Crystallization of Perylene Diimides for Organic Field Effect Transistors

Bristee DasOctober 3, 2014

Outline of Presentation

1. Overview of Organic Field Effect Transistors

2. Background on N1100 semiconductor

3. Goal of project

4. Experimental Design

5. Results

6. Future work

What are OFETs?

• The field effect transistor is a major component of modern electronics and circuitry that functions as an on-off switch to control and amplify electric signal

• In recent decades, increased interest in organic field effect transistors (OFETs), which contain organic small molecule or polymer-based semiconductors, has developed due to their inexpensiveness, mechanical flexibility, and easy processability

How do OFETs work?

• OFETs consist of source, drain, and gate electrodes. The organic semiconductor acts as a bridge between the source and drain, and an insulating dielectric layer keeps it spaced from the gate.

• When a gate bias is applied between the gate and semiconductor, charges accumulate at the semiconductor-dielectric interface that balances layer of charge of opposite polarity on gate electrode

• Applying a bias across the source and drain creates a lateral electric field that allows these accumulated charges to move. Further adjustment of the gate voltage modulates the conductivity of the channel.

Image: Y-L Loo, AIChE Journal, 2007, 113

Background on N1100

• In particular, the perylene alkyldiimide (PDIR) family is known for having “one of the highest n-type mobilities known”2

Image: K. Willa, R. Hausemann, T. Mathis, A. Facchetti, Z. Chen, B. Batlogg, Journal of Applied Physics, 2013, 113

2C. Piliego, F. Cordella, D. Jarzab, S. Lu, Z. Chen, A. Facchetti, M.A. Loi, Appl. Phys. A, 2009, 95

N1100 Single crystal mobility = up to 6 cm2/V.s

Goals of Summer Project

• Learn how to fabricate thin film transistors

• Utilize various post-deposition annealing techniques on a variety of substrate surfaces to gain a better understanding of the effects of surface modifications, solvent vapor annealing treatments, and thermal annealing treatments on crystallization kinetics in thin films and how to control the crystallization process

General Experimental Design

• Surface treatments included OTS treatment of SiO2 and PFBT treatment of gold for bottom contact, bottom gate geometry devices

• N1100 was evaporated to a thickness of 45 nm• As evaporated films are amorphous

• Conducted ex-situ and in-situ thermal and solvent vapor annealing of N1100 thin films using:

Toluene THF DCM Hexanes Chlorobenzene

Solvent

Stands for substrates

Glass Cover

Experimental design: ex-situ SV annealing

Ex-situ SVA Morphology

Toluene Hexanes Chlorobenzene

DCM

Results: Summary of ex-situ testing

Ex-situ Treatment Method

Mobility (cm2/Vs)

Threshold Voltage (V)

Thermal annealing, 130c, 1 hr

0.856 +/- 0.195

-7.15 +/- 15.4

Toluene1.73E-06 +/-

1.29E-06 12.8 +/- 25.2

Hexanes3.66E-03 +/-

3.80E-04-2.943

+/- 1.73

DCM5.01E-02 +/-

3.08E-03 13.0E +/- 0.879

THF1.29E-04

+/- 7.29E-06-6.472E+01

+/4.93

Chlorobenzene2.69E-03 +/-

1.47E-031.50E+01 +/-

4.51

Experimental design: in-situ SV annealing

N2

Mass Flow Controller 2 75 mL/min

Mass Flow Controller 1 425 mL/min

 Solvent

Probe Station

 

Cold Trap

 

Exhaust

Results: in-situ Toluene SVA

N1100 In-situ Thermal Annealing 120C

Conclusions

• Ex-situ treatments – Performance of TA devices was better than that of SVA devices

– For various SVA devices, DCM gave the largest mobility, Hexanes and Chlorobenzene treatment gave the largest on/off ratio

• In-situ treatments – THF fastest – mobility plateau’d out after 30 min– Chlorobenzene slowest – took around 840 min to plateau– Need to retest DCM with video capture

• Generally, thermal annealing yields better performance compared to SVA for both ex-situ and in-situ treatment

Future Work

• Continue in-situ SVA with accompanying video for remaining solvents

• Further analysis and comparison of in-situ and ex-situ data for each solvent

• Perform AFM to obtain a better understanding of how morphology is changing with solvent choice

• Attempt simultaneous in-situ thermal and solvent-vapor annealing to see the effects on the crystallization process

Acknowledgements