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Solar Cells -- Faissal's Presentation to Dorsinville Group and guests, on Friday 8th October 2010
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Solar Cells
Quantum Dot Enhanced SWCNT-Polymeric Solar Cells
M. Faisal HalimProf. Dorsinville, Walser,
Hovhannisyan
What is a Solar Cell?
A devices that generates electricity using light.
A Photovoltaic device generates a voltage when illuminated.
Source: http://staff.science.nus.edu.sg/~chmxqh/research.html 8th October, 2010
Why Solar Cells?
• Tremendous potential for generating electricity
• Government thrust: Green economy initiatives
• Market forces: Other fuel sources are scarce resources
Current Solar Cells use Crystalline Technology
Disadvantages of Crystalline Technology
• Crystals need to be grown – expensive process
• Lack of flexibility
• Polycrystalline cells lack efficiency
• Challenges in fabrication
Nanocrystal-Polymer Hybrid Solar Cells
Advantages• Cheap• Mechanically Flexible• High Efficiency• Solution Processible
– Can take Advantage of Molecular Self Assembly– Processes are highly scalable
• Ease of Fabrication• Low Toxicity of Processing Methods
Basic Solar Cell Architecture
Source: http://staff.science.nus.edu.sg/~chmxqh/research.html 8th October, 2010Source: Solar Energy Materials and Solar CellsVolume 87, Issues 1-4, May 2005, Pages 733-746
Photo Active Layer:
Absorbs light and produces an electric voltage.
• Quantum Dots (QD) absorb light
• Carbon Nanotubes (SWCNT): conduct electrons from QD to cathode
• P-type polymer (P3OT) conducts holes to anode
Area of interestSource: Solar Energy Materials and Solar CellsVolume 87, Issues 1-4, May 2005, Pages 733-746
Photo Active Layer
Tasks Involved
• Material Synthesis– Synthesis– Characterization: ABS, PL, Z-Scan
• Deposition of the Active Layer– Synthesis– Characterization: ABS, PL, Z-Scan, Film Thickness,
Film Surface Morphology, Film Uniformity
• Device Fabrication– Synthesis– Characterization: VI Characteristics, Response to
Light
Tasks: Material Synthesis
• Synthesis of CdSe Quantum Dots
• Purification of Single Walled Carbon Nanotubes (SWNT)
• Making Solutions of P3OT Polymer
• Making Solutions of PEDOT:PSS
• Making Appropriate Solution Mixtures
Tasks: Deposition of Active Layer
• Appropriate Solution Mixtures Spin Coated. Films are of:– Optical Quality– Uniform Thickness– Uniform Composition
• Films Grown Layer by Layer– Deposition at 80 RPM– Coating, 10 secs, 1000 RPM– Drying, 200 RPM
• Films of Different Materials Deposited Sequentially
Tasks: Device Fabrication
• Spin Coating PEDOT:PSS onto ITO Coated Substrate
• Spin Coating Active Layer Material
• Vapor Depositing Al electrodes
CdSe Quantum Dot SynthesisCdSe QD Preparation
55 degrees CelciusRelatively Low Toxicity Materials:
1. Add Decylamine to Aqueous CdNTA2. Add Aqueous Na2SeSO3
3. Add Toluene4. CdSe QDs Migrate to the Toluene
Phase5. Add a Polymer Solution to Preserve
QDs
Source: Published online: 25 January 2004; doi:10.1038/nmat1056
Absorption Spectrum of CdSe QDs (aq)
Carbon Nanotube Purification
Carbon Nanatubes Purchased in Impure Form. Purification Removes:– Soot (470oC in
Oven, in Air)– Metal Catalyst
(Sonicating in HCl)– HCl (Sonicating and
Centrifuging in DI Water)
Absorption Spectrum of SWCNTs (aq)
Active Layer Film
• Optical Quality
• Uniform Thickness
• Homogeneous
Absorption Spectrum of 6 Layer Film of SWCNT in P3OT
Z-Scan Characterization
• Open Aperture– Measures Multi-
Photon Absorption– Measures
Saturable Absorption
• Closed Aperture– Measures
Refractive Index as a Function of Intensity
– Can be used as a measure of Optical Activity
What the Measurements Will Tell Us
• Absorption Spectra– Exciton Peak Wavelength
• Fluorescence Spectra– Quantum Dot Size– Quantum Dot Surface Roughness
• Open Aperture Z-Scan– Evidence of Excitation of Charge Carriers
• Closed Aperture Z-Scan– Optical Response of Material in Resonant and Non-
Resonant Wavelength Regimes
How We May Use The Experimental Data
The data will influence how and what parameters in the solar cells we optimize:
• Surfactant, for:– QD Surface Passivation– QD Shape– QD Size– QD’s Electrical Contact with Carbon Nanotubes– QD Surface roughness
• Carbon Nanotube, for:– Diameter
• Polymer, for:– Chain Length– Number of Side Chains– Functional Groups– Conductivity
Other Experiments• Third Order Nonlinear
measurements performed for novel polymers
• Possible Application in all-optical switching
• Collaborative project with Professor Ogawa, Universidad Nacional Autónoma de México
Source: Dyes and PigmentsVolume 88, Issue 2, February 2011, Pages 129-134
Questions?
End