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“The Future of Thin-film Solar Cells” - TV Worldwide

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UNSW Photovoltaics Centre of Excellence

- supported by the Australian Research Council

“The Future of Thin-film Solar

Cells”

Martin A. Green

University of New South Wales

Sydney

UNSW

Photovoltaics - Electricity from Sunlight


Photovoltaics booming

10

New Capacity, GW

8

6

4

2

0

UNSW

2000

Source: Photon International

2002

2004

Bulk

2006

2008

2010

Thin-film

Photovoltaics - Electricity from Sunlight


First generation cells

150-200 µm

n ++

2-3 m m

Larger Si wafer area than ICs

Issues

. thinner cells

. simpler Si purification

. higher conversion efficiency

p +

p-type

UNSW

metal

Photovoltaics - Electricity from Sunlight


Second Generation: thin-film

Advantages

. low materials cost

. large manufacturing unit

. fully integrated modules

. aesthetics, ruggedness?

UNSW

Thin-film Technologies

. Silicon

. amorphous

. microcrystalline

. polycrystalline

. Chalcogenide (polycrystalline)

. CIS, CIGS [Cu (In,Ga(

In,Ga) ) (Se,S) 2 ]

. CdTe

. Dye sensitised, Organics

Photovoltaics - Electricity from Sunlight


Silicon Thin-Film

UNSW

a-Si,

µc-Si, c-Sic

amorphous, microcrystalline, (poly-)crystalline

Photovoltaics - Electricity from Sunlight


Chalcogenides: : CdTe and CIGS

CdTe

glass

TCO

window

alloy layer

SnO2

CdS

CdSxTe1-x

. highest efficiency

. tricky to deposit

. Cd toxic, In scarce

absorber

metal contact

. easily deposited

. Cd toxic, Te scarce

UNSW

CdTe

TCO

window

absorber

contact

substrate

glass

ZnO

CdS

CuInGaSeS

Cu (Ga,In) (Se,S) 2

Mo

Photovoltaics - Electricity from Sunlight

CIGS


Other Advanced Thin-

Films:

Dye-sensitised; Organic

UNSW

Photovoltaics - Electricity from Sunlight


Cost reduction

20000

10000

1981

Photovoltaics

(learning ~20%)

UNSW

2003 US$/kW

5000

2000

1000

500

Wind turbines

1982

Gas turbines (USA)

(~20%, ~10%)

USA (~20%)

1987

1963

2002

1993

2001

1980

200

0.01 0.1 1.0 10.0 100.0

Cumulative GW installed

World (~5%)

Adapted from

Grübler

et al.,1999

Photovoltaics - Electricity from Sunlight


Cost reduction

20000

10000

1981

Photovoltaics

(learning ~20%)

UNSW

2003 US$/kW

5000

2000

1000

500

Wind turbines

1982

Gas turbines (USA)

(~20%, ~10%)

USA (~20%)

1987

1963

2002

1993

2001

1980

200

0.01 0.1 1.0 10.0 100.0

Cumulative GW installed

Thin-film” Photovoltaics

World (~5%)

Thin-film

Adapted from

Grübler

et al.,1999

Photovoltaics - Electricity from Sunlight


The 3 generations

100

US$0.10/W

US$0.20/W

US$0.50/W

UNSW

Efficiency,%

80

60

40

20

II

III

0 100 200 300 400 500

I

Cost, US$/m2

Thermodynamic

limit

US$1.00/W

Present limit

US$3.50/W

Photovoltaics - Electricity from Sunlight

Bulk


The 3 generations

100

US$0.10/W

US$0.20/W

US$0.50/W

Thin-film

UNSW

Efficiency,%

80

60

40

20

II

III

0 100 200 300 400 500

Cost, US$/m2

Includes dye, organic

I

Thermodynamic

limit

US$1.00/W

Present limit

US$3.50/W

Photovoltaics - Electricity from Sunlight


Thermodynamic efficiency limits

E s

T A

W

S s

E c

T c

Q

S = Q/T A

S c

S G >0

UNSW

η ≤ (1-T A S s /E s ) = 93.3% (direct) = 73.7% (global)

Photovoltaics - Electricity from Sunlight


The 3 generations

?

