1. Solar Cells Fabrication: Surface Processing
Aleksei Grigorev
Fys9310

2. Source: http://www.pveducation.org
Typical solar cell
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3. Source: http://www.pveducation.org
Optical losses
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4. How to reduce the optical losses
Minimize the coverage of the cell surface by top contacts
Application of anti-reflection coatings
The surface can be textured (texturing)
Increase the thickness of SC
Make the back surface reflective

5. Reflection of a silicon surface
Reflection for silicon is over 30 % Silicon SC only operate in 400 to 1100 nm range typically
Source: M. A. Green and Keevers, M. J., Progress in Photovoltaics: Research and Applications, vol. 3, pp , 1995

6. Anti-Reflection Coatings (ARC)
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7. Source: http://www.cleanroom.byu.edu
ARC thickness
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8. Multi layer anti reflection coatings
Double layer ARC (DLARC)
OPAL2

9. Types of ARC films Titanium Oxide (TiO2)
Atmospheric pressure chemical vapor deposition
Indium Tin Oxide (ITO)
Transparent conducting oxide
Silicon Oxide (SiO2)
Thermal oxidation
High temperature
Passivates surface
Silicon Nitride (SiNx:H)
Plasma enhance chemical vapor deposition (PECVD)
Low Temperature
Passivates surface and bulk

10. Silicon nitride deposition
SiH4 + N2O
SiOxNy:H
n = 1.46 – 1.9
SiH4 + NH3 / N2
SiNx:H
n = 1.85 – 3.3
SiH4
a-Si:H
n = 4.2
PECVD setup
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11. Surface texturing
Random pyramid texturing
Inverted pyramid texturing

12. Anisotropic texturing
Etching
Commonly used on the <100> crystallographic oriented c-Si wafers.
Produces pyramids on the wafer surfaces on the <111> crystallographic direction, usually with an angle of 70.5º.
Reduces the reflection from 35% to around 10% for the incident light with an angle of 35º.
Alkaline solution etching.
Typically, KOH or NaOH aqueous solutions with isopropyl alcohol (IPA)
Also acidic texturing, performed with an aqueous solution based in a mix of nitric acid, hydrofluoric acid, water and some additives (as IPA). Porous silicon layer is formed
Anisotropic texturing
Source: E. Vazsonyi et al. /Solar Energy Materials & Solar Cells 57 (1999) 179Ð188

13. Other types of texturing
Plasma texturing, Reactive Ion Etching (RIE)
performed in chlorine or fluorine plasma
can be used with a mask
low production output
Laser texturing
laser grooving to create different patterns
most accurate texturing
high cost and slow

14. ARC and texturing can be combined

15. Nanowires and nanoparticles
Source: Pritesh Hiralal, Chihtao Chien et al. The Royal Society of Chemistry 2014
Source: Z. Starowicz & M. Lipiński et al. Plasmonics (2013) 8:41–43

16. Nanowires
MBE grown GaN NWs

17. Solar cells surface processing
Texturing