Transcript Overview of solar cells activity at SunPower Corporation

High performance silicon solar cells
Gabriela Bunea Ph.D.
SunPower Corporation
17 October 2003
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Outline
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Background
SunPower brief history
High efficiency solar cells
High volume manufacturing
Future directions
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Questions often heard from the
general public
• Why have solar cells never become a
substantial source of energy?”
• “Too bad solar never made it, it seemed so
promising back in the 1970s.”
• “When will the big breakthrough come that will
make solar cells practical?”
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Answers and fun facts
• Solar cell manufacturing is a vital and rapidly growing
industry, enjoying over 30% annual growth over the last
10 years.
• In 2002, more square inches of silicon was used by the
solar cell industry than the IC industry.
• There will be no big breakthrough that impacts the
industry for at least 10 years, and probably 20 years.
• Instead, the existing technologies will evolve to where
they will be cost effective in most distributed applications
in 10 years, and will be competitive with fossil fuel
generation in 20 years.
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Solar Cell Price Exhibits a Classic
Experience Curve Behavior
100
Module Price ($/W) ($2002)
Historical
1980
$21.83/W
Projected
1985
$11.20/W
10
1990
$6.07/W
1995
$4.90/W
2000
$3.89/W
2002
$3/W
2005
$2.70/W
2010
$1.82/W
2013
$1.44/W
1
1
10
100
1000
10000
100000
Cum ulative Production (MW)
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Solar Cell Rules of Thumb
• The annual production of solar modules
increases ten-fold every decade
• The price of solar cell modules decreases by
half every decade
– 2002: $3.00/W
– 2012: $1.50/W
– 2022: $0.75/W
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Silicon Module Cost Components
Module
Assembly
30%
Ingot
Growth
30%
Higher efficiency leverages cost
savings throughout the value
chain
Investing in high efficiency cell
processing makes economic
sense
Cell
Processing
20%
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Wafering
20%
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Factors Driving Past
Cost Reduction
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Poly silicon price: $300/kg → $30/kg
Wire saws: now < $0.25/W
Larger wafers: 3” → 6”
Thinner wafers: 15 mil → 8 mil
Improved efficiency: 10% → 16%
Volume manufacturing: 1MW → 100MW
Increased automation: none → some
Improved manufacturing processes
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The Renewable Energy Revolution
• Renewable energy will capture a
meaningful share of the Global
Energy Market in the next 25
years.
• Key drivers will be:
– Falling costs for renewable
energy
– Declining fossil fuel
production
– Increasing energy demand
worldwide
– Environmental concerns
Oil industry consensus:
production will peak between 2004 and
2010
Source: C.J.Campbell “World Oil Resources” Dec 2000
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The Future of Renewables
Projected World Energy Production
200
2060
2040
2020
1999
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Geo
Solar
Wind
Hydro
Biomass
Nuclear
Gas
0
Oil
100
Coal
Exajoules
300
Source: Royal Dutch Shell Group
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SunPower company history
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1985: Record efficiency Silicon Solar Cell developed at Stanford
Univ.
1988: SunPower formed to commercialize technology for
concentrator applications
1993: SunPower supplies solar cells for Honda Dream, winner of
World Solar Challenge
1994: Opto product line introduced
1996: Honda invests
1998: HP selects SunPower for IrDA detectors
1998: Pegasus product line introduced.
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Company History (cont.)
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2000: SunPower ships 35 kW to
AeroVironment for Helios solar
airplane.
2001: Helios flies to 96,500 ft.
2001: Low-cost, back-contact cell
manufacturing process developed
2002: Cypress Semiconductor
invests
2002: 21.1% efficiency one-sun in
Austin, TX pilot line
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Solar cell operation
I
dark
qV


