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

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

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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

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SLIDE 1

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

1 Australia, June 2014

Polymeric Semiconductors: Molecular Ordering, Charge Transport and Macroscale Mobility

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SLIDE 2

An Introduction to Georgia Tech

Australia, June 2014 2

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

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SLIDE 3

Polymers in Electronics and Photonics

30 mm

3 cm

3 Australia, June 2014

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SLIDE 4

Materials and Processes

  • Lithographic materials and processes
  • Silicon device processing
  • Dielectric materials (low and high-k)
  • Packaging materials

4

  • Organic semiconductor materials for

plastic electronics

  • Active device layers

Australia, June 2014

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SLIDE 5

‘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

5 Australia, June 2014

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SLIDE 6

Semiconductor Mobility Magnitudes (cm2/Vs)

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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

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SLIDE 7

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

7 Australia, June 2014

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SLIDE 8

Charge Transport in Organic Semiconductors:

Materials Issues Device Issues Process Issues

Increased electrode conductivity Increased semiconductor mobility Improved gate dielectric Decreased conductor resistivity: understand mechanism Control of carrier transport in organics Control of FET properties: effect of impurities, charge traps, etc Charge injection

Needs:

Identify critical limiting bulk/surface Improved semiconductor properties Control of thin film morphology

8 Australia, June 2014

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SLIDE 9

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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- film morphology evolution.

400 nm

Polymers in Electronics and Photonics

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SLIDE 10

MECHANISM OF CONDUCTING CHANNEL FORMATION

Order and Disorder

ROLE OF CRYSTALLINITY CONJUGATION EFFECTS: INTRA- VS INTER-CHAIN CONTROL OF MICROSTRUCTURE

 Semiconducting polymer properties strongly dependent on final thin film morphology (microstructure).

  • highly process dependent

 Microstructure development during film formation not well understood

10 Australia, June 2014

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SLIDE 11

Role of Microstructure

Sirringhaus et.al. Nature 1999, 401, 685.

Regioregularity dependent texture Effect of polymer MW

Kline et.al., Adv. Mater. 2003, 15, 1519.

  • J. Am. Chem. Soc. 2011, 133, 7244.
  • J. Phys. Chem. C 2011, 115, 11719.

0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 50 100 150 200 500 1000 1500

mobility (cm2/Vs) threshold voltage (V) time (s)

1000 2000 3000 4000 5000 600 800 1000 1200 1400 1600 1800

Raman Intensity (A.U.) Raman Shift (cm

  • 1)

Semiconductor-dielectric interface

Kim et.al., Adv. Func. Mater. 2005,15, 77

* Aiyar, et al., Chem, Mater. 2012

50 60 70 80 90 100 110

CHCl3 Xylene MCB BCl

P100 P200

W (meV)

 What is the role of microstructure?  How can microstructure be tuned?

Australia, June 2014 11

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SLIDE 12

Conducting Channel Formation

SiO2

Drain Source

n+ Si

VD

2 10

  • 5

4 10

  • 5

6 10

  • 5

8 10

  • 5

1 10

  • 4

1.2 10

  • 4

1.4 10

  • 4

50 100 150 200 250 300

  • drain current (A)

time (seconds)

 Drain current fluctuates during film formation  Polymer chains rearrange as a function of time: percolation effects  Bulk vs interface effects  Evolution of microstructure?

*in chloroform

Intermediate phase transitions?

12 Australia, June 2014

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SLIDE 13

Extending Solvent Evaporation Time

10

  • 11

10

  • 10

10

  • 9

10

  • 8

10

  • 7

10

  • 6

2 4 6 8 10 12 14

  • drain current (A)

time (hours)

10

  • 13

10

  • 11

10

  • 9

10

  • 7

10

  • 5

0.001 50 100 150 200 250 300 350 400

  • drain current (A)

time (sec.)

CHCl3 Thiophene 1,2,4-TCB 61.2 ° C 84 ° C 214 ° C

VD=-3V VG=-15V

  • Time required for conducting channel formation scales with solvent

evaporation rate

  • As evaporation proceeds, polymer concentration increases - percolation

13 Australia, June 2014

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SLIDE 14

Correlation with Structure?

10

  • 11

10

  • 10

10

  • 9

10

  • 8

10

  • 7

10

  • 6

2 4 6 8 10 12 14

  • drain current (A)

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

  • scopi
  • pic

c charge e transp spor

  • rt
  • J. Am. Chem. Soc. 2011, 133, 7244.

