dye sensitized solar cells

DYE SENSITIZED SOLAR

CELLS

Dileep V Raj

Mtech Renewable Energy Technologies

Amrita Vishwa Vidyapeetham,Coimbatore

1

What’s Solar Energy?

• Solar energy Originates with the thermonuclear fusion

reactions occurring in the sun.

• Represents the entire electromagnetic radiation (visible light,

infrared, ultraviolet, x-rays, and radio waves).

• This energy consists of radiant light and heat energy from

the sun.

• Out of all energy emitted by sun only a small fraction of

energy is absorbed by the earth.

• Just this tiny fraction of the sun’s energy is enough to meet

all our power needs.

2

• Energy produced by the sun

• Clean, renewable source of energy

• Harnessed by solar collection methods such as solar cells

• Converted into usable energy such as electricity

Photovoltaic (solar)

panel

Set of solar panels

3

What is a Photovoltaic Cell

• A device that can convert sunlight directly in electricity.

• Traditional types are based on two types of silicon sandwiched together (n-type and p-type).

• Based on using photons to separate charges: electron-hole pairs

• Many new types are in research/production stage.

4

Recap : Photo means light in Greek and Volt is the name of a

pioneer in the study of electricity Alessandro Volta

Solar cell: Solar cell is a photovoltaic device that converts

the light energy into electrical energy based on

the principles of photovoltaic effect

Albert Einstein was awarded the 1921 Nobel Prize in physics

for his research on the photoelectric effect—a phenomenon

central to the generation of electricity through solar cells.

5

Solar Panel Use Today

• Large companies like

Google, Walmart, and

Microsoft use solar

energy to partially power

some of their facilities

Solar panels on Microsoft building

Solar panels being tested

on Walmart store6

• Renewable energy sources such as solar energy areconsidered as a feasible alternative because

“More energy from sunlight strikes Earth in 1 hour than all of the energy consumed by humans in an entire

year.”(Lewis, 2007).

• The use of natural dye extracts provides natural, non toxicand low cost dye sources with high absorbance level ofUV, visible and near IR.

• Examples of such dye sources are Bahraini Henna(Lawsonia inermis L.) and Bahraini raspberries (Rubus spp.).

7

Disadvantages of Conventional Solar

cells

o Inefficient and costly equipment

o Environmental Impact of PV Cell Production

o Initial cost is very high

o Requires expert hand and equipment in

manufacture

8

Semiconductor Solar

Cells

DSSC

Transparency Opaque Transparent

Environment(Material&

Process)

Normal Great

Power Generation cost High Low

Power Generation

efficiency

High Normal

Color Limited Various

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What is a DSSC?

A dye sensitized solar cell is a new kind of

relatively low cost solar cell with great

potential as its materials are considerably

cheaper and it is simple to make.

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Past

• Michael Grätzel and Brian O’Regan invented “Dye-

sensitized solar cells”, also called “Grätzel cells”, in

2005.

• The first cells were only capable of using light at the

Ultraviolet and Blue end of the spectrum.

• By the turn of the century, advances in technology

were able to broaden the frequencies in which these

cells were able to respond.

• The most efficient of the dyes were simply known as

“Black dyes” due to their very dark colors.

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So What Does this Mean for Solar Cells?

• In dye-sensitized solar cells…

– Talk about highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)

• In single-crystal silicon solar

cells…

– Talk about “conduction

band” (excited states) and

“valence band” (ground

states)12

How does a DSSC function?

A DSSC functions due to the interactions

between the cell's anode and the cathode,

and the nanoparticles of titanium oxide,

coated with light sensitive dye and

surrounded by electrolyte.

13

Components Of DSSC

• Transparent conducting and counter conducting

electrodes

• The nanostructured wide band gap

semiconducting layer

• The dye molecules (sensitizer)

• The electrolyte.

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Dye Sensitized Solar Cells - Working Principles,

Challenges and Opportunities Khalil Ebrahim Jasim Department of Physics, University of Bahrain Kingdom of Bahrain

Schematic of the structure of the dye sensitized solar cell.

