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