Amphiphilic Block Copolymers for Morphology Control in Organic...
Transcript of Amphiphilic Block Copolymers for Morphology Control in Organic...
Amphiphilic Block Copolymers for Morphology Control in Organic Solar Cells
Valerie Mitchell ACAP Fellow, University of Melbourne
2 4 Dec 2018 Bio21 Institute Valerie D. Mitchell
Jones Group, University of Melbourne
Can we improve the industrial viability of organic photovoltaics through material design?
3 4 Dec 2018 Bio21 Institute Valerie D. Mitchell
Johnson, K.; Huang, Y.-S.; Huettner, S.; Sommer, M.; Brinkmann, M.; Mulherin, R.; Niedzialek, D.; Beljonne, D.; Clark, J.; Huck, W. T. S.; Friend, R. H., J. Am. Chem. Soc. 2013, 5074-5083
Importance of Morphology
Bulk Heterojunction Solar Cell
Efficiency decreases with • Large domains (>20 nm) • Small domains (<7 nm) • Lack of percolation pathways
⇢ Exciton decay ⇢ Recombination ⇢ Recombination
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Issues to address for industrial application
In order to be industrially viable, these morphologies must be:
• Stable
• Reproducible
• Obtainable with minimal and environmentally friendly processing
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Block Copolymer Self-Assembly
Block Copolymers
• Covalent linkage of donor and acceptor molecule
• Self-assembly leads to well defined domains
• Allows direct control over size and interface of the donor and acceptor domains
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Challenges in Block Copolymer Applications
• Morphological control: achieving phase separation
• Synthetic difficulties: reliance on polycondensations
• Purification: Isolation of block copolymer
NS
NS
H13C6
SS
C6H13
H13C6
n m
SSPh
H13C6 C6H13
H17C8 C8H17
NS
NS
H13C6
SS
C6H13
H13C6
n m
SSPh
H17C8 C8H17
NS
NS
H13C6
SS
C6H13
H13C6
n m
SSPh
R2 R2
R1 R1
R1 = CH3, C6H13, C8H17
R2 = C6H13, 2-ethylhexyl
P3HT-b-PFTBT
P3HT-b-PFT6BT
3.1% efficiency
No microphase separation
1. Sommer, M. et al. Macromolecules 2012, 45(10): 4142-4151 2. Smith, K. A. et al. Macromolecules 2015, 48(22): 8346-8353.
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Challenges in Block Copolymer Applications
• Morphological control: achieving phase separation
• Synthetic difficulties: reliance on polycondensations
• Purification: Isolation of block copolymer
BB AA+A +
m
m
Am
NS
NS
H13C6
SS
C6H13
H13C6
n m
SSPh
H13C6 C6H13
H17C8 C8H17
NS
NS
H13C6
SS
C6H13
H13C6
n m
SSPh
H17C8 C8H17
NS
NS
H13C6
SS
C6H13
H13C6
n m
SSPh
R2 R2
R1 R1
R1 = CH3, C6H13, C8H17
R2 = C6H13, 2-ethylhexyl
P3HT-b-PFTBT
P3HT-b-PFT6BT
P3HT-b-PFTBT, 3.1% efficiency • 52% block copolymer, • 48% additional polymer
contaminants
1. Guo C. et al. Nano Lett 2013, 13(6): 2957-2963.
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Amphiphilic Block Copolymers
Amphiphilic Analog
NSN
S
H13C6
SS
C6H13
H13C6
nSS
OO4 4
b.
