Advanced Thin-Film Silicon Solar Cells · Thin-film Si solar cells on glass Power plant Roof...
Transcript of Advanced Thin-Film Silicon Solar Cells · Thin-film Si solar cells on glass Power plant Roof...
Miro ZemanDelft University of Technology, The Netherlands
Acknowledgments:• Nuon Helianthos, OM&T, IPV Julich, Ljubljana University• SenterNovem for financial support
Advanced Thin-Film Silicon Solar Cells
Outline
Helianthos project
Status of thin-film Si solar cell technology
Issues for further improvement
Conclusions
Photon management
World of PhotovoltaicsPV industry: the fastest growing industry in the world
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1256
1815
~3800
MW Solar cell production 1999-2007
42% 40% 39% 34%68%
45%
50%
Photon International, March 2007
2006: 90% wafer-type c-Si technology
Estimation market:
2007Cumulative installed capacity of PV systems
~ 9200 MW
Turnover (modules+BOS)
~ 15x109 €~ 70 000 jobs
2536
40%
World of PhotovoltaicsPV industry: announced increase in capacity
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oduc
tion
Cap
acity
[MW
]
2006 2007 2008 2009 2010 2012
Crystalline SiliconThin Films
Arnulf Jäger-Waldau, EU-PVSEC-23, Valencia, 2008
World of PhotovoltaicsPV industry: announced increase in capacity
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silicon basedCdTeCISDye + others
Oerlikon
Applied Materials
Arnulf Jäger-Waldau, EU-PVSEC-23, Valencia, 2008
Strategic Research Agenda: EU roadmap
www.eupvplatform.org
Wim Sinke (ECN, Leader of WG 3 : Science, technology & applications of EU PV Technology Platform)
Current developments:• Increase in TF Si solar-cell production (in 2010 ~ 8 GW capacity)• Complete production lines available
Future developments:• Short term: optimize tandem cell• Long term: optimize triple cell, breakthrough concepts for high
efficiency (η>17%)
Thin-film Si solar cell technologyPresent status:+ Promising low-cost solar cell technology+ Industrial production experience (Flat panel display industry)- Relatively low stabilized efficiencies (η ≈6-7%)+ Double-junction micromorph solar cell (η>10%)
• ideal combination of materials (a-Si:H/μc-Si:H) for converting AM1.5 solar spectrum into electricity
Thin-film Si solar cell technology
Thin-film Si solar cells on glass
Power plant
Roof integration and new designs
Thin-film Si solar cell technology
Flexible thin-film Si solar cells
Roof integration
Consumer electronics
Stand-alonesystem
Flexible module
-20
-15
-10
-5
0
5
-0.2 0.0 0.2 0.4 0.6 0.8 1.0Voltage [V]
Cur
rent
den
sity
[mA
cm-2]
initial
degraded
p-i-n a -Si:H Initial Degradedsolar cell
Jsc [mA/cm2] 16.2 15.7Voc [V] 0.75 0.74fill factor 0.69 0.64efficiency [%] 8.4 6.3
• Creation of extra metastable defects in a-Si:H under illumination
• Extra trapping and recombination centres
• Initial versus stabilized efficiency
Thin-film Si solar cell issues
Degradation of a-Si solar cells
Thin-film Si solar cells challenges
Increasing efficiency
Light trapping techniques• Textured substrates - scattering• Back reflector• Novel approaches
Multi-bandgap concept• Low band-gap materials
Suppressing degradation
Stable material• pc-Si:H, μc-Si:H or poly c-Si• New deposition techniques• Hydrogen diluted silane
Multi-junction concept• Tandem solar cells
