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

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Work and results
Alternative Back Contacts
We have developed CIGS solar cells on soda lime glass substrates with TiN and ZrN back contacts.
Both were done by reactive sputtering. The sheet resistance and the approximate thickness of those
layers are listed in table I.
R� [�/�] d [nm]
Mo (reference) 0.2 1000
TiN 3.1 500
ZrN 5.5 500
Table I: Sheet resistance and approximative thickness of used back contacts
On some samples a thin (10nm) Mo film was deposited with dc sputtering on top of the TiN ("Mo
(10 nm)"). In some cases this thin Mo layer was converted into MoSe2 by the Se-oven method
("MoSe2 (10 nm)"), which consist of letting evaporated Se flow over the substrate along with N2 carrier
gas at a few mbar pressure. With this method the conversion of Mo into MoSe2 could be clearly
demonstrated (see "LARCIS Annual Report 2006").
The CIGS absorber layers were grown using the 3-stage process. The nitrides act as diffusion barrier
for Na. Therefore we have also compared the effects of Na on some samples, by adding Na with a
post-deposition treatment (PDT). Since the PDT shows the best performance for CIGS layers
deposited at temperature in the range of 400 - 500°C, we decided to keep the max. temperature at
450°C for all samples. The solar cells were completed by depositing CBD-CdS buffer, RF sputtered
ZnO:Al/i-ZnO and an Al/Ni-grid.
Figure 1: IV-curves of CIGS solar cells with ZrN back contacts and intermediate Mo layers.
LARCIS, D. Brémaud, ETH Zurich
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