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

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Average
composition
(at% EDX) Std Dev
Cu 24.5 0.79
In 29.9 0.43
Ga 7.3 0.50
Se 38.3 0.86
thickness (nm) 1542 29
Table 2: Average composition of a selenium deficient CIGS layer measured over an area of
25x25cm 2 and standard deviation
Construction and tests of improvised CdS chemical bath deposition (CBD) system for 30 x 30 cm 2
foils
Up-scaling of the chemical bath deposition step required a complete redesign of the deposition
equipment in order to reduce the precursor concentrations per area of deposited layer. This is of special
importance due to the usage of toxic Cd acetate solutions. The newly designed setup allowed a
reduction of the precursor concentrations by a factor of ~10 while still yielding good surface coverage.
This could be achieved by substantially reducing the contact area of the solution with parts other than
the solar cell surface. A flexible heating system was installed and optimized to control the temperature
during the deposition reaction. First homogeneity results show promising results. Further optimization
of the deposition reaction is required to reduce particle generation which may occur during the later
stage as a precipitation of Cd(OH,S) particles.
Figure 5: Large area solar cell covered with thin buffer layer. The buffer layer (~40nm) is deposited
in a chemical bath where the reaction of the precursor leads to the formation of a homogenous
thin layer on the absorber surface with excellent coverage.
Development of complete solar cells on 30 x 30 cm 2 area substrates
Mo, CIGS, CdS and ZnO layers deposited on 30x30cm 2 substrates were used to make the conventional
CIGS solar cell structure and evaluated in performance. Flexible foils were transported in metal
frames to facilitate the handling of the thin structures. Solar cells on 30x30 cm 2 area substrates need
to be cut down to smaller area or need to be partitioned into modules for meaningful characterization.
Several process runs have resulted in solar cells with efficiencies of over 8% but reproducibility needs
still to be improved. Further optimisation of the process parameters is required for envisaged 12%
efficiency cells made in the in-line processing. Figure 6 shows a 30x30cm 2 coated flexible substrate
including patterning of the layers for singles cells and modules.
Large Area Flexible CIGS, D. Brémaud, ETHZ
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