Guha Presentation 2011

8/4/2019 Guha Presentation 2011

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From Innovation toCommercialization the Story of

Solar Cells

Subhendu Guha

United Solar Ovonic


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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 newera, leading eventually tothe realization of

harnessing the almostlimitless energy of the sunfor the uses of civilization.

Evolution of Invention of Solar Cell


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Phases of Commercialization

1956 Searching for Applications

During the first years after the

discovery of the silicon solar cell,its prohibitive cost kept it out of theelectrical power market. Desperateto find commercial outlets for solarcells, novelty items such as toysand radios run by solar cells were

manufactured and sold as thisadvertisement illustrates.

3

Late 1950s - Saved by theSpace Race

Dr. Hans Ziegler advocated for

powering satellites with siliconsolar cells. Solar cells used inVanguard satellite


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Early 1970s - The First Mass

Earth MarketSolar cells power navigation

warning lights and horns on mostoff-shore gas and oil rigs

throughout the world

4

1980s - Electrifying the Unelectrified

A common sight in French Polynesia:solar modules on thatched roofs

1980s - Solarizing the Electrified

Solar electric modules cover the rooftops ofthis apartment complex in Bremen,

Germany

Phases of Commercialization


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5

Shipment Growth and Price Reduction

PV is a $50 billion business today; the shipment has gone up3000 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

PVm

oduleprice($/W)

Years

MW


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Topics to Discuss

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Semiconductor physics

Solar cells

Different materials for solar cells

Thin film silicon solar cell

Building-integrated photovoltaic

Future direction


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Physics of Semiconductor

Intrinsic semiconductor n-type semiconductor p-type semiconductor

PN junction


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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 inseries and encapsulate to completethe module
http://upload.wikimedia.org/wikipedia/commons/9/90/Solar_cell.png


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Requirement for high efficiency solar cell

Optimum bandgap to match the solar spectrumHigh quality material so that the electron-hole pairs can be transported tothe contacts without recombination

Si GaAs CdTe

Materials for High Efficiency Cells
http://upload.wikimedia.org/wikipedia/commons/4/4c/ShockleyQueisserFullCurve.svghttp://upload.wikimedia.org/wikipedia/commons/4/4c/ShockleyQueisserFullCurve.svg


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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


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Other Technologies are Gaining Traction

11

Tota

l

Total

Total

Total

Glass

Glass

Glass

Glass

Flexible

Flexible F

lexible

Flexible

0

1000

2000

3000

4000

5000

6000

a-Si CdTe CIGS Other

Announced2012

Capacity(MW)

Announced production Capacities - 2010


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Major Players

12

Sharp

SolarPowerKyoceraBP SolarQ-CellsMitsubishiSolarWorldPanasonic

(Sanyo)Schott SolarIsofotonMotechSuntechEvergreen Solar

JA Solar

United Solar

KanekaFuji ElectricSharpMitsubisihiSchott SolarTronyEPV

PowerFilmAMAT licenseesOrelikon

licensees

Nanosolar

AvancisSolar

FrontierWurth

SolarGlobal

Solar

HondaSoltec

First Solar

Antec SolarAbound SolarPrimeStar SolarCalyxo

There are currently more than 300 companies developing or producing solarcells.

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


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Global Cell Production

U.S. lags behind in both production and deployment


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Manufacturing of Silicon Solar Cell

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Growth of

polysiliconchunks/grains

Deposition ofanti-reflectioncoating and

sintering

Interconnectand

encapsulate

Apply junctionboxes and test

Screen-printing/evapo

ration ofcontacts

Growth ofsilicon ingots

Slicing into

wafers andetching

Diffusion ofimpurities

Ship


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Cell process steps and structure

Silicon Solar Cell


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High Efficiency Devices

BURIED CONTACT BACK CONTACT

PERL (PASSIVATED EMITTER)


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CdTe Solar Cell

Recognized as a semiconductor with near-ideal bandgap match to solar spectrum

1960s : 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 worlds largest PV manufacturer


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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


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Monolithic Module


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CIGS Solar Cell

Of all the thin film technologies, CIGS has received a great deal of efficiencybecause of high efficiency obtained in the laboratory. Manufacturing hasbeen a challenge. Degradation due to moisture is another issue

1973 : First thin film CIS solar cell demonstrated1980s: Boeing leads efforts in CIS cells; ARCO Solar joins the race

1990s: NREL demonstrates high efficiency solar cells2000 2010: Many companies enter the field

Manufacturing processCo-evaporationSputteringSputtering followed by selenizationElectroplatingInk-growth


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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


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22

1969: First report of amorphous silicon (a-Si) thin film deposited by glow-dischargedecomposition of silane: Chittick, STL, U.K.

