SolutionProcessed OPV on Metal MultiTerminal Multijunction Cells RolltoRoll Deposition

1
Solution-Processed OPV on MetalMulti-Terminal
Multijunction CellsRoll-to-Roll Deposition

• Whitney Gaynor, Jung-Yong Lee, Albert Liu, and
  Peter Peumans
• Stanford University
• August 26, 2009

2
Fully-Solution Processed Advantages

• No ITO
• No vacuum steps or switching between solution and
  vacuum
• Possible roll-to-roll printing fabrication
• Possible encapsulation during fabrication process
• Low cost

Source Deutsche Bank
2
3
Metal Foil Advantages

• Cost
• 11/m2 for ITO-glass
• 5/m2 for glass
• 5/m2 for metal
• Substrate Texturing
• Enhancing light trapping
• V-shaped cell
• Random texturing
• Superior Barrier Properties
• Measure oxygen (OTR) and water transport (WVTR)
  through film
• To protect OPV OTR 10-5 cm3m-2d-1, WVTR
  10-6 gm-2d-1
• PET, 25 ?m OTR 31-93, WVTR 16-20
• Al film, gt20 ?m OTR 0, WVTR 0

Rim et al, Appl. Phys. Lett. 91 243501 (2007)
3
Klauk, ed. Organic Electronics Wiley-VCH,
2006-2007
4
Previously Reported Work
J. Meiss et. al, Appl. Phys. Lett. 93 103311
(2008)
T. Nyberg, Synth. Met. 140 281286 (2004)
M. Glatthaar et. al, Thin Solid Films 491 298-300
(2005)
4
5
Ag Nanowires Replacing ITO

• Ag nanowires in
• suspension drop-cast
• onto glass substrate
• Low-T (180C) anneal
• lowers sheet resistance
• Compatible with glass
• and plastic substrates
• Performance comparable to ITO at 10 - 15 ?/sq at
  85 solar transmissivity

J. Y. Lee et. al, Nano Lett. 8 689-692 (2008)
6
Device Fabrication
1?m
1?m

• Every step from solution
• Possible encapsulation during fabrication

6
7
Top Electrode

• Left SEM of Ag Nanowire electrode laminated on
  top of OPV cell (PEDOT underlayer)
• Right SEM cross-section image of OPV cell on
  metal foil

7
8
Transmission Through Ag NWs
Nanowire Electrode
8
9
Initial Results
Ag Nanowire Mesh
PEDOT
P3HTPCBM
Cs2CO3
Ag
9
10
Dark Current Reduction
10
11
Dark Current Reduction
11
12
Dark Current Reduction
12
13
Partially Optimized Results

• Optimized
• Solvent o-DCB
• No final anneal
• Pulse at -15 V prior to measurement
• Issues
• Low Voc
• Remaining dark current

13
14
Effect of Cs2CO3

• XPS data show Cs metal film forming at interface
• Literature data gives workfunction of Cs2CO3
  layer
• 3.46 eV as cast
• 3.06 eV annealed

Liao et. al, Appl. Phys. Lett. 92 173303 (2008)
14
15
Preliminary Results StainlessSteel Foil
15
16
Conclusions

• Demonstrated first fully solution-processed,
  ITO-free, OPV cell on metal substrate
• Device characteristics (0.8 sun AM1.5G)
• Voc 0.51 V
• Jsc 10.59 mA/cm2
• FF 0.46
• PCE 2.5
• Demonstrated preliminary results on stainless
  steel foil
• Device characteristics (1.2 suns AM1.5G)
• Voc 0.45 V
• Jsc 15.4 mA/cm2
• FF 0.30
• PCE 1.73
• Issues
• Low Voc
• Leakage current - low fill factor

16
17
Future Work

• Improve Lamination process onto foil
• Reduce leakage current on foil
• Investigate other methods of applying NW
  electrode to device
• Spraying
• Optimize processing parameters
• NW electrode thickness
• Anneals
• Investigate source of low Voc
• Other possible salts at the interface (e.g. CsF,
  LiF)
• UPS

17
18
Motivation for Multi-Terminal Multijunction Cells

?A
?EQE
0.9
Ag
SnPcC60
SubPcPTCBI
SubPcPTCBI
0.6
ClAlPcC60
2-terminal, 3-cells 11.2
h
ClAlPcC60
SnPcC60

TCO
Glass
0.3
ARC
0.0
400
600
800
1000
l
(nm)
?A
0.9
Ag
?EQE
SubPcPTCBI
0.6
3-terminal, 2-cells 12.3
ClAlPcC60
h
SubPcPTCBI
TCO

Glass
0.3
ClAlPcC60
ARC
0.0
400
600
800
l
(nm)
19
Module Need 4 Terminals
Top and bottom cell need to be scribed at
different pitch
TCE
Cathode

_
Intermediate Substrate
Substrate
20
Proof-of-Concept Demo
ITop
Patterned ITO
-
Top Cell
Bottom Cell

IBottom
Parallel-connected multijunction cell
Laminated AgNW mesh
21
Results
22
Roll-to-Roll Coater
take up roller
pay out roller
4 ft radius
web travel path (dotted lines)
tension sensors
left drum
1
3
evaporation source cradle, location 2
2
23
Source Design
deposited CuPc film
PET substrate
water-cooled heat shield
2 m/min
12
heated distribution manifold
web direction
insulator spacer
water-cooled base
Local deposition rate53nm/s
adjustable vapor outlet slit
pathway of random molecule
CuPc source powder
adjustable base plate
heated mesh
24
Film Morphology
Point source evaporated CuPc Rms roughness
1.440nm
R2R evaporated CuPc Rms roughness 1.879nm
25
Cross-Web Uniformity
Localized CuPc loading (1 in2)
Distributed CuPc loading (10 in2)
26
OPV Performance
PET/CNT (Unidym)/PEDOTPSS/20nm CuPc/20nm
PTCBI/10nm BCP/100nm Ag