14 Australia, June 2014

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SLIDE 15

Sharp Onset of the Drain Current

VD 50μm

Solution drop P3HT+TCB (3mg/mL)

15 Australia, June 2014

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SLIDE 16

Raman Spectral Changes

B B+30 seconds B+60 seconds B+90 seconds B+120 seconds C

16 Australia, June 2014

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SLIDE 17

Crystalline vs Amorphous Phases

Raman spectroscopy: regio-regular P3HT (Semi-crystalline) vs. regio-random P3HT (Amorphous)

17 Australia, June 2014

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SLIDE 18

Evolving Microstructure

Raman Shift (cm-1)

1300 1350 1400 1450 1500 1550 1600

Raman Shift (cm-1)

1300 1350 1400 1450 1500 1550 1600

Raman spectrum at point C Raman spectrum at point B+30secs

1463 cm-1 from less ordered state 1446 cm-1 from highly ordered state 1446 cm-1 from highly ordered state

 Asymmetric peak shape evolves rapidly into a symmetric profile

  • Rapid nucleation and crystallization of P3HT chains

18 Australia, June 2014

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SLIDE 19

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Polarized Optical Microscopy of aged P3HT solutions show long- range order and monodomain character isotropic nematic

1.5 2.0 2.5 3.0 3.5 0.0 0.2 0.4 0.6 0.8 1.0

Normalized Absorption Energy (eV) Aged 1 Day Aged 2 Days Aged 3 Days

Low Energy Absorption from weakly interacting H-aggregates1

Aged 1 Day Aged 2 Days Aged 3 Days

Liquid Crystal Poly(3-hexylthiophene) Solutions

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SLIDE 20

Processing: Ultrasound Induced Effects

300 400 500 600 700 800

Absorbance (AU) Wavelength (nm)

300 400 500 600 700 800 300 400 500 600 700 800 300 400 500 600 700 800

Pristine 5 min sonicated Pristine 5 min sonicated

Red- shift

Pronounced shoulder Solid state Solution state

  • Film-like

properties apparent in solution state

  • Increased

backbone planarization

  • Increased π- π

stacking evidenced by (0-0) transition in solid state

Color emanates from additional low energy transitions

Ordered precursor s

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SLIDE 21

Microstructure and Crystallinity

200 nm

Pristine 30 secs 1 min 3 min 5 min 10 min

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SLIDE 22
  • Almost 2 order of magnitude

increase in mobility

  • Saturation of mobility

beyond 1-3 mins sonication 0.0001 0.001 0.01 0.1

2 4 6 8 10

Mobility (cm2V-1s-1) Ultrasonication time (mins)

SiO2

Drain Source

n++ Si

VG VD

Impact on Charge Transport

500 550 600 650 700

Absorbance (AU) Wavelength (nm)

Percolation type charge transport

Australia, June 2014 22

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SLIDE 23

Multiphase Morphology

*Holdcroft, S. et.al. Macromolecules 1996, 29, 6510.

30 nm 80 nm

1 min pristine Disordered Quasi-ordered Ordered

Australia, June 2014 23

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SLIDE 24

4.3  10-3 cm2/Vs 1.7  10-2 cm2/Vs 2,3-dimethylbutane (poor solvent, bp 58° C) Chlorobenzene (good solvent, bp 131° C) Increased lamellar packing

  • f the polymer chains

Acetone volume %

Solvent Characteristics and Molecular Ordering

Impact of binary solvent:

  • high volatility
  • hydrogen bonds with the majority solvent

Increased π- π stacking evidenced by (0-0) transition in solid state Acetone (bp 56° C) CHCl3 (bp 61° C) Acetone volume %

  • M. Chang, et al, ACS Nano, 2013
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SLIDE 25

2 2 2 2

) (

H P D

E/V        

2 2 2 2

) ( ) ( ) 4(

H2 H1 P2 P1 D2 D a

R            

1

R Ra / RED 

: Total solubility parameter E: Cohesion energy V: Molar volume D: Dispersive solubility parameter P: Polar solubility parameter H: H-bonding solubility parameter Ra: Distance between polymer and solvent Hansen parameters in Hansen space D1, P1 and H1 : Hansen solubility parameters of polymer D2, P2 and H2 : Hansen solubility parameters of solvent RED: Relative energy difference R0: Interaction radius RED < 1 polymer will dissolve RED = 1 polymer will partially dissolve RED > 1 polymer will not dissolve

