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- 1. Charge motion in Poly(3-hexylthiophene-2,5-diyl) studied with Scanning Probe Microscopy Jason Moscatello, Chloe Castaneda, Katherine Aidala APS March Meeting Session L41: Focus Session: Organic Electronics and Photonics - Transport in Polymer Thin Films Wednesday, March 4, 2015 9:12AM
- 2. Organic potential Organic electronics can be used in many applications we cannot use traditional silicon architectures. For example: Large-area, low-cost electronics Printed electronics Flexible electronics Transparent electronics Image Source: Techradar.com ImageSource: National Research Council Canada jmoscate@mtholyoke.edu
- 3. Why SPM? jmoscate@mtholyoke.edu Image Source: Agilent Organics are an inherently disordered system with many local effects such as: • Trap states • Contact resistance • Carrier density dependent mobility • Environment environment/interface SPM techniques are capable of measuring local effects. Allows us to focus on electrical interactions in order to follow charges.
- 4. Kelvin Probe Force Microscopy (KPFM) • a local surface potential measurement • measured relative to tip potential Measuring Potentials jmoscate@mtholyoke.edu
- 5. Measuring Potentials jmoscate@mtholyoke.edu Force at resonant frequency, ωac -1 V 3 V Kelvin Probe Force Microscopy (KPFM) • a local surface potential measurement • measured relative to tip potential
- 6. Measuring Potentials jmoscate@mtholyoke.edu -1 V 3 V -1 V -1 V Vtip = Vsample 0 Kelvin Probe Force Microscopy (KPFM) • a local surface potential measurement • measured relative to tip potential minimize oscillation Force at resonant frequency, ωac
- 7. KPFM in Space and Time jmoscate@mtholyoke.edu Pass 1: Topography 40 35 30 25 20 µm 403020100 µm -40 -20 0 20 40 nm 40 35 30 25 20 µm 403020100 µm 0.8 0.7 0.6 0.5 0.4 0.3 V Pass 2: KPFM 1. Topography 2. KPFMImage Source: Asylum Research Device On v Au AuP3HT Au AuP3HT 2 1
- 8. jmoscate@mtholyoke.edu Potential Time ? v = 0 Event Pass 1: Topography 40 35 30 25 20 µm 403020100 µm -40 -20 0 20 40 nm 40 35 30 25 20 µm 403020100 µm 0.8 0.7 0.6 0.5 0.4 0.3 V Pass 2: KPFM 1. Topography 2. KPFMImage Source: Asylum Research v 2 1 KPFM in Space and Time Device On Au AuP3HT Au AuP3HT
- 9. P3HT Organic Field Effect Transistor (OFET) P3HT ≥96% RR >32k MW D S G (n-type Si, .01 Ω-cm) 200 nm thermally grown SiO2 Au poly(3-hexylthiophene) jmoscate@mtholyoke.edu
- 10. Real Time Screening - Controls • No P3HT • Tip above metal electrode • Gate turned on and off D S G Tip Expect to see 0V above the Au, because the electrons move too quickly to resolve, screening the back-gate. grounded Apply -7V grounded jmoscate@mtholyoke.edu
- 11. Real Time Screening - Controls • No P3HT • Tip above metal electrode • Gate turned on and off Tip No change in measured potential Apply -7V D S G Expect to see 0V above the Au, because the electrons move too quickly to resolve, screening the back-gate. jmoscate@mtholyoke.edu
- 12. Real Time Screening - Controls • No P3HT • Tip above bare dielectric • Gate turned on and off D S G What happens for the same sequence, but above the dielectric? Tip jmoscate@mtholyoke.edu
- 13. Real Time Screening - Controls • No P3HT • Tip above bare dielectric • Gate turned on and off D S G What happens for the same sequence, but above the dielectric? Tip t = 3 ms Cannot screen jmoscate@mtholyoke.edu