H13C6 C6H13
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
n
OO4 4
C6H13
PhS
H13C6
SS
C6H13
H13C6
nBr
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
H13C6
n
P3HT-b-PFTEGT6BT
• Enhanced phase separation
• Increased solubility
• Facilitate purification
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Synthesis of P3HT-b-PFTEGT6BT
S
H13C6
SS
C6H13
H13C6
nBr +
NS
NS
H13C6
SS
C6H13
H13C6
n m
SS
OO4 4
NS
NSS
OO4 4
BB Br BrO
O
O
O
Ph
+
H13C6 C6H13
H13C6 C6H13
NS
NSS
OO4 4
BB Br BrO
O
O
O+
H13C6 C6H13
NS
N
m
SS
OO4 4
Ph
H13C6 C6H13
Ph
1 eq 0.9 eq
0.07 eq 1 eq 1 eq
Pd(PPh3)4TEA-OH (20%)Aliquat 336Toluene90˚C O/N
Pd(PPh3)4TEA-OH (20%)Aliquat 336
Toluene90˚C O/N
P3HT-b-PFTEGT6BT Synthesis
V. D. Mitchell; W. W. H. Wong; M. Thelakkat; D. J. Jones, Polym. J., 2017, 49, 155-161.
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Purification of Reaction Mixture
CHCl310% MeOH
CH2Cl210% MeOHCHCl3
P3HT PFTEGT(R)BT P3HT-b-PFTEGT(R)BTPolymer mixture
loaded on silica gel
Purification Technique
-Amphiphilic design allows easy separation of polymeric impurities -Improvement over other reported systems with no selectivity between blocks
Polymeric impurities BCP Product
NSN
S
H13C6
SS
C6H13
H13C6
nSS
OO4 4
b.
H13C6 C6H13
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
n
OO4 4
C6H13
PhS
H13C6
SS
C6H13
H13C6
nBr
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
H13C6
n
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Properties of P3HT-b-PFTEGT6BT
V. D. Mitchell; W. W. H. Wong; M. Thelakkat; D. J. Jones, Polym. J., 2017, 49, 155-161.
Mn(kg/mol) PDI P3HT(%) Yield(%)
P3HT 17.6 1.1 41P3HT-b-PFTEGT6BT 37.3 1.9 47 26
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AFM of Homopolymer Blend and BCP
As-Spun Annealed
P3HT/PFTEGT6BT Blend • As-spun: some fibrillar domains • Nodules after annealing
BCP/P3HT/PFTEGT6BT Blend (50:25:25) • As-spun: some linear domains • Mostly featureless
P3HT-b-PFTEGT6BT • Nice linear domains in as-spun films,
retained with annealing
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Resonant Soft X-Ray Scattering Domain Analysis
Showed domains of 17 nm in as-spun films, 20 nm after annealing
2
46
10-7
2
46
10-6
2
46
I2 q (a
u)
90.01
2 3 4 5 6 7 8 90.1
2 3 4 5 6
q (nm-1)
2
3
4
5
6
7
8
9
2
3
4
5
6
10
100
d spacing (2π/q) (nm)
P3HT-b-PFTEGTBT As-Spun P3HT-b-PFTEGTBT Annealed As-spun roughness Annealed roughness
Thanks to A/Prof Chris McNeill (Monash University, Australian Synchrotron), Dr Eliot Gann (NIST), and Dr. Lars Thomsen (Australian Synchrotron) for RSoXS and NEXAFS measurements
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P3HT-b-PFTEGT6BT
• Great morphology
• Poor performance due to lack of electron mobility
NSN
S
H13C6
SS
C6H13
H13C6
nSS
OO4 4
b.
H13C6 C6H13
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
n
OO4 4
C6H13
PhS
H13C6
SS
C6H13
H13C6
nBr
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
H13C6
n
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P3HT-b-PNDIegT2 Materials
N
N
OO
O O
O
O O
O2 2
O
O O
O2 2
S
C6H13
SS
C6H13
C6H13
nS
Sm
N
N
OO
O O
O
O O
O2 2
O
O O
O2 2
SS
m
P3HT-b-PNDISDEGT2 PNDISDEGT2CHCl3 wash
DCM/MeOHwash
CHCl3/MeOHwash
P3HT PNDIEGT2 BCP
Mn(kg/mol) PDI P3HT(%) Yield(%)
P3HT 19.3 1.1 51P3HT-b-PNDISDEGT2 71 1.6 26 12
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Solution UV/Vis
300 400 500 600 700 8000.0
0.5
1.0
0.0
0.5
1.0
300 400 500 600 700 800
Wavelength (nm)
Nor
mal
ized
Abs
orba
nce
(a.u
.)
