are made out of powder. To achieve this, the powder is heated up to a temperature below
the melting point. At such high temperatures, atoms in the particles can diffuse across the
particle boundaries. The particles thus fuse together forming one solid. This process has to
be followed by a selenization step.
An important advantage of the CIGS PV technology is that it has achieved the highest
conversion efficiencies among the different thin-film techologies except the III-V
technology. The current record for lab-scale CIGS solar cells processed on glass is 20.8%
and was achieved by the German research institute ZSW [47]. This record cell has a V oc of
0.757 V, a J sc of 34.77 mA/cm
2
, and a FF of 79.2%. The world record on flexible
substrates is held by the Swiss Federal Laboratories for Materials Science and Technology
(EMPA). On flexible polymer foil they achieved a conversion efficiency of 20.4% [82].
For making CIGS modules, interconnections are made as we discussed already in
detail in Chapter 15. As is generally true for the different PV technologies, the record
efficiencies of modules are significantly lower than that of lab-scale cells. The record
efficiencies of 1 m
2 modules are in the order of 13%, whereas the aperture-area
efficiencies are just above 14% as confirmed by NREL. The German manufacturer Manz
AG has presented a 15.9% aperture-area efficiency and a total area efficiency of 14.6%.
The Japanese company Solar Frontier claims a 17.8% aperture-area efficiency on a small
module of 900 cm
2 size.
Despite the very high conversion efficiencies, the CIGS technology faces several
challenges. As CIGS is deposited in a complex deposition process, it is challenging to
perform large area deposition with a high production yield, i.e. with a high percentage of
modules coming off the production line that fulfil the product specifications.
Kesterites
Figure 13.1 shows the abundance in the Earth’s crust for several elements. As we can see,
indium is a very rare element. However, it is a crucial element of CIGS solar cells.
Because of its scarcity, In might be the limiting step in the upscaling of the CIGS PV
technology to future terawatt scales. In addition, the current thin-film display industry
depends on In as well, as ITO is integrated in many display screens.
As a consequence, other chalcogenic semiconductors are investigated that do not
contain rare elements. An interesting class of materials are the kesterites which are
quarternary or pentary semiconductors consisting of four or five elements, respectively.
When mineral kesterite (Cu 2 (ZnFe)SnS 4 ), where zinc and iron atoms are interchangeable,
is not used as a semiconductor, kesterite without iron (Cu 2 ZnSnS 4 ) is used. It also is
known as copper zinc tin sulphide (CZTS) and is a I 2 -II-IV-VI 4 semiconductor. Other
kesterites are for example copper zinc tin selenide (Cu 2 ZnSnSe 4 , CZTSe), or ones using a
the melting point. At such high temperatures, atoms in the particles can diffuse across the
particle boundaries. The particles thus fuse together forming one solid. This process has to
be followed by a selenization step.
An important advantage of the CIGS PV technology is that it has achieved the highest
conversion efficiencies among the different thin-film techologies except the III-V
technology. The current record for lab-scale CIGS solar cells processed on glass is 20.8%
and was achieved by the German research institute ZSW [47]. This record cell has a V oc of
0.757 V, a J sc of 34.77 mA/cm
2
, and a FF of 79.2%. The world record on flexible
substrates is held by the Swiss Federal Laboratories for Materials Science and Technology
(EMPA). On flexible polymer foil they achieved a conversion efficiency of 20.4% [82].
For making CIGS modules, interconnections are made as we discussed already in
detail in Chapter 15. As is generally true for the different PV technologies, the record
efficiencies of modules are significantly lower than that of lab-scale cells. The record
efficiencies of 1 m
2 modules are in the order of 13%, whereas the aperture-area
efficiencies are just above 14% as confirmed by NREL. The German manufacturer Manz
AG has presented a 15.9% aperture-area efficiency and a total area efficiency of 14.6%.
The Japanese company Solar Frontier claims a 17.8% aperture-area efficiency on a small
module of 900 cm
2 size.
Despite the very high conversion efficiencies, the CIGS technology faces several
challenges. As CIGS is deposited in a complex deposition process, it is challenging to
perform large area deposition with a high production yield, i.e. with a high percentage of
modules coming off the production line that fulfil the product specifications.
Kesterites
Figure 13.1 shows the abundance in the Earth’s crust for several elements. As we can see,
indium is a very rare element. However, it is a crucial element of CIGS solar cells.
Because of its scarcity, In might be the limiting step in the upscaling of the CIGS PV
technology to future terawatt scales. In addition, the current thin-film display industry
depends on In as well, as ITO is integrated in many display screens.
As a consequence, other chalcogenic semiconductors are investigated that do not
contain rare elements. An interesting class of materials are the kesterites which are
quarternary or pentary semiconductors consisting of four or five elements, respectively.
When mineral kesterite (Cu 2 (ZnFe)SnS 4 ), where zinc and iron atoms are interchangeable,
is not used as a semiconductor, kesterite without iron (Cu 2 ZnSnS 4 ) is used. It also is
known as copper zinc tin sulphide (CZTS) and is a I 2 -II-IV-VI 4 semiconductor. Other
kesterites are for example copper zinc tin selenide (Cu 2 ZnSnSe 4 , CZTSe), or ones using a