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Semitransparent ultrathin CdTe solar cells Semitransparent ultrathin CdTe solar cells and durabilityand durability
Alvin Compaan President and CTOAlvin Compaan, President and CTOXunlight 26 Solar, LLCXunlight 26 Solar, LLC
presented at the Solar Durability WorkshopCase Western Reserve University
April 9, 2012
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Advantages of X26 technologyAdvantages of X26 technology
• X26 uses ultrathin, transparent PV coatings based on CdTe.
…for transparent window PV:…for transparent window PV:
, 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 PV window coatings (250 500 nm of CdTe) are attractive very low cost and• X26 PV window coatings (250‐500 nm of CdTe) are attractive, very low cost and out‐perform any other transparent, thin‐film PV material.
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X26 market focus X26 market focus ‐‐ PV windowsPV 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 BuildingDallas, Texas
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X26 market focus X26 market focus ‐‐ PV windowsPV windows
Low cost:
• Insulating glass units (IGUs) already include construction equivalent to fully encapsulated PV modules
• PV window incremental cost < $0.50/Watt
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6” x 9” prototype
X26 vs. the competitionX26 vs. the competition
PV window products‐‐potential competitors with existing or announced plans • Si wafers spaced out across windows
• Prism coupling to Si wafers ( d ff b bl d )
(very poor aesthetics)
(good efficiency but venetian blind appearance, expensive) 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)
Image retrieved from: http://www.pythagoras‐solar.com/why‐bipv/, 03.31.12
(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 sensitized solar thin films• Dye sensitized solar thin films(strongly colored, unproven stability in field)
• Organic PV thin films(very low efficiency, highly colored, unproven)
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a‐Si with etched lines for transparency
Examples of X26 R&D facilitiesExamples of X26 R&D facilities
Back contact deposition chamber: Cu, Mo
resources resources from Xunlight Corp.from Xunlight Corp.
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The basics of sputter depositionThe basics of sputter deposition
Glass
TCOHRTCdS
CdTeZnTegrid
Back contact shown is ZnTe:N forBack contact shown is ZnTe:N for transparency. Typically the back contact is a metal or carbon paste. Sputter deposition chamber
configuration.
Dual chamber sputter
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deposition system at UT
X26 technology X26 technology ‐‐ ultrathin CdTe cellsultrathin CdTe cells
X26 state‐of‐the‐art compared with other CdTe deposition:[X26 technology has been developed jointly with the University of Toledo]
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10
15
20
, mA/
cm2
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
-10
-5
0
5
0.25 m CdTe 0.50 m CdTe0 CdT )C
urre
nt d
ensi
ty
Voltage, V
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 R h (MOCVD)[ f 2]
-20
-15
10 0.75 m CdTe) 1.15 m CdTe
CJ‐V curves of UT/X26 champion cells with thin CdTe layers
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)2 W J V i S J C I i L b “ d l hi Cd l ll i OCV ” hi S lid il 1 (2009)
CSER=Centre for Solar Energy Rsrch (MOCVD)[ref. 2], TIT=Tokyo Institute of Technology (CSS) on borosilicate glass [ref. 3], this work=Paudel, Wieland, Compaan, subm. to APL 2012
/ 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]
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2. E.W. Jones, V. Barrio, S.J.C. Irvine. D. Lamb. “Towards ultra‐thin CdTe solar cells using MOCVD.” Thin Solid Films. 517, 7 (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)
Light soak stress Light soak stress of of bare bare CdSCdS/CdTe cells/CdTe cellsvs. CdTe thicknessvs. CdTe thickness
c)a) c))
d)b)
Normalized cell performance parameters of four different CdTe thickness solar cells; a) open‐circuit voltage b) short‐
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Normalized cell performance parameters of four different CdTe thickness solar cells; a) open circuit voltage, b) shortcircuit 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.
Leading the technology Leading the technology d l f i dd l f i ddevelopment of PV windowsdevelopment of PV windowsAlvin Compaan, Pres.419.265.2641 (mobile)[email protected]
Xunming Deng, CEO419.509.1238 (mobile)[email protected]
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