CdTe and other thin-film polycrystalline solar cells have potential spatial non-uniformities in their photovoltaic response
that can both lower their performance and complicate the analysis of their current-voltage curves. Polycrystalline cells
have inherent non-uniformities associated with their grain structure, but there are a variety of other possibilities
including thickness variations, local shunts, and weak-diode areas. Additionally, there are possible issues associated
with the fabrication process due to cleaning residues, scratches, thermal variations, and particulate inclusions. The
primary measurements described here to map the non-uniformities of CdTe cells are light-beam-induced current (LBIC),
which gives a direct measure of the local PV response, and electroluminescence (EL), which is the inverse of the PV
effect. The former is attractive, because it can be used to deduce the local current-voltage curve, but data collection is
time consuming. The latter though the use of modern CCD cameras takes only a few seconds and is compatible with
production-line screening.
Individual shunts and "weak diodes" can have a significant effect, one much larger than implied by their physical area,
on the performance of laboratory-sized (~ 1cm2) solar cells. For larger areas typical of thin-film modules, the sheet
resistance of the transparent contact minimizes the impact of a single, small-area non-uniformity. If there are significant
numbers of shunts or weak diodes throughout a module, however, its performance may also be reduced. In this case, the
number, the magnitude, the nature, and the distribution of the non-uniformities combine to affect the degree of reduction.
In particular, a concentration of most shunts or weak diodes in a small number of module cells will be less destructive
than if they are distributed among a greater number of cells. In the case of non-uniform illumination, however, module
performance is less degraded if the shadowing is spread relatively uniformly over all or most of the cells.
We have fabricated 13.7%-efficient CuIn1-xGaxSe2 (CIGS)-based devices from electrodeposited precursors. As- deposited electrodeposited precursors are Cu-rich films. Additional In, Ga, and Se were added to the electrodeposited precursor film by physical evaporation to adjust the final composition to CuIn1-xGaxSe2. Three devices with Ga/(In + Ga) ratio of 0.16, 0.26, and 0.39 were fabricated from electrodeposited precursors. The films/devices have been characterized by inductive-coupled plasma spectrometry, Auger electron spectroscopy, x-ray diffraction, electron-probe microanalysis, current-voltage characteristics, capacitance- voltage, and spectral response. The electrodeposited device parameters are compared with those of a 17.7% physical vapor deposited device.
Conference Committee Involvement (5)
Thin Film Solar Technology III
21 August 2011 | San Diego, California, United States
Thin Film Solar Technology II
1 August 2010 | San Diego, California, United States
Thin Film Solar Technology
2 August 2009 | San Diego, California, United States
Photovoltaic Cell and Module Technologies II
10 August 2008 | San Diego, California, United States
Photovoltaic Cell and Module Technologies
27 August 2007 | San Diego, California, United States
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