As the Reflection of Sunlight, falling on the solar cells is an big issue for its performance, this presentation deals with some Morphologies, mostly used these days in industries and some others also which was in trend years before, for c-Si cells. The objective is to find out the most appropriate technology for Surface texturing either with or without AR coating that can reduce reflection to its minimum possible value. Although, it is understood that, with best technology, cost also increases. Therefore, it is a quite challenging task at the present time to provide a cost effective surface Morphologies to limit the Panel cost to not to rise much.

1. JATIN KUMAR
D E P A R T M E N T O F M E C H A N I C A L E N G I N E E R I N G , T E I O F W E S T E R N , G R E E C E ,
M . A L E X A N D R O U 1 , K O U K O U L I - 2 6 3 3 4 P A T R A S , G R E E C E .
Study of different morphologies for surface of
Crystalline Silicon (c-Si) Solar cells
30-Jan-15RES (M.Sc.), TEI of Western Greece
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2. Content
Introduction
Morphologies Principles & results
Conclusions
References
30-Jan-15RES (M.Sc.), TEI of Western Greece
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3. Various types of PV cell
 Crystal cell (Single crystal and Poly crystalline Silicon)
Formed by melting high purity
silicon like as Integrated Circuit
For mass production, cell is sliced
from roughly crystallized ingot.
30-Jan-15RES (M.Sc.), TEI of Western Greece
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4. Efficiency values and properties
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5. Working of PV and the need for Texturization
 Light can be separated into different
wavelengths
 Only photon has more energy required
can generate electron-hole pair
• Reflection is at the same angle
• At least second reflection
• The effective absorption length of the
silicon layer will be reduced  the light
way through the layer increases
• The area of the surface becomes bigger
• Total reflection on the inside of the front
layer possible
30-Jan-15RES (M.Sc.), TEI of Western Greece
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6.  Efficiency of silicon solar cells greatly depends on the surface of
silicon wafers
 Texturization techniques reduces the reflectance of the silicon
surface & improves the light trapping ability
 Polished (Un-textured) silicon surface has a high natural
reflectivity (>35%)
 Texturization two approaches,
 Chemical/electrochemical (first five techniques)
 Mechanical/Optical (last two techniques)
30-Jan-15RES (M.Sc.), TEI of Western Greece
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7. Morphologies Principles
A. Texturing of monocrystalline silicon by depositing a layer of Si3N4 by sputtering
• Basic principle of this technique is anisotropic etching various pyramid
structures depending on the thickness of the Si3N4 layer.
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8. Cont…
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 On seeing the results, the thinner
Si3N4 layer results in uneven
pyramid size, poor surface
coverage and higher average
reflectivity
 Small pyramid, good surface
coverage and uniformly
distributed pyramids gives
excellent anti-reflection
properties

9. 2. Wet-chemical method
 Saw damage removal (SDR) done by
dipping the wafers in aqueous NaOH
(20 % wt) at 80 0C for 10min,
followed by modified solution
treatment of NaOH (1.5 %), IPA
(Isopropyl Alcohol, 4 %) and some
additives, for 25 min.
 Results shows the lowest reflectivity
of 11.2% with 1𝜇m sample
 Degradation of the reflectance with
pyramid size < 300nm
30-Jan-15RES (M.Sc.), TEI of Western Greece
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10. 3. Isotropic texturing with HF–
HNO3–H2O (14:1:5) solution
 Formation of 3 different meso- and
macro-porous structures on mc-Si
 First, dipping in 1.5% dilute NaOH
solution for 15 s. followed by DI-
water rinsing and drying
 Second, baking in conveyor IR belt
furnace at 450 C for 5min followed
by 10 s dipping in 10% HF solution
 Third, dipped in HNO3:HF (98:2)
for 2 and 5min followed by DI-
water rinsing and drying
 The higher the roughness, the
higher the scattering and the
lower the reflectance
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11. 4. Anisotropic Etching with Na2SiO3
 With initial cleaning in HNO3 solution
(< 10 wt %) , the wafers are etched
using aqueous solutions of Na2SiO3 (2,
4, 6, 8 and 10 wt %) at 70 – 90 °C and
etching times (5 – 25) min.
 The optimum concentration of Na2SiO3
and etching time were at 6.2 wt% and 5
min, respectively at T = 80°C
 Reflectance was found to be 9.27%
 Lowest value was 0.160 mg⋅cm-2⋅min-1
(textured by 2 wt% Na2SiO3 at 80oC
for 10 min) while the highest was
0.671 mg⋅cm-2⋅min-1 (10 wt% Na2SiO3
at 80oC for 5 min)
30-Jan-15RES (M.Sc.), TEI of Western Greece
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12. 5. Monocrystalline Silicon Solar Cells
with K3PO4/K2HPO4 Solutions
 Basically, to etch the sample in
different mass ratios of (K3PO4) and
(K2HPO4).
 Samples textured using 1wt%
K2HPO4 solution and different K3PO4
concentrations (10wt%, 15wt%,
20wt% and 25wt%) for 25 min at
85℃.
 Etching time also affects the
reflectivity with minimum for 15 min
at 85 ℃
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13. Mechanical/Optical
6. Ultrasonic Standing Wave with
acid mixture
 Using ultrasonic generator with
acid solution which is mixed with
HF–HNO3–CH3COOH ( 2:15:5 by
vol)
 Regular and evenly distributed
pyramids as compared to by mixed
acid alone
7. Silicon surface by Nd:YAG
laser
 By means of diode-pumped pulsed
Neodymium-doped Yttrium
Aluminum Garnet laser crystal
(Nd:YAG)
 High temperature may induce the
stress and changes in crystalline
phase
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14. 30-Jan-15RES (M.Sc.), TEI of Western Greece
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 Comparison Reflectivity for Textured, plane (polished) and Textured with AR
coating surfaces

