22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Development of antireflective silicon nanostructures for multicrystalline silicon
solar cells
P.Y. Lin1, K.B. Lin1, K.Y. Fong1, Y.C. Wang1, T.M. Kuan2, C.W. Kuo2, C.Y. Yu2 and I.C. Chen1
1
Institute of Materials Science and Engineering, National Central University, Zhongli 320, Taiwan
2
TSEC Corporation, Hsinchu 303, Taiwan
Abstract: The textured multicrystalline silicon with nano-sized structures was carried out
using chemical wet etching followed by reactive ion etching (RIE). Compared to standard
industrial alkaline etching or RIE process, the combined wet etching/RIE technique could
result in lower reflectance on silicon surface.
Keywords: multicrystalline silicon, surface texture, reactive ion etching, wet etching
1. Introduction
In order to reduce the production costs, multicrystalline
silicon solar cells is obtained much attention in academia
and Industry. Reducing the surface reflection of silicon
wafer is one of important development technology in
silicon solar cells research that is called antireflection
technology. Currently, antireflection technology of silicon
solar cells is mainly divided into two parts, one of the
method is fabricated an anti-reflection coating (ARC) on
silicon surface [1], the other method is processed texture
treatment. Single-crystal silicon solar cells are generally
textured with random pyramids, which are produced by
etching in an isotropic alkaline solution such as KOH [2]
or NaOH [3]. The random nature of the crystal orientation
of multicrystalline silicon wafers makes such techniques
much less effective for this material because only a
minority of grains are properly orientated. For the reason,
RIE which is belonged to anisotropic etching is more
suitable to produce nano-sized structures as anti-reflection
for multicrystalline solar cells [5]. In this work, we
combine chemical wet etching and dry etching for
texturing the front surface of multicrystalline Si.
2. Experimental
The surface saw damage of the as-cut multicrystalline
silicon wafer will conduct surface treatment in saw
damage removal (SDR) method by two different ratios
that is mixed nitric acid-hydrofluoric acid (HF/HNO 3 )
solution in 1:18 and 1:4, respectively [5]. The surface
nano-sized texturing structure is produced by RIE which
reactive gas is mixed SF 6 /O 2 at 400 w, 300 mTorr.
Besides, the standard industrial alkaline etching will be
the reference sample that is processed in 80 oC KOH.
The scanning electron microscope (SEM) and UV-Vis
spectrum analyse the surface profile of multicrystalline
silicon and reflectance, respectively.
3. Results and discussion
Figure 1 shows SEM images of multicrystalline silicon
wafers with various surfaces. In the as-cut wafer (Fig. 1a),
the heavy surface damage is evident as deep fissures and
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cracks, resulting in reasonable reflection control but high
recombination. After HF: HNO 3 =1:18 SDR process,
multicrystalline silicon surface appear the bowl-like
features surface such as Figure 1(b). When increase HF
ratio of SDR solution to HF: HNO 3 =1:4, multicrystalline
silicon surface becomes smooth and flat along showed in
Figure 1 (c). Figure 1 (d) is standard industrial alkalineetched wafer. It appears to have some micro-sized, graindependent texturing.
(a)
(b)
(c)
(d)
Fig. 1 SEM images of multicrystalline silicon wafers
with various surfaces. (a) Raw wafer, (b) HF:
HNO 3 =1:18, (c) HF: HNO 3 =1:4, (d) standard industrial
alkaline etching.
The images in Figure 2 show the RIE process after the
ratio 1:18 and 1:4 of HF: HNO 3 mixture solution in
Figure 2(a) and (b), respectively. Both the condition has
uniform nano-sized structure, but the low HF ratio
condition maintains bowl-like features surface.
Figure 3 shows the reflectance of multicrystalline
silicon processed reactive ion etching process after the
ratio 1:18 and 1:4 of HF: HNO 3 mixture solution and
standard industrial alkaline etching. Compared to standard
industrial alkaline etching, RIE method can reduce the
1
reflectance greatly. And the reflectance is lower when
contained
(a)
(b)
Fig. 2 SEM images of reactive ion etching process after
(a) HF: HNO 3 =1:18 and (b) HF: HNO 3 =1:4 SDR
treatment.
(a) 1:18
(b) 1:4
(c) Satndard
30
Reflectance (%)
25
20
15
10
5
400
500
600
700
800
900
Wavelength (nm)
Fig. 3 The reflectance of reactive ion etching process
after HF: HNO 3 = (a) 1:18, (b) 1:4 SDR treatment. (c)
standard industrial alkaline etching.
2
higher HF ratio condition. Consequently, by controlled
the process parameters, we obtained optimize nano-sized
structure which is provide with high etching rate and low
reflection.
4. Conclusion
We combined chemical wet etching method by HF:
HNO 3 mixtures solution and dry etching by reactive ion
etching to produce nano-sized structures on silicon
surface that is applied as anti-reflection of multicrystalline
solar cells. The reflectance of such techniques is lower
than standard industrial alkaline etching. There is lower
reflectance when SDR solution contained higher HF ratio.
5. References
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Solar Energy Materials & Solar Cells, 57 179 (1999).
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Kraiem, J.F. Lelievre, A. Chaumartin, A. Fave and M.
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(2006)
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