1. Silicon Nanowire based Solar Cells
International Congress On Renewable Energy
ICORE 2010
2nd December, 2010.
Pragya Singh
Pratul K Singh

2. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

3. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

4. Light Trapping in Cells:
Sun already provides all the energy needed to support life.
So the Challenge?
ICORE , Pragya Singh, Pratul K Singh

5. Light Trapping in Cells:
One to One conversion:
Blue photon = 2 times more energy than the Red Photon
Both produce 1 electron each.
Effective light energy utilized?
ICORE , Pragya Singh, Pratul K Singh

6. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

7. ICORE - 2010, Pragya Singh, Pratul K Singh
Solar Cell
Cell is thin Si wafer
Size 10x10 cm : size of a CD
Thickness is in fractions of mm
Metal pattern is to make electrical contacts.
ICORE , Pragya Singh, Pratul K Singh

8. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

9. Energy Conversion in Solar Cell
Light is shone
Electrons are knocked out
Electrons and holes move in opposite directions
Electrical output is generated between the contacts.
ICORE , Pragya Singh, Pratul K Singh

10. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

11. Solar Cells Everywhere
Safe
Clean
Quiet
Durable
Reliable
Installable anywhere
ICORE , Pragya Singh, Pratul K Singh

12. ICORE - 2010, Pragya Singh, Pratul K Singh
The Main Catch
Material Cost
Thickness of material
Purity
Fabrication Cost
ICORE , Pragya Singh, Pratul K Singh

13. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

14. Planar Silicon Solar Cells:
Thickness for an efficient light absorption
High purity to avoid recombining
High Reflectance
High Recombination Rate.
ICORE , Pragya Singh, Pratul K Singh

15. Sliced into Nano-scale
Diameters from 1 to 50nm
Nano scale Silicon has a color difference
Quantum Confinement
Nano sized Silicon shows:
Physical
Optical
Electronics properties change
Electrons occupy different energy levels
ICORE , Pragya Singh, Pratul K Singh

16. Conductance can be Improved
Bulk Silicon atom:
Tetravalent
Tend to achieve Stability
Bond with 4 other atoms
Silicon Nanowire:
Tend to achieve stability
Cling with atmospheric Oxygen
Silica is formed
ICORE , Pragya Singh, Pratul K Singh

17. Conductance can be Improved
Prevention of Silica:
Conductivity increases 10 times
Prevention at high temperatures – 700C
High Vaccum
ICORE , Pragya Singh, Pratul K Singh

18. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

19. Nanowires- Properties
No Lattice Mismatch.
Flexibility to create heterostructures.
Broad range of materials.
Integration of compound semiconductor based optoelectronic devices with silicon based microelectronics.
ICORE , Pragya Singh, Pratul K Singh

20. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

21. Silicon Nanowires- Properties
Recombination:
Poor efficiency may be due to recombination within the bulk silicon element.
Photon strikes the p-n junction in bulk silicon, Produces an electron-hole pair.
Electron and hole must travel along the wire to produce current.
ICORE , Pragya Singh, Pratul K Singh

22. Silicon Nanowires- Properties
Recombination: Tendency to recombine with other oppositely charged charge carrier Resulting in heat generation rather than electrical energy
ICORE , Pragya Singh, Pratul K Singh

23. Silicon Nanowires- Properties
Reduced Recombination in SiNW:
Small diameters.
SiNWs grown vertical, perpendicular to the surface of the substrate.
Electrons strikes on the surface.
Distance of hole/electron travel is minimized.
Distance is of the order of nanometers.
ICORE , Pragya Singh, Pratul K Singh

24. Silicon Nanowires- Properties
Light Trapping: Light falling on the substrate gets reflected and once again gets absorbed by silicon nanowires.
ICORE , Pragya Singh, Pratul K Singh

25. Silicon Nanowires- Properties
Increased Surface Area:
Very narrow pointed structures.
Diameter in nanometers.
Length in micrometers.
Greater area made of p-n junctions is exposed to sunlight.
Increases absorptivity.
ICORE , Pragya Singh, Pratul K Singh

26. Silicon Nanowires- Properties
Reduced size
Increased absorptivity
Reduced reflectivity
Efficient electron transport
Reduced Recombination
ICORE , Pragya Singh, Pratul K Singh

27. Silicon Nanowires- Properties
Tiny PV Cells:
Composed of 3 layers:
Inner P region
Intrinsic or pure silicon
Outer N region
ICORE , Pragya Singh, Pratul K Singh

28. Silicon Nanowires- Properties
Photon strikes the outer shell
Electron-hole pair is created
Travels in the radial direction towards the P layer (core) before recombination.
ICORE , Pragya Singh, Pratul K Singh

29. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

30. ICORE - 2010, Pragya Singh, Pratul K Singh
Fabrication
Catalyst Particles :
The catalyst must be inert to the reaction products (during CVD nanowire growth).
Gold
Aluminum
Tin
Indium
Gallium
ICORE , Pragya Singh, Pratul K Singh

31. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

32. Techniques for SiNW Deposition
Supercritical-Fluid-Based and Solution-Based Growth Techniques
Molecular Beam Epitaxy
Laser Ablation
Silicon Monoxide Evaporation
PECVD
ICORE , Pragya Singh, Pratul K Singh

33. Silicon Nanowire based Solar Cells
Outline:
Light Trapping in Cells
Solar Cell
Energy Conversion in Solar Cell
Solar Cells Everywhere
Planar Silicon Solar Cell
Nanowires- Properties
Silicon Nanowires- Properties
Fabrication
Techniques for SiNW Deposition
Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

34. Experiment at the SSN Research Centre
ICORE , Pragya Singh, Pratul K Singh

35. Si-NW Growth Principle
ICORE , Pragya Singh, Pratul K Singh

36. Si-NW Deposition Process Steps
The sample introduced in the PECVD chamber
Heated to 580 degrees to form Nano particles
Silane introduced with hydrogen for 30 minutes at various temperatures
Silicon (4 inch) n-type Substrate Cleaned
Chromium layer of 10.7nm deposited by EBE Method
Gold Layer of 2.6nm deposited by EBE Method
ICORE , Pragya Singh, Pratul K Singh

37. SiNW – Deposition Experiment
Catalyst Nano Particles:
Gold Film Layer (2.6nm) Deposited on Silicon Substrate by EBE
Heated at 580 degrees to form Nano Particles
Figure1 SEM image of Nano particles of Gold
Figure 1. SEM Image of Gold Nano Particles on Silicon Substrate
ICORE , Pragya Singh, Pratul K Singh

38. SiNW – Deposition Experiment
PECVD system. Temperature : 380 degrees Pressure in mTorr : 500mT Time of Deposition : 30 minutes Gases Used : Silane, Hydrogen and Argon
ICORE , Pragya Singh, Pratul K Singh

39. ICORE - 2010, Pragya Singh, Pratul K Singh
Si NW Comparison
Si Nano Wire at SSNRC
Literature Survey
Reference: IRAM, Saclay Institute of Matter and Radiation 
ICORE , Pragya Singh, Pratul K Singh

40. ICORE - 2010, Pragya Singh, Pratul K Singh
Thank You
ICORE , Pragya Singh, Pratul K Singh