Ion Beam Treatment of Functional Layers in Thin-Film Silicon Solar ...

6 Ion beam treatment of the TCO surface
H a z e
0 .6
0 .4
0 .2
0 .0
Z n O o n A r/O tre a te d
2
te x tu re d g la s s
A r/O tre a te d
2
te x tu re d g la s s
4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0
W a v e le n g th [n m ]
(a) Haze
In te n s ity [r. u .]
1 0 -2 Z n O o n A r/O tre a te d
2
te x tu re d g la s s
1 0 -3
1 0 -4
1 0 -5
1 0 -6
A r/O tre a te d
2
te x tu re d g la s s
1 0 -7
0 2 0 4 0 6 0 8 0
A n g le [ o ]
(b) Angular resolved scattering (ARS)
Figure 6.24: Haze (a) and ARS (b) of the Ar/O 2 treated textured glass (solid squares)
and the ZnO:Al films grown on Ar/O 2 treated textured glass (open circles).
α indicate that both the ZnO:Al film becomes rougher than the textured glass both in
large and small scale.
Fig. 6.24 gives the haze and ARS measurements of the two samples, in which the
textured glass is shown in full squares and the ZnO:Al film grown on the textured
glass is shown in open circles. The ZnO:Al film has nearly two times higher haze at
wavelength range 350 − 800 nm. The significantly increase of haze at short wavelength
region is contributed by the small texture of ZnO:Al film. At the rest of the wavelength
range, the haze of the two samples are similar. The ARS curves also have difference at
the angle range of 18 − 90 ◦ . ZnO:Al film scatter more light to the large angle region.
It can be concluded that for the ZnO:Al films, the peak at 7 ◦ is contributed by the
textured glass substrate, while the high light scattering in the angle range of 30 − 90 ◦ is
contributed by the as-grown textured ZnO:Al films. Therefore, with the double texture
features, more light can be scattered to large angles.
6.5.4.3 ZnO:Al films on cleaned textured glass
This section examines the growth of ZnO:Al film on cleaned textured glass. Similar to
the previous sections, a standard ZnO:Al film was etched in 0.5% diluted HCl solution
for 90 s, then the textured ZnO:Al film was dry etched by Ar ion beam to remove all
ZnO:Al material. Afterwards, the textured glass was re-cleaned by the standard cleaning
process. Finally standard ZnO:Al film was deposited on the textured glass. The growth
of ZnO:Al film shall be different to the Ar or Ar/O 2 treated textured glass as expected
from the experiments on flat glass investigated in Section 5.2.2. In the following, the
AFM images and the optical properties of textured glass and ZnO:Al film are studied.
Fig. 6.25 shows the AFM images of cleaned textured glass (a) and the ZnO:Al films on
the glass (b). The textured glass exhibit a large fraction of flat bottom due to the long
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