from innovation to commercialization – the story of solar ...from innovation to commercialization...
TRANSCRIPT
From Innovation to Commercialization – the Story of
Solar Cells
Subhendu GuhaUnited Solar Ovonic
2
Pearson, Chapin and Fuller, 1954Inventor of Si solar cell Bell lab document
1839 : Becquerel observed photovoltaic action in an electrolytic cell1876: Adams and Day discovered PV effect in solid Selenium1925: Czochralski grew single crystal silicon1940-1950: Golden era of semiconductor research including invention of pnjunction and transistor1954: First silicon solar cell demonstrated with 4.5% efficiency
New York Times - 1954
“…the beginning of a new era, leading eventually to the realization of harnessing the almost limitless energy of the sun for the uses of civilization.”
Evolution of Invention of Solar Cell
Phases of Commercialization
1956 Searching for ApplicationsDuring the first years after the discovery of the silicon solar cell, its prohibitive cost kept it out of the electrical power market. Desperate to find commercial outlets for solar cells, novelty items such as toys and radios run by solar cells were manufactured and sold as this advertisement illustrates.
3
Late 1950s - Saved by the Space Race
Dr. Hans Ziegler advocated for powering satellites with silicon solar cells. Solar cells used in Vanguard satellite
Early 1970s - The First Mass Earth Market
Solar cells power navigation warning lights and horns on most
off-shore gas and oil rigs throughout the world
4
1980s - Electrifying the UnelectrifiedA common sight in French Polynesia:
solar modules on thatched roofs
1980s - Solarizing the ElectrifiedSolar electric modules cover the rooftops of
this apartment complex in Bremen, Germany
Phases of Commercialization
5
Shipment Growth and Price Reduction
PV is a $50 billion business today; the shipment has gone up 3000 times and price has come down by a factor of 20 in the last three decades
1
10
100
1000
10000
100000
1
10
100
1000
1970 1975 1980 1985 1990 1995 2000 2005 2010
PV m
odul
e pr
ice
($/W
)
Years
MW
Topics to Discuss
6
•Semiconductor physics
•Solar cells
•Different materials for solar cells
•Thin film silicon solar cell
•Building-integrated photovoltaic
•Future direction
7
Physics of Semiconductor
Intrinsic semiconductor n-type semiconductor p-type semiconductor
PN junction
Physics of Solar Cell
8
Photons are absorbed to create free carriers; these are transported to the contacts
Light createselectron-hole pair
You can connect several solar cells in series and encapsulate to complete the module
9
Requirement for high efficiency solar cell
•Optimum bandgap to match the solar spectrum•High quality material so that the electron-hole pairs can be transported to the contacts without recombination
Si GaAs CdTe
Materials for High Efficiency Cells
1010
Global Shipment by Technology
Source: PV News, May 2011
Silicon technology still dominates the market United Solar is the third largest thinfilm silicon solar cell manufacturer
Other Technologies are Gaining Traction
11
Tota
l
Tota
l
Tota
l
Tota
l
Gla
ss
Gla
ss
Gla
ss
Gla
ssFlex
ible
Flex
ible Fl
exib
le
Flex
ible
0
1000
2000
3000
4000
5000
6000
a-Si CdTe CIGS Other
Ann
ounc
ed 2
012
Capa
city
(MW
)
Announced production Capacities - 2010
Major Players
12
Sharp SolarPowerKyoceraBP SolarQ-CellsMitsubishiSolarWorldPanasonic (Sanyo)Schott SolarIsofotonMotechSuntechEvergreen SolarJA Solar
United SolarKanekaFuji ElectricSharpMitsubisihiSchott SolarTronyEPVPowerFilmAMAT licenseesOrelikonlicensees
NanosolarAvancisSolar FrontierWurthSolarGlobal SolarHonda Soltec
First SolarAntec SolarAbound SolarPrimeStar SolarCalyxo
There are currently more than 300 companies developing or producing solar cells.With prices continuing to decrease, and more companies entering themarket, many small companies and start-ups are likely to fail
C-Si or pc-Si Thin Film Si CIGS CdTe
Ref: Carlson, APS Meeting, 2010
13
Global Cell Production