1974: Report by Walter Spear of University of Dundee that a-Si has low defectstates 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 ChrisWronski 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


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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


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Advantages

Low material cost

Short energy pay backtime

Superior hightemperatureperformance

Environmentally safe

Rugged and flexibleproducts

Challenges

Light-to-electricityconversion efficiency

Manufacturability

Amorphous Silicon


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GROWTH OF AMORPHOUS SILICONUSING HYDROGEN DILUTION

The best material is grown withhydrogen dilution of the activegas. As the hydrogen dilutionincreases, there is a transitionfrom amorphous tonanocrystalline structure. Thehighest quality materials forboth the nanocrystalline andamorphous phases areobtained near the edge of this

transition. Materials grown onboth sides of the edge arereceiving a great deal ofattention for solar cellapplications. 2

6

10

14

18

1 10 100

IR

ERDA

HydrogenContent[at.-%]

Silane Concentration [% ]

a-Si:H regimec-Si:H regime

SiH4 --- Si + 2H2Deposition of amorphous SiH alloy

HEATER

GAS(SiH4)

SUBSTRATE

TOVACUUM

RFPOWER

Amorphous Silicon


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Amorphous Materials

Unlike crystals, amorphous or disordered

materials do not have any long-range order.There is no periodicity in the arrangement of theatoms.

Crystals Amorphous


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What Does Disorder Cause?

Weak bonds, danglingbonds, band tails

- these defects impede

carrier transport Facilitates efficient

light absorption

- allows use of thin film


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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


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Amorphous Silicon Alloy Triple-Junction Cell Processor

Six rolls ofstainless steel,each 2.5 km

long, processedin a single run in65 hours.

Manufacturing

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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

U it d S l A Diff ti t d P d t


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United Solar- A Differentiated Product

Conventional Solar Cells UNI-SOLAR

Laminates

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Competitive Advantages


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Competitive Advantages

Photo courtesy Solar Integrated

Low-impact solar roof solution

Lightweight, durable, flexible

Ideal for Building Integrated (BIPV)

Easy to install

Removable

New lightweight BAPV application


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UNI-SOLAR Largest Rooftop Solar Installations


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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

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I d Li ht T i B k R fl t


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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

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Nano Technology


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Nano Technology

Nano Technology replacesgreen 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% inin 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

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0

1000

2000

3000

4000

5000

6000

7000

8000

2004 2005 2006 2007 2008 2009

JAP

ITA

ROE

USA

ROW

Germa

nySpain

MW

INCENTIVE DRIVEN GROWTH

Global Shipment of PV

Challenge for PV Ho to Reach Grid Parit


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Grid parity

Cost per kW hour

(in constant2005 US dollars)

Source: Solar America Initiative

$0.00

$0.20

$0.40

$0.60

$0.80

$1.00

1990 2000 2010 2020

Year

Challenge for PV--How to Reach Grid Parity

Cost of solar electricity is decreasing

every year. We are on our path to grid parity.

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Problems with Conventional Fuel

PollutionThe power plants emit mercury and sulphur dioxide resulting inacid rain. There is particulate (soot) emission, too. Thepollution causes diseases having a severe impact on theeconomy.

Global WarmingThe emission of greenhouse gases like CO2 and NOx lead toglobal warming; research studies attribute many of the recentsevere weather calamities to global warming.

Energy Poverty

There are 2 billion people in the world without access toelectricity. Distributed power in the form of renewables like PVis the only option for them.


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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 Athens

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Guha Presentation 2011

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