uniform growth of large area a-si / c-si tandem junction thin film solar cells … · 2017. 6....
TRANSCRIPT
Applied Materials ExternalDisplay & SunFab Solar
UNIFORM GROWTH OF LARGE AREA a-Si / c-Si TANDEM JUNCTION THIN FILM SOLAR CELLS BY CAPACITIVE COUPLED PECVD
Yi Zheng, Alan Tso, Fan Yang, Rongping Wang, Tom Tanaka, Ned Hammond, Lin Zhang, Zheng Yuan and Brian Shieh
Thin Film Solar Products Division, Applied Materials, Santa Clara, CA 95054
AVS PAG MeetingAVS PAG Meeting
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Types of Solar Cells
Crystalline Silicon– Monocrystalline, Multicrystalline, Ribbon, etc.
Thin Films– Amorphous and crystalline silicon– Cadmium Telluride (CdTe)– Copper Indium Selenide (CIS, CIGS)
Concentration– Silicon, multi-junction III-V, thermophotovoltaic
Emerging Technologies– Organic materials, Nanostructures, etc.
Crystalline Si and Thin Films dominate market today
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NREL Cell Efficiency Map
Thin Film Efficiencies Rapidly Advancing
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PV Module Price Reduction
$1
$10
$100
1 10 100 1,000 10,000 100,000 1,000,000Cumulative Production (MWp)
Mod
ule
Pric
e (2
006
$/W
p)Historical Prices
1980
2007e
$3.98/Wp
$1.00/W @ ~300 GWp
$1.00/W @ <20 GWp
Thin Film2007e
c-Si
Source: Adapted from NREL;Historical data from Navigant Consulting
Module price decreases 20% for every 2x production increase
2003$3.53/Wp
1995$6.88/Wp
1985$12.01/Wp
1982$18.73/Wp
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Thin-film Advantages and Disadvantages
Advantages
CIS– Highest thin-film efficiencies– Good cell stability– Good product appearance
CdTe– High deposition rate– Proven large-volume mftg– Current low cost leader
Si– Well-known Si-based PV science– Multi-junctions for high efficiency– Large-area, large-volume mftg
Disadvantages
CIS– Mftg yield and volume– Indium price / availability– Field durability
CdTe– Mftg and product restrictions (Cd)– High-temperature process– Absorber thickness ; Te availability
Si– Single-junction efficiency– Deposition rate– Multi-junction mftg control
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Leading Thin Film PV Technologies
Ag/AlZnO:Al
a-Si
Low Iron Glass Superstrate
doped Si
SnO2 :F, ZnO:Al
Barrier
µc-Si
Mo
CIGS
CdS
Soda Lime Glass Substrate
i-ZnOZnO:Al
Barrier
TF Si CIGS
Back Metal
CdTe
CdS
Soda Lime Glass Superstrate
SnO2 :F
Barrier
CdTe
Back Material
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Thin Film Technology Comparison
CIGS CdTe TJ a-Si/uc-SiModule Size (m2) ≤ 0.72 m2 ≤ 0.72 m2 1.43m2, 2.86m2, 5.72m2
Stabilized Module Efficiency Today 8-12% 10% 8%
Stabilized Module Efficiency Roadmap to 2010
15% 12% 10%
Best Laboratory Cell Efficiency 19.5% 17% 13.5%
Temperature Coefficient, Power -0.36 % / °C - 0.25 % / °C - 0.2 % / °C
Raw Materials for PV 3 – 5 GW annual (limited Indium increases
cost)
3 – 5 GW annual (limited Telluride
increases cost)Unlimited Si supply
Volume Production Ramp Readiness
Material, uniformity, t-put, equipment maturity,
etc.In volume production In volume production
Module Reliability Limited field data impacts financiability
Limited but growing field data a-Si >20 years
Production Cost / Wp in 2010
No volume production cost data <$1.00 /Wp <$1.00 /Wp
Applications Rooftop, BIPV Solar Farms, Rooftop, BIPV
Solar Farms, Rooftop, BIPV
*Sources: NREL, Deutsche Bank, USGS, Photon International
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Thin Film Si PV Cell - Single Juction & Tandem Junction
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
20
0
40
60
80
100
0
1
2
3
4
5
Num
ber o
f Sun
light
Pho
tons
(m-2
s-1 m
