Thermoelectrics

Vijitha IJRF, CSIR-NIIST

THERMOELECTRIC MATERIALS

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

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….

Seebeck Effect

Peltier Effect

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.

Seebeck Coefficient

Open circuit voltage produced per unit temperature difference (Thermo EMF)

TV

H

CH

CH

TTZT

ZTTTT

1

11

TZT 2

Thermoelectric Figure of Merit

Thermoelectric Efficiency

High Seebeck coefficient

High electrical conductivity

Low thermal conductivity

n

TKEE

eK

B

FCB

From transport calculations in nanoscale

LTe

Wiedemann-Franz Law

α σ

EC

EV

EF

N-type

α σ

phe

The Sweet Spot

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

Quantum confined structures (α, )

Unusual band structures (α )

Control over the disorder (α , )

The Breakthrough

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 effectiveLow intrinsic thermal conductivityHigh flexibilityAmenability to large area applications

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.

PEDOT:PSS

Te-PEDOT:PSS

aEstimated from the thermal conductivity (0.20Wm−1K−1) of PEDOT:PSSbEstimated 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.

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.

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.

12.75mV 10.59nW

5kΩ

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

Thank You