Tobin Marks Presentation

Inorganic and Organic/Plastic
Photovoltaics
Traditional Si
Plus
Power Efficiency
~ 24.7% lab
~ 16 - 20% market
Durable
Minus
High Module Cost
$ 2.38/W
Mechanically Rigid, Heavy
Other Inorganics
CIGS < $ 1.00/W
CdTe ~$ 0.86/W
a-Si < $ 1.00/W
(toxicity, earth abundance
issues)
Organic (OPV)
Plus
High-Throughput Mfg.
Cheap, Earth-Abundant Materials
Mechanically Flexible
Tailorable Properties
Integrate with Bldg. Materials
Large Voc, Optical Absorption
Minus
Power Efficiency
3 → 10% (Increasing Dramatically!)
Durability: Little Data
Est. ~$ 0.25/W
Possibility of a BreakThrough, of Learning
Something Really New!
OUTLINE
Engineering Interfaces in Organic Photovoltaics
 Can We Learn from OLEDS?
 Organic and Inorganic Interfacial Layers
New Donor Materials
 Low Bandgaps, Microstructure on Electrode
 New Nanoscale Interfacial Layers
Transparent Conducting Electrode Materials
 Opportunities?
Where are We? How to Move Ahead?
Acknowledgments
Henry Yan
Michael Irwin
Alex Hains
Antonio Facchetti
Diego Bagnis
Jun Liu
Brett Savoie
Rocio Ortiz
Mimi Luo
Charusheela Ramanan
Jon Servaites
Ben Leever
Xugang Guo
Assunta Marrocchi
Stephen Loser
Nanjia Zhou
Ian Murray
BP Solar
NREL
Bob Chang
Lin Chen
Mike Wasielewski
Mark Ratner
Sam Stupp
Mark Hersam
Mike Bedzyk
Art Freeman
Luping Yu (U. Chicago)
Dave Ginley, Keith Emery (NREL)
Mike Durstock (AFML)
Fabio Silvestri, Giorgio Pagani (U. of
Milano)
Juan Bisquert (U. Jaume I)
DOE-EFRC
ONR
NSF-MRSEC
I. Organic
Photovoltaic (OPV) Challenges
How To:
•
•
p-Type
Donor
h+
h+
e-
•
en-Type
Acceptor
h+
TCO
h ≥
Eg
•
Hole-Transporting
Layer
eV
z
e-
•
Capture Maximum Solar
Radiation
Create Long-Lived Excitons
Efficiently Split Excitons,
Using Minimum Energy
Achieve High Hole & Electron
Mobilities
Efficiently Extract Charge at
the Electrodes
Low-Φ
metal
Terrestrial Solar
Spectrum
Review: Servaites, J.D.; Ratner, M.A.; Marks, T.J. Energy Environ. Sci., 2011, 4, 4410.
OLED Function: Implications for OPVs
e- + h+ → exciton → photon
Interfaces All Over!
Samsung
$2.5B in 2011
Spin-Coated Polymer OLED
V
Metal cathode
ORGANIC LAYER
hv
ITO anode
energy [eV]
LUMO
e-
ITO
Metal cathode
ETL
V
EML
hv
h
Metal
LUMO
ehv
HTL
ITO anode
HOMO
Polymer
energy [eV]
Vapor-Deposited Molecular OLED
h
v+
h+
h
HTC, Nokia,
Pantech,
Motorola,
etc.
