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FABRICATION, CHARACTERIZATION AND PERFORMANCE

EVALUATION OF DYE-SENSITIZED SOLAR CELL (DSSC)

A Project Report

Submitted in partial fulfilment of the

Requirements for the award of the degree

Of

Integrated Masters in Technology

in

ENERGY ENGINEERING

By:

DHARMVEER KUMAR (CUJ/I/2012/IEE/009)

PRANAV ANAND (CUJ/I/2012/IEE/019)

ASHUTOSH PANDEY (CUJ/I/2012/IEE/004)

CENTRE FOR ENERGY ENGINEERING

CENTRAL UNIVERSITY OF JHARKHAND

RANCHI, JHARKHAND -835205

APRIL,2016

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Central University of Jharkhand

Brambe

CERTIFICATE

This is to certify that the thesis entitled, “DYE-SENSITIZED SOLAR CELL (DSSC)” submitted by,

DHARMVEER KUMAR, PRANAV ANAND and ASHUTOSH PANDEY to the Central University

of Jharkhand, Brambe in partial fulfillment of the requirement for the award of Integrated Master of

Technology degree in Energy Engineering is a bonafide record of the project work carried out by

them under my supervision during semester VIII.

Signature:

Name: Dr Basudev Pradhan

Designation: Assistant Professor, CUJ

Place: Brambe, Jharkhand

Date: 26/04/2016

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ACKNOWLEDGEMENT

It gives us great pleasure to submit my B.Tech project report on ‘DYE-SENSITIZED SOLAR CELL

(DSSC)’.

This project was carried out under the guidance of Dr. Basudev Pradhan, Asst. Professor, Centre for

Energy Engineering, Central University of Jharkhand. We would like to express our appreciation for

him to give his valuable suggestions. We would thank him for constantly motivating us to work

harder.

We also want to thanks Prof. S. K. Samdarshi, Head of the Department and all faculty members of

Centre for Energy Engineering, Central University of Jharkhand for motivation and encouragement to

complete our project work.

Last but not least, our sincere thanks to all our friends who have patiently extended all sorts of help

for accomplishing this undertaking.

DHARMVEER KUMAR (CUJ/I/2012/IEE/009)

PRANAV ANAND (CUJ/I/2012/IEE/019)

ASHUTOSH PANDEY (CUJ/I/2012/IEE/004)

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TABLE OF CONTENTS

Abstract

1. Introduction

2. Background and Literature Review

2.1. Solar cells

2.2. Titanium dioxide (TiO2)

2.3. Construction and mode of operation

3. Experiment Methodology

3.1 Assembling the Dye-Sensitized Solar Cell

4. Results and Discussion

5. Future Work

References

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ABSTRACT

The dye-sensitized solar cells (DSC) provides a technically and economically credible alternative

concept to present day p–n junction photovoltaic devices. In contrast to the conventional systems

where the semiconductor assume both the task of light absorption and charge carrier transport the two

functions are separated here. Light is absorbed by a sensitizer, which is anchored to the surface of a

wide band semiconductor. Charge separation takes place at the interface via photo-induced electron

injection from the dye into the conduction band of the solid. Carriers are transported in the conduction

band of the semiconductor to the charge collector. The use of sensitizers having a broad absorption

band in conjunction with oxide films of nanocrstalline morphology permits to harvest a large fraction

of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a

large spectral range extending from the UV to the near IR region. Overall solar (standard AM 1.5) to

current conversion efficiencies (IPCE) over 10% have been reached. There are good prospects to

produce these cells at lower cost than conventional devices. Here we present the current state of the

field, discuss new concepts of the dye-sensitized nanocrystalline solar cell (DSC) including

heterojunction variants and analyze the perspectives for the future development of the technology.