15. Conclusions
Technique Reflectivity (%) Conditions
Si3N4 treated surface 12.3 2.6 μm pyramid size and
without AR coating
Wet-chemical method 11.2 1 μm & efficiency is 18.17
%
HF–HNO3–H2O textured
surface
15 PSE2 (double acid
treatment)
Textured with Na2SiO3 9.27 uniform pyramid structure
& high Etching rate
K3PO4/K2HPO4 11.27 -
Ultrasonic standing wave NA -
Laser NA -
30-Jan-15RES (M.Sc.), TEI of Western Greece
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16. References
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 Bohr-Ran Huanga, Ying-Kan Yanga, Wen-Luh Yangb, Key technique for texturing a uniform pyramid structure with a layer of silicon nitride on monocrystalline silicon
wafer, Applied Surface Science 266 (2013) 245– 249.
 Chao Yan, Wu Liqun, Yang Xianlong, A Study of Texturing on the Surface of Multi-crystalline Silicon Based on Ultrasonic Standing Wave, 2012 International Conference on
Solid State and Materials Lecture Notes in Information Technology, Vol.22
 C.L. Su, C.H. Hsu, K.H. Lan, R. Leron, A. Soriano and M.H. Li, Texturization of Silicon Wafers for Solar Cells by Anisotropic Etching with Sodium Silicate Solutions,
(ICREPQ’12) Santiago de Compostela (Spain), 28th to 30th March, 2012
 F. Llopis and I. Tob´ıas, “Influence of texture feature size on the optical performance of silicon solar cells,” Progress in Photovoltaics, vol. 13, no. 1, pp. 27–36, 2005
 H. Park, S. Kwon, J.S. Lee, H.J. Lim, S. Yoon, D. Kim, Improvement on surface texturing of single crystalline silicon for solar cells by saw-damage etching using an acidic
solution, Solar Energy Materials and Solar Cells 93 (2009) 1773–1778.
 Kyunghae Kim, S. K. Dhungel, Sungwook Jung: Sol. Eng. Mater. & Cells Vol. 92 (2008), p. 960.
 L.A. Dobrzański and A. Drygała, Processing of silicon surface by Nd: YAG laser, Journal of Achievements in Materials and Manufacturing Engineering, Volume 17 Issue 1-2
July-August 2006.
 Qian-Run Zhao, Ning Zhang, Jun-Qi Tang, Investigation of Texturization for Monocrystalline Silicon Solar Cells with K3PO4/K2HPO4 Solutions, International Conference on
Mechatronics, Electronic, Industrial and Control Engineering (MEIC 2014).
 Ricardo l. Guerrero Lem, Dietmar Borchert, Texturization processes of monocrystalline silicon with Na2CO3/NaHCO3 solutions for solar cells, Soportes Audiovisuales e
Informáticos, Curso 2012/13ciencias Y Tecnologías/13.
 U. Gangopadhyay, S.K. Dhungel, P.K. Basu, S.K. Dutta, H. Saha, J. Yi, Comparative study of different approaches of multicrystalline silicon texturing for solar cell
fabrication, Solar Energy Materials & Solar Cells 91 (2007) 285–289
 Yangang Han, Xuegong Yu, Dong Wang, and Deren Yang, Formation of Various Pyramidal Structures on Monocrystalline Silicon Surface and Their Influence on the Solar
Cells, Journal of Nanomaterials, Volume 2013, Article ID 716012, 5 pages.

17. Thank you!
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