+
h+
HOMO
ITO HTL EML ETL Metal
OLED Frailties. Self-Assembled Interfacial Layers
(IFLs)
TPD
N
N
N
OLED Layer Structure
N
N
N
O
O
Si
O
O Si O
O
N
Cu
N
N
N
Interlayer
Interlayer
Cu(Pc)
Self-Assembled TPDSi2 monolayer
Affects of Thermal Stress
50μ
TPDSi2 SAM
Bare ITO
Cu(Pc) Buffer
50 μ
Characterization: Synchrotron x-ray reflectivity, AFM, conducting AFM, complex
impedance spectroscopy, electrochemistry, molecular substituents
Adv. Mater.’04, J. Amer. Chem. Soc. 2005, 2007
Effects of Interfacial Layers on OLED Performance,
Durability, Hole Injection
Device Layer Structure
N
N
N
N
N
N
N
N
Interlayer
O
Si
O
O
Interlayer
N
O Si O
O
Cu(Pc) Buffer layer
TPDSi2 Interfacial layer
Electroluminescent Response
5
TPDSi2
4
10
104
Cu(Pc)
0.8
100
Cu(Pc)
0.6
10
10
0.4
1.0
0.2
0.1
0
5
10
15
20
Voltage (v)
25
30
1000
1.0
Bare
ITO
100
TPDSi2
TPDSi2
1.2
1000
35
Thermal Stress Affects
on EL Response
External Quantum Efficiency
1.4
10
0
N
Cu
Cu(Pc)
1.0
Bare ITO
0
5
10
15
Voltage (v)
20
25
0.1
0
5.0
10
15
20
25
30
Voltage (v)
102 -103 X Enhanced Hole Injection; Impedance: Suppression of Interfacial Defects
J. Amer. Chem. Soc. 2005, 2007; J. Appl. Phys. 2006; Chem. Mater. 2007, APL 2008, Org. Electronics 2008
Proposed Organic Photovoltaic
Design Based on OLED Experience
New TCO
materials for
alternative
anodes
IFL
Hole-extracting,
electron-blocking layer
Donor-Acceptor
Interface
Donor
Phase
Cathode
Anode
hv
IFL
Interfacial
stabilizers
Acceptor Phase
Electronextracting
hole/excitonblocking layer
IFL
Science Issues/ Technology Implications
ITO-Alternative TCOs
Interfacial Layers
Film Growth
Approximate Energy Levels for MDMO-PPV:PCBM Cell with
10-15 nm Interfacial Layer (IFL)
N
N
*
+
TPDSi2
Cl
Si Cl
Cl
N
C8H17
*
n
C8H17
TFB
C4H9
Interfacial
Layer/Blend
Cl Si
Cl Cl
•
Hole transporting/electron
blocking interfacial layer
μhole = 5 x 10-4 cm2/Vs
• Spin coating forms smooth
•
•
•
•
films
TPDSi2 crosslinks in air, films
stable to 350ºC
Covalently bonds to ITO
Insoluble in organic solvents
General approach for other
OPV donors
UPS data : H. Yan, et al J. Am. Chem. Soc. 2005, 127, 3172
OPV Response with Various IFLs
Glass/ITO/ TPDSi2:TFB/MDMO-PPV:PCBM/LiF/Al
(After Optimization)
Control with
PEDOT
Voc = 0.74 V
Jsc = 4.56 mA/cm2
FF = 43.4%
PCE = 1.46%
TPDSi2:TFB
Voc = 0.89 V
Jsc = 4.62 mA/cm2
FF = 54.4%
PCE = 2.29% (NREL verified)
PEDOT + IFL
Voc = 1.08 V
Jsc = 4.83 mA/cm2
FF = 37.2%
PCE= 1.63%
Only IFL Cell Survives Heating at 60°C for 1 Hour
Appl. Phys. Lett., 2008; ACS Appl. Mater. Interfaces, 2010, Advan. Funct. Mat 2010
NiO as an Inorganic Interfacial Layer
PEDOT:PSS Replacement?
NiO Film optical spectra
NiO
• p-Type oxide semiconductor
• Transparent in visible at nm
thicknesses
• Films grown at RT by Pulsed
Laser Depostion (PLD)
• Φ = 5.3 eV
• Highly correlated material
Appl. Phys. Lett. 2002, 81, 10, 1899-1901
Grow NiO Films by Pulsed Laser Deposition
R.P.H. Chang
Optimized NiO Device; 5 – 77nm Films on ITO
High Power Conversion Efficiency
Dark J-V
NREL: 5.6%
efficiency for 10
nm NiO device
Illuminated J-V
Highest
5.2%
Chang, Marks, Hersam, Ratner Proc. Nat. Acad. Sci, 2008, 105, 2783; Chem. Mater., 2011, 23, 2218.
What Is On the ITO?
Electron Microscopy and Selected Area Electron Diffraction:
ITO/10 nm NiO/P3HT:PCBM/LiF/Al
Electron Diffraction
Conclusion: fcc NiO Down to the ITO Surface
R.P.H. Chang
Synchrotron Grazing Incidence X-Ray
Diffraction (GIXRD) ITO/NiO Thin Films
GIXRD patterns calculated for randomly oriented NiO films; experimental
patterns for 10 nm and 50 nm thick NiO films. Cubic NaCl-type NiO (hkl)
reflections labeled accordingly; (111) texturing in the surface-normal
direction evident from (111):(200) integrated area ratios for 10 nm NiO film
J. Emery, M. Bedzyk
Capturing More of the Solar Spectrum: New Active
Layer Donor Family PTB7
Yu JACS 2009
PTB7
P3HT
PC70BM
Voc = 0.744 V
Jsc = 15.63 mA/cm2
FF = 62.3%
Efficiency = 7.6%
Theory: Servaites, Ratner, Marks Energy Environ. Sci., 2011, 4, 4410-4422
Luping Yu, Stephen Loser
PTB7 + PCBM
Intensity (a.u.)
