Polymeric Semiconductors: Molecular Ordering, Charge Transport and - PowerPoint PPT Presentation

Polymeric Semiconductors: Molecular Ordering, Charge Transport and Macroscale Mobility El Elsa R Reic ichmanis is School of Chemical and Biomolecular Engineering School of Chemistry and Biochemistry School of Materials Science and Engineering Georgia Institute of Technology Australia, June 2014 1

An Introduction to Georgia Tech One of the oldest ChBE programs in the US Founded in 1901 One of the largest ChBE programs in the US 215+ Graduate students 900+ Undergraduate students 45 Faculty One of the most respected ChBE programs in the US Undergraduate and Graduate Programs ranked in top 10 College of Engineering ranked in top 5 internationally Australia, June 2014 2

Polymers in Electronics and Photonics 30 m m 3 cm Australia, June 2014 3

Materials and Processes  Lithographic materials and processes  Silicon device processing  Dielectric materials (low and high-k)  Packaging materials  Organic semiconductor materials for plastic electronics  Active device layers Australia, June 2014 4

‘All - Printed’ Plastic Electronics Silicon based semiconductor technology today: • Conducted in $5B+ Fabs (clean rooms a must!) • Features smaller than 30 nm • Rigid, inflexible 12” diameter substrates • Subtractive processing All-printed plastic electronics alternative: – Using cost-effective printing presses, or even ink-jet printers – Large-area, reel-to-reel processing – Flexible, conformable, bendable plastic and paper-like substrates – Additive,’ink - like’ processing Australia, June 2014 5

Semiconductor Mobility Magnitudes (cm 2 /Vs) Semiconductor Mobility Silicon single crystal >1,000 Polysilicon 100 Amorphous silicon 0.1-1 Single nanotube 100-1,000 Organic single crystal 10 Pentacene film 1-10 Polycrystalline sublimed organic 0.01-10 Soluble oligomer/polymer 0.01->1 Australia, June 2014 6

Advantages of Organics  mobilities can be more uniform, and less limited by surface states and grain boundaries  covalent integration with molecular receptors for sensors  moderate temperature processing  large area coverage, solution deposition possible  mechanical and thermal compatibility with plastic and other flexible substrates  rational control of polarity and threshold voltage, for circuit tuning and memory applications Australia, June 2014 7

Charge Transport in Organic Semiconductors: Needs: Increased electrode conductivity Increased semiconductor mobility Materials Issues Improved gate dielectric Decreased conductor resistivity: understand mechanism Control of carrier transport in organics Device Issues Control of FET properties: effect of impurities, charge traps, etc Charge injection Identify critical limiting bulk/surface Process Issues Improved semiconductor properties Control of thin film morphology Australia, June 2014 8

Polymers in Electronics and Photonics Polymer/hybrid materials and processes for plastic electronics and photovoltaics:  Design and development of new materials chemistries  Develop structure-process- property relationships to guide robust materials and process design  Understand and utilize mechanisms associated with thin- 400 film morphology evolution. nm Australia, June 2014 9

Order and Disorder  Semiconducting polymer properties MECHANISM OF strongly dependent on final thin film CONDUCTING CHANNEL FORMATION morphology (microstructure). CONTROL OF  highly process dependent MICROSTRUCTURE ROLE OF CRYSTALLINITY  Microstructure development during film CONJUGATION EFFECTS: formation not well understood INTRA- VS INTER-CHAIN 10 Australia, June 2014

Role of Microstructure Kim et.al., Adv. Func. Mater. 2005,15, 77 Sirringhaus et.al. Nature 1999, 401, 685. Kline et.al., Adv. Mater. 2003, 15, 1519. Semiconductor-dielectric Regioregularity dependent texture Effect of polymer MW interface 5000 0.18 200 110 P100 0.17 P200 threshold voltage (V) 4000 100 Raman Intensity (A.U.) 0.16 mobility (cm 2 /Vs) 150 0.15 90 3000 W (meV) 0.14 80 100 2000 0.13 70 0.12 1000 50 60 0.11 0.1 50 0 Xylene CHCl 3 MCB 1800 1600 1400 1200 1000 800 600 BCl 0 500 1000 1500 time (s) -1 ) Raman Shift (cm J. Am. Chem. Soc. 2011, 133, 7244. * Aiyar, et al., Chem, Mater. 2012 J. Phys. Chem. C 2011, 115, 11719.  What is the role of microstructure?  How can microstructure be tuned ? Australia, June 2014 11

