NASA Scientific and Technical Aerospace Reports

GaInNAs, potentially useful in a 4-junction GaInP(sub 2)/GaAs/GaInNAs/Ge solar cell, suffers from very low
minority-carrier collection lengths. To date, the currents available from GaInNAs solar cells are not high enough to increase
the efficiency of a 3-junction device by adding this fourth junction. Here, we grow p-i-n GaInNAs solar cells by
molecular-beam epitaxy with wide, intrinsic base layers and internal quantum efficiencies near 1.0. If similar 1.0-eV GaInNAs
junctions can be successfully integrated into the 3-junction structure, the resulting 4-junction cell would have a higher
efficiency.
NTIS
Depletion; Molecular Beam Epitaxy; Solar Cells
20060002226 National Renewable Energy Lab., Golden, CO USA
Performance Parameters for Grid-Connected PV Systems
Marion, B.; Adelstein, J.; Boyle, K.; Hayden, H.; Hammond, B.; Feb. 2005; 14 pp.; In English
Report No.(s): DE2005-15016389; NREL/CP-520-37358; No Copyright; Avail.: Department of Energy Information Bridge
The use of appropriate performance parameters facilitates the comparison of grid-connected photovoltaic (PV) systems
that may differ with respect to design, technology, or geographic location. Four performance parameters that define the overall
system performance with respect to the energy production, solar resource, and overall effect of system losses are the following:
final PV system yield, reference yield, performance ratio, and PVUSA rating. These performance parameters are discussed for
their suitability in providing desired information for PV system design and performance evaluation and are demonstrated for
a variety of technologies, designs, and geographic locations. Also discussed are methodologies for determining system a.c.
power ratings in the design phase using multipliers developed from measured performance parameters.
NTIS
Photovoltaic Effect; Solar Energy
20060002355 National Renewable Energy Lab., Golden, CO USA
Excess Dark Currents and Transients in Thin-Film CdTe Solar Cells: Implications for Cell Stability and Encapsulation
of Scribe Lines and Cell Ends in Modules
McMahon, T. J.; Berniard, T. J.; Albin, D. S.; Demtsu, S. H.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016455; NREL/CP-520-37380; No Copyright; Avail.: Department of Energy Information Bridge
We have isolated a non-linear, metastable, shunt-path failure mechanism located at the CdS/CdTe cell edge. In such cases,
most performance loss, usually erratic, can be associated with the shunt path. We studied these shunt paths using dark
current-transients and infrared (ir) imaging and find only one shunt path per cell and only at the cell corner wall, even in badly
degraded cells. The effect on diminishing the cell’s efficiency far exceeds what would be expected from the cell’s linear
shunt-resistance value. We propose that current transients and ir imaging be used as a ‘’fingerprint’’ of the source and
magnitude of excess currents to evaluate the contribution of scribe-line edges and cell ends in thin-film module performance
and degradation due to environmental stress. Protection afforded by, or contamination due to, new or currently used
encapsulants can then be evaluated.
NTIS
Cadmium Tellurides; Encapsulating; Modules; Solar Cells; Stability; Thin Films
20060002356 National Renewable Energy Lab., Golden, CO USA
Diamond-Like Carbon Coatings as Encapsulants for Photovoltaic Solar Cells
Pern, F. J.; Touryan, K.; Panosyan, Z.; Gippius, A. A.; Kontsevoy, J. A.; Feb. 2005; 12 pp.; In English
Report No.(s): DE2005-15016452; NREL-CP-520-37374; No Copyright; Avail.: Department of Energy Information Bridge
High-quality single-layer and bilayer diamond-like carbon (DLC) thin films are fabricated by two technologies, namely,
ion-assisted plasma-enhanced deposition (IAPED) and electron cyclotron resonance (ECR) deposition. Deposition on various
substrates, such as sapphires and solar cells, has been performed at low substrate temperatures (50 (approx) 80 C). The two
deposition technologies allow good control over the growth conditions to produce DLC films with desired optical properties,
thickness, and energy bandgap. The bilayer-structured DLC can be fabricated by using IAPED for the bottom layer followed
by ECR for the top layer, or just by IAPED for both layers with different compositions. The DLC films have shown good
spatial uniformity, density, microhardness, and adhesion strength. They exhibit excellent stability against attack by strong
acids, prolonged damp-heat exposure at 85 C and 85% relative humidity, mechanical scratch, ultrasonication, and irradiation
by ultraviolet (UV), protons, and electrons. When deposited on crystalline Si and GaAs solar cells in single-layer and/or
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