PTB7
P3HT
Intensity
Intensity(a.u.)
P3HT vs. PTB7: Organization & Orientation by GIWAXS
Grazing Incidence Wide Angle X-Ray Scattering
1000
1500
1000
500
0
0.2
0.3
qy((Å-1)
PTB1
PTB1/PCBM pristine
PTB1/PCBM annealed
500
0.4
0.5
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
qz(q(Å
(Å-1-1))
3.7 Å
Average domain sizes of 27.3Å
with stacks of 6-7 chains
Scherrer equation
PEDOT:PSS
Polymer backbone
π planes ┴ to
electrode surface
Polymer backbone
π planes || to electrode
surface
Dhkl 
0.9
 hkl cos
Chen, Yu J. Phys. Chem. C, 2010
Yu, Chen, Marks, Advan. Mater. 2010
2.0
PTBX OPV Response as a Function of
Interplanar Spacing by GIWAXS
Black = C60 PCBM
Red = C71 PCBM
Chen, Yu, Marks Advan. Mater. 2010, 22, 5468–5472.
GIWAX: P3HT Orientation on NiO vs PEDOT:PSS
• Change in π-π stacking
peak location indicates a
change in P3HT
orientation
2.0
1.5
1.5
on PEDOT:PSS
substrate
-1
qz (Å )
2.0
-1
qz (Å )
• Grazing incidence x-ray
scattering used to
determine P3HT
orientation
on NiO substrate
1.0
0.5
0.0
1.0
0.5
0.0
0.0
0.5
1.0
1.5
-1
qy (Å )
2.0
0.0
0.5
1.0
1.5
2.0
-1
qy (Å )
• Change in orientation
correlates with increase
in PCE of P3HT:PCBM
solar cells on NiO (5.2%)
vs. PEDOT (3.5%)
Face-on
alignment on NiO
Edge-on alignment on
PEDOT:PSS
Luo, Zhou, Chang, Chen, Marks, submitted
Weaker PTB7 π-π Stacking on NiO vs.
PEDOT:PSS
•
on NiO substrate
on PEDOT:PSS substrate
2.0
1.5
1.5
qz (Å )
2.0
-1
1.0
0.5
0.0
1.0
0.5
0.0
0.0
0.5
1.0
1.5
2.0
0.0
0.5
1.0
1.5
2.0
-1
-1
qy (Å )
qy (Å )
PTB7 π-π stacking peak
300
250
I(Q) (a.u.)
-1
qz (Å )
No change in orientation
on NiO substrate
• Weaker π-π stacking on
NiO substrate may be
due substrate chemistry
or morphology
• Corresponding decrease
in PCE by 50% on NiO
200
150
PEDOT
fit PEDOT
NiO
fit NiO
100
50
0
1.4
1.5
1.6 -1
Q (Å )
1.7
1.8
Luo, Zhou, Chang, Chen, Marks, submitted
PTB7 Performance with 1 Layer Graphene Oxide
Vs. PEDOT:PSS
GIWAX: PTB7 π-Stacks on GO
GO
Hersam, Marks, Chen J. Phys. Chem. Lett.,
2011, 2, 3006–3012
PEDOT:PSS vs. Graphene Oxide as OPV Interfacial
Layer
GO is
•More Transparent
•Has Higher
External Quantum
Efficiency
Present GO Coating is
e-
h+
Recombination
•“Leakier”
•PCE as High as 10%?
Hersam, Marks, Chen J. Phys. Chem. Lett.,
2011, 2, 3006–3012
OPV Lifetime Enhancement Vs. PEDOT:PSS Using
Graphene Oxide Interfacial Layer
 GO enhances lifetime 5x under thermal stress
 GO enhances lifetime 20x under humid conditions
Encapsulated
Unencapsulated
Hersam, Marks, Chen J. Phys. Chem. Lett.,
2011, 2, 3006–3012
LowD-A
Bandgap
Polymers
Low Bandgap
Copolymers
Example: Bithiophene Imide-Dithienosilole Donor-Acceptor Copolymers
Optical Spectra
Inverted BHJ Cell Architecture
•Egap = 1.75 eV
•HOMO = -5.43 eV
•PCE = 5.5 - 8.7 %
•Voc > 0.80 V
•FF = 62 – 80%
Chang, Chen, Marks, Advan. Mater. 2012; J. Amer. Chem. Soc. 2012, in press; 2012 submitted
Subtask 2OPV
Industrial
Single Junction
with Collaboration
PCE = 9.1%
Newport Confirmed!
