Semitransparent ultrathin CdTe solar cells and durability
Alvin Compaan, President and CTO
Alvin
Compaan President and CTO
Xunlight 26 Solar, LLC
presented at the Solar Durability Workshop
Case Western Reserve University
April 9, 2012
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Advantages of X26 technology
…for transparent window PV:
• X26 uses ultrathin, transparent PV coatings based on CdTe.
,
p
g
• The X26 core technology is built around • sputter deposition
• CdS/CdTe cell structure
• Extensive IP
• No direct competition with First Solar, Primestar/GE, Abound because sputtering is uniquely suited for ultrathin CdTe
• X26
X26 PV window coatings (250‐500 nm of CdTe) are attractive, very low cost and PV window coatings (250 500 nm of CdTe) are attractive very low cost and
out‐perform any other transparent, thin‐film PV material. 2
X26 market focus ‐
X26 market focus ‐ PV windows
The value of window PV:
• Window area >> rooftop space
• PV windows produce power and reduce Solar Heat Gain (SHG).
Generate power evenly across the day and year
Bank of America Building
Dallas, Texas
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X26 market focus ‐
X26 market focus ‐ PV windows
Low cost:
• Insulating glass units (IGUs) already include construction equivalent to fully encapsulated PV modules
• PV window incremental cost < $0.50/Watt
6” x 9” prototype
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X26 vs. the competition
PV window products‐‐potential competitors with existing or announced plans • Si wafers spaced out across windows (very poor aesthetics)
• Prism coupling to Si wafers (
(good efficiency but venetian blind appearance, expensive)
d ff
b
bl d
)
Solar Roof.jpg, Image retrieved from: http://commons.wikimedia.org/wiki/File:Solar_Roof.JPG, 03.31.12
• Thin‐film Si on glass, laser or chemically etched to remove lines
(available in large sizes but poor efficiency striped appearance)
(available in large sizes but poor efficiency, striped appearance)
• Thin‐film CdTe, laser or chemically etched to remove lines
• Thin‐film CIGS—not available in transparent form
• Dye
Dye sensitized solar thin films
sensitized solar thin films
(strongly colored, unproven stability in field)
Image retrieved from: http://www.pythagoras‐
solar.com/why‐bipv/, 03.31.12
• Organic PV thin films
(very low efficiency, highly colored, unproven)
a‐Si with etched lines for transparency
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Examples of X26 R&D facilities
Back contact deposition chamber: Cu, Mo
resources from Xunlight Corp.
resources from Xunlight Corp.
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The basics of sputter deposition
Glass
TCO
HRT
CdS
CdTe
ZnTe
grid
Back contact shown is ZnTe:N
Back
contact shown is ZnTe:N for for
transparency. Typically the back contact is a metal or carbon paste.
Sputter deposition chamber configuration.
Dual chamber sputter deposition system at UT
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X26 technology ‐‐ ultrathin CdTe cells
X26 technology X26 state‐of‐the‐art compared with other CdTe deposition:
[X26 technology has been developed jointly with the University of Toledo] Current density, mA/cm
C
2
20
15
10
5
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
-5
0.25 m CdTe
Voltage, V
10
-10
-15
State‐of‐the‐art thin CdTe cells from various groups. IEC=Inst. of Energy Conversion (VTD)[ref. 1] , CSER C t f S l E
CSER=Centre for Solar Energy Rsrch
R h (MOCVD)[ref. 2], (MOCVD)[ f 2]
TIT=Tokyo Institute of Technology (CSS) on borosilicate glass [ref. 3], this work=Paudel, Wieland, Compaan, subm. to APL 2012
0.50 m CdTe
0.75 m CdTe
0
CdT )
1.15 m CdTe
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J‐V curves of UT/X26 champion cells with thin CdTe layers /
p
y
(0.25µm to 1.15µm). The inset table provides the metrics for UT champion cells with up to 2.1µm of CdTe [ref. 4]
1. B.E. McCandless, W.A. Buchanan. “High throughput processing of CdTe/CdS solar cells with thin absorber layers.” 33rd IEEE PV Specialists Conf. (2008)
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2. E.W. Jones, V. Barrio,
W J
V
i SS.J.C. Irvine. D. Lamb. “Towards ultra‐thin CdTe
JC I i
L b “
d l
hi Cd solar cells using MOCVD.” Thin Solid Films. 517, 7 (2009)
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ll
i
OCV ” hi S lid il
1
(2009)
3. N. Amin, T. Isaka, A.Yamada, M. Konagai. „Highly efficient 1 µm thick CdTe solar cells with textured TCOs.” Solar Energy Materials & Solar Cells, 67 (2001)
4. N.R. Paudel, K.A. Wieland and A.D. Compaan, “Improvements in Ultra‐thin CdS/CdTe Solar Cells,” 36th IEEE PV Specialists Conf. (2011) 9
Light soak stress of bare Light soak stress of bare CdS
CdS/CdTe cells
/CdTe cells
vs. CdTe thickness
a))
c)
b)
d)
Normalized
Normalized cell performance parameters of four different CdTe thickness solar cells; a) open
cell performance parameters of four different CdTe thickness solar cells; a) open‐circuit
circuit voltage, b) short
voltage b) short‐
circuit current c) fill factor and d) efficiency. An average of 20 dot cells was plotted as a function of stressing. CdS/CdTe cells were light soaked at VOC , room ambient and 85 oC.
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Leading the technology d l
development of PV windows
f
i d
Alvin Compaan, Pres.
419.265.2641 (mobile)
acompaan@xunlight26.com
Xunming Deng, CEO
419.509.1238 (mobile)
deng@mwoe.com
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