1) Solar cells are fabricated from silicon through a process of purification, doping, and wafer slicing. Impure silicon is purified using a floating zone technique and sliced into thin wafers. 2) Wafers are polished, doped with phosphorus or boron, and coated with anti-reflective layers to improve light absorption. Surface texturing through etching also increases light trapping. 3) Nanowires and multi-layer anti-reflection coatings can further reduce optical losses to increase a solar cell's efficiency. Combining surface texturing with anti-reflective coatings optimizes light absorption in silicon solar cells.

1. Solar Cell Fabrication and Surface
Processing
~ Chandan Kumar

2. Typical solar cell
The Solar cell is like an ordinary diode. It consist of silicon, germanium PN junction with a
glass windows on the top surface layer of P-Type, the P-Type material is made very thin and
wide so that the incident light photon may easily reach to PN junction.

3. Fabrication Processes

4. Raw Materials
• The basic component of a solar cell is pure silicon, which is not pure in its
natural state.
• Pure silicon is derived from such silicon dioxides as quartzite gravel (the
purest silica) or crushed quartz.
• The resulting pure silicon is then doped (treated with) with phosphorous and
boron to produce an excess of electrons and a deficiency of electrons
respectively to make a semiconductor capable of conducting electricity.
• The silicon disks are shiny and require an anti-reflective coating, usually
titanium dioxide.

5. The Manufacturing Process
1. The silicon dioxide of either quartzite gravel or crushed quartz is placed into an electric arc
furnace. A carbon arc is then applied to release the oxygen. The products are carbon dioxide
and molten silicon. This simple process yields silicon with one percent impurity, useful in many
industries but not the solar cell industry.
2. The 99 percent pure silicon is purified even further using the floating zone technique. A rod
of impure silicon is passed through a heated zone several times in the same direction. This
procedure "drags" the impurities toward one end with each pass. At a specific point, the silicon
is deemed pure, and the impure end is removed.
3. silicon wafers are sliced one at a time using a circular saw whose inner diameter cuts into
the rod. (A diamond saw produces cuts that are as wide as the wafer—. 5 millimeter thick.) the
wafer is then cut to be rectangular or hexagonal. Rectangular or hexagonal wafers are
sometimes used in solar cells because they can be fitted together perfectly, thereby utilizing all
available space on the front surface of the solar cell.

6. • 5. The wafers are then polished to remove saw marks. (It has recently
been found that rougher cells absorb light more effectively, therefore
some manufacturers have chosen not to polish the wafer.)
• 6. A more recent way of doping silicon with phosphorous is to use a
small particle accelerator to shoot phosphorous ions into the ingot. By
controlling the speed of the ions, it is possible to control their
penetrating depth. This new process, however, has generally not been
accepted by commercial manufacturers.

7. The following are the different types of solar
cells.
• Amorphous Silicon solar cell (a-Si)
• Biohybrid solar cell.
• Cadmium telluride solar cell (CdTe)
• Concentrated PV cell (CVP and HCVP)
• Copper indium gallium selenide solar cells (CI(G)S)
• Crystalline silicon solar cell (c-Si)
• Float-zone silicon.

8. Optical losses
Optical losses consist of light which could have generated an electron-hole pair, but does
not, because the light is reflected from the front surface, or because it is not absorbed in the
solar cell.

9. 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 Solar cell
• Make the back surface reflective
• Nanowires and nanoparticles

10. Reflection of a silicon surface
Reflection for silicon is over 30 %
Silicon SC only operate in 400 to 1100 nm range typically

11. 1. Anti-Reflection Coatings(ARC)

12. ARC thickness

13. Multi layer anti reflection coatings

14. Types of ARC films and their properties
• Titanium Oxide (TiO2)
Atmospheric pressure chemical vapor deposition
• IndiumTin Oxide (ITO)
Transparent conducting oxide
• SiliconOxide (SiO2)
Thermal oxidation
High temperature
Passivates surface
• Silicon Nitride (SiNx:H)
Plasma enhance chemical vapor deposition (PECVD)
LowTemperature
Passivates surface and bulk

15. 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

16. 2. Surface texturing
Random pyramid texturing
Inverted pyramid texturing
Surface texture promotes enhanced light absorption in Si solar cells. The quality of lower cost multi-crystalline-silicon (mc-Si)
has increased to the point that its cell performance is close to that of single c-Si cells, with the major difference resulting from
the inability to texture mc-Si affordably.

17. Etching/ Anisotrpic texturing
Anisotropic texturing
Commonly used on the crystallographic oriented
Si- wafers.
Produces pyramids on the wafer surfaces on the
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.
Typically, KOH or NaOH aqueous solutions with
isopropyl alcohol (IPA) is used for etching.
Also acidic texturing, performed with an aqueous
solution based in a mix of nitric acid, hydrofluoric
acid, water and some additives (as IPA). To
perform Etching.

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

19. 3.ARC andTexturing can be combined

20. 4. Nanowires and nanoparticles

21. Nanowires
MBE grown GaN NWs

22. Conclusion
• As the absorber ability of solar cell is increased by 2-3 time then the
efficiency will also get increased with the same multiple.
• As absorber ability is increased the temp. of the solar cell will also increase,
so we must have a backup plan to dimmish it out otherwise semiconductor
will get malfunctioned.

23. THANKYOU!!