Pristine OPV3
OPV3:PC71BM
Current Density / mA/cm
2
20
10
Voc = 800 mV
Jsc = 16.2 mA/cm^2
FF = 70%
 = 9.1%
(010)
Polymer Donor = OPV3
(100)
0
(001)
-10
-20
-0.8
-0.4
0.0
Voltage / V
0.4
0.8
π-stacking peak is along qz axis, so OPV3
exhibits π-face-on alignment. π-stacking
distance = 3.7 Å. PC71BM addition
enhances OPV3 crystallinity
cooperative
interaction between OPV3 + PCBM.
http://www.polyera.com/newsflash/polyera-achievesworld-record-organic-solar-cell-performance
Facchetti (Polyera Corp.), Chen, Marks, Ratner, Hersam
New Push-Pull Small Molecule Donor NDT(TDPP)2
OPTICAL
XRD
TFT
TFT
NDT(TDPP)2
Single crystal XRD
Highly Ordered Films From Solution
Neat Film: µh = 7.2 x 10-3 cm2/V·s
HOMO/LUMO Energies → Air Stability, Good Voc
BHJs with PCBM Highly Ordered (Fabricate in Air)
Blend Film: µh = 3.3 x 10-3 cm2/V·s
Stupp, Marks J. Amer. Chem. Soc., 2011, 133, 8142; submitted
New Push-Pull Small Molecule Donor NDT(TDPP)2
ITO/PEDOT:PSS/1.5:1.0 NDT(TDPP)2:PC61BM/LiF/Al
Processable in Air
Uses Cheap C60 Acceptor
VOC = 0.840.01 V
JSC = 11.270.21 mAcm-2
FF = 0.420.02
PCE = 4.060.06%
Best PCE = 4.7 – 6.5%
NDT(TDPP)2
PCBM
Small LUMO-LUMO Offset & FF!
Stupp, Marks J. Amer. Chem. Soc., 2011, 133, 8142.
Marks, Chem. Commun. 2012, , 48, 8511.
Bisquert, Guerrero, Marks, 2012, submitted.
Simulation: TCO Anode Resistance vs.
Efficiency
Cd-In-O
ITO
J.D. Servaites, T.J. Marks, M.A. Ratner Appl. Phys. Lett., 2009; Adv. Funct. Mater. 2010.
CIO/ITO Double-Layer TCO Anodes
Tuning CdO Corrosion Resistance and Work Function.
Grow ITO by IAD
current pathway
In-doped CdO (105 nm)
TCO1
TCO2
MOCVD
Substrate
1
1 1
 
Rsheet R1 R 2
Substrate
Sample
Thickness
(nm)
Sheet Resistance
(/□)
Transmittance
(%)
Figure of Merit
 = T/Rsheet (10-3-1)
In-Content
(%)
CIO
167
5.6
86.4
41
4.3
CIO/ITO (23 nm)
180
5.6
87.1
45
15.8
CIO/ITO (37 nm)
194
6.1
88.0
46
21.4
ITO
130
18.0
95.1
34
90
 Lower sheet resistance, ideal for large OPVs
 Similar optical transparency
 Smoother surface morphology
 Tunable work function
 Higher environment stability
 Lower cost, reduced In content
For Lab-Scale OPVs, Performance ≥ ITO Anode
Cells
Chem. Mater. ’09, Thin Solid Films ‘10
Optical Properties
100
Transmittance (%)
Results
80
60
40
CIO
CIO+ITO(23nm)
CIO+ITO(37nm)
20
0
500
1000
1500
Wavelength (nm)
2000
Conclusions
• Small bandgap polymers with high power conversion
efficiencies possible
• Importance of templating π-face-on donor polymer growth
• 7.6% - 9.1% BHJ efficiencies due to better light capture, local
orientation on anode, ordering, + unknown factors
• Nanoscopic organic, inorganic anode IFLs significantly increase
BHJ efficiency, durability
• High-efficiency BHJ cells achieved without PEDOT:PSS
• Graphene Oxide is a very effective interfacial layer
• Theory and computation essential for materials design
OPV Prospects. What Next?
å
p-Type
Donor
h+
h+
?
e-
Capture Maximum Solar
Output
Create Long-Lived
Exciton
?•
en-Type
Acceptor
h+
TCO
hυ ≥ Eg
Hole-Transporting
Layer
eV
z
Challenges
eLow-Φ
metal
?•
å
?•
Efficiently Split Exciton,
but Use Minimum Energy
Achieve High Hole and
Electron Mobilities
Through Active Solid
Efficiently Extract Charge
at the Electrodes
Carry Charges Away