icro
n-1 )
E+19
Rel
ativ
e Ex
tern
al Q
uant
um E
ffici
ency
, %
c-Si:H junctiona-Si:H junction
AM 1.5 global spectrum
Wavelength, microns
~2 µm
a-Si Single Junction
a-Si/µc-Si Tandem Junction
AgTCO
n
p
i
n
p
i
~2-3 µm
Glass Substrate
Transparent Conductor
Amorphous Silicon
Microcrystalline Silicon
Back Contact
AlTCO
n
p
i
Glass Substrate
Transparent Conductor
Amorphous Silicon
Back Contact
thin a-Si
µc-Si
back contact
a-Si:H/µc-Si:H advantages
Low-cost Better temperature
stabilityBetter diffuse light
efficiency Paths to higher CE
a-Si:H/µc-Si:H challenges
Large area film uniformity
High equipment cost Low dep rateLow CE
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AppliedApplied’’s Tool Boxs Tool Box
Baccini*Baccini*
SiliconSystems
Advancing Technology Innovating Productivity
DisplayBusiness
Delivering NewTechnology and Scale
Energy & Environmental
SolutionsChanging the
Energy Equation
Fab SolutionsDriving Fab Productivity
Thin Film Crystalline
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ACLS
25K / 25KA1500x1800 1500x1850
27,750 cm2(1.78 from 15 K)
5/ '03~
Gen 6Gen 5.5
19,500 cm2(1.25 from 15 K)
20K 1300x1500
ACLS
8/ '04~
Gen 8
ACLS
50K 2160x2400 class
53,136 cm2(1.21 from 40 KA)
2006
Panel sizeInch
10.4 12.1 15 ~ 17 19 ~ 23 21 ~ 24 46W37W32W 52W
Panel/sub 4 6 6 6 6 666 6
Application Note PC -----------------> Monitor TV ----------------->
1600370x470400x500
3500 / 4300 / 4300A550x650600x720620x750
5500/5500A680x880730x920
10K1000x1200
15K / 15KA1100x12501200x1300
Substrate Area
2,000 cm2(1.00)
4,650 cm2(2.33 from 1600)
6,716 cm2(1.44 from 4300)
12,000 cm2(1.79 from 5500)
15,600 cm2(1.30 from 10K)
40K / 40KA1870x22001950x2250
41,140 cm2(1.52 from 25 K)
ModelSubstrate Size (mm)
Gen 2 Gen 3 / 3.5 Gen 4 Gen 5 Gen 5 Gen 7 / 7.5
System Layout
ACLS ACLS
2/ '93~ 4/ '95~ 1/ '00~ 8/ '01~ 6/ '02~ 7/ '04~1st Release
4 up 10.4”
6 up 12.1”
6 up15.0” ~ 17.0”
6 up19.0” ~ 24.0”
6 up37.0” Wide panels
6 up46.0” Wide panels
6 up52.0” Wide panels
2160x2460
AKT PECVD Size EvolutionAKT PECVD Size Evolution
Our demonstrated capability in large area TFT-LCD tools
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SunFab Value Proposition – 12 Lines Worldwide
Module Right Sizing Advantage & Flexibility– Flexible panel size (¼, ½, and Full Size) serves multiple markets: residential rooftop, commercial
rooftop, BIPV, and utility scale– SunFab full size panel (5.7m2), world’s largest, delivers the highest power out per panel 560Wp
Leading Technology– High Efficiency Tandem Junctions, Better Energy Harvest due to lower temperature coefficients– High-speed, high-yield processing of thin glass substrates (2.2x2.6m)
Fastest to Scale– World class equipment serves as foundation for Factory performance– <6 months from factory ready to Volume Production
Cost
Watts
Applied SunFab Gen 8.5 PECVD
Full Size SunFab Panel
560 Wp
¼ Size
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PECVD chamber structure
Process gases:– SiH4 , H2– Dopants (C3 H9 B for p-doping and
PH3 for n-doping)– Single gas feed through at the
center of the chamber lid
Diffuser:– Distribute gas flow– RF electrode– Proprietary hallow cathode design
Enhanced gas dissociation
Uniformly dissociated reactant gases
Susceptor– Multiple heating and cooling zones
Ensure temperature uniformity– RF ground
Slit valve for substrate loading / unloading
RF power supply
Gas feed
To pump
Slit valveObservation window
SusceptorGlass substrate
Diffuser
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Big Challenge - 5.7m2 Substrate µc-Si Filmamorphous phase at corners
20
30
40
50
60
70
80
0 500 1000 1500 2000 2500Distance (mm)
fc (%
)
Crystalline fraction along diagonal
