
1959
Home refrigerator,
General Electric,
Westinghouse
1959
Radioactive
Thermoelectric Generator
(RTG) "SNAP III"
1970
Cardiac pacemaker
1998
Seiko introduces the
Thermic watch
1999
Seat coolers in the
Lincoln Navigator and
Toyota's Lexus
36 years
Voyager 1
The First Thermoelectric….

4. Seebeck Effect

5. Peltier Effect

6.  In a thermoelectric material there are free carriers which carry both charge
and heat.
 In the steady state, the effect of the density gradient will exactly counteract
the effect of the temperature gradient so there is no net flow of molecules.
 If the molecules are charged, the buildup of charge at the cold end will also
produce a repulsive electrostatic force (and therefore electric potential) to
push the charges back to the hot end.

7. Seebeck Coefficient
Open circuit voltage produced per unit temperature difference (Thermo EMF)
T
V


H
CH
CH
T
T
ZT
ZT
T
TT



1
11

TZT

2

Thermoelectric Figure of Merit
Thermoelectric Efficiency

8.  High Seebeck coefficient
 High electrical conductivity
 Low thermal conductivity








 n
TK
EE
e
K
B
FCB

From transport calculations in nanoscale
LTe



Wiedemann-Franz Law
α σ
EC
EV
EF
N-type
α σ
phe  

9. Semiconductor
Semimetals &
highly doped
semiconductors Metals
Adapted from Heikes, R. R., and Ure, R. W., Jr. Thermoelectricity: Science and Engineering;
Interscience Publication: New York, 1961; p 20

10.  Quantum confined structures (α,  )
 Unusual band structures (α )
 Control over the disorder (α ,  )
The Breakthrough

12. Organic?
PEDOT:PSS - easy to handle, water-soluble, has high electrical
conductivity, and offers the possibility of achieving even higher
electrical conductivity.
Polypyrrole, Polyaniline,
Polycarbazol, Polythiophene,
Poly(3,4-ethylenedioxythiophene)
(PEDOT),
PEDOT:poly(styrenesulfonate) (PSS)
Cost effective
Low intrinsic thermal conductivity
High flexibility
Amenability to large area
applications

13. 0.5 μm 10 nm 5 nm
The formation of the nanocrystalline structure of Te-PEDOT:PSS hybrids was
confirmed by transmission electron microscopy (TEM). The Te-PEDOT:PSS
hybrids consist of Te nanorods (diameter: 20–30 nm; length: ca. 800 nm) coated
with a thin PEDOT:PSS layer.
For the chemical treatment, the PEDOT:PSS and Te-PEDOT:PSS films were
immersed in H2SO4 solutions with various volume ratios (20–100%) for 10 min
under ambient conditions. The films were then washed in methanol and annealed at
160 °C for 10 min.

14. PEDOT:PSS
Te-PEDOT:PSS
aEstimated from the thermal
conductivity (0.20Wm−1K−1)
of PEDOT:PSS
bEstimated from the thermal
conductivity (0.22Wm−1K−1)
of Te-PEDOT:PSS
The improved
crystallinity of
PEDOT:PSS leads
to an increase in
the electrical
conductivity.

15. PEDOT:PSS
PEDOT:PSS
Te-PEDOT:PSS
Te-PEDOT:PSS
PSS:PEDOT = 2.23 PSS:PEDOT = 1.45
PSS:PEDOT = 1.28 PSS:PEDOT = 1.34
The decreased PSS/PEDOT ratio is
reflective of the structural
rearrangement induced by the decrease
in the PSS content of the composites. The
change in the PSS content also influences
the crystallinity of PEDOT:PSS and the
concentration of charge carriers.

16. 600 nm 600 nm 600 nm
600 nm 600 nm 600 nm
SEM images of surface of Te-
PEDOT:PSS hybrid composite films
treated with various concentrations
of H2SO4: (a) 0, (b) 20, (c) 40, (d) 60,
(e) 80, and (f) 100 vol%
AFM images of surface of Te-
PEDOT:PSS hybrid composite films
treated with various concentrations
of H2SO4: (a) 0, (b) 20, (c) 40, (d) 60,
(e) 80, and (f) 100 vol%
The surface of the Te-PEDOT:PSS film before H2SO4 treatment consists of composite
nanorods that are densely packed together and interconnected with each other. The
surface of the composite nanorods was also smooth and clear. Therefore, the electrical
conductivity of the Te-hybrid increases, which arises from nanostructural rearrangement
of PEDOT:PSS which is interconnected on the surface of the Te nanorods.

17. 12.75mV
10.59nW
5kΩ

20. A voltage of
over 2mV from
human body
heat
Enhanced the thermoelectric properties
by simply immersing the materials into H2SO4
Structural rearrangement of PEDOT:PSS
due to the removal of PSS, which induces
the formation of a more crystalline structure
and increases the number of charge carriers
Flexible TEG was successfully fabricated by
simple printing process using the treated
Te-PEDOT:PSS composite having a
high power factor of 284 μ W m−1 K−2
Electrical power generation capability
was demonstrated with a maximum
power output of 10.59 nW
Summary

21. Thank You