300 500 700 900 1100 1300 1500Wavelength [nm]
Pho
ton
flux
[1027
ph
/ m3 s
]
4.13 2.48 1.77 1.38 1.13 0.95 0.83
Photon energy [eV]
5.0
4.0
3.0
2.0
1.0
0.0
a-Si a-SiGe
AM1.5 global solar spectrum
Increase efficiency
Multi-bandgap solar cell concept
Efficient use of solar spectrum
EFEner
gy
p ni
a-Si
EF
p ni
a-Si
EF
p nin pi
a-Si a-Si
Multi-junction solar cell concept
EF
p nin p
a-Si
i
a-SiGe or μc-Si
Suppress degradation
Thin-film Si solar cell structures
uc-Si:H bottom absorber
Ag ZnO
surface textured - TCOZnO:Al
glass
a-Si:H top absorber
a-Si :HGe middle absorber
surface textured TCO-
uc-Si:H absorber
Ag ZnO
surface textured - TCOZnO:Al
glass
a-Si:H absorber
interlayer
surface textured TCO-
glass
uc-Si:H layers
back metal contact (Ag)
pin
ZnO
single-junctionamorphous (a-Si:H)microcrystalline (uc-Si:H)
double-junctionmicromorpha-Si:H/uc-Si:H
triple-junctione.g. a-Si:H/a-SiGe:H/uc-Si:H
Record ηst (confirmed) 9.5% (a-Si) Un. Neuchatel
10.1% (μc-Si) Kaneka
11.7% (a-Si/ μc-Si) Kaneka
12.4% (a-Si/a-SiGe) USSC* 13.0% (Si/SiGe/SiGe) USSC*
Photon management
Proper handling of incident photons which have to
be trapped in the absorber layers of a solar cell
Photon management
Light trapping techniques:• Manipulation of light propagation: multiple passes
Engineering of optically-active layers(back and intermediate reflectors, layers for optical matching)
• Light scattering: change direction of propagation
Design of surface texture (random or periodically textured surfaces)
Trap photons in the absorber layer and enlarge their average path
Importance of light trapping
1x
10x
50x
a-Si:H 300 nm
Wavelength (nm)
400 500 600 700 800 900 1000 1100 1200
AM 1
.5 s
pect
rom
(mW
/(cm
2 um))
0
20
40
60
80
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120
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180
1x13.11 mA/cm2
10 x19.87 mA/cm2
+ 52 %
50 x23.30 mA/cm2
+ 78 %
a-Si:H film
• change of direction• multiple passes
Janez Krc, 2008
Importance of light trapping
1x
10x
50x
uc-Si:H 1 um
Wavelength (nm)
400 500 600 700 800 900 1000 1100 1200
AM
1.5
spe
ctro
m (m
W/(c
m2 um
))
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40
60
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120
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160
180
1x14.87 mA/cm2
10 x28.27 mA/cm2+ 90 %
50 x35.31 mA/cm2
+ 137 %
uc-Si:H film
Janez Krc, 2008
Light trapping
AP CVD SnO2:F Wet etched ZnO:Al
Standard techniques:• Random surface-textured substrates
Asahi U-type AP CVD SnO2:F, Julich wet-etched ZnO:Al
• Back reflectorThin ZnO layer between Si and metal
Light trapping
State-of-the-art uc-Si:H solar cell:
Wavelength (nm)
400 500 600 700 800 900 1000 1100 1200
AM
1.5
spe
ctro
m (m
W/(c
m2 um
))
0
20
40
60
80
100
120
140
160
180
di-uc-Si:H = 1 um
cell23.22 mA/cm2
10x
surface textured TCO-
glass
uc-Si:H layers
back metal contact (Ag)
pin
ZnO
Janez Krc, 2008
Wavelength (nm)400 600 800 1000
Abs
orpt
ion
loss
es
0.0
0.2
0.4
0.6
0.8
1.0
Rtot
BR
TCOsub.
i-uc-Si:H
p+n
Light trapping
surface textured TCO-
glass
uc-Si:H layers
back metal contact (Ag)
pin
ZnO
State-of-the-art uc-Si:H solar cell: analysis of optical losses using modeling
Janez Krc, 2008
Wavelength (nm)400 600 800 1000
J SC d
ensi
ty d
istri
butio
n (m
A/(c
m2 um
))
0
20
40
60
80
Rtot
BR
TCOsub.