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1. Transparent substrate for both the conducting

electrode and counter electrode

• Clear glass substrates are commonly used as substrate because of

their relative low cost, availability and high optical transparency in

the visible and near infrared regions of the electromagnetic

spectrum.

• TCFs for photovoltaic applications have been fabricated from both

inorganic and organic materials.

• Inorganic films typically are made up of a layer of transparent

conducting oxide (TCO),generally in the form of indium tin oxide

(ITO), fluorine doped tin oxide (FTO), and doped zinc oxide.

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2.Nanostructured photoelectrode

• In the old generations of photo electro chemical solar

cells (PSC) photo electrodes were made from bulky

semiconductor materials such as Si, GaAs or CdS.

• However, these kinds of photo electrodes when

exposed to light they undergo photo corrosion that

results in poor stability of the photoelctrochemical cell.

• The use of sensitized wide bandgap semiconductors

such as TiO2, or ZnO resulted in high chemical stability

of the cell due to their resistance to photo corrosion.18

• The problem with bulky single or poly-crystalline

wide band gap is the low light to current

conversion efficiency mainly due to inadequate

adsorption of sensitizer because of limited surface

area of the electrode.

• One approach to enhance light-harvesting

efficiency (LHE) and hence the light to current

conversion efficiency is to increase surface area (the

roughness factor) of the sensitized photo electrode.

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• One of the important factors that affect the cell's efficiency is

the thickness of the nanostructured TiO2 layer which must be

less than 20 nm to ensure that the diffusion length of the

photoelectrons is greater than that of the nanocrystalline TiO2

layer.

• TiO2 is the most commonly used nanocrystalline semiconductor

oxide electrode in the DSSC as an electron acceptor to support

a molecular or quantum dot QD sensitizer is TiO2 (Gratzel,

2003).

• Other wide band gap semiconductor oxides is becoming

common is the zinc oxide ZnO. ZnO possesses a band gap of

3.37 eV and a large excitation binding energy of 60 meV.

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3.Photosensitizer

• Dye molecules of proper molecular structure are used to

sensitized wide bandgap nanostructured photoelectrode.

• Upon absorption of photon, a dye molecule adsorbed to

the surface of say nanostructured TiO2 gets oxidized and

the excited electron is injected into the nanostructured

TiO2.

• Sensitizations of natural dye extracts such as shiso leaf

pigments, Black rice, Fruit of calafate, Rosella ,Natural

anthocyanins ,Henna and wormwood have been

investigated and photovoltaic action of the tested cells

reveals some opportunities. 21

Photosensitizer

Fig. (a) Ruthenium based red or "N3" dye adsorbed onto a titanium dioxide

surface (from Martinson et al., 2008), and

(b) Proposed structure of the cyanin dye adsorbed to one of the titanium metal

centers on the titanium dioxide surface (From Smestad, 1988).

N3 dye it has been an outstanding solar light absorber and charge-transfer

sensitizer.

The red dye or N3 dye is capable of absorbing photons of wavelength ranging

from 400 nm to 900 nm.22

Dye-sensitizers

‘Increasing the Efficiency of Solar Cells by Combining Silicon- and Dye Sensitized Devices’ B. Ohms, A. Kleine and U. Hilleringmann International

Conference on Renewable Energies and Power Quality (ICREPQ’12) Santiago de Compostela (Spain), 28th to 30th March, 2012 23

Natural Dye Performances

Dye-Sensitized Solar Cells: A Successful Combination of Materials : Claudia Longo and Marco-A. De Paoli* Instituto de Química, Universidade Estadual

de Campinas, CP 6154, 13084-971 Campinas - SP, Brazil

Measured absorbance of some extracted natural dyes in methanol as solvent.

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Redox electrolyte

• Electrolyte containing I-/I3 redox ions is used in DSSC to regenerate the

oxidized dye molecules

• This will complete the electric circuit by mediating electrons between the

nanostructured electrode and counter electrode.

• Cell performance is greatly affected by ion conductivity in the electrolyte

which is directly affected by the viscosity of the solvent.

