METROLOGY
specimens becomes possible without breaking the
vacuum.
Analysis and imaging
Numerous analysis methods are available
depending on the number of detectors and their
combination. Below are a few examples with short
explanations:
barb1right EDS (= Energy Dispersive x-ray Spectrometry)
for high-resolution, elemental mapping.
barb1right EBSD (=electron backscatter diffraction) for
microstructural properties, e.g., grain size, grain
orientation, texture...
Issue II 2009
EDS maps acquired from a cross section of a CdTe based thin film solar
cell, providing compositional information of the various layers. The following detectors are available for imaging:
Right: Nominal layer stack of the solar cell.
Courtesy of Prof. W. Jaegermann, TU Darmstadt (Germany) barb1right In-lens or chamber mounted SE detectors
(= secondary electrons) for high-resolution
topographical imaging in the nanometer range.
-pv-management.com barb1right In-lens EsB detector
(= energy-selective backscattered electron
.solar
detector) for nano-scale imaging with excellent
www
material contrast.
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The versatility of the instrument is even enhanced
by a charge compensation system that enables the
full use of all of the methods mentioned, applied
on insulating samples without compromising the
quality of images and analytics. This will be of
particular importance for thin-film solar cells on
EBSD maps from a CdTe based thin film solar cell, providing microstructural glass or polyimide substrates.
information of the various layers. The EBSD data were acquired on the
identical sample position as the EDS maps in the top figure. Note: For Efficient preparation
amorphous materials such as the thin Te layer and the glass substrate, no SEM investigations of cross-sections prepared by
EBSD patterns can be obtained. Right: Nominal layer stack of the solar cell. cleaving or grinding as state of the art technique in
Courtesy of Prof. W. Jaegermann, TU Darmstadt the PV segment have constraints due to disruption
(Germany) or smearing artefacts. The quality of the results is
often limited by charging effects, in particular at
locations close to the insulating glass substrate. In
contrast, images of FIB-prepared cross sections
may provide an overview of the layer stack in a
thin-film solar cell as well as the compositions and
microstructures of the individual layers. During the
in-situ preparation the entire milling process can
be observed and controlled by use of the SEM.
The large number of parameters in the
manufacture of thin film solar cells makes their
optimisation a Sisyphean task. Whether it is the
temperature of the substrate, the partial pressure during
evaporation or the sputtering rate, the key to process optimisation
is a fast feedback loop to enable a quick response
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