Dr. Khalil Ebrahim Jasim

Department of Physics

University of Bahrain

Enhancement of Quantum Dot-sensitized Solar Cell

Efficiency with Natural Dye Extract

Introduction

Motivation

Experimental

Results and discussion

Conclusion

Outline

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Solar Park

Jenny Nelson, The Physics of Solar Cells, 2003.

e-

usable photo-voltage (qV)

Energy

e-

n-type

p-type

heat loss

heat loss

hν

h+

Conventional p-n Junction Photovoltaic Cell

Shockley-Queisser Limit

Optimal bandgap for single-junction solar cell

Solar Cells Generations

January 2005 Materials Research Society Bulletin

Nanostructured Solar Cells

3rd Generation Solar Cells: Emerging PV

Quantum Dots Solar CellWhat limits the

efficiency:Photons with lower

energy than the band

gap are not absorbed.

Photons with greater

energy than the band

gap are absorbed but

the excess energy is

lost as heat.

K. E. Jasim, “Dye sensitised solar cells—working principles, challenges and opportunities,” in Solar Cells/Book 2, INTECH, 2011.

Quantum dots, also known as nanocrystals, are a special class of

materials known as semiconductors, which are crystals composed of

periodic groups of II-VI, III-V, or IV-VI materials.

Quantum dots are unique class of

semiconductor because they are

so small, ranging from 2-10 nm

in diameter.

What Is a Quantum Dot?

A PbSe Quantum Dot as seen through a transmission electron microscope (TEM).

Semiconductors such as:

CdS, CdSe, CdTe, CuInS2, Cu2S, PbS, PbSe,

InP, InAs, Ag2S, Bi2S3 and Sb2S3 have been

synthesized as QDs and deposited onto wide

bandgap semiconductors as sensitizers.

Especially CdS, CdSe and PbS have been

used to investigate the operating principles of

QDSCs.

QD Materials

How Can Quantum Dots Improvethe Efficiency?

Quantum dots can generate multiple exciton (electron-hole pairs) after collision with one photon.

Hot Carriers

In bulk semiconductors recombination of hot electron‐holes is very fast and hence Multiple Exciton Generation (MEG) though present is very rare.

Recombination in QDs is

much slower than in bulk

because of confinement

effects.

Conversion of photons into charge carriers without (A)and with (B) carrier multiplication.

Multiple Exciton Generation (MEG)

Richard D. Schaller, Milan Sykora, Jeffrey M. Pietryga, and Victor I. Klimov, NANO LETTERS 2006 Vol. 6, No. 3, 424‐429.

0

1

2

3

4

5

0 5 10 15 20 25 30 35 40 45 50

Ene

rgy

ban

dga

p (

eV

)

Quantum dot radius (nm)

GaN

CdS

CdSe

InAs

InPPbTe

PbS

CTeGaAs

Figuresare from “Quantum Dots Explained.” Evident Technologies. 2008.

Effective Mass Model

Filter or

Monochromato

r

hDifference

amplifier

00

100

Lens

Mirror

Mirror

Shutter

Beam

Splitter

Sample

cell

Reference

cell

PO

P

Photo

detector 1

Photo

detector2

Readout

Filter or

Monochromato

r

Filter or

Monochromato

r

hDifference

amplifier

Difference

amplifier

00

100

Lens

Mirror

Mirror

Shutter

Beam

Splitter

Sample

cell

Reference

cell

PO

P

Photo

detector 1

Photo

detector2

Readout

400 600 800 1000 1200 1400 1600

0

1

2

3

4

5

2.4 nm

3.2 nm 5.0 nmAb

so

rba

nce

(a

.u.)

Wavelength (nm)

Absorbance of PbS Quantum Dots of Different Radii and Dye Extract

400 600 800 1000 1200

0

1

2

3

4

Ab

so

rban

ce (

au

)

Wavelength (nm)

Think Green Biomimicry

A dye monolayer

chemically absorbed on

the semiconductor is the

primary absorber of

sunlight; free charge

carriers are generated by

electron injections from a

dye molecule, excited by

visible radiation

K. E. Jasim, “Dye sensitized solar cells—working principles, challenges and opportunities,” in Solar Cells/Book 2, INTECH, 2011.

© Dyesol

- +

Electron

energy

Eredox

qVmax

SnO2

Glass

TiO2

Nanolayer

Quantum

Dots

Conduction

Band

Valance

Band

Counter

Electrode

Electrolyte

e-e-

e-

e-

e- e-

e-

3I-

I3-

Load

Light

1D(e)

1P(e)

1S(e)

1D(h)

1P(h)

1S(h)

h+

Dye

Molecule

e-

LUMO

h+

HUMO

Graphite

layer

Cell Preparation & Testing

Nanostructured TiO2 Layer

K. E. Jasim, S. Al-Dallal, and A.M. Hassan, “Natural dye-sensitised photovoltaic cell based on nanoporous TiO2”. Int. J. Nanoparticles, Vol. 4, No. 4, pp. 359-368, 2011.

KISS Approach

Keep It Simple & Smart

Approach

I-V Characteristics

0 50 100 150 200 250 300 350

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Mixed QD

2.4 nm

5.0 nm

3.2 nmP

ho

tocu

rren

t (m

A)

Voltage (mV)

I-V characteristics of 2.4 nm PbS QDs

0 50 100 150 200 250 300 3500.0

0.1

0.2

0.3

0.4

0.5

0.6

Without Dye

With DyeP

ho

tocu

rren

t (m

A)

Voltage (mV)

I-V characteristics of 3.2 nm PbS QDs

0 50 100 150 200 250 300 350 400

0.0

0.2

0.4

0.6

0.8

1.0

Without Dye

With Dye

Ph

oto

cu

rren

t (m

A)

Voltage (mV)

0 50 100 150 200 250 300

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Without Dye

With Dye

Ph

oto

cu

rren

t (m

A)

Voltage (mV)

I-V characteristics of 5.0 nm PbS QDs

Measured and calculated parameters for the three assembled QDs sensitized solar cells and

the dye enhanced solar cells using pomegranate as dye sensitizer

3.5 1.6 10.7

Transmittance of the Electrode

500 1000 1500 2000 2500 30000

10

20

30

40

50

60

70

Uncoated electrode

Coated electrode with

annealed TiO2

%T

Wavelength (nm)

Semiconductor Sensitized Solar Cells:

Like DSSCs they are quite cheaper to produce.

Tunability of QD optical properties with size.

In QD‐sensitized solar cell, the production of quantum yield is

greater than one due MEG (inverse Auger effect). Dye molecules

cannot undergo this process.

Dye Extract Enhances Quantum Dot-sensitized Solar Cell Efficiency.

Conclusion

Thank you for your attention