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“ “ The Future of ThinThe Future of Thin--film Solar film Solar
CellsCells” ”
Martin A. GreenMartin A. GreenUniversity of New South WalesUniversity of New South Wales
Sydney Sydney
UNSW Photovoltaics Centre of Excellence- supported by the Australian Research Council
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Photovoltaics booming Photovoltaics booming
2 0 0 0
2 0 0 2
2 0 0 4
2
0 0 6
2 0 0 8
2 0
1 0
0
2
4
6
8
10
N e w C a p a c i t y , G W
Source: Photon International
ThinThin--filmfilm
Bulk Bulk
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First generation cells First generation cells
p-type
n ++
p +
metal
150-200 µm2-3 m m
Larger Si wafer area than ICs Larger Si wafer area than ICs
Issues Issues
. thinner cells. thinner cells. simpler Si purification. simpler Si purification
. higher conversion efficiency. higher conversion efficiency
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Second Generation: thin Second Generation: thin - - film film
Advantages Advantages
. low materials cost . low materials cost . large manufacturing unit . large manufacturing unit
. fully integrated modules. fully integrated modules
. aesthetics, ruggedness?. aesthetics, ruggedness?
Thin Thin - - film Technologies film Technologies
.. Silicon Silicon . amorphous. amorphous. microcrystalline. microcrystalline. polycrystalline. polycrystalline
.. Chalcogenide Chalcogenide (polycrystalline)(polycrystalline). CIS, CIGS [Cu ( . CIS, CIGS [Cu ( In,GaIn,Ga ) (Se,S) ) (Se,S)2 2 ] ] .. CdTeCdTe
.. Dye sensitised Dye sensitised ,, Organics Organics
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Silicon Thin Silicon Thin - - Film Film
aa--Si,Si, µ µ c c --Si, c Si, c --Si Si
amorphous, microcrystalline, (poly amorphous, microcrystalline, (poly -- )crystalline )crystalline
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Chalcogenides Chalcogenides : CdTe and CIGS : CdTe and CIGS
. easily deposited . easily deposited
. Cd toxic, Te scarce . Cd toxic, Te scarce
. highest efficiency . highest efficiency
. tricky to deposit . tricky to deposit
. Cd toxic, In scarce . Cd toxic, In scarce CdTeCdTe
CIGSCIGS
glass
TCO
windowalloy layer
absorber
metal contact
SnO2CdS
CdSxTe1-x
CdTe
contact Mo
TCOwindow
absorber
ZnO
glass
Cu (Ga,In) (Se,S)2
CdS
substrate
CuInGaSeSCuInGaSeS
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Other Advanced Thin Other Advanced Thin - - Films: Films:
Dye Dye - - sensitised; Organic sensitised; Organic
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Cost reduction Cost reduction
20000
10000
5000
2000
1000
500
200 0.01 0.1 1.0 10.0 100.0
Gas turbines (USA)
(~20%, ~10%)
1980
1963
1982
1987 1993
2001
Wind turbines
2002
Cumulative GW installed
1981
Photovoltaics (learning ~20%)
USA (~20%)
World (~5%)
2 0 0 3 U S $ / k
W
Adapted from Adapted from
Gr Gr ü ü bler bler et al.,1999 et al.,1999
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ThinThin--filmfilm
Cost reduction Cost reduction
20000
10000
5000
2000
1000
500
200 0.01 0.1 1.0 10.0 100.0
Gas turbines (USA)
(~20%, ~10%)
1980
1963
1982
1987 1993
2001
Wind turbines
2002
Cumulative GW installed
1981
Photovoltaics (learning ~20%)
USA (~20%)
World (~5%)
2 0 0 3 U S $ / k
W“ “ Thin Thin - - film film ” ” Photovoltaics Photovoltaics
Adapted from Adapted from
Gr Gr ü ü bler bler et al.,1999 et al.,1999
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The 3 generationsThe 3 generations
II
100
80
60
20
0 100 200 300 400 500
US$0.50/W
US$1.00/W
US$3.50/W
Cost, US$/m2
US$0.10/W US$0.20/W
Present limitIII
Thermodynamiclimit
40
I
E f f i c i e n
c y , %
Bulk Bulk
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The 3 generationsThe 3 generations
II
100
80
60
20
0 100 200 300 400 500
US$0.50/W
US$1.00/W
US$3.50/W
Cost, US$/m2
US$0.10/W US$0.20/W
Present limitIII
Thermodynamiclimit
40
I
E f f i c i e n
c y , %
Includes dye, organic Includes dye, organic
ThinThin--filmfilm
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Thermodynamic efficiency limitsThermodynamic efficiency limits
Tc
Es
Ss
Ec
Sc
SG>0
TA
W
Q
S = Q/TA
η ≤ (1-T ASs /E s ) = 93.3% (direct) = 73.7% (global)
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The 3 generationsThe 3 generations
?