. high-efficiency

. thin-film

. abundant

. non-toxic

. durable

UNSW

Efficiency,%

100

80

60

40

20

US$0.10/W

II

III

US$0.20/W

0 100 200 300 400 500

I

Cost, US$/m2

US$0.50/W

Thermodynamic

limit

US$1.00/W

Present limit

US$3.50/W

Photovoltaics - Electricity from Sunlight


UNSW approach

I

Evolutionary emphasis

upon crystalline silicon

(robust, abundant, non-

toxic)

UNSW

Photovoltaics - Electricity from Sunlight


UNSW approach

I

Evolutionary emphasis

upon crystalline silicon

(robust, abundant, non-

toxic)

II

UNSW

Photovoltaics - Electricity from Sunlight


I

UNSW approach

Evolutionary emphasis

upon crystalline silicon

(robust, abundant, non-

toxic)

III

?

II

UNSW

Photovoltaics - Electricity from Sunlight


Third generation options

100%

circulators

74%

68%

58%

54%

49%

44%

39%

31%

tandem (n )

hot carrier

tandem (n = 6)

thermal, thermoPV, thermionics

tandem (n = 3)

impurity PV & band, up-converters

impact ionisation

tandem (n = 2)

down-converters

single cell

UNSW

0%

Photovoltaics - Electricity from Sunlight


Third generation options

100%

circulators

74%

68%

58%

54%

49%

44%

39%

31%

tandem (n )

hot carrier

tandem (n = 6)

thermal, thermoPV, thermionics

tandem (n = 3)

impurity PV & band, up-converters

impact ionisation

tandem (n = 2)

down-converters

single cell

UNSW

0%

Photovoltaics - Electricity from Sunlight


Si-based tandems

Sunlight

Decreasing band gap

Free choice

or Si cell

AM1.5G Efficiency

40

30

20

10

29%

42.5%

33%

47.5%

45%

50.5%

UNSW

Free choice

Si bottom cell

Intrinsic radiative and Auger losses included

0

0

1 2 3

Number of cells

Photovoltaics - Electricity from Sunlight


Si-tandem concept

Up-converters ?

Metal

Resin

p+

p

n+

p+

p

'Crater' 'Groove' 'Dimple'

n+

Textured glass

CSG Solar approach

. high-T T silicon

. high-density contacts

. good optics

. deposit then process

. also suits hot-carrier

1 - 3 QD cells ?

Light In

UNSW

Photovoltaics - Electricity from Sunlight


Fabrication of Si quantum dots

SiOx, SiyNx, SiCx

SiO2, Si3N4, SiC

100nm

UNSW

Zacharias et al., APL 80, , 661, 2002

Photovoltaics - Electricity from Sunlight


Si quantum dot photoluminescence

Norm. PL Spectra

(2-5nm dots; 300K)

5nm (270s)

4nm (240s)

3nm (180s)

2nm (120s)

100nm

0

1.2 1.4 1.6 1.8 2

Photon energy, eV

UNSW

Photovoltaics - Electricity from Sunlight


Third generation options

100%

circulators

74%

68%

58%

54%

49%

44%

39%

31%

tandem (n )

hot carrier

tandem (n = 6)

thermal, thermoPV, thermionics

tandem (n = 3)

impurity PV & band, up-converters

impact ionisation

tandem (n = 2)

down-converters

single cell

UNSW

0%

Photovoltaics - Electricity from Sunlight


quantum dot

absorber

Hot-carrier cell concept

T a

Efficiency > 4 cell tandem

electron contact

hole contact

80

InN

T c

Si

tunneling

contact

Efficiency (%)

60

40

20

1

UNSW

2

hot carriers

cold carriers

0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Bandgap (eV)

absorber

100nm

Photovoltaics - Electricity from Sunlight


Summary

. need to fix carbon problem at source

– provide clean, more cost-effective electricity options

. photovoltaics provides a solution provided

– volumes increased and costs reduced dramatically

. high energy conversion efficiency is the key to lowest

possible long-term costs

. high efficiency thin-film technologies described for

post-2020 era

UNSW

Photovoltaics - Electricity from Sunlight

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