Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

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IR laser source
Pumping line
IR detector
v
Ref. IR detector
Figure 1: Image of the laser source and optics (left) and sketch of the infrared absorption spectroscopy
setup.
Laser scattering
In order to detect the onset of powder formation under different microcrystalline deposition conditions
a diagnostic tool has been specifically developed for this purpose. The setup relies on the light diffusion
of poly-silane and powder particles inside or outside the deposition chamber. This diagnostic tool
has been installed in a configuration that will allow measuring the scattered laser light at the exit of the
plasma reactor.
Structural and compositional analyses techniques
Microcrystalline intrinsic layers deposited at different deposition rates in a large area industrial reactor
at IMT have been characterized through SIMS and XRD measurements. These two techniques allow
assessing the oxygen content of the layers and the crystallite’s orientation, respectively. It is widely
accepted that device grade microcrystalline material is characterized by low oxygen (< 2·10 19 cm -3 )
and carbon (< 7·10 18 cm -3 ) content. In addition, impurities related to cleaning gases, like F or S, must
be kept at reasonably low levels.
SIMS and XRD measurements for microcrystalline material grown at different deposition rates showed
results that correlate well with the solar cell efficiencies obtained so far in these two deposition regimes:
8.1% at low deposition rate and 7.1% at high deposition rate.
Part B
Synthesis and tuning of the sensitizers/inorganic semiconductors
Very good photovoltaic performance has been reached with a new ruthenium-complex sensitizer
showing a high molar extinction coefficient. The latter allows for a large photocurrent using only thin
and transparent films of titanium dioxide (TiO2). A power conversion efficiency of 8.7% was measured
using an 8 µm thin transparent TiO2 film and even higher photocurrents and efficiencies up to the record
efficiency of 11.3% could be achieved with thicker films. Due to its superior properties the new
dye is the material of choice for high-efficiency tandem cells composed of a top dye sensitized solar
cell (DSC) and a bottom CuIn(Ga)Se (CIGS) solar cell.
The comparison of the total short circuit current measured in the tandem device with the top cell’s
current suggested that the overall current is limited by the bottom cell when using the efficient dye in
monolithical tandem cells. Therefore, a lower [Ga]/[In+Ga] ratio will be chosen to achieve current
matching in future cells. Additionally, efforts will be made for increasing the transmittance of the zinc
oxide layer. This is especially important for thicker oxide layers that provide a better resistance against
the DSC electrolyte.
ThinPV, F. Nüesch, Empa
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