Universidade do Minho
Thin film silicon solar cells
and modules
Pedro Alpuim
Department of Physics
Universidade do Minho
Guimarães, Portugal
Mikkeli, March 17
17-19,
19, 2010, Finland
Outline
Universidade do Minho
•
•
•
Motivation: market analysis
a-Si:H
a
Si:H and nc-Si:H
nc Si:H thin film solar cell fundamentals
High efficiency concepts:
– Multijunction solar cells
– Light trapping
•
•
Low cost flexible thin film Si solar cells and modules
Conclusions
Universidade do Minho
Motivation: PV will continue to grow
US, Italy, and China, together 50% of the 2010 growth picture
Average Selling Prices
50
40
25
-25%
20
15
30
10
20
5
10
0
0
* * * *
Sources: iSupply, EPIA, DisplaySearch
Annual P
A
PV marrket (GW
Wp)
30
1998
1999
2000
2
2001
2
2002
2
2003
2
2004
2
2005
2
2006
2
2007
2
2008
2
2009
2
2010
2
2011
2
2012
2
2013
2
G
Global
ccumulattive PV
V
power in
p
nstalled
d (GWp)
60
Year
*estimated
Universidade do Minho
Motivation: thin film will grow
faster than wafer PV market
Source: OerlikonSolar, Photovoltaics World
2010-2012
2010• 2010 year of adapting FIT in Germany (others will follow…)
• Supply & demand will continue to swing between over and under supply
• Production capacity still exceeds installations (slower price decline than 2009)
• Margins reduced to installations, module prices under pressure
Universidade do Minho
Thin film PV: 3 leading technologies
Module production 2009: thin films => 496 MW; wafer => 1007 MW
Module prognostics 2010: thin films => 819 MW; wafer => 1658 MW
PV Modules (MWp)
1000
1000
production
d i 2009
capacity 2009
808
800
prognostic 2010
capacity 2010
988
800
Nano solar (640 MW)
600
600
318
400
200
FirstSolar (99%)
213 237
198
85
0
a-Si:H
Si H
CIGS
CdT
CdTe
400
367
428
225
227 237
200
0
a-Si:H
CIGS
CdTe
Thin film solar module production in Germany 2009
2009-2010
2010
Source: Photon
Universidade do Minho
Light absorption by thin
thin--film
materials for solar cells
A. Shah et. al., Thin Solid Films 502 (2006) 292
The efficiency of the solar cell
Universidade do Minho
•
The electric current in the PV cell depends on:
i) N
Number
b off electron-hole
l
h l pairs
i generated
db
by iincident
id
lilight
h
(absorption in the semiconductor)
ii) Carrier collection efficiency at the contacts (mobility-lifetime
product).
product)
•
•
•
The voltage depends on:
i) the
th b
bandgap
d
off th
the semiconductor
i
d t
ii) the doping level of the contacts
The fill factor depends on:
i) the series and the shunt resistances
ii)) the defect density
y in the i-layer
y
Operative electrical parameters of the solar cell are obtained from its
I – V curve.
The single junction aa-Si:H p
p--i-n solar cell
Universidade do Minho
Substrate
Superstrate
ZnO:Al SnO2:F
ZnO:Al,
p
Glass or transparent plastic
ZnO:Al, ZnO:Ga
p
TCO (0.7-1.8 um)
p+-a-Si:H
(15 nm)
i
a-Si:H (250- 300 nm)
n
n+-a-Si:H (30 nm)
Al or Ag
i
n
Al or Ag
Glass, plastic or
stainless steel
Opaque substrate
No light-trapping schemes: effmax~7-8%
The pp-i-n junction under illumination
Universidade do Minho
h t carrier
hot
i
E-field
E
field
Ec
photons
EFn
qV
Vph
EFn
p
Ev
Trapping
i
-
electron
hole
A
+
n
Load
I = Idiode-Iph
Simulation with AMPS program
PV performance parameters
Universidade do Minho
I
Vmax
VOC
ma
0
V
Vmax × J max
FF =
<1
J SC × VOC
Pmax
Imax
ISC
J SC × VOC × FF
=
×100 %
2
100 mW / cm
(
)
Iph
I
RS
Idiode
+
V
RLoad
L
Pout
η=
× 100 %
Poptical
RP
AM1 5 light
AM1.5
li ht
Load resistance, Rload
Solar cell
Universidade do Minho
Chemical Vapor Deposition
rf-PECVD HW-CVD
SunFab™ AMAT
Parameter
PRF
Tfil
RF or VHF
PECVD
50-700
mWcm-22
HW-CVD
HW
CVD
• Gases: SiH4, H2, PH3, B(CH3)3
• Base pressure: better than 10-5 Torr
1750-2500˚C
pw
0.1-6 Torr
10-200 mTorr
ds-e(f),
1 – 4 cm
3-7 cm
In HWCVD:
single or multi Ta or W filaments
• Tsub= 150 - 350ºC
• Substrate: glass,
glass stainless steel
steel,
plastics
• Plasma excitation frequency:
13.56 MHz, 27.12 MHz, 40.68 MHZ…
Universidade do Minho
Light--induced degradation
Light
R=
FH 2
FSiH 4
C. Wronski, 1st Intl. Workshop on Staebler-Wronski