P3HT-b-PNDIDEG
T2
CBTolTol/Ani
PNDIDEG
T2
• Preaggregation in solution has been shown to induce microphase separation in film
• P3HT block unchanged
• PNDI block shows some aggregation
Solution UV/Vis in chlorobenzene, toluene, or toluene/anisole (1:1)
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AFM of BCP films
200nm200nm200nm200nm200nm200nm 200nm200nm200nm200nm200nm200nm200nm200nm
6.276.276.276.276.276.276.276.276.27
0.000.000.000.000.000.000.000.000.00
-6.27-6.27-6.27-6.27-6.27-6.27-6.27-6.27-6.27
°2.652.652.652.652.652.652.652.652.65
0.000.000.000.000.000.000.000.000.00
-2.65-2.65-2.65-2.65-2.65-2.65-2.65-2.65-2.65
°
200nm200nm200nm200nm200nm200nm200nm200nm200nm200 nm 200 nm 200 nm200 nm 200 nm
3.403.403.403.403.403.403.403.40
0.000.000.000.000.000.000.000.000.00
-3.40-3.40-3.40-3.40-3.40-3.40-3.40-3.40-3.40
3.4˚
-3.4˚
0.0˚
3.403.403.403.403.403.403.403.40
0.000.000.000.000.000.000.000.000.00
-3.40-3.40-3.40-3.40-3.40-3.40-3.40-3.40-3.40
6.3˚
-6.3˚
0.0˚
3.403.403.403.403.403.403.403.40
0.000.000.000.000.000.000.000.000.00
-3.40-3.40-3.40-3.40-3.40-3.40-3.40-3.40-3.40
2.7˚
-2.7˚
0.0˚
Chlorobenzene Toluene Toluene/Anisole(50/50)
Distinct variations in microstructure depending on solvent choice visible in AFM. Globular domains in CB, linear in toluene and toluene/anisole.
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GIWAXS of BCP films
As-spun Annealed
CB
Tol/Ani
• Greater degree of P3HT crystallization in films spun from CB
• Higher order reflections attributable to both blocks with annealing
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RSoXS of BCP films
Anisole/TolueneChlorobenzene
Thanks to A/Prof Chris McNeill (Monash University, Australian Synchrotron), Dr Eliot Gann (NIST), and Dr. Lars Thomsen (Australian Synchrotron) for RSoXS and NEXAFS measurements
-Clear peak in film deposited from chlorobenzene indicates 22 nm domains. -Weak separation in toluene/anisole, annealing film at 220˚C for 15 minutes did not increase phase separation
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Device performance
CB 2.3 0.54 41 0.5Tol/Ani 3.1 0.54 48 0.8
Solvent J SC
(mA/cm2)VOC (V) FF (%) PCE (%)
P3HT-b-PNDIDEGT2
AgMoO3
ZnOITO
• Despite weaker phase separation, the film deposited from Tol/Ani performed better than the CB film
• The morphology obtained with preaggregation of PNDI is more favorable
Thanks to Dr. Jegadesan Subbiah (University of Melbourne) for device measurements
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Conclusions
• Our amphiphilic block copolymer system improved purification and phase separation
• We demonstrated self-assembly in as-spun films and stability with annealing
• We showed the morphological benefit of BCP purification
• Future work: develop synthetic strategies to allow efficient incorporation of high-perfomance polymers
200nm
Self-AssemblyDonor-AcceptorBlock Copolymer
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Acknowledgements
Monash University and the Australian Synchrotron Dr. Eliot Gann, Prof. Chris McNeill and Dr. Lars Thomsen for RSoXS and NEXAFS measurements, analysis, and beamtime Nigel Kirby, Stephen Mudie, and Adrian Hawley at the SAXS/WAXS beamline
University of Melbourne Dr. David Jones, Prof Ken Ghiggino, and Dr. Wallace Wong Jianing Lu for advice on AFM measurements Thanks to members of the Jones and Wong labs past and present
Sincere thanks to
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Analysis of Purification
GPC Analysis of Fractions
P3HT PFTEGT6BT P3HT-b-PFTEGT6BT
Insets show traces from isolated homopolymers for comparison
10 15 20
DCM/MeOH
Abso
rban
ce (a
.u.)