• NaI, LiI and R4NI (tetraalkylammonium iodide) are well known examples

of mixture of iodide usually dissolved in nonprotonic solvents such as

acetonitrile, propylene carbonate and propionitrile to make electrolyte.

• The redoxing electrolyte needs to be chosen such that the reduction of

I3ions by injection of electrons is fast and efficient

Dye-Sensitized Solar Cells: A Successful Combination of Materials Claudia Longo and Marco-A. De Paoli* Instituto de Química,

Universidade Estadual de Campinas, CP 6154, 13084-971 Campinas - SP, Brazil

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How Does DSSC Work?

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TiO2 Dye Electrolyte Cathode

Wide band-gap semiconductor

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-0.5

0

0.5

TiO2

1.0

S*

S°/S+

Dye Electrolyte

OxRed

Cathode

Electron energy(eV vs. NHE)

-1.0

e-

Wide band-gap semiconductor

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1. Light absorption -0.5

0

0.5

TiO2

1.0

S*

S°/S+

hν

Dye Electrolyte

OxRed

Cathode

1

Electron energy(eV vs. NHE)

-1.0

e-

Wide band-gap semiconductor

h+

29

1. Light absorption

2. Injection to

semiconductor

3. Percolation

-0.5

0

0.5

TiO2

1.0

S*

S°/S+

hν

Dye Electrolyte

OxRed

Cathode

1

23

Electron energy(eV vs. NHE)

-1.0

e-

Wide band-gap semiconductor

h+

30

1. Light absorption

2. Injection to

semiconductor

3. Percolation

4. Regeneration of

oxidized dye

-0.5

0

0.5

TiO2

1.0

S*

S°/S+

hν

Dye Electrolyte

OxRed

Cathode

1

23

4

Electron energy(eV vs. NHE)

-1.0

Wide band-gap semiconductor

e-

h+

31

1. Light absorption

2. Injection to

semiconductor

3. Percolation

4. Regeneration of

oxidized dye

5. Regeneration of

oxidized species

-0.5

0

0.5

TiO2

1.0

S*

S°/S+

hν

Dye Electrolyte

OxRed

Cathode

LOAD

e-

External circuit

1

23

4

Electron energy(eV vs. NHE)

-1.0

Wide band-gap semiconductor

h+

5

h+

e-

32

Maximum Voltage in DSSCs

-0.5

0

0.5

TiO2

1.0

S*

S°/S+

Dye Electrolyte

OxRed

Maximum Voltage

Cathode

LOAD

e-

External circuit

Electron energy(eV vs. NHE)

-1.0

e-

Wide band-gap semiconductor

The voltage is

determined

mainly by the

titania and

redox couple

in the

electrolyte.

h+

33

Gratzel, M. (2005). Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells. Inorg. Chem., Vol. 44, pp. 6841-6851.34

Illustration of operation principle of dye sensitized solar cell

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Summary of Dye Sensitized Solar

Cell

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DSSC Preparation

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Image Source : www.thesolarpark.co.uk

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Commercialization of DSSC

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N

N

N

N

N

N

Ru

COOH

COOH

COOH

HOOC

HOOC

COOH

N

N

N

N

Ru

COOH

HOOC

HOOC

COOH

NC

S

NC

S

N

N

N

Ru

COOH

HOOC

HOOCN

C

S

NC

S

NC

S

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Applications Of DSSC

• Because of the physical nature of the dye sensitized solar cells, inexpensive,

environment friendly materials, processing, and realization of various colors,

power window and shingles are prospective applications in building integrated

photovoltaics

• The availability of lightweight flexible dye sensitized cells or modules are

attractive for applications in room or outdoor light powered calculators,

gadgets, and mobiles.

• Flexible dye sensitized solar modules opens opportunities for integrating them

with many portable devices, baggage, gears, or outfits.

• In power generation, dye sensitized modules with efficiency of 10% are

attractive choice to replace the common crystalline Si-based modules.

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Applications of DSSC(a) 200 m2 of DSSC panels installed in Newcastle (Australia)– the first

commercial DSSC module

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(c) flexible DSSC-based solar module developed by Dyesol (http://www.dyesol.com)

(d) jacket commercialized by G24i (http://www.g24i.com).