Amorphous Microcrystallinea-Si due to lower power density
Result is lower cell Jsc & FF
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Silane concentration, power, frequency, temperature, ...Decreasing crystalline volume fraction
stationarycolumnar growth
incubation zone
substrate
voidsamorphous regionscrystallites
several100 nm
~30-50 nm
PorousCracks/columns
in TEMHigh
spin
densityBad solar cells
Compact Cracks/columns
in TEMLow spin
densityGood solar cells
Structure of µc-Si:H
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Parameters that Affect Film Uniformity
Plasma Uniformity
Gas Flow Distribution
Pumping Mechanism
Susceptor
Spacing
Diffuser Gas Flow
To pump
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Plasma Uniformity - Proprietary Electrode Design
0
100
200
300
400
500
-1250 -750 -250 250 750 1250Distance from Edge (mm)
Thic
knes
s (n
m)
Gen 5
Gen 6
Gen 7
Gen 8
Gate Insulator quality SiNx film
Uniformity: < +/- 10%
0500
10001500200025003000
0 500 1000 1500 2000
Distance (mm)
Dep
o. R
ate
(A/m
in)
Before standing wave correction
Susceptor
Diffuser Profile Change
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Chamber Flow Simulation
Chamber pumping flow simulation indicated non-uniform flow distribution
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Full Size 5.7m2 uc-Si Film
20
30
40
50
60
70
0 500 1000 1500 2000 2500
Distance (mm)
f c(%
)
µc-Si layer with LCD Hardware Crystalline Fraction (fc )
• a-Si deposition in the corners due to lower power density
• Result is lower cell Voc & FF
µc-Si layer with New Hardware TJ Cell Efficiency & Jsc
0
2
4
6
8
10
12
0 500 1000 1500 2000 2500
CE
(%
), J s
c(m
A/c
m2 ) CE
Jsc
• New Hardware improved uniformity and crystalline fraction
• Results in better homogeneity and higher efficiency
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0
50
100
150
200
250
300
350
400
450
500
0 400 800 1200 1600 2000 2400
X (mm)
Dep
Rat
e (A
/min
)
Two Remaining Issues:
40
45
50
55
60
65
70
75
80
0 400 800 1200 1600 2000 2400
X (mm)Fc
(%)
TL to BRBL to TR
Thickness Across PanelThickness Across Panel Crystalline Fraction Across PanelCrystalline Fraction Across Panel
2600 mm
2200
mm
5.7 m5.7 m22
• Asymetry of uc-Si Crystalline Fraction Uniformity • Corner low dep rate
• Asymetry of uc-Si Crystalline Fraction Uniformity• Corner low dep rate
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Balance the Plasma – Unbalance the Feed
(a) (b)
RF field intensity w/ original RF feed
RF field intensity w/ displaced RF feed
RF power supply
Slit valveObservation window
-1000-50005001000
-1000
-500
0
500
1000
Mean = 128.3, NU = 49.3%
213
72
100
150
200
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0
50
100
150
200
250
300
350
400
450
500
0 400 800 1200 1600 2000 2400
X (mm)D
ep R
ate
(A/m
in)
0
50
100
150
200
250
300
350
400
450
500
0 400 800 1200 1600 2000 2400
X (mm)
Dep
Rat
e (A
/min
)
RF Fee Location Effects on mc-I Thickness and Fc Uniformity
Unif: 17.8% Unif: 7%
40
45
50
55
60
65
70
75
80
0 400 800 1200 1600 2000 2400
X (mm)
Fc (%
)
TL to BRBL to TR
40
45
50
55
60
65
70
75
80
0 400 800 1200 1600 2000 2400
X (mm)
Fc (%
)
TL to BRBL to TR
0
50
100
150
200
250
300
350
400
450
500
0 400 800 1200 1600 2000 2400
X (mm)
DR
(A/m
in)
Unif: 5%
BKM RF Feed RF Feed Rev1 RF Feed Rev2
40
45
50
55
60
65
70
75
80
0 400 800 1200 1600 2000 2400
X (mm)
Fc (%
)
TL to BRBL to TR
Rev2 RF Feed improved thickness and fc uniformity
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Good correlation between simulation and experiment
Local RF Density Enhancement – GroundingApproach: modify grounding configuration to modulate the electrical field at corners.
