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

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