Tuning the Threshold Voltage in Organic FieldEffect Transistors

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Tuning the Threshold Voltage in Organic Field-Effect Transistors by Solvent-Vapor Annealing Abhiram Karuppur Organic

Tuning the Threshold Voltage in Organic Field-Effect Transistors by Solvent-Vapor Annealing Abhiram Karuppur Organic Polymer and Electronics Laboratory – Professor Lynn Loo 09/30/2016

Background • Transistors are used in everyday electronics – Computers, TVs, Phones • Are

Background • Transistors are used in everyday electronics – Computers, TVs, Phones • Are analogous to an electrical “switch” • Can control the current amplitude by altering the gate-source voltage http: //www. sigmaaldrich. com/content/dam/sigma-aldrich/product 9/140/msc_f 0007. eps/_jcr_content/renditions/msc_f 0007 -medium. jpg http: //www. pixuffle. net/wp-content/uploads/2014/01/computers 2. jpeg

Organic field-effect transistors Au Au Organic Semiconductor Si. O 2 (300 nm) Si (gate)

Organic field-effect transistors Au Au Organic Semiconductor Si. O 2 (300 nm) Si (gate) Bottom gate, top contact Lee, Stephanie. (2012). Ph. D. Thesis. Princeton University, USA L Top-down view of BGTC device W

Goals • How can we control the threshold voltage without affecting other device parameters?

Goals • How can we control the threshold voltage without affecting other device parameters? – Determine if threshold voltage is correlated with solvent properties • Dipole Moment • Hansen’s Polarity Index – Can threshold voltage be predicted with different conditions: • Mixtures of solvents – Can the threshold voltage be changed? • 2 -step SVA with Methanol

Overview • Deposited TES-ADT thin films – 2 wt% in toluene – Spin at

Overview • Deposited TES-ADT thin films – 2 wt% in toluene – Spin at 1000 rpm for 60 seconds – Place on hot plate at 100 C for 2 minutes • Annealing Method: – Initially placed substrates in sealed chamber with reservoir of different solvents, remove when crystallization complete – Better Method: Vent chamber every 15 seconds Spin-coat from 2 wt% solution in toluene Expose to 1, 2 -dichloroethane vapor μ 50 2 as-spun film m based on Dickey, K. C. ; Anthony, J. E. ; Loo, Y. -L. Adv. Mater. 2006, 18, 1721 μ 50 m 2 crystallized film

DCE

DCE

SVA with Different Solvents DCE Propyl Acetate DCM Toluene Cyclohexane Pentane Acetone

SVA with Different Solvents DCE Propyl Acetate DCM Toluene Cyclohexane Pentane Acetone

SVA with Different Solvents Device μave (cm 2 V-1 s-1) VT – V 0

SVA with Different Solvents Device μave (cm 2 V-1 s-1) VT – V 0 (V) Dipole Pentane 0. 376± 0. 0487 0 0 0 Cyclohexane 0. 471± 0. 115 +1. 3 0 0 Toluene 0. 513± 0. 204 +6. 2 0. 31 1. 4 DCM 0. 489± 0. 306 +5. 3 1. 6 6. 3 Propyl Acetate 0. 489± 0. 131 +19. 3 1. 78 4. 3 Acetone 0. 608± 0. 124 +19. 6 2. 69 10. 4 DCE 0. 419± 0. 0834 -0. 1 1. 8 7. 4 Pentane is the reference point �� P

Quantifying Trends Pentane is the reference point

Quantifying Trends Pentane is the reference point

Re-testing SVA with Different Solvents Device μave (cm 2 V-1 s-1) VT – V

Re-testing SVA with Different Solvents Device μave (cm 2 V-1 s-1) VT – V 0 (V) Dipole Pentane 0. 675± 0. 112 0 0 0 61: 39 Acetone: Pentane 0. 261± 0. 0515 +6. 9 1. 64 6. 3 Acetone 0. 393± 0. 106 +16. 1 2. 69 10. 4 Acetone x=0. 61 �� P Pentane

SVA with Methanol DCE 60

SVA with Methanol DCE 60

Conclusions • Different Solvents affect Threshold Voltage – Positive correlation between polarity/dipole moment of

Conclusions • Different Solvents affect Threshold Voltage – Positive correlation between polarity/dipole moment of the solvent and the threshold voltage – Different solvents result in different spherulite shapes – The kinetics of spherulite formation are different with different solvents • Threshold Voltage Can be Modified Ex-situ – VT can be shifted after treatment with methanol – Preliminary results suggest this is reversible • Exposing these films to nonpolar solvents results in a negative VT shift

Acknowledgements

Acknowledgements