U.S. lags behind in both production and deployment
Manufacturing of Silicon Solar Cell
14
Growth of polysilicon
chunks/grains
Deposition of anti-reflection coating and
sintering
Interconnect and
encapsulateApply junction boxes and test
Screen-printing/evapo
ration of contacts
Growth of silicon ingots
Slicing into wafers and
etching
Diffusion of impurities
Ship
15
Cell process steps and structure
Silicon Solar Cell
16
High Efficiency Devices
BURIED CONTACT BACK CONTACT
PERL (PASSIVATED EMITTER)
17
CdTe Solar Cell
Recognized as a semiconductor with near-ideal bandgap match to solar spectrum
• 1960’s : Solar cells made by GE, Matsushita, Monosolar
• 1981 : Kodak enters the field with 10% efficiency
• 1992 : University of South Florida demonstrates 15% cell
• 2002 : 7% products available from First Solar
• 2009 : First Solar emerges as the world’s largest PV manufacturer
18
Glass
Tin Oxide
CdS
CdTe
Interface layer
Metal
Wet chemical process*
Closed space sublimation, vapor transport*
Sputtering*
* Other processes are also used
CdTe Cell Structure
19
Monolithic Module
20
CIGS Solar Cell
Of all the thin film technologies, CIGS has received a great deal of efficiency because of high efficiency obtained in the laboratory. Manufacturing has been a challenge. Degradation due to moisture is another issue
• 1973 : First thin film CIS solar cell demonstrated•1980’s: Boeing leads efforts in CIS cells; ARCO Solar joins the race•1990’s: NREL demonstrates high efficiency solar cells•2000 – 2010: Many companies enter the field
Manufacturing process•Co-evaporation•Sputtering•Sputtering followed by selenization•Electroplating•Ink-growth
21
Zinc Oxide
CdS
CIGS
Mo
Metal/glass
Wet chemical process*
Co-evaporation, sputtering, plating*
Sputtering*
* Other processes are also used
Cell Structure and Manufacturing
Manufacturing: Laser-integrated or cell interconnected
22
1969: First report of amorphous silicon (a-Si) thin film deposited by glow-discharge decomposition of silane: Chittick, STL, U.K.
1974: Report by Walter Spear of University of Dundee that a-Si has low defect states in the band gap
1975: Report by Walter Spear that a-Si can be doped n-type or p-type
1976: First solar cell made at RCA laboratory by David Carlson (2% efficiency)
1977: Report of light-induced degradation of a-Si by Dave Staebler and Chris Wronski of RCA
1979: First a-Si alloy solar cell for calculators introduced in the market
1981: ECD/Uni-Solar enters the field
2010 : 1300 MW global manufacturing
Amorphous Silicon
From Innovation to Commercialization
NREL validation
2 MW Machine
Prototype Machine
0.5 MW Machine
5 MW Machine Auburn Hillsfacility (1&2) 60MW
Greenville 120 MW
Building-integrated(BIPV) product
Acquisition ofSolar Integrated
Technologies
1981 1986 1991 1994 1996 1997 2003 2007 2009
More than 65 issued U.S. Patents
23
24
Advantages• Low material cost• Short energy pay back
time• Superior high
temperature performance
• Environmentally safe• Rugged and flexible
products
Challenges• Light-to-electricity
conversion efficiency• Manufacturability
Amorphous Silicon
25
GROWTH OF AMORPHOUS SILICON USING HYDROGEN DILUTION
The best material is grown with hydrogen dilution of the active gas. As the hydrogen dilution increases, there is a transition from amorphous to nanocrystalline structure. The highest quality materials for both the nanocrystalline and amorphous phases are obtained near the edge of this transition. Materials grown on both sides of the edge are receiving a great deal of attention for solar cell applications. 2
6
10
14
18
1 10 100
IRERDA
Hyd
roge
n C
onte
nt [a
t.-%
]
Silane Concentration [%]
a-Si:H regimeµc-Si:H regime
SiH4 --- Si + 2H2Deposition of amorphous SiH alloy
HEATER
GAS (SiH4)
SUBSTRATE
TO VACUUM
RF POWER
Amorphous Silicon
26
Amorphous Materials
• Unlike crystals, amorphous or disordered materials do not have any long-range order. There is no periodicity in the arrangement of the atoms.
