morphologies of c-si solar cell - targeting the approach with least light reflection

RES (M.Sc.), TEI of Western Greece

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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

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Content

IntroductionMorphologies Principles & resultsConclusionsReferences

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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.

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Efficiency values and properties

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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

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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)

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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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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


92. 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 1 m sample𝜇

Degradation of the reflectance with pyramid size < 300nm

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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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114. 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)

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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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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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Comparison Reflectivity for Textured, plane (polished) and Textured with AR coating surfaces


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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 -

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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.


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Thank you!

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morphologies of c-si solar cell - targeting the approach with least light reflection

Engineering

g r e e c e

n e e r i n g

tei of western greece

silicon layer

t e i o f w e s t e

e n t o f

n d r o u

layer of si3n4