Conducting Channel Formation V D Drain Source Intermediate phase SiO 2 transitions? n + Si -4 1.4 10  Drain current fluctuates during -4 1.2 10 film formation -4 1 10 -drain current (A)  Polymer chains rearrange as a -5 8 10 function of time: percolation -5 6 10 effects -5 4 10  Bulk vs interface effects -5 2 10  Evolution of microstructure? 0 0 50 100 150 200 250 300 time (seconds) *in chloroform 12 Australia, June 2014

Extending Solvent Evaporation Time CHCl 3 Thiophene 1,2,4-TCB -6 0.001 10 -5 -7 10 10 -drain current (A) - drain current (A) -7 -8 10 10 -9 -9 10 10 -11 -10 10 10 V D =-3V V G =-15V -13 10 -11 10 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 14 time (hours) time (sec.) 61.2 ° C 84 ° C 214 ° C  Time required for conducting channel formation scales with solvent evaporation rate  As evaporation proceeds, polymer concentration increases - percolation Australia, June 2014 13

Correlation with Structure? -6 10 -7 10 -drain current (A) -8 10 -9 10 -10 10 -11 10 0 2 4 6 8 10 12 14 time (hours)  Lyotropic LC phase coincident with sharp increase in current  Long range order in LC phase  Potentia tial l consequ quenc nces es for macrosc oscopi opic c charge e transp spor ort Australia, June 2014 14 J. Am. Chem. Soc. 2011, 133, 7244.

Sharp Onset of the Drain Current V D 50 μ m Solution drop P3HT+TCB (3mg/mL) Australia, June 2014 15

Raman Spectral Changes B B+30 seconds B+60 seconds B+90 seconds B+120 seconds C Australia, June 2014 16

Crystalline vs Amorphous Phases Raman spectroscopy: regio-regular P3HT (Semi-crystalline) vs. regio-random P3HT (Amorphous) Australia, June 2014 17

Evolving Microstructure  Asymmetric peak shape evolves rapidly into a symmetric profile  Rapid nucleation and crystallization of P3HT chains 1446 cm -1 from 1446 cm -1 from Raman spectrum Raman spectrum highly ordered state highly ordered state at point B+30secs at point C 1463 cm -1 from less ordered state 1300 1350 1400 1450 1500 1550 1600 1300 1350 1400 1450 1500 1550 1600 Raman Shift (cm-1) Raman Shift (cm-1) Australia, June 2014 18

Liquid Crystal Poly(3-hexylthiophene) Solutions Aged 1 Day Aged 1 Day 1.0 Aged 2 Days Aged 2 Days Aged 3 Days Aged 3 Days 0.8 Normalized Absorption Low Energy Absorption from 0.6 weakly interacting H-aggregates 1 0.4 0.2 isotropic nematic 0.0 1.5 2.0 2.5 3.0 3.5 Energy (eV) Polarized Optical Microscopy of aged P3HT solutions show long- range order and monodomain character Australia, June 2014 19

Processing: Ultrasound Induced Effects Pristine 5 min sonicated Solution state Pristine Red- 5 min sonicated shift  Film-like Pronounced properties Absorbance (AU) shoulder apparent in solution state Solid  Increased state backbone planarization Ordered  Increased π - π precursor stacking s evidenced by (0-0) transition in solid state Color emanates from additional low 300 300 300 300 400 400 400 400 500 500 500 500 600 600 600 600 700 700 700 700 800 800 800 800 energy transitions Wavelength (nm) Australia, June 2014 20

Microstructure and Crystallinity Pristine 30 secs 1 min 3 min 5 min 10 min 200 nm Australia, June 2014 21

Impact on Charge Transport 0.1 Mobility (cm 2 V -1 s -1 ) Absorbance (AU) 0.01 V D 0.001 Drain Source SiO 2 500 550 600 650 700 n ++ Si Wavelength (nm) V G  Almost 2 order of magnitude 0.0001 0 2 4 6 8 10 increase in mobility Ultrasonication time (mins)  Saturation of mobility beyond 1-3 mins sonication Percolation type charge transport Australia, June 2014 22

Multiphase Morphology pristine Disordered 30 nm 1 min Quasi-ordered Ordered 80 nm *Holdcroft, S. et.al. Macromolecules 1996, 29, 6510. Australia, June 2014 23

Solvent Characteristics and Molecular Ordering Impact of binary solvent:  high volatility  hydrogen bonds with the majority solvent Acetone (bp 56 ° C) CHCl 3 (bp 61 ° C) Increased lamellar packing of the polymer chains 1.7  10 -2 cm 2 /Vs Acetone Acetone volume % volume % 4.3  10 -3 cm 2 /Vs 2,3-dimethylbutane (poor solvent, bp 58 ° C) Chlorobenzene (good solvent, bp 131 ° C) Increased π - π stacking evidenced by (0-0) transition in solid state M. Chang, et al, ACS Nano , 2013