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Silicon Nanowire based Solar Cells
International Congress On Renewable EnergyICORE 2010
2nd December, 2010.Pragya Singh
Pratul K Singh
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
Light Trapping in Cells:
ICORE - 2010, Pragya Singh, Pratul K Singh
Sun already provides all the energy needed to support life.
So the Challenge?
Light Trapping in Cells:
ICORE - 2010, Pragya Singh, Pratul K Singh
One to One conversion:Blue photon = 2 times more energy than the Red Photon Both produce 1 electron each.
Effective light energy utilized?
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
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
ICORE - 2010, Pragya Singh, Pratul K Singh
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
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
ICORE - 2010, Pragya Singh, Pratul K Singh
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
Solar Cells Everywhere
Solar cells :SafeCleanQuietDurableReliableInstallable anywhere
ICORE - 2010, Pragya Singh, Pratul K Singh
The Main Catch
ICORE - 2010, Pragya Singh, Pratul K Singh
Material Cost
Thickness of material Purity
Fabrication Cost
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
Planar Silicon Solar Cells:
ICORE - 2010, Pragya Singh, Pratul K Singh
Thickness for an efficient light absorption
High purity to avoid recombining
High Reflectance
High Recombination Rate.
Sliced into Nano-scale
ICORE - 2010, Pragya Singh, Pratul K Singh
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
Conductance can be Improved
ICORE - 2010, Pragya Singh, Pratul K Singh
Bulk Silicon atom:TetravalentTend to achieve StabilityBond with 4 other atoms
Silicon Nanowire:TetravalentTend to achieve stabilityCling with atmospheric OxygenSilica is formed
ICORE - 2010, Pragya Singh, Pratul K Singh
Prevention of Silica:
Conductivity increases 10 timesPrevention at high temperatures – 700CHigh Vaccum
Conductance can be Improved
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
– 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
Nanowires- Properties
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
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
ICORE - 2010, Pragya Singh, Pratul K Singh
Reduced size
Increased absorptivity
Reduced reflectivity
Efficient electron transport
Reduced Recombination
Silicon Nanowires- Properties
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 shellElectron-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
ICORE - 2010, Pragya Singh, Pratul K Singh
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
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
ICORE - 2010, Pragya Singh, Pratul K Singh
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
Techniques for SiNW DepositionTechniques:
Supercritical-Fluid-Based and Solution-Based Growth Techniques
Molecular Beam EpitaxyLaser AblationSilicon Monoxide EvaporationPECVD
ICORE - 2010, Pragya Singh, Pratul K Singh
Silicon Nanowire based Solar Cells
ICORE - 2010, Pragya Singh, Pratul K Singh
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
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
ICORE - 2010, Pragya Singh, Pratul K Singh
• 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
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 ExperimentPECVD 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