- 14. Real Time Screening – P3HT D S G What will KPFM measure when the tip is above a poor conductor, which is connected to grounded metal electrodes? Tip Can you record the screening as the carriers move through the film? P3HT Au jmoscate@mtholyoke.edu
- 15. For a material with holes as the majority carrier: Real Time Screening – P3HT jmoscate@mtholyoke.edu
- 16. Negative gate Initial negative potential Then holes rush in to screen For a material with holes as the majority carrier: Real Time Screening – P3HT jmoscate@mtholyoke.edu
- 17. Vg = 0 Initial surplus of holes Positive potential Holes leave the film For a material with holes as the majority carrier: Real Time Screening – P3HT jmoscate@mtholyoke.edu Negative gate Initial negative potential Then holes rush in to screen
- 18. Vg = 0 Initial surplus of holes Positive potential Holes leave the film For a material with holes as the majority carrier: Real Time Screening – P3HT jmoscate@mtholyoke.edu Negative gate Initial negative potential Then holes rush in to screen
- 19. Vg = 0 Initial surplus of holes Positive potential Holes leave the film Positive gate Initial positive potential Holes leave film to screen For a material with holes as the majority carrier: Real Time Screening – P3HT jmoscate@mtholyoke.edu Negative gate Initial negative potential Then holes rush in to screen
- 20. Vg = 0 Initial surplus of holes Positive potential Holes leave the film Positive gate Initial positive potential Holes leave film to screen Too few holes Negative potential Holes rush in Vg = 0 For a material with holes as the majority carrier: Real Time Screening – P3HT Negative gate Initial negative potential Then holes rush in to screen jmoscate@mtholyoke.edu
- 22. Real Time Screening – PDI-CN2 electrons Vgs > 0 jmoscate@mtholyoke.edu Initial positive potential then electrons rush in to screen Electron surplus leads to Initial negative potential Electrons leave the film PDI-CN2
- 23. Real Time Screening – PDI-CN2 electrons Vgs > 0 jmoscate@mtholyoke.edu Initial positive potential then electrons rush in to screen Electron surplus leads to Initial negative potential Electrons leave the film PDI-CN2
- 24. Real Time Screening – PDI-CN2 jmoscate@mtholyoke.edu holes Vgs < 0 electrons Vgs > 0 PDI-CN2 P3HT
- 25. Real Time Screening – PDI-CN2 jmoscate@mtholyoke.edu holes Vgs < 0 electrons Vgs > 0 PDI-CN2 P3HT (1) Inject carriers Quick initial screening (2) Extract carriers Charges slower to exit (1) (1) (2) (2)
- 26. Real Time Screening – PDI-CN2 jmoscate@mtholyoke.edu Initial negative potential Electrons leave film to screen Too few electrons Positive potential Electrons rush in electrons Vgs < 0 PDI-CN2
- 27. Real Time Screening – PDI-CN2 jmoscate@mtholyoke.edu holes Vgs > 0 P3HT electrons Vgs < 0 PDI-CN2
- 28. Real Time Screening – PDI-CN2 jmoscate@mtholyoke.edu holes Vgs > 0 P3HT electrons Vgs < 0 PDI-CN2 (1) Extract carriers Very slow exit (2) Inject carriers Charges quickly return (1) (1) (2) (2)
- 29. Ongoing & Future Studies jmoscate@mtholyoke.edu The affect of bias stress in N2 environment on P3HT OFETs. How does it change in ambient with or without stress? a
- 30. Ongoing & Future Studies jmoscate@mtholyoke.edu Other materials, such as PbS quantum dots. With Scott Geyer, Moungi Bawendi, and Vladimir Bulovic (MIT). P3HT
- 31. jmoscate@mtholyoke.edu Ongoing & Future Studies How does tip distance affect measurement? Can we distinguish between contact-limited and bulk-limited transport? VGS = 0V VGS = -6V VGS = 0V outward outward
- 32. Thank You NSF CAREER Award DMR-0955348 Thank you! jmoscate@mtholyoke.edu Chloe Castaneda Katherine Aidala