Eight19 Limited Advanced Electron Transport Materials for ... · Advanced Electron Transport...
Transcript of Eight19 Limited Advanced Electron Transport Materials for ... · Advanced Electron Transport...
Advanced Electron Transport Materials for Application in Organic
Photovoltaics (OPV)
Alan Sellinger
GCEP Research Symposium 2011
October 5, 2011
1
Eight19 Limited
Why Solar?
1 % of land with solar cells could meet our electricity needs
6 Boxes at 3.3 TW Each
• Amount of solar energy in hours, received each day on an optimally tilted surface during the worst month of the year.
3 Germany 50%
USA 9%! Total PV installation:
Types of Solar Technologies
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Lowest cost $/W
Attractive properties:
•Abundant: ~100,000 tons/year
•Mature industry/markets
•Low materials cost: ~$1/g 15¢/m2
•Low-cost processing: printing
•Excellent stability
•Non-toxic
CuPc Copper Phthalocyanine
Why Organic Semiconductors?
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Organic LEDs for Displays
Organic LEDs for Lighting
New Applications for Organic Solar Cells
Chemistry Nobel Prize Day! Organic Electronics: Combination of 3 Nobel Prizes!
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S
O O
n
PEDOT
C60 C70
• 2000 Nobel Prize in Chemistry - Alan Heeger, Alan G. MacDiarmid, Hideki Shirakawa for their discovery and development of conductive polymers
• 2010 Nobel Prize in Chemistry - Richard F. Heck, Ei-ichi Negishi, Akira Suzuki for palladium-catalyzed cross couplings in organic synthesis • C-C bond formation
• 1996 Nobel Prize in Chemistry - Robert F. Curl Jr., Sir Harold Kroto, Richard E. Smalley for their discovery of fullerenes (C60)
N
O
O
NS
N
N
O
O
S
S
C6H13
S
S
C6H13
C6H13
C6H13
n/4
Motivation for Organic-Based PV
• Lower production cost
– Roll-to-roll coating
– Inexpensive active materials
– Inexpensive processing
– Lower capital cost
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Energy Payback Time (yrs)
CO2 Emission in Production (g)
Crystalline silicon 2.3 1560
Thin film (CIGS, CdTe, etc.) 1.2-3.2 900-2560
Polymer PV (Glass substrate) 1.3 820
Polymer PV (Plastic substrate) 0.2 130
Inhabitat.com
Roes et al., Prog. Photovoltaics. 2009 (17) 372-393
• Lower environmental impact - $/W
Cost Analysis for Solar Cell Technologies
Ingot Paint
Crystalline Si
Thin Film
Organic/Hybrid
Material and Manufacturing Cost
today
near term/today
future
Eff
icie
ncy
•$/W basis competitive
Recombination
Charge Separation
+
-
++
+
+ + ++
+ +-
-
--
-
- - -
Generation
-
Diffusion
Drift/Diffusion
Donor Material Acceptor Material
Photon
Exciton
HoleElectron
Photon
An
od
eC
ath
od
eSimplified Working Principle
Kietzke, T., Adv. OptoElect., 2007, Article ID 40285.
What is an Organic Photovoltaic?
50-200 nm
Progress in Organic Solar Cells
Solution processes (Polymer, PCBM) Vacuum processed
2005 2010
•Similar development for organic solar cells as for amorphous silicon 20 years ago
•Both approaches are reaching nearly similar efficiencies
•Improvements are largely materials discovery based
10%? Mitsubishi 2011
?