Obtained by Hansen solubility parameter software

Hansen Solubility Parameter Analysis

< 5 mg/ml  Poor solvent assigned a value of “0” > 5 mg/ml  Good solvent assigned a value of “1”

P3HT Hansen solubility parameters: D: 19.45 MPa1/2 P: 3.97 MPa1/2 H: 4.19 MPa1/2 R0: 4.20 MPa1/2

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SLIDE 26

Mechanistic Illustration of Molecular Ordering

  • Molecular ordering of P3HT chains and subsequent charge transport

characteristics of resultant thin films can be influenced through solvent characteristics

  • Hansen solubility parameters provide valuable insight into the relationships

between thin-film morphology, molecular ordering and device performance

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SLIDE 27

Generic P3HT self- assembly: a case for 2- step crystallization

P3HT Aggregation Revisited

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SLIDE 28

Rational Design of Branched Side Chains for Enhanced Mobility

Polymer Design:

  • DPP deepens HOMO energy level further enhancing air

stability

  • ICT (formed by BT-thiophene-DPP coupling) narrows

bandgap

  • Fused feature of DPP facilitates charge carrier transport

Side Chain Design:

  • Enhance pTBTD solution processability
  • Enhance π-π intermolecular interaction of pTBTD via

branch position

Electron deficient Diketopyrrolopyrrole (DPP) Side-Chain Engineering Australia, June 2014 28

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SLIDE 29

pTBTD-5DH (MW: 44K, PDI: 2.3) pTBTD-5DH_(H) (MW: 50K, PDI: 2.1) pTBTD-2DT (MW: 28K, PDI: 2.5) pTBTD-OD (MW: 14K, PDI: 2.5)

Branching remote from backbone facilitates polymerization and solution processability.

Polymer Synthesis

Australia, June 2014 29

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SLIDE 30

π-π stacking distance

Polymer Characterization

UV/vis absorption spectroscopy

  • π-conjugation enhances due to branching

position Bathochromatic shift

pTBTD-5DH(H) pTBTD-5DH pTBTD-2DT pTBTD-OD d-spacing (Å) 24.55 24.88 22.07 22.29 π-π stacking (Å) 3.59 3.61 3.73 3.62

  • π-π interchain stacking is narrowed due to branching position away

7b 7a 7c

pTBTD_5DH

  • π-π intermolecular interaction enhances

due to branching position (reduced steric hindrance between side chains)

2D-GIWAXS

Bathochromatic shift

Australia, June 2014 30

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SLIDE 31

Mobility and Side Chain Design

Solubility π - π Intermolecular Interaction 5-DH (branching remote to backbone) Superior Superior 2-DT (branching close to backbone) Superior Reduced OD (linear chain) Reduced Superior

Remote branching merges the advantages of Branched and linear chains

Polymer thin film Australia, June 2014 31

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SLIDE 32

Conclusions

 All aspects of structure, regioregularity, molecular weight, molecular weight distribution, substitution pattern, etc. have a significant impact on conjugated polymer performance.  Impact of intermediate phases between the isotropic solution and crystalline states requires investigation.

32 Australia, June 2014

Molecular structure in conjunction with materials processing influences electronic properties/device performance of polymeric semiconducting materials

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SLIDE 33

Acknowledgements

Bell Labs, Alcatel-Lucent

  • O. Nalamasu
  • S. Yang
  • E. A. Chandross
  • Z. Bao
  • H. E. Katz
  • A. Maliakal
  • S. Vaidyanathan
  • S. Liu

Georgia Tech

Avishek Aiyar*

Mincheol Chang Rui Chang Dalsu Choi Ping Hsun Chu Boyi Fu Jeff Hernandez Ji-Hwan Kang Nabil Kleinhenz

Jiho Lee*

Nils Persson

Ashwin Ravi Sankar*

Gang Wang

Zhaokang Hu Byoungnam Park Elena Argyropais Daniel Acevedo*

Nathan Bates

Jessica Daigle Jessica Izumi* John Jang

Yundi Jiang Abishek Mukund Orayne Mullings Jamillah Parsons

Caryn Peeples* Luis Reyes* Sven Schlumpberger

Mohan Srinivasarao Karthik Nayani

Min Sang Park* Jung-Il Hong*

David Collard Martha Grover

Rakesh Nambiar*

John Reynolds

Laren Tolbert

Samuel Graham 33 Australia, June 2014

Funding NSF – CMDITR NSF – DMR AFOSR ACS-PRF Georgia Tech