Transcript Silicon Nanowire based Solar Cells

Silicon Nanowire based Solar Cells
International Congress On Renewable Energy
ICORE 2010
2nd December, 2010.
Pragya Singh
Pratul K Singh
Silicon Nanowire based Solar Cells
Outline:
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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 - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowire based Solar Cells
Outline:
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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 - 2010, Pragya Singh, Pratul K Singh
Light Trapping in Cells:
Sun already provides all the energy needed to support
life.
So the Challenge?
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowire based Solar Cells
Outline:
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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 - 2010, Pragya Singh, Pratul K Singh
Solar Cell
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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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Solar Cells Everywhere
Solar cells :
 Safe
 Clean
 Quiet
 Durable
 Reliable
 Installable anywhere
ICORE - 2010, Pragya Singh, Pratul K Singh
The Main Catch
 Material Cost
 Thickness of material
 Purity
 Fabrication Cost
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Planar Silicon Solar Cells:
 Thickness for an efficient light absorption
 High purity to avoid recombining
 High Reflectance
 High Recombination Rate.
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Conductance can be Improved
Bulk Silicon atom:
Tetravalent
Tend to achieve Stability
Bond with 4 other atoms
Silicon Nanowire:
Tetravalent
Tend to achieve stability
Cling with atmospheric Oxygen
Silica is formed
ICORE - 2010, Pragya Singh, Pratul K Singh
Conductance can be Improved
Prevention of Silica:
Conductivity increases 10 times
Prevention at high temperatures – 700C
High Vaccum
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowires- Properties
Recombination:
Tendency to recombine with other oppositely charged
charge carrier
Resulting in heat generation rather than electrical
energy
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowires- Properties
Light Trapping:
Light falling on the substrate gets reflected and once
again gets absorbed by silicon nanowires.
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowires- Properties
 Reduced size
 Increased absorptivity
 Reduced reflectivity
 Efficient electron transport
 Reduced Recombination
ICORE - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowires- Properties
Tiny PV Cells:
Composed of 3 layers:
– Inner P region
– Intrinsic or pure silicon
– Outer N region
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
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 - 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 - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Techniques for SiNW Deposition
Techniques:
 Supercritical-Fluid-Based and Solution-Based
Growth Techniques
 Molecular Beam Epitaxy
 Laser Ablation
 Silicon Monoxide Evaporation
 PECVD
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
Experiment at the SSN Research
Centre
ICORE - 2010, Pragya Singh, Pratul K Singh
Si-NW Growth Principle
ICORE - 2010, Pragya Singh, Pratul K Singh
Si-NW Deposition Process Steps
• 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
• 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
ICORE - 2010, Pragya Singh, Pratul K Singh
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 - 2010, Pragya Singh, Pratul K Singh
SiNW – Deposition Experiment
PECVD system.
Temperature
Pressure in mTorr
Time of Deposition
Gases Used
: 380 degrees
: 500mT
: 30 minutes
: Silane, Hydrogen and Argon
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 - 2010, Pragya Singh, Pratul K Singh
Thank You
ICORE - 2010, Pragya Singh, Pratul K Singh