8.3% Heliatek 2010
9% Solarmer 2011
Estimated lifetimes of OPVs
Burn-in loss Burn-in time
Lifetime in linear regime*
P3HT:PCBM 16% 55 days 3.5 years
PCDTBT:PC70BM 27% 38 days 6.7 years
*Lifetime assumes 5.5 hrs/day of one-sun intensity1
1. C. Peters, M. McGehee, Adv. Energy Mater. in press, 2011
• Heliatek (BASF and Bosch) has achieved 30 year lifetimes with tandem OPVs2
2. www.heliatek.com
Bulk heterojunction (BHJ) Polymer Solar Cell
• Advantages:
– Solution processing (roll-to-roll), increased contact area between active phases,
• Disadvantages:
– Difficult to achieve optimum morphology, polymers generally less pure than molecules, solvent dependence
Current world record: • 8-10%
• Extrapolated lifetimes >6 years
http://www.solarmer.com/
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High-efficiency BHJ solar cells
• Record OPV cells ALL use fullerene derivatives
• Recent development based on donor materials discovery
PBT7:PC70BM
7.4% PCE
Liang et al., Adv. Mat. 2010 (22) E135-E138
PCDTBT:PC70BM
6.1% PCE
Park et al., Nat. Phot. 2009 (3) 297-303
P3HT:ICBA*
6.5% PCE
Zhao et al., Adv. Mat. 2010 (22) 4355-4358
* ICBA: Indene-C60 Bisadduct
PC60BM
O
O
PC70BM
O
O
PC70BM
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Drawbacks for fullerenes
Reduced solar spectrum
absorption
300 400 500 600 700 8000
0.5
1
1.5
2
2.5x 10
5
Wavelength (nm)
Ab
so
rpti
on
Co
eff
icie
nt
(M-1
cm
-1)
New Acceptor
PC60
BM
PC70
BM
Lower VOC
-3.1 eV
-5.1 eV
P3HT
PCBM
-4.3 eV
-3.7 eV
-6.1 eV
-5.6 eV
-3.1 eV
-5.1 eV
P3HT -3.9 eV
-6.1 eV
New
Acceptor
-3.4 eV
-5.9 eV
Difficult synthesis and purification = Higher cost
PC60BM: $50/g
CuPc: $1-5/g
Fullerene acceptor – up to 10% of total PV system cost
Roes et al., Prog. Photovoltaics. 2009 (17) 372-393
Effect of Production Steps on Cost
• Significant increases (2X) for higher purification
• PC71BM approximately 3.4X more expensive than PC61BM
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Anctil et al., Environ. Sci. Technol. 45, (2011) 2353-9
O
OO
O
PC60BM PC70BM
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Non-fullerene acceptors
• Lower efficiencies due to lower JSC and lower FF
POPT:CN-PPV
2% PCE
Holcombe et al., J. Am. Chem. Soc. 2009 131 (40)
14160-14161
P3HT:99’BF
~2% PCE
Brunetti et al., Ang. Chem. Int. Ed. 2010 49 (3) 532-536
Verreet et al., Adv. Ener. Mat. . 2011 (1) 565-568
POPT:EV-BT
1.4% PCE
Woo et al., Chem. Mater. 2010 22 (5) 1673-1679
SubPc:FSubPc dimer
2.5% PCE (vacuum)
OO
O
O
NC
CN
O
O
n
NS
N
N
NNC
NCN
NCN
CN
N N
N
N
N
B
N
N
N
B
N
NN
N
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
Cl
Cl
New Acceptors based on Vinazene
• Original applications as high nitrogen containing materials for reduced flammability. Without vinyl groups has been used in the agriculture sector (fertilizers)
• Their highly electron deficient properties make them candidates as acceptor materials in organic electronic applications
Vinazene 2-vinyl-4,5-dicyanoimidazole 4,5-dicyanoimidazole
HN N
NC CN
HN N
NC CN
R
HN N
NC CN
R
Commercially available
Alkylation of 2-Vinyl-4,5-dicyanoimidazole
NHN
NC CN
Vinazene
Acetone, K2CO3
Acetone, K2CO3
I
NN
NC CN
1-Butylvinazene (90%)
NN
NC CN
1-Hexylvinazene (90%)
NN
NC CN
1-Ethylhexylvinazene (56%)
DMF, K2CO3, 70oC
Reflux
Reflux
I
Br
Tunable Synthesis: Heck Chemistry
Shin R.Y.C., Sonar, P., Siew, P.S., Chen, Z.C., Sellinger, A., J. Org. Chem., 2009, 74 (9), 3293–3298.
Optical properties of selected vinazene derivatives
300 350 400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lis
ed
In
ten
sit
y (
a.u
.)
Wavelength (nm)
1
4
5
10
13
350 400 450 500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lis
ed
In
ten
sit
y (
a.u
.)Wavelength (nm)
1
4
5
10
13
UV spectra of the molecules in toluene
PL spectra of the molecules in toluene
Significant absorption in visible spectrum
(1)
NS
N
(4)
NS
N
S
S
(5)
(10) (13)
Vinazenes used for OPVs
HV-BT
EV-BT Better solubility
N
N
CN
CN
N
N
NC
NC
NS
N
Solubilizing groups for
solution processing
Electron accepting sites
Conjugated
chemical links
•Can be thermally sublimed as well
Preparation of OPV Devices
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New Electron Acceptor
POPT donor polymer
• Solution processed active layer
POPT with HV-BT
• Kietzke, T., Shin R.Y.C., Egbe, D.A.M., Chen, Z.K., and Sellinger, A., Macromolecules, 2007, 40, 4424-4428. • Shin R.Y.C., Kietzke, T., Sudhakar, S., Dodabalapur A., Chen, Z.K., and Sellinger, A., Chem. Mater., 2007, 19(8), 1892-
1894. • Woo, C.W., Holcombe, T.W., Tam, T.L., Sellinger, A., Frechet, J.M.J., Chem. Mater. 2010, 22 (5), 1673–1679
Voc = 0.62 V, FF = 0.40, PCE = 1.41%
POPT
Can we make better acceptors?