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CHAPTER 1: INTRODUCTION

Photovoltaic devices are based on the concept of charge separation at an interface of two

materials of different conduction mechanism. To date this field has been dominated by solid-

state junction devices, usually made of silicon, and profiting from the experience and material

availability resulting from the semiconductor industry. The dominance of the photovoltaic

field by inorganic solid-state junction devices is now being challenged by the emergence of a

third generation of cells, based. A dye sensitized solar cell (DSSC) is a cost effective group of

thin film solar cells which is based on a semiconductor formed between a photo sensitized

anode and an electrolyte. The quantitative conversion of incident photon into electric current

is achieved over a large spectral range extending from the ultraviolet to the near Infra-red

region. Although its conversion efficiency is less, the ratio to its price to performance is

proven to be good enough to allow it to compete with fossil fuel electrical generation. DSSCs

provide a technically and economically convincing substitute concept to present day p–n

junction photovoltaic devices. The function of light absorption and charge carrier transport is

separated here. Light is absorbed by a sensitizer which is anchored to the surface of a wide

band semiconductor. The separation of charge takes place through the photo-induced electron

injection from the dye into the conduction band of the solid at the interface. Carriers are

transported in the conduction band of the semiconductor to the charge collector. The

sensitizers having a broad absorption band permits to harvest a large fraction of sunlight.

DSSCs split the two functions provided by silicon in a conventional cell design. Normally the

silicon acts as both the source of photoelectrons, as well as a provision to separate the charges

resulting in the electric field. Here the photoelectrons are provided from a separate

photosensitive dye and the bulk of the semiconductor is used only for charge transport. The

separation occurs at the surface between the dye, electrolyte, and semiconductor. Dye

sensitizer absorbs the incident sunlight and exploits the light energy to induce vectorial

electron transfer reaction. It is not sensitive to the defects in semiconductors, easy to form

and supports direct energy transfer from photons to chemical energy.

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CHAPTER 2: BACKGROUND AND LITERATURE REVIEW

Invented by Grätzel in 1991, a later version of dye-sensitized solar cell is a low-cost solar cell

belonging to thin film solar cell. DSSC provided a technically and economically credible

alternative concept to present day p-n junction photovoltaic devices. Unlike the conventional

solar cell systems in which semiconductors function as both photon absorber and charge

carrier, DSSC separate these two functions to two different materials. (Grätzel, 2003) As

mentioned in last section, a light sensitized organic dye functions as the photon absorber,

leaving the charge carrier function to the semiconductor. Dye sensitized solar cells (DSSC)

were introduced already 16 years ago but the learning curve up to this point is modest

compared to other types of solar cells [20]. In 1993, the “Institut für angewandte

Photovoltaic” was founded to upscale the device and it was estimated by that time that 1 m²

modules with an efficiency of around 10 % should be available in 1995. Nine years later the

institute was closed due to tremendous technical problems. Today the introduction of DSSC

on the market is hard to predict. Though much progress was achieved in terms of intrinsic

cell stability and upscaling, investors are reluctant due to the promises that were never

fulfilled after the introduction in 1991. In the following the key problems of DSSC – low

efficiency, low stability and low scalability – are discussed briefly. The heart of this solar cell

is composed of nano-particles of meso-porous (with the pore width of 2-50 nm) oxide layer,

which allows electronic conduction taking place. Since inorganic nano-particles have several

advantages such as size tenability and high absorption coefficients, it is always the first

choice when considering the cost and performance, etc. The material choice is mainly TiO2.

Titanium dioxide was recognized as semiconductor of choice due to its great properties in

photochemistry and photoelectrochemistry; it is a low-cost, widely available, non-toxic and

biocompatible semiconductor material. Besides, experimental results showed meso-porous

TiO2 layer has a highly efficient charge transport. (Nelson, 1999).

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2.1 Solar Cells

Solar cells are one type of photovoltaic cells which generate electrical power by converting

energy of light into direct current electricity by using semiconductors that exhibit the

photovoltaic effect. In the photovoltaic effect, electrons are transferred between different

bands (usually