NASA Scientific and Technical Aerospace Reports

plays a significant role in the device conversion efficiency of NREL’s three-stage Cu(In,Ga)Se2 device.
NTIS
Fracturing; Grain Boundaries; Microscopy; Photovoltaic Conversion; Thin Films
20060002395 National Renewable Energy Lab., Golden, CO USA
Development of Automated Production Line Processes for Solar Brightfield Modules. Annual Technical Progress
Report 1 January 2003-30 June 2004
Nowlan, M. J.; Murach, J. M.; Sutherland, S. F.; Jun. 2005; 50 pp.; In English
Report No.(s): DE2005-15016397; NREL/SR-520-36608; No Copyright; Avail.: National Technical Information Service
(NTIS)
This report describes how Spire Corporation is addressing the PV Manufacturing R&D project goals of improving
photovoltaic (PV) manufacturing processes and products while reducing costs and providing a technology foundation that
supports significant manufacturing scale-up. To accomplish this, we are focusing our efforts on the design of a large-area
utility-scale module and the development of the necessary manufacturing techniques and equipment to manufacture such a
module in a high-volume production environment. A three-phase program is under way for developing and demonstrating new
automated systems for fabricating very large PV modules ideal for use in multi-megawatt grid-connected applications. We
designed a large-area 800 W module and we are developing associated module production equipment that will minimize the
total installed system cost for utility-scale PV arrays. Unique features of the module design include a cantilevered glass
superstrate to reduce the glass thickness and internally laminated bypass diodes that simplify internal busing and junction-box
designs. Other program activities include the development of automation for solar cell string inspections, string busing,
materials lay-up, and lamination; enhancements to the lamination process; and performance testing of large-area modules.
NTIS
Manufacturing; Modules; Photovoltaic Conversion
20060002396 National Renewable Energy Lab., Golden, CO USA
Effect of Na Incorporation on the Growth and Properites of CdTe/CdS Devices
Dhere, R.; Ramanathan, K.; Keane, J.; Zhou, J.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016401; NREL/CP-520-37368; No Copyright; Avail.: Department of Energy Information Bridge
Sodium is known to enhance p-type doping in copper indium diselenide (CIS)-based devices fabricated on soda-lime glass
substrates, and similar amounts of Na are present in commercial cadmium telluride (CdTe) devices. We present the results on
the effects of Na incorporation on the properties of CdTe/CdS solar cells prepared on borosilicate glass substrates. A NaF layer
10 to 30 nm thick was incorporated at either the CdS/CdTe interface or on the CdTe surface, as a source of Na. CdTe layers
were deposited by close-spaced sublimation at substrate temperatures from 425 C (LT) to 620 C (HT), followed by
heat-treatment in the presence of CdCl2 vapor. Atomic force microscopy analysis showed that the samples with NaF at the
CdS/CdTe interface deposited in He ambient have larger grains with a sub-grain structure that disappears after CdCl2 heat
treatment accompanied by an increase in grain size. Samples deposited in O2 ambient have smaller grains without a sub-grain
structure. For samples with NaF deposited on the CdTe surface, LT samples with CdCl2 heat treatment showed a morphology
similar to samples without NaF layers; but samples heat-treated in He ambient at 500 C prior to CdCl2 treatment showed a
different microstructure with platelets on the surface.
NTIS
Additives; Cadmium Tellurides; Copper; Photovoltaic Conversion; Selenides
20060002397 National Renewable Energy Lab., Golden, CO USA
Evolution of CdS/CdTe Device Performance During Cu Diffusion
Gessert, T. A.; Smith, S.; Moriarty, T.; Young, M.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016393; NREL/CP-520-36472; No Copyright; Avail.: Department of Energy Information Bridge
Cu diffusion from a ZnTe:Cu/Ti back contact onto CdS/CdTe thin-film solar cells is studied. We find if Cu diffusion is
insufficient, the entire CdTe layer is depleted. However, if Cu diffusion is excessive, the depletion width can become too
narrow to provide optimum current collection. This analysis suggests that most contact processes used for CdS/CdTe devices
are optimized (often unknowingly) to result in a depletion width that extends just far enough into the CdTe to yield the highest
possible field in the region where light absorption occurs. Analysis of the samples with very high Cu concentration also
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