i-uc-Si:H
p+n
available JSC
(from AM1.5)
i-uc-Si:H1) R2) TCO sub3) BR4) p+n
23.208.374.813.902.33
JSC (mA/cm2)54 %20 %11 %10 %5 %
Light trapping
State-of-the-art uc-Si:H solar cell: analysis of optical losses using modeling
Janez Krc, 2008
Light-In projectTUD, Helianthos
ECN, OM&T
Advanced concepts for light trapping
• Wavelength-selective manipulation of reflection and transmission of light at interfaces using 1-D photonic crystals
• Concept of modulated 1-D photonic crystals
• Applied as back and intermediate reflectors
Wavelength (nm)600 800 1000 1200 1400
Ref
lect
ance
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1.0 100 %
PC_1
50/100 nm
Wavelength (nm)
600 800 1000 1200 1400
Ref
lect
ance
0.0
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0.4
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0.8
1.0 100 %
PC_2
70/140 nm
Wavelength (nm)600 800 1000 1200 1400
Ref
lect
ance
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0.8
1.0 100 %
PC_1 PC_2+
MODULATED PC
Wavelength (nm)
300 400 500 600 700 800 900 1000
Abs
orpt
ance
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1.0
thin lines - single IR (150 nm ZnO)thick lines - PC stack IR
IRTES projectTUD, TU/e, Helianthos
• Intermediate reflector (IR)
glass substrate
ZnO:Al
a-Si:H cell
uc-Si:H cell
ZnO:B
WP
n-a-Si:HZnO
Simulation results:
ZnO(d = 70 nm)uc-Si:H(d = 20 nm)
Advanced concepts for light trapping
Jsc,top = 9.4 mA/cm2
Jsc,top = 10.1 mA/cm2
Jsc,top = 12,0 mA/cm2
Jsc,top = 10.1 mA/cm2
Light-In projectTUD, Helianthos
ECN, OM&T
• Angle-selective manipulation of light scattered at the rough interfaces using 1-D and 2-D diffraction gratings
Scattering angle (ϕscatt)
-90 -60 -30 0 30 60 90
AD
F T (a.
u.)
0.0
0.2
0.4
0.6
0.8
1.0
P = 700 nmh = 80 nm
Asahi U-type
ϕinc = 0o
ZnO:Al(40" etched)σr � 110 nm
Advanced concepts for light trapping
0 50 100 150 200 250 3007.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
Period = 600 nm
Asahi reference
Ave
rage
Effi
cien
cy (%
)
Feature height (nm)
Light-In projectTUD, Helianthos
ECN, OM&T
Average efficiency of 10 best cells plotted versus groove height
Advanced concepts for light trapping
• Angle-selective manipulation of light scattered at the rough interfaces using 1-D diffraction gratings
Light-In projectTUD, Helianthos
ECN, OM&T
0 50 100 150 200 250 3007.47.67.88.08.28.48.68.89.09.29.4
Period = 600 nm 2D period = 500-800 nm
Asahi reference
Ave
rage
Effi
cien
cy (%
)
Feature height (nm)
Advanced concepts for light trapping
• Angle-selective manipulation of light scattered at the rough interfaces using 2-D diffraction gratings
Helianthos project
• Development of low-cost roll-to-roll technology for fabrication of thin-film silicon solar modules (started in 1996)
• Dutch route: Temporary superstrate solar cell concept
By courtesy of Helianthos bv.
Helianthos manufacturing sequence
- Al foil
Al foil + TCO + a-Si:H + back contact + carrier foil
+ series connect + contact wires+ cutting
+ encapsulant
Status Helianthos project
Flexible lab-size tandem moduleFlexible a-Si:H module: ready for production
1st generation modulesSingle junction a-Si:H module ηin > 7%ηst = ~6%
Achieved:2nd generation modulesTandem a-Si:H/μc-Si:H module ηin > 11%ηst = ~10%
Challenge:
By courtesy of Helianthos bv.
Summary
Thin-film Si solar cell technology• Promising future option for large-area low-cost PV
• Expected large increase in production capacity
• Large scale of applications (rigid + flexible)
• Modules with 10% efficiency
Challenges:• Increase efficiency (photon management)
• Development and implementation of novel ideas