II
100
80
60
20
0 100 200 300 400 500
US$0.50/W
US$1.00/W
US$3.50/W
Cost, US$/m2
US$0.10/W US$0.20/W
Present limitIII
Thermodynamiclimit
40
I
E f f i c i e n
c y , %
. high . high--efficiencyefficiency . thin . thin-- film film . abundant . abundant
. non . non-- toxic toxic . durable . durable
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UNSW approachUNSW approach
I I
Evolutionary emphasis Evolutionary emphasis upon crystalline silicon upon crystalline silicon
(robust, abundant, non (robust, abundant, non - -
toxic) toxic)
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UNSW approachUNSW approach
I I
II II
Evolutionary emphasis Evolutionary emphasis upon crystalline silicon upon crystalline silicon
(robust, abundant, non (robust, abundant, non - -
toxic) toxic)
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Third generation optionsThird generation options
100%
74%
68%
54%49%44%
39%31%
0%
58%
circulators
tandem (n )hot carrier
impurity PV & band, up-converterstandem (n = 3)thermal, thermoPV, thermionics
impact ionisationtandem (n = 2)
down-converterssingle cell
tandem (n = 6)
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Third generation optionsThird generation options
100%
74%
68%
54%49%44%
39%31%
0%
58%
circulators
tandem (n )hot carrier
impurity PV & band, up-converterstandem (n = 3)thermal, thermoPV, thermionics
impact ionisationtandem (n = 2)
down-converterssingle cell
tandem (n = 6)
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Si Si --based tandemsbased tandems
42.5%
47.5%50.5%
Number of cells
1 2 3
10
20
30
40
0
0
Si bottom cell
Free choice
29%
33%
45%
A M 1 . 5
G
E f
f i c i e n c y
Free choice
or Si cell
Decreasing band gap
Sunlight
Intrinsic radiative and Auger losses included Intrinsic radiative and Auger losses included
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Si Si --tandem concept tandem concept
CSG Solar approach CSG Solar approach
. high . high - - T silicon T silicon
. high . high - - density contacts density contacts
. good optics . good optics
. deposit then process . deposit then process
. also suits hot . also suits hot - - carrier carrier
Metal
Resin
p+
n+
Light In
p+p
n+
p
Textured glass
'Crater' 'Groove' 'Dimple'
Up-converters ?
1 - 3 QD cells ?
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100nm100nm
Fabrication of Si quantum dotsFabrication of Si quantum dots
SiOx, SiyNx, SiCx
SiO2, Si3N4, SiC
Zacharias et al., APLZacharias et al., APL 80 80 , 661, 2002 , 661, 2002
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Si quantum dot photoluminescenceSi quantum dot photoluminescence
Norm. PL Spectra
(2-5nm dots; 300K)
01.2 1.4 1.6 1.8 2
Photon energy, eV
5nm (270s)4nm (240s)
3nm (180s)2nm (120s)
100nm100nm
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Third generation optionsThird generation options
100%
74%
68%
54%49%44%
39%31%
0%
58%
circulators
tandem (n )hot carrier
impurity PV & band, up-converterstandem (n = 3)thermal, thermoPV, thermionics
impact ionisationtandem (n = 2)
down-converterssingle cell
tandem (n = 6)
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Hot Hot --carrier cell concept carrier cell concept
tunnelingcontact
absorber
100nm100nm
Bandgap (eV)
cold carriers
0.0 0.5 1.0 1.5 2.0 2.5 3.0
80
60
40
20
0
E f f i c i e n c y ( % )
1
2hot carriers
InN Si
quantum dot absorber
hole contactelectron contact
TTaa
TTcc
Efficiency > 4 cell tandem
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Summary Summary
.. need to fix carbon problem at sourceneed to fix carbon problem at source – – provide clean, more cost provide clean, more cost --effective electricity optionseffective electricity options
. photovoltaics provides a solution provided . photovoltaics provides a solution provided
– – volumes increased and costs reduced dramatically volumes increased and costs reduced dramatically
. high energy conversion efficiency is the key to lowest . high energy conversion efficiency is the key to lowest
possible long possible long --term coststerm costs. high efficiency thin. high efficiency thin--film technologies described for film technologies described for
post post --2020 era2020 era