Staebler Wronski effect, April 20-23,
20 23, 2009, Berlin
Another effect of H2 dilution
Universidade do Minho
Transport
10
Structure
DH =
6
10
-7
FH 2
FSiH 4 + FH 2
5
10
4
σph/σdk
10
DH
3
10
10
-8
95%
10
1
50
-1
-1
σd ( Ω cm )
2
10
10
10
10
-11
70
80
H2 dilution
90
100
photosensitivity
-9
9
-10
60
90%
80%
65%
50
60
70
80
H2 dilution (%)
Dark conductivity
50%
90
300 350 400 450 500 550 600
Raman Shift
Shift, cm
-1
Raman spectra
High efficiency solar cells: multijunctions
Universidade do Minho
Tandem micromorph solar cell
IMT
hν
105
glass
TCO
p
104
Absorption [1/cm]
i
103
a-Si:H
n
p
µc-Si:H
μc-Si:H
102
i
101
n
TCO
Back contact
a-Si:H
100
10
0.5
SEM micrograph
c-Si
-1
1
1.5
2
Energy [eV]
ZnO
2.5
µc- Si:H
a Si:H
a-Si:H
MicroZnO
morph
glass
INSTITUT DE
MICROTECHNIQUE
NEUCHÂTEL
Band Gapp
1.7 eV
1.1 eV
The micromorph solar cell
Universidade do Minho
High efficiency SCs: light trapping
Universidade do Minho
Single junction SC
a-Si:H
nip
n-i-p
Light
Tandem solar cell
IMT
INSTITUT DE
MICROTECHNIQUE
NEUCHÂTEL
ZnO
top cell
IR
N-layer
bottom cell
IR
a-Si:H top cell
mc-Si:H bottom cell
Ag/ZnO
T. Söderström et al, Appl. Phys. Lett. 94,
063501 (2009)
Glass
V-shape
U-shape
Matching the cell current with IR
Universidade do Minho
Flexible Solar cells on plastic
Universidade do Minho
10 W Ù 350 mW / cm2
20 W Ù 700 mW / cm2
PEN\GZO\p-RF\b-RF(9nm)\i-(350nm)\n-RF
Deposition rate (Å / s)
amorphous
4
nanocrystalline
2
5
0
-5
-10
p-i-n on PEN
p-i-n
i on PEN
-15
-1.0 -0.8 -0.6 -0.4 -0.2 0.0
0
96
97
98
98.5
99
0.2
0.4
0.6
0.8
1.0
Voltage (V)
Hydrogen dilution (%)
PEN substrates, Tsub=150ºC
100
ZnO:Ga sputtered on PEN at RT
80
%T, %R, %A
A
SC91
i-layer by HW
FF= 51.0
51 0 %
2
Jsc= -12.7 mA/cm
Voc= 0.699 V
EFF= 4.53 %
SC88
i-layer by RF
FF 54.2
FF=
54 2 %
2
Jsc= -11.2 mA/cm
Voc= 0.830 V
EFF= 5.03 %
2
6
Current Densitty (mA/cm )
C
20W,6Torr,1.2cm
10W,6Torr,1.2cm
10W 3 T
10W,3
Torr,1.2cm
12
10W,1.5Torr,1.2cm
10W,1.5Torr, 1.2cm
10
60
Transmitance
Reflectance
Absorbance
40
20
0
300
400
500
600
wavelength (nm)
700
800
Thickness
(μm)
Band
gap (eV)
1.35
1.39
Resistivity
Mobility
(cm2/ Vs)
Carrier conc.
(cm-3)
Rsh (Ω/)
ρ (Ω cm)
3.53
5.1
1 × 10-3
16.3
4.28 × 1020
3.55
3.9
7 × 10-4
17.5
5.13 × 1020
900
P. Alpuim et al., Proc. 23rd European PV Solar Energy Conference and
Exhibition (23rd EU PVSEC), Valencia, Spain (2008) 2455
Roll--toRoll
to-roll deposition of modules
Universidade do Minho
In-situm series connection (ISSC)
Universidade do Minho
Conclusions
Universidade do Minho
• Cost structure & differentiation will matter
more than before
• Direct competition with c-Si wafers PV (1st
generation PV ) will be harder
• Find niche markets, make unique products,
avoid price competition
• Improve conversion efficiency:
• R&D to improve optical part of device
• Develop multijunction devices
• Develop in
in-line
line deposition systems
Thank you for your attention!
Universidade do Minho
Record efficiencies for solar cells
and modules
Highest reported small area cell eff.
Highest reported module eff.
Type of cell
Eff.
(%)
Area
(cm2)
Reference
Type of module
Eff.
(%)
Area
(cm2)
Reference
Crystalline Si
25.0
4.0
UNSW1, PERL2
Crystalline Si
22.9
778
UNSW/Gochermann
Thin film transfer Si
16.7
4.0
U. Stuttgart
Large c-Si
20.3
16 300
SunPower
Multicrystalline Si
20.3
1.0
FhG-ISE3
Multicrystalline Si
15.3
1 017
Sandia/HEM
Nanocrystalline
N
t lli Si
Amorphous Si
10.1
10
1
9.5
1.2
1
2
1.1
K
Kaneka
k
U. Neuchatel
Thi fil
Thin
film
polycrystalline Si
82
8.2
661
P ifi S
Pacific
Solar
l
a-Si / mc-Si
11.7
14.2
Kaneka
a-Si/a-SiGe/a-SiGe
10.4
905
USSC4
CIGS
19.4
0.99
NREL5
CIGS
13.5
3 459
Showa Shell
CdTe
16.7
1.0
NREL
CdTe
10.9
4 874
BP Solarex
Organic polymer
5.1
1.0
Konarka
Organic submodule
2.1
223.5
Plextronics
1UNSW,
University of New South Wales
2PERL, passivated emitter rear locally diffused
3FhG-ISE, Fraunhofer Institute for Solar Energy Systems
4USSC,
USSC United Solar Systems Corporation
5NREL, National Renewable Energy Lab
Adapted from M.A. Green et al., Prog. Photovolt: Res. Appl. 17 (2009) 320