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

2. Thrust 3: Novel Characterization Tool: Gated Seebeck New technique to elucidate carrier transport in networks of hybrid interfacial junctions Measures S as function of V g S (V g ) gives info about density of states (DOS) and E f - Can scan through DOS by varying E f without changing lattice or morphology

3. 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 EFEF New technique to elucidate carrier transport in networks of hybrid interfacial junctions Measures S as function of V g S (V g ) gives info about density of states (DOS) and E f - Can scan through DOS by varying E f without changing lattice or morphology

4. Thrust 3: IV vs. FET measurements IV curves: tells you if material is conductive, but doesn’t tell anything about transport or carriers FET measurements: can understand transport or mobility of carriers and effects on conductivity Determine how electrical conductivity and mobility change with carrier concentration Threshold voltage – how many trap states in semiconductor FET mobility – how carriers respond to applied electric field – can better understand carrier scattering  (S cm -1 ) = (R×L/A) -1 I V I I IV curve

5. Thrust 3: IV vs. FET measurements IV curves: tells you if material is conductive, but doesn’t tell anything about transport or carriers FET measurements: can understand transport or mobility of carriers and effects on conductivity Determine how electrical conductivity and mobility change with carrier concentration Threshold voltage – how many trap states in semiconductor FET mobility – how carriers respond to applied electric field – can better understand carrier scattering Adding one more dimension gives more information! Carrier concentration (n) FET mobility (μ) Carrier transport FET curves I V I I I VGVG

6. Thrust 3: Seebeck vs. Gated Seebeck Seebeck coefficient is related to asymmetry in electron and hole distributions

7. Hot Cold I TT I V I VGVG Thrust 3: Seebeck vs. Gated Seebeck Pernstich et al., Nat. Mater. (2008) EFEF EFEF Transport modes Density of States

8. Hot Cold I TT I V I VGVG Thrust 3: Seebeck vs. Gated Seebeck Trap DOS Transport modes Pernstich et al., Nat. Mater. (2008) Energy landscape EFEF EFEF

9. Thrust 3: Analogy to metal-molecule-metal transmission function Energy Slope~-S EFEF

10. Thrust 3: Analogy to metal-molecule-metal transmission function EFEF EFEF

11. Thrust 3: Gated Seebeck – Precedent in Inorganic and Organic Inorganic 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

12. Thrust 3: Example Composite Material Trapped carriers cannot contribute to conduction Only carriers in organic molecule contribute to conduction Organic molecule Inorganic NP

13. Thrust 3: Example Composite Material Carriers become conductive Carriers are conductive without thermal excitation Trapped carriers can now be excited by thermal energy VgVg VgVg

14. σ I II Thrust 3: Expected Trend for σ VgVg III

15. S I Thrust 3: Expected Trend for S VgVg II III

16. S I Thrust 3: Expected Trend for S VgVg II III σ

17. 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 SiO 2 ?

18. Acknowledgements Prof. Rachel Segalman Dr. Jeff Urban Segalman Group The Molecular Foundry, LBNL MURI NSF GFRP