Silicon Nanowire based Solar Cells
Silicon Nanowire based Solar Cells
International Congress On Renewable Energy
ICORE 2010
2 nd December, 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 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
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:
•
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
•
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
•
The sample introduced in the PECVD chamber
•
Chromium layer of 10.7nm deposited by EBE Method
•
Heated to 580 degrees to form Nano particles
•
Gold Layer of 2.6nm deposited by EBE Method
•
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 : 380 degrees
Pressure in mTorr : 500mT
Time of Deposition : 30 minutes
Gases Used : 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