° °• ° • °•
° •° °• °•
° °• ° • °•
° °• °• •°Crystals °Amorphous •
9
2727
What Does Disorder Cause?
• Weak bonds, dangling bonds, band tails
- these defects impede carrier transport
• Facilitates efficient light absorption
- allows use of thin film
How to Improve Efficiency?
• Have better order with more stable structure - Role of hydrogen dilution• Use multijunction cells to facilitate better absorption
Blue
Green
Red
Reflector
Nano -crystalline
28
Amorphous Silicon Alloy Triple-Junction Cell Processor
Six rolls of stainless steel, each 2.5 km long, processed in a single run in 65 hours.
Manufacturing
29
30
Small area machine 2” by 2” substrate Large area machine 15” by 14” substrate
Large-area machine (3 14” webs) Roll-to-roll production machine
From Lab to Production
31
United Solar- A Differentiated Product
Conventional Solar Cells UNI-SOLAR® Laminates
31
32
Competitive Advantages
Photo courtesy Solar Integrated
Low-impact solar roof solutionLightweight, durable, flexible Ideal for Building Integrated (BIPV)Easy to installRemovableNew lightweight BAPV application
GM Facility / Zaragoza, Spain / 11.8 MW Enel Green Power / Nola, Italy / 25 MW
Tesco | Fresh & Easy / Riverside, CA / 2 MW Posco Warehouse / Pohang, South Korea / 1 MW
UNI-SOLAR Largest Rooftop Solar Installations
37
Improved Light Trapping: Back Reflector
Improved Light Trapping
Anti-reflective coating
Blue light-absorbing cell
Green light-absorbing cell
Red light-absorbing cell
Back reflector
Stainless steel substrate
Cross-section of a solar cell
Back reflector
38
Nano Technology
Nano Technology replaces green and red light-absorbing layers
• Compatible with a-Si alloy deposition
• Ideal for middle and bottom cells of multi-junction structure
• Improved light absorption and no light-induced degradationof nano layers has resulted in conversion efficiency of 12% in in the lab
Anti-reflective coating
Blue light-absorbing cell
Green light-absorbing cell
Red light-absorbing cell
Back reflector
Stainless steel substrate
Results in greater stability and higher conversion efficiency
39
40
0
1000
2000
3000
4000
5000
6000
7000
8000
2004 2005 2006 2007 2008 2009
JAP
ITA
ROE
USA
ROW
GermanySpain
MW
INCENTIVE DRIVEN GROWTH
Global Shipment of PV
Grid parity
Cost per kW hour (in constant 2005 US dollars)
Source: Solar America Initiative
$0.00
$0.20
$0.40
$0.60
$0.80
$1.00
1990 2000 2010 2020Year
Challenge for PV--How to Reach Grid Parity
Cost of solar electricity is decreasing every year. We are on our path to grid parity.
41
42
Problems with Conventional Fuel
• PollutionThe power plants emit mercury and sulphur dioxide resulting in acid rain. There is particulate (soot) emission, too. The pollution causes diseases having a severe impact on the economy.
• Global WarmingThe emission of greenhouse gases like CO2 and NOx lead to global warming; research studies attribute many of the recent severe weather calamities to global warming.
• Energy PovertyThere are 2 billion people in the world without access to electricity. Distributed power in the form of renewables like PV is the only option for them.
43
“In the end, more than they wanted freedom, they wanted a comfortablelife-and they lost both comfort and freedom. When the Athenians wantednot to give to society but for society to give to them, when the freedomthey wished for most was freedom from responsibility, then Athensceased to be free” – Edith Hamilton