10 15 2
CHCl3
0.00.20.40.60.81.01.2
12 14 16 18 20
CHCl3/MeOH
360 nm 450 nm
Retention time (min)
0
0 12 14 16 181 12 14 16 1801 01
NSN
S
H13C6
SS
C6H13
H13C6
nSS
OO4 4
b.
H13C6 C6H13
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
n
OO4 4
C6H13
PhS
H13C6
SS
C6H13
H13C6
nBr
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
H13C6
nNSN
S
H13C6
SS
C6H13
H13C6
nSS
OO4 4
b.
H13C6 C6H13
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
n
OO4 4
C6H13
PhS
H13C6
SS
C6H13
H13C6
nBr
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
H13C6
nNSN
S
H13C6
SS
C6H13
H13C6
nSS
OO4 4
b.
H13C6 C6H13
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
n
OO4 4
C6H13
PhS
H13C6
SS
C6H13
H13C6
nBr
NSN
m
SS
OO4 4
Ph
H13C6 C6H13
S
H13C6
SS
C6H13
H13C6
n
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Analysis of Charge Mobility
μh#(cm2/V!s)#100˚C% 150˚C% 220˚C%
P3HT# 1.25x10*2%P3HT/b/PFTEGTBT# 1.52x10*4% 7.31x10*4% *%P3HT/b/PFTEGT6BT# 4.22x10*5% 9.89x10*4% 1.13x10*3%
Hole mobilities (µh) calculated from the slope of (Id)0.5 vs V(g) in the saturated regime
-Materials showed no electron transport in OFET configuration in as-spun films or after annealing at 100˚C, 150˚C, and 220˚C for 10 min -Measurement of hole mobility as a function of annealing showed development of charge percolation pathways -Charge mobility determined by SCLC confirmed low electron mobility
μe##(cm2/V!s)#
Avg#μe#(cm2/V!s)#
μh##(cm2/V!s)#
Avg#μh##(cm2/V!s)#
PFTEGTBT#4.5x10'10( 1.7x10'9( 1.4x10'4( 8.4x10'5(3.0x10'9( 2.7x10'5(
PFTEGT6BT#1.3x10'8(
1.3x10'8(2.3x10'8(2.0x10'9(
SCLC Analysis
OFET Analysis
SCLC analysis performed with the help of Dr. Chetan Singh, Bayreuth University
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Analysis of Device Performance
Active'Layer'(~100'nm)'Al'(100'nm)'
PEDOT:PSS'(40'nm)'ITO'Glass'Substrate'
Active'layer'(~100'nm)'
Ag'(100'nm)'
ZnO'(40'nm)'ITO'Glass'Substrate'
MoO3'(10'nm)'
JSC$$(mA/cm2)$
VOC$(V)$
FF$(%)$
PCE$(%)$
P3HT5b5PFTEGTBT$Inverted$
PA$ 0.22$ 0.89$ 27.6$ 0.05$A$ 0.25$ 0.32$ 37.8$ 0.03$
Normal$PA$ 0.18$ 1.03$ 27.2$ 0.05$A$ 0.63$ 0.95$ 21.2$ 0.13$
P3HT5b5PFTEGT6BT$Inverted$$
PA$ 0.18$ 0.80$ 35.9$ 0.05$A$ 0.10$ 0.47$ 39.9$ 0.02$
Normal$PA$ 0.03$ 0.50$ 23.1$ 0.003$A$ 0.03$ 0.53$ 24.5$ 0.003$
Normal Architecture Inverted Architecture
PA- before annealing, A- annealed at 150˚C for 10 min
Device analysis performed with the help of Dr. Chetan Singh, Bayreuth University
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UV/Vis
4.1 3.1 2.5 2.1 1.8 1.6
300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0 Photon Energy (eV)
Abso
rban
ce (
a.u.)
Wavelength (nm)
PFTEG
T6BT
P3HT-b-PFTEG
T6BT
P3HT
.