Novel Thermoelectric Characterization Tool: Gated Seebeck Cynthia Chen February 7, 2013 MURI Informal Meeting.

Novel Thermoelectric Characterization Tool:Gated Seebeck

Cynthia Chen

February 7, 2013

MURI Informal Meeting

Thrust 3: Novel Characterization Tool: Gated Seebeck

• New technique to elucidate carrier transport in networks of hybrid interfacial junctions

• Measures S as function of Vg

• S (Vg) gives info about density of states (DOS) and Ef

- Can scan through DOS by varying Ef without changing lattice or morphology

Thrust 3: Novel Characterization Tool: Gated Seebeck

What can we uniquely learn from gated Seebeck?

• Models for carrier transport and DOS in inorganic-organic materials systems

• Chemistry for composites with well-defined electronic alignment at interfaces

DOS

E

EF

• New technique to elucidate carrier transport in networks of hybrid interfacial junctions

• Measures S as function of Vg

• S (Vg) gives info about density of states (DOS) and Ef

- Can scan through DOS by varying Ef without changing lattice or morphology

Thrust 3: IV vs. FET measurements

(S cm-1) = (R×L/A)-1

I

IVR

V

II

IV curve

Thrust 3: IV vs. FET measurements

Adding one more dimension gives more information!

Carrier concentration

(n)FET mobility

(μ)

Carrier transport

FET curves

IV

II

IVG

Thrust 3: Seebeck vs. Gated Seebeck

Seebeck coefficient is related to asymmetry in electron and hole

distributions

Thrust 3: Seebeck vs. Gated Seebeck

Pernstich et al., Nat. Mater. (2008)

EF

EFTransport modes

Density of States

Thrust 3: Analogy to metal-molecule-metal transmission function

HS SH

Energy

Slope~-S

EF

Thrust 3: Analogy to metal-molecule-metal transmission function

EFEF

Thrust 3: Gated Seebeck – Precedent in Inorganic and OrganicInorganic Materials

Organic Materials

BUT gated Seebeck has not been utilized to fullest potential!

Pernstich et al., Nat. Mater. (2008)

Gated Seebeck in rubrene

Bubnova, O. et al., JACS, 134 (2012)

Gated Seebeck in PEDOT

Thrust 3: Example Composite Material

Trapped carriers cannot contribute to conduction

Only carriers in organic molecule contribute to conduction

Organic molecul

e

Inorganic NP

Thrust 3: Example Composite Material

Carriers become conductive

Carriers are conductive

without thermal

excitation

Trapped carriers can now be excited by thermal energy

Vg Vg

σ

I II

Thrust 3: Expected Trend for σ

Vg

III

S I

Thrust 3: Expected Trend for S

Vg

II

III

S

I

Thrust 3: Expected Trend for S

Vg

II

IIIσ

Progress so far

• Built new characterization tool: gated Seebeck device

• Made preliminary measurements of Seebeck coefficient on PEDOT:PSS

• Troubleshooting gated Seebeck measurements

• Leaky gate results in high gate currents- Some pathway from

gate to film- Possible pinholes in

SiO2?

Acknowledgements

• Prof. Rachel Segalman

• Dr. Jeff Urban

• Segalman Group

• The Molecular Foundry, LBNL

• MURI

• NSF GFRP