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Aesthetic Advantages of DSSCversus

conventional Solar Cells

• Dyes determine the

color of the device.

• Can be transparent

• Can be flexible

• Easy to make

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Solar Powered Solar Panel Sun GlassesThe SIG, or “Self-Energy Converting Sunglasses” are quite simple. The lenses of the glasses have

dye solar cells, collecting energy and making it able to power your small devices through the power jack

at the back of the frame. “Infinite Energy: SIG”

Court

esy:

Sony C

orp

.

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The DSC vs. Conventional Silicon PV

TiO2

Dye

Electrolyte

Cathode

+

n-typeSilicon

p-typeSilicon

+

+

+

+

• Charge carriers (excited

electrons) are produced

throughout the semiconductor

• Semiconductor considerations:

• Precise doping

• high purity

• high crystalinity

• Light absorption and charge

transport are decoupled

• Relaxed constraints on individual

components (each can be

separately tuned)

• Only monolayer of dye on TiO2

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Solar Cell Efficiencies

Silicon Solar Cell Efficiencies:

Theoretical Maximum: 26%

Best in Lab: 25% (Green, UNSW)

Modules: 15-22%

Thin Film Solar Cell Efficiencies:

Theoretical Maximum: >22%

Best in Lab: 20% (Noufi, NREL)

Modules: 9-12%

Dye-Sensitized Solar Cell Efficiencies:

Theoretical Maximum: 14-20%

Best in Lab: 12% (Grätzel, EPFL)

Modules: 6-9% 70

Conclusions• In short, compared to Si based solar cells dye sensitized solar

cells are of– low cost and ease of production,

– their performance increases with temperature,

– possessing bifacial configuration - advantage for diffuse light,have transparency for power windows, color can be varied byselection of the dye, invisible PV-cells based on near-IR sensitizersare feasible, and they are outperforms amorphous Si.

• Moreover, DSSC shows higher conversion efficiency thanpolycrystalline Si in diffuse light or cloudy conditions.

• It is believed that nanocrystalline photovoltaic devices arebecoming viable contender for large scale future solarenergy converters.

• The search for green sources or generators of energy isconsidered one of the priorities in today's societies andoccupies many policy makers' agendas.

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Reference

• Gratzel, M. (2005). Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells. Inorg.Chem., Vol. 44, pp. 6841-6851.

• Lewis, N. S. (2007). Toward Cost-Effective Solar Energy Use. Science, Vol 315, pp. 798-801.

• Meyer, G. J. Inorg. Chem. 2005, 44, 6852.

• Mallouk, T. E.; Hoertz, P. G. Inorg. Chem. 2005, 44, 6828.

• Nakade, S.; Kubo, W.; Saito, Y.; Kanzaki, T.; Kitamura, T.; Wada, Y.; Yanagida, S. J. Phys.Chem. B 2003, 107.

• Plass, R.; Pelet, S.; Kruger, J.; Gratzel, M.; Bach, U. J. Phys. Chem. B 2002, 106, 7578.

• Nozik, A. J. Quatum dot solar cells. Next Gener. Photovoltaics 2004, 196.

• Liska er al. 2006, 88, 203103. Marcus, R. A. 1992, Nobel Lecture.

• Bernards, D. A.; Samuel, F. T.; Hector, D. A.; George, G. M. Science, 2006, 313, 1416.

• Amao, Y. & Komori, T. (2004).

• Bio-photovoltaic conversion device using chlorine-e6 derived from chlorophyll from Spirulinaadsorbed on a nanocrystalline TiO2 film electrode. Biosensors Bioelectronics, Vol. 19, Issue 8,pp. 843-847.

• Harding, H.E.; Hoke, E.T.; Armistrong, P.B.; Yum, J.; Comte, P.; Torres, T.; Frechet, J.M.J.;Nazeeruddin, M.K.; Gratzel, M. & McGehee, M.D. (2009). Increased light harvesting in dye-sensitized solar cells with energy relay dyes. Nature Photonics, Vol. 3, pp. 406-411.

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