Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE

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Work and results
Large area in-line experiments were performed focusing on the following tasks:
� Improvements of in-house developed evaporation sources.
� Testing of thickness, chemical composition of CIGS layers grown on in-line moving glass and
polymer foil substrates
� Construction and tests of improvised large area CdS chemical bath deposition (CBD) system
� Development of complete solar cells on 30 x 30 cm 2 area substrates and characterisation of layers
Improvements of in-house developed evaporation sources.
Typical point evaporation source profiles lead to substantially reduced layer thickness towards the
edges of the deposition zone. This becomes very critical for large area substrates and therefore new
configurations of evaporators have to be developed for homogeneous material deposition and layer
thicknesses. Therefore linear evaporators were designed and used to improve the evaporation profiles
in the deposition zone.
In the following graph the results of a successful source design for selenium evaporation is shown
(see Figure 3). Thickness measurements at various positions in the deposition zone were recorded
and corresponding points lying on the same line perpendicular to the substrate movement direction
were linked to display the evaporation profiles in this direction. The flatness of the lines expresses
homogeneous deposition thickness. Selenium is normally evaporated in excess to account for its relatively
low sticking coefficient.
Similar lines can be recorded for the other materials. The following paragraph will show the elemental
uniformity of the CIGS components (see Figure 4) where a slightly selenium deficient layer was grown
to proof a homogeneous selenium incorporation with the optimized selenium evaporator (which would
not be proven in the case of excessive selenium evaporation).
Due to the limited size of the deposition equipment the sodium source could not be incorporated yet.
Being essential for high cell efficiencies a suitable solution remains to be found for the doping step.
layer thickness (a.u)
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
extremity 1
center 1
center 2
extremity 2
-12.5 -4 4 12.5
Substrate position perpendicular to substrate movement (cm)
Figure 3: Selenium flux distribution perpendicular to substrate movement direction. Flat lines indicate
a homogeneous flux profile over a distance of 25cm in the width of the substrate. Each line
represents a different position in the direction of the substrate movement. The highest flux
of selenium is obtained near the centre of the deposition zone where at the same time the
metals are deposited to form the CIGS compound.
Large Area Flexible CIGS, D. Brémaud, ETHZ
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