I  I 0 exp(
)  1  I L
nkT


Voc
V
light Isc
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Solar cell parameters
V I
Fill Factor: FF  MP MP
VOC I SC
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VMP I MP
Efficiency:  
PIN
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Solar spectrum
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SunPower solar cells
• One-sun
• Concentrator
Building integrated
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Remote industrial
Remote for habitat
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SunPower one-sun Si solar cell
A-300
5” semi-square
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Efficiency Losses in Silicon
Detailed balance limit
Silicon material intrinsic loss
(Auger recombination,
non-optimum bandgap)
Implementation loss
Conventional
Cell
Practical
Efficiency
Limit
4.0%
4.0%
33%
4.4%
29%
Silicon
Limit
14.3%
24.6%
Resulting efficiency
14.7%
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Conventional Solar Cell Loss Mechanisms
Reflection Loss
I2R Loss
1.8%
0.4%
0.4%
0.3%
1.54%
3.8%
Recombination
Losses
2.0%
1.4% Back Light
Absorption
Limit Cell Efficiency
Total Losses
Generic Cell Efficiency
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2.6%
29.0%
-14.3%
14.7%
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Popular Efficiency-Enhancing Processes
•Aluminium or boron back-surface field (BSF)
•Silicon nitride ARC
•Laser buried grid metallization.
•Selective emitter
•Oxide passivation with restricted metal contact
openings.
•Rear surface reflector.
•Higher lifetime silicon wafers
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17 October 2003
e
tiv
le
c
te
d
Em
e
el
l
Ba
s
C
(R
LC
)
(B
SF
)
itt
e
ts
ld
ta
c
Fi
e
lC
on
e
im
e
Em
itt
18.0%
r(
PE
)
er
(S
E)
BS
F+
H
ig
PE
h
Li
S
fe
E
tim
+
RC
e
+
L
SE
+
R
CL
Se
ca
iva
ss
Lo
rfa
c
fe
t
on
lS
ilic
14.7%
Pa
ea
r
Su
Li
na
ig
h
tio
Cell Efficiency
16.0%
R
ck
H
en
on
v
Ba
C
Impact of High Efficiency Processes
22.0%
21.2%
19.7%
20.0%
18.3%
16.5% 16.8%
17.1%
14.8%
15.6%
14.0%
12.0%
10.0%
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High-Efficiency Back-Contact Loss
Mechanisms
0.5%
0.8%
1.0%
0.2%
0.3%
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0.2%
0.2%
1.0%
Limit Cell Efficiency
29.0%
Total Losses
-4.4%
Enabled Cell Efficiency
24.6%
I2R Loss
0.1%
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Efficiency vs Lifetime
• This effect is magnified in
rear-contact solar cells.
• Conclusion: desire > 1
ms.
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Cell efficiency (%)
• A lower lifetime
– reduces the collection
of minority carriers,
– increases bulk
recombination.
15
10
5
0
0.01
0.1
1
10
Minority-carrier lifetime (ms)
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Efficiency vs Cell Thickness
• A thinner cell
• But thinner cells lose
photogenerated current
because not all photons
absorbed.
• Over range 160–280 um
efficiency is about
constant.
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Cell efficiency (%)
– increases the collection
efficiency of minority
carriers,
– reduces bulk
recombination.
20
18
16
160
200
240
280
320
Cell thickness (um)
Simulated with t = 3 ms.
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Concentrators solar cells
• Can achieve a higher efficiency because a higher carrier
density increases output voltage
Heda312 with cover glass Efficiency vs. Irradiance
NREL
30.00
Efficiency (%)
25.00
20.00
15.00
10.00
0
5
10
15
20
25
30
35
40
45
50
Irradiance (W/cm2)
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Concentrator Solar Cells
HECO
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HEDA
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One-sun
Concentrator
P+
1/
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FSF
1/
N+
P+
N+
N+
P+
FSF
SiO2
SiO2
n
n
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High efficiency Si Concentrators solar cells
Cross section
Texture + ARC
Front
Passivating
Oxide
Single Crystal Silicon
P+
Back
N+
P+
N+
P+
Gridlines
N+
Localized Point
Contacts
Record efficiency=26.8% at 25W/cm2 Irradiance
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Challenges in processing high
efficiency Si solar cells
• Process thin wafers
• Anti-reflection coating
• Low temperature passivation
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Conclusions and future directions
• Solar generated energy will play a major
role in energy generation
• One sun: high volume manufacturing of
20% efficiency solar cells
• Concentrators:
– 30% Si cell
– 6” wafers
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Acknowledgments
• Dr. Dick Swanson
• Dr. Akira Terao
• Dr. David Smith
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