Delta: Ground Strap Rev4 - BKM (SF BKM5)
Thickness delta map
(Experiment)
g-20 - -17.9
-17.9 - -15.8
-15.8 - -13.7
-13.7 - -11.6
-11.6 - -9.5
-9.5 - -7.4
-7.4 - -5.3
-5.3 - -3.2
-3.2 - -1.1
-1.1 - 1
1 - 3.1
3.1 - 5.2
5.2 - 7.3
7.3 - 9.4
9.4 - 11.5
11.5 - 13.6
13.6 - 15.7
15.7 - 17.8
17.8 - 19.9
19.9 - 22
22 - 24.1
24.1 - 26.2
26.2 - 28.3
28.3 - 30.4
30.4 - 32.5
32.5 - 34.6
34.6 - 36.7
36.7 - 38.8
38.8 - 40.9
40.9 - 43
43 - 45.1
45.1 - 73.1
Corner thickness increase
Thickness delta map
(Simulation)
Corner RF straps removed
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Uniform uc-Sicoating
Uniform Large-Area uc-Si Film
Unif: 5% (1s, 400pts)
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a-Si:H single layer uniformity change
With original RF feed– Average thickness 390 nm– Standard deviation of thickness,
t = 20 nm– Non-uniformity = 4.3%
After modifying the RF feed location– Average thickness unchanged– t = 21nm– Non-uniformity was 3.2%
Insignificant change in thickness profile and uniformity Sl
it va
lve
minmax
minmax (NU) uniformity-nontttt
0
100
200
300
400
500
600
700
800
0 500 1000 1500 2000 2500
Distance (mm)
a-Si
thic
knes
s (n
m)
Original RF feedModified RF feed
win
dow
Slit
val
ve
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25
010
2030
405060
7080
90100
0 500 1000 1500 2000 2500
Distance (mm)
FF (%
)
Original
RF Rev 1
0
2
4
6
8
10
12
14
0 500 1000 1500 2000 2500
Distance (mm)
Jsc
(mA
/cm
2 )
Original
RF Rev 1
0.6
0.7
0.8
0.9
1
1.11.2
1.3
1.4
1.5
1.6
0 500 1000 1500 2000 2500
Distance (mm)
Voc
(V)
Original
RF Rev 1
Solar cell performance uniformity
Uniformity of Jsc– Improved from 7.9% to 2.9%
Uniformity of Voc– Improved from 4.8% to 3.3%
Uniformity of FF– Improved from 5.8% to 4.1%
Legend RF feed NU (%)
Original 7.9
Modified 2.9
win
dow
Slit
val
ve
win
dow
Slit
val
ve
Legend RF feed NU (%)
Original 4.8
Modified 3.3
win
dow
Slit
val
ve
Legend RF feed NU (%)
Original 5.8
Modified 4.1
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Development of High Dep Rate uc-Si ProcessesConventional Approach [1]
High H2 dilution ratio, R~100High total flowMedium RF power (0.5~0.7W/cm2)
ResultsGood cell efficiencyMedium deposition rateLarge area
[1] B. Rech, etc., Solar Energy Materials & Solar cells 66 (2001) 267-273.
Conventional Approach [1]
High H2 dilution ratio, R~100High total flowMedium RF power (0.5~0.7W/cm2)
ResultsGood cell efficiencyMedium deposition rateLarge area
[1] B. Rech, etc., Solar Energy Materials & Solar cells 66 (2001) 267-273.
Pure Silane Approach [2]
Zero H2 dilution ratio, R=0Very low total flowSmall RF power
ResultsGood cell efficiencyMedium deposition rateSmall area
[2] M. N. Donker, etc., J. Mater. Res., Vol. 22. No. 7, Jul 2007.
Pure Silane Approach [2]
Zero H2 dilution ratio, R=0Very low total flowSmall RF power
ResultsGood cell efficiencyMedium deposition rateSmall area
[2] M. N. Donker, etc., J. Mater. Res., Vol. 22. No. 7, Jul 2007.
Compromising ApproachLow H2 dilution ratio, R~30Medium total flowHigh RF power
ResultsGood cell efficiencyHigh deposition rateLarge area
Compromising ApproachLow H2 dilution ratio, R~30Medium total flowHigh RF power
ResultsGood cell efficiencyHigh deposition rateLarge area
CO
MPR
OM
ISING
CO
MPR
OM
ISING
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Film properties at high deposition rate
Raman,
XRD
Stress
Conductivity
TEM shows clear column structure, which agrees with XRD and Raman
measurement.
TEM shows clear column structure, which agrees with XRD and Raman
measurement.
20 25 30 35 40 45 502 Theta (degree)
Inte
nsity
(a.u
.)
(220)
(111)
(220) / (111) = 2.1(220) / (111) = 2.1
380 430 480 530 580Raman shift (cm-1)
Inte
nsity
(a.u
.)
Experimental dataa-SiGrain boundaryc-SiTotal
Fc = 55.6%Fc = 55.6%
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IV and QE performance comparison
The high deposition rate one (HD with DR=660A/min) have initial IV performance comparable to its reference with DR=400A/min.
All the data shown is taken 6 months after cell fabrication, high deposition rate ones show stable performance same as reference.
LID (two sun light intensity, 300 hours, 50˚C) performance is the same for high deposition rate and its reference. (Data not showing here.)
The high deposition rate one (HD with DR=660A/min) have initial IV performance comparable to its reference with DR=400A/min.
All the data shown is taken 6 months after cell fabrication, high deposition rate ones show stable performance same as reference.
LID (two sun light intensity, 300 hours, 50˚C) performance is the same for high deposition rate and its reference. (Data not showing here.)
Same top cell QE response for all the cells. No obvious damage/change to top cell under high deposition rate for bottom cell I layers.
High deposition rate bottom cells have QE response comparable to its reference.
Same top cell QE response for all the cells. No obvious damage/change to top cell under high deposition rate for bottom cell I layers.
High deposition rate bottom cells have QE response comparable to its reference.
0
10
20
30
40
50
60
70
80
90
100
300 500 700 900 1100Wavelength (nm)
QE
(%)
ReftopHDtopRefbotHDbot
0
2
4
6
8
10
12
0 0.25 0.5 0.75 1 1.25 1.5Voltage (V)
Cur
rent
den
sity
(mA
/cm2 )
RefHD
Initial IV performance
CE (%)
FF (%)Voc (V)
Jsc (mA/cm2)
Parameters10.7
71.51.33611.2
HD10.7
71.71.37910.8
Reference
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SunFab: Unlocking Cost ReductionSunFab: Unlocking Cost ReductionSunFab Solar Projected Output
60 MWp (TJ) per year
0.75 km2 of panels per year
5.7m2 panels – largest in the world
>20,000 homes (3kWp each)
$1/Watt Production Cost 2010
0.72 km2
Forbidden City Beijing China
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JapanJapanChinaChina
IndiaIndia
BrazilBrazil
S. AfricaS. Africa
Southern Southern EuropeEurope
GermanyGermany
Middle EastMiddle East
AustraliaAustralia
NorthNorthAmericaAmerica
1min of Solar energy > 1 year of world energy consumption
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Cell to Cell Connection
Front Glass
Front TCO
a-Si p-i-n
Back Reflector (Back TCO and Metal)P1 Scribe
P2 ScribeP3 Scribe
Active Area
Scribe Loss Area
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End Scribe
P1 Scribe
P2 Scribe
Bus Bar(–)
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Light trapping
Incoming Light
Front Glass
Front TCO
n-Type a-SiIntrinsic a-Sip-Type a-Si
Back TCOBack Metal
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c-Si:H layer uniformity change
No significant thickness change
Fc: crystalline fraction– Calculated from film Raman
absorption spectrum– Raman condition:
Laser wavelength = 532 nm
Temperature = -49 C– fc is defined as:*
With modified RF feed– fc non-uniformity significantly
improved from 8.5% to 3.0%
ac
c
II
Ifc
250100exp1.0
100
250300350400450500550600
Raman shift (cm-1)
Measured
Ram
an a
bsor
ptio
n in
tens
ity ,
a.u.
IcIa
* R. E. I. Schropp and M. Zeman, Amorphous and microcrystalline silicon solar cells, Kluwer Academic Publishers, 1998
0
10
20
30
40
50
60
70
80
0 500 1000 1500 2000 2500
Distance (mm)
fc (%
)Series1
Series3
Legend RF feed NUfc (%)
Original 8.5
Modified 3.0
win
dow
Slit
val
ve