Getting Power from Plastic – Solar Power Generation Using Blends of

Organic Polymers and Nanostructures

By Dave Black and Shashi Paul

Solar Power

• World energy demand increasing

• Photovoltaics currently <1%

• Two types– Conventional Semiconductor (CSC)– Excitonic Semiconductor (XSC)

Types of Solar Cell

• First Generation (CSC)• Second Generation

(CSC)• Third Generation

(CSC)• Organic (XSC)• Hybrid (XSC)

CSC Device Structure

EncapsulationP-N junction

Bottom Contact

Top Contact

Typical 1st and 2nd generation CSC solar cell structure

CSC Device Structure

3rd generation CSC multijunction

Anti Reflectioncoating

Top Cell(GaInP)

Bottom Contact

Top Contact

Middle Cell (GaAs)

Tunnel Junction

Bottom Cell(Ge) Substrate

(Ge)

XSC Device Structure

Transparent Substrate

ITO transparentelectrode

PEDOT:PSS

Active layer

Exciton blocking layerAl/Ag electrode

Typical organic heterojunction solar cell structure.

Why Organic?

• Potentially Cheap– Materials expensive now– Price decreases as

production increases• Quick to produce

– Simple processes• Sputtering• Spin coating• Thermal Evaporation• Printing

• Flexibility– Plastic substrates– Clothing– Fabric (already used by US Army)

The Voltaic Generator, by New York-based Voltaic Systems, is the first solar bag powerful enough to charge a laptop. Photograph: PR

7 Stages of Excitonic Charge Generation

• Photon incoupling• Photon absorption• Exciton formation• Exciton Migration• Exciton Dissociation• Charge Transport• Charge collection

e- h+

Exciton

Nano-particle

e-

h+

What is EMTERC Doing?

• Next generation hybrid PV– Novel blends of polymers and

nanostructures– Increased efficiency– Increased absorption– Low cost?

Permittivity

• Increased Permittivity– Tune Debye Length– Control exciton type– Increase diffusion length

• Barium Titanate– High permittivity– Ferroelectric– Tetragonal structure

Debye Length

Debye length defined as:

The scale over which mobile charge carriers screen out electric fields

As LD increases so does charge separation.

Increasing Permittivity

2.00

3.00

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0 5 10 15 20 25 30

Mea

n Re

lati

ve P

erm

ittivi

ty

BaTiO3Concentration (mg/ml)

Increase in relative permittivity with increasing concentration of barium titanate with phosphonic acid ligand.

Increasing Photoconductivity

Increase in photo-conductivity in light and dark conditions for polymers with and without “novel” material.

The EMTERC Hybrid

• Uses blend of polymer and NP

• Has diode like behaviour

• Difference between light and dark states

• Work in progress

Future Work in EMTERC• Incorporating

Nanostructures:– Improve the number of

incident photons captured by the solar cell

– Improve the number and type of excitons produced from incident photons

– Increase the exciton diffusion length

– Increase the number and quality of interfacial boundaries

Transparent electrode

Aluminium electrode

Nanowires

Active polymer matrix

Any Questions?