N
N
CN
CN
N
N
NC
NC
NS
N
Solubilizing groups for
solution processing
Electron accepting sites
Conjugated
chemical links
•Corresponding electron donor has charge mobility (cm2/V sec) in 10-4 range. Is charge transport mis-match a problem?
Improving Organic Acceptor Materials
Improved Acceptor Materials?
NS
N
N
O
O
N
O
O
Acceptor Materials: Computational Studies
Ground-state geometries
LUMO
HOMO
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Synthetic Scheme for PI-BT/NI-BT
PI-BT
PI-BT
NI-BT
NI-BT
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New Acceptor Properties
• Larger ELUMO,Acc – EHOMO,Don than for P3HT:PC60BM
200 300 400 500 600 700 800 9000
0.2
0.4
0.6
0.8
1
Wavelength (nm)
No
rmal
ized
Ab
sorp
tio
n (
arb
. u
nit
s.)
PI-BT
NI-BT
Thin Film
-3.69 eV
-6.05 eV
-3.1 eV
-5.1 eV
-3.84 eV
-5.99 eV
-3.1 eV
-5.1 eV
P3HT
PI-BT NI-BT
P3HT
ELUMO ~ 0.6 eV
EHOMO ~ 0.9 eV
ELUMO ~ 0.7 eV
EHOMO ~ 0.9 eV
• Peak acceptor absorption is in visible spectrum
• Tunable LUMO – expected higher Voc than fullerenes
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J-V Curve – Optimal Devices
• Believed highest efficiency BHJ with non-fullerene acceptor and commercially available P3HT donor
P3HT:PI-BT P3HT:NI-BT
Solvent Chlorobenzene Chloroform
Thickness (nm) ~ 90 ~ 120
Cathode LiF(1nm)/Al Ca(7nm)/Al
Anneal Pre/Post Post Pre
Ann. Temp/Time 110 C/3min 110 C/10min
Jsc (mA/cm2) 4.7 1.2
Voc (V) 0.96 0.51
FF 0.56 0.35
PCE (%) 2.54 0.22
-1 -0.5 0 0.5 1 1.5-8
-6
-4
-2
0
2
4
6
8
Voltage (V)
Cu
rre
nt D
en
sity (
mA
cm
-2)
PI-BT
NI-BT
• High voltage as expected with higher-lying LUMO
• Why is the efficiency for NI-BT 10X lower?
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EQE Spectra of P3HT:PI-BT Device
• Significant photocurrent generation from acceptor absorption
300 400 500 600 700 800 9000
0.1
0.2
0.3
0.4
0.5
Wavelength (nm)
EQ
E (
%)
or
Ab
so
rptio
n (
arb
. u
nits) P3HT:PI-BT EQE
P3HT Absorption
PI-BT Absorption
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Molecular Simulation – Ground State Geometry
• Twisting of NI-BT molecule due to steric interactions may prevent crystallization in films
PI-BT NI-BT
2.06
2.06 27.3
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GIXS – Acceptor Crystallization
• More acceptor peaks in PI-BT sample than NI-BT
P3HT:PI-BT (CB) P3HT:NI-BT (CF)
P3HT Only - CB P3HT Only - CF
OPV Conclusions
• Very promising new acceptor materials as potential replacement for fullerene derivatives
– Synthesized in minimal step/moderate yield reactions
– Tunable energy levels
– Anticipated to be much less expensive than fullerenes
• Initial device performance very promising
– From initial PCE of 0.1% >2.54% PCEmax, 5 years of R&D, (5-7 total researchers)
– Close interaction between chemists and device engineers/physicists
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Acknowledgements
• Co-PI - Prof. Michael McGehee
• Synthesis – Dr. Xu Han (now at DuPont R&D Shanghai), Dr. Andrew Higgs Device Fabrication/Characterization – Jason Bloking, Jack Kastrop
• Quantum Calculations – Dr. Chad Risko, Dr. Joe Norton, Laxman Pandey, Dr. Jean-Luc Bredas (Georgia Tech)
• Funding Sources: