Nanostructures for High-Efficiency
Solar Cells.
Bertrand FILLON
CEA LITEN Grenoble
Arrhus, Denmark, June 2012
Content
Introduce CEA/LITEN
Nanotechnology for bulk silicon
Nanotechnology for thin film PV cells
Conclusion
One BU of Technological Research Division
R&D
for nuclear
15.000 researchers
4 Billions Euros annual
9 Instituts
energy
Fundamental
Defense
Research
programs
Technological
Research
for industry
Getting ready for the
New Economy
LITEN Key figures
Chambéry : Solar Energies
& Smart Building
Grenoble : Green Transportation
& Biomass
Experimental area
Manpower
2012
1000 collaborators
Patents
600 in portfolio
150 new patents in 2011
Budget 150 M€
120 M€ turnover
30 M€ of CEA Funding
LITEN
Electric
Transports
Electric Power
Batteries
Fuel Cells
Hybridation
Solar Energy
& Buildings
Solar Energy
Solar PV, CPV, OPV
Electrical systems
Energetic efficiency
Large area
electronics
Nanomaterials
Biomass
& Hydrogen
Solid Storage
µ-sources
Energy recovery
Organic electronics
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H2 Storage
Usages
Industrial partnerships
Large companies
Building/Solar Energy
• Photovoltaic devices
• Thermal devices
• Positive energy building
Transportation
• Fuel cell
• Energy storage
• Hydrogen
Nomad
• Micro power sources
• Energy scavenging
• Organic Electronic
Small companies
Content
Introduce CEA/LITEN
Nanotechnology for bulk silicon
Nanotechnology for thin film PV cells
Conclusion
Three main categories for solar cells
New concepts
3rdgénération cells
Thin film technologies aSi/mc-Si, CIGS (CuInSe,
CdTe)
Crystalline Si cells
Improvements in silicon yield
High metallic
impurities, High
[Cs],
SiC contamination
Wafering zone
Diffusion of
the transition
metals
Diffusion of
the transition
metals
- Avoid contamination zones.
- Maintain the purity of the feed stock to the ingot and wafer.
- Improvement of feedstock yield. Etc……
4
3
2
Fe diffusion
High content of [Oi]
> 20 mm
To be gettered before processing
1
> 40 mm
TIV 48
> 20 mm
Lifetime pattern of an ingot cross section
Pictures obtained with µwave Photon Conductivity Decay
> 20 mm
Nanophenomena for the bulk silicon
> 20 mm
> 20 mm
4
2
3
1
•
•
•
> 20 mm
> 40 mm
Taking in account 2 cm top, bottom and side crop we remove 22% ( 100 kg) of the total
industrial weight (standard industrial G5 ingots is 450 Kg)
Zones 1, 2 and 3 can be recycled
Zone 4 (Carbon cut) is not recycled
Improvement and better understanding of the trapping offer a higher free carrier life time
thanks for the development of an advanced crucible and a well controlled gettering
Silica crucible with diffusion barrier
Fe (ppmw)
Al (ppmw)
-
-
8.4
20
5
-
29
(Fe2O3)
1500
(Al2O3)
Fe (ppmw)
Al (ppmw)
-
0.15
10
37
29
(Fe2O3)
1500
(Al2O3)
Aluminum
Iron
Silicon
High purity Si3N4 coating
High purity
crucible
High purity diffusion barrier
Fused silica crucible
Silicon
Si3N4 coating
Fused silica crucible
Standard fused
silica crucible
Silica crucible with diffusion barrier
Standard crucible+ Si
HPC Crucible + Si
Melted Si
Si3N4 Coating
High Purity Coating
Silica crucible
Pictures obtained with µwave Photon Conductivity Decay
Gettering effect on six inches mono like P type wafer
Improvement of the free carrier life time
Strong gettering on ingot bottom wafers
Pictures obtained with µwave Photon Conductivity Decay
Content
Introduce CEA/LITEN
Nanotechnology for bulk silicon
Nanotechnology for thin film PV cells
Conclusion
Three main categories for solar cells
New concepts
3rdgénération cells
Thin film technologies aSi/mc-Si, CIGS (CuInSe,
CdTe)
Crystalline Si cells
Absorption coefficient
of material
Electromagnetic field
Light absorption = f(ad,
2
E)
Length of Light path
3 routes to enhance coupling between solar light and cell
 Longer path for light (scattering substrates): d↑
 Plasmonic structure: E↑
 New nanocomposite absorbers: a↑
Conventional
Scattering effect
Plasmonic effect
A
A
A
Lost
Lost
Lost
Longer Light path d 
Enhanced electric field E 
A ∞ (1-
R)(1-e-ad)

 a ∞ E2 
 A ∞ (1- R)(1-e-ad) 
Light management: scanning effect
TCO texturation
(a)
(b)
(c)
a) “Commercial” Texturing of TCO (ASAHI-U)
b) ZnO-Al texturing : 10 s with HCl.
c) Associated Haze measurement: H= scattering in transmission / total transmission
Better control of the TCO nanostructure
Scanning effect: substrate nano-structuring
Bead self assembly : 2D nano-structuring
• Capability: 2D spatial control of thin film nano-structuration.
• Basic concept: Langmuir-blodget film of spheres deposited by
capillarity mechanism => periodic array
• Potential interest: spectral tuning of the light scattering
inside the solar absorber
High control of periodicity
via the sphere size
Bead self assembly : 2D nano-structuring
High control of periodicity
via the sphere size
The texturing widens the spectral response
Glass
ZnO deposit
Beads deposit
ZnO deposit
Example of light scattering enhancement
Direct
texturing
(H=Tscat./Ttotal)
100
Glass
ZnO
HAZE (%)
80
60
40
Direct
texturing
ref.:400 nm ZnO
Reverse
texturing
20
ZnO
ASAHI W-texture
0
300
500
700
900
l (nm)
Glass
Periodicity range:
=1000nm
=> Red-IR scattering
1100
1300
1500
Texturing of a-SiGe:H cell
Reverse texturing
1
18
0,8
+10% Jsc
η=4.9%
J (mA/cm²)
14
0,6
EQE
Textured
0,4
Not Textured
0
-6
500
600
700
Wavelength (nm)
Solar cell:
a-SiGe:H
η=4.28%
+15% in efficiency
2
-2
400
Not Textured
6
0,2
300
Textured
10
800
900
-100
0
100
200
300
400
V(mV)
500
600
700
800
Results predictable by optical simulation
• Comsol multiphysics software
• 2D Optical calculations
100
TCO
a-SiGe:H
Glass
TCO
a-SiGe:H
-
Ag
-
60
40
20
-
TCO
80
Ag
A (a-SiGe:H)
TCO
plan
texturé
0.5 µm
1.0 µm
0
600
700
800
900
1000
lambda (nm)
E-field mapping
=> Simulation predictive approach and tunable texturing technology easily adaptable
to various solar cell absorbers (Si, SiGe, CIGS, CdTe, ….)
Conventional
Scattering effect
A
A
Lost
Plasmonic effect
Lost
Longer Light path d 
A ∞ (1- R)(1-e-ad) 
A
Lost
Enhanced electric field E 
 a ∞ E2 
 A ∞ (1- R)(1-e-ad) 
Plasmonic effect in Solar Cells : principle
Proposed solution: enhance the absorption of active layer by coupling it with a
PGNM.
resonance on metal nanoparticles (NPs)
Electric field

enhancement
innanoparticle
the NP
L absorption inside
absorption in
inside
active layer
J absorption
the active layer
J scattering
PGNM
NPs in surrounding
medium
Active layer
Challenge: Promote the light scatt./abs. (fNP ↑) while limiting the NP absorption
 Adapted nanotechnology for a fine tuning of NP size and density,
 Adapted Optoelectronic (O/E) modelling to define the optimum PGNM
localization inside the cell stack.
Plasmonic phenomena

Previous work :
- no fine control of nanoparticles
- localization of nanoparticles only on the surface
EBPVD + 1h 200°C
wet process
[Yu et al., 2006, (USA)]
[Pillai, 2007 (UNSW - Australia)]
EU project:
 Low T° deposition of nanoparticles with finely controlled properties
(size distribution, shape, surface density, environment)
 Optimal design of solar cells structures containing nanoparticles
NP synthesis: dedicated nanotechnology
NP
Source
Turbo
pump
Deposition chamber
~10-3mbar
Water cooling
Mass
spectrometer
Grid +18V
Substrate
ФAr
Ar
Pchamber
Psource
Microbalance
~10-5mbar
~10-1mbar
NP Size/density not
correlated
The NPs can be
manipulated
Room temperature
deposition
Nanotechnology facilities @ Cea
The NP source has been installed in a
commercial Sputtering deposition chamber
Substrate holder
NP source
exit
The source faces the rotating
substrate holder compatible
with 200mm wafer.
NP size control and density
Nanoparticles size range: 2-10 nm
+
Density
(particles/cm2)
2.1011
200nm
1.1011
7.1010
200nm
1.1010
decahedral particle (7 nm)
icosahedral particle (8 nm)
NPs integration in real cells: Organic C
Example: small NPs in contact with or inside the active layer
+5%
60
50
NP on PJetN (d1)
NP on PJetN (d1)
NP on PJetN (d2)
NP on PJetN (d2)
Ref (NP on PJetN)
40
IPCE
•
30
d2= 4.1010 cm-2
20
d1= 1.1011 cm-2
10
0
300
400
500
600
700
800
900
l(nm)
The global NP effect is positive
Content
Introduce CEA/LITEN
Nanotechnology for bulk silicon
Nanotechnology for thin film PV cells
Conclusion
Materials and technologies will offer great opportunities
LITEN/INES
LITEN/INES
LITEN/INES
LITEN/INES
www.eupvclusters.eu
Optical modelling
Nanotechnology
Organic solar cell
(UK)
(NL)
Nanotechnology
a-Si:H solar cell
Crucible technology
(CH)
University of Ljubjana (SL)
Thank
Numerical modelling of full cells
DSSC cell
Expertise on
plasmonic systems
University of New South Wales (AUS)
DSSC cell
Nanocrystal
caracterization
A
bientôt
Thank you
www.eupvclusters.eu
Thank you for your attention
Bertrand FILLON
Tel:0033685324833
bertrand.fillon@cea.fr