novel thermoelectric characterization tool: gated seebeck cynthia chen february 7, 2013 muri...
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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