NASA Scientific and Technical Aerospace Reports

An orthogonal full-factorial design was used to study the effect of CdS and CdTe layer thickness, oxygen ambient during
vapor CdCl(sub 2) (VCC) and the use of nitric-phosphoric (NP) acid as a pre-contact etch on the initial and stressed
performance of CdS/CdTe small-area devices. The best initial device efficiency (using thinner CdS, thicker CdTe, no oxygen
during VCC, and NP etch) also showed poor stability. Increasing the CdS thickness significantly improved stability with only
a slight decrease in resulting initial performance. All devices used a thin margin of CdTe around the perimeter of the
backcontact that was shown to significantly reduce catastrophic degradation and improve overall test statistics. The latter
degradation is modeled by the formation of a weak-diode/low shunt resistance localized near the edge of finished devices. This
shunting is believed to occur through the CdS/CdTe interface, rather than along the device edge, and is exacerbated by thinner
CdS films.
NTIS
Cadmium Tellurides; Correlation; Fabrication; Solar Cells; Stability
20060002204 National Renewable Energy Lab., Golden, CO USA
Rapid Mapping of AR Coating Thickness on Si Solar Cells Using GT-FabScan 6000
Sopori, B.; Amieva, J.; Butterfield, B.; Li, C.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016489; NREL/CP-520-37478; No Copyright; Avail.: National Technical Information Service
(NTIS)
A new technique for rapid mapping of the thickness of an antireflection (AR) coating on a solar cell is described. A
filtered, reflectance (intensity) image of the AR-coated wafer is generated by a CCD camera mounted on a GTFabScan. This
image is converted into a thickness image using a transformation relating local AR thickness to the local intensity in the image
plane. The thickness map is generated in less than 100 ms.
NTIS
Antireflection Coatings; Coating; Solar Cells; Thickness
20060002206 National Renewable Energy Lab., Golden, CO USA
Direct Write Contacts for Solar Cells
Kaydanova, T.; van Hest, M. F. A. M.; Miedaner, A.; Curtis, C. J.; Alleman, J. L.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016490; NREL/CP-520-37524; No Copyright; Avail.: Department of Energy Information Bridge
Ag, Cu, and Ni metallizations were inkjet-printed with near-vacuum deposition quality. The approach developed can be
easily extended to other conductors such as Pt, Pd, and Au. Thick, highly conducting lines of Ag and Cu demonstrating good
adhesion to glass, Si, and PCB have been printed at 100-200 deg C in air and N(sub 2), respectively. Ag grids were
inkjet-printed on Si solar cells and fired through the silicon nitride antireflective layer at 850 deg C resulting in 8%-efficient
cells. Next-generation multicomponent inks (including etching agents) have also been developed with improved fire-through
contacts leading to higher cell efficiencies. PEDOT-PSS polymer-based conductors were inkjet-printed with conductivity as
good or better than that of spin-coated films.
NTIS
Printing; Solar Cells
20060002208 National Renewable Energy Lab., Golden, CO USA
High-Throughput Approaches to Optimization of Crystal Silicon Surface Passivation and Heterojunction Solar Cells
Wang, Q.; Page, M.; Yan, Y.; Wang, T.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016491; NREL/CP-520-37439; No Copyright; Avail.: Department of Energy Information Bridge
We use a high-throughput (combinatorial) hot-wire chemical vapor deposition system to passivate the crystal silicon
surface and to grow heterojunction silicon solar cells. We study the effectiveness of crystal surface treatments by atomic H
or/and NH(sub x) radicals, followed by the growth of thin hydrogenated amorphous silicon (a Si:H) films. Treatment and layer
properties such as times, thicknesses, and gas mixtures can be continuously graded, creating a two-dimensional sample with
each variable varying in one direction. This results in high-throughput optimization of the processes. Effective carrier lifetime
is measured by photoconductive decay to evaluate the effectiveness of the surface passivation by surface treatments. The
effective carrier lifetime increases from about 5 (micro)s without passivation to about 24 (micro)s with an optimized surface
treatment and thickness a-Si:H on single-sided c-Si. Transmission electron microscopy reveals that a-Si:H, a mixed phase, or
epitaxial growth of thin-film Si depending on the surface treatment. Improvement in effective carrier lifetime correlates with
an immediate a-Si:H growth on c-Si, rather than a mixed phase and epitaxial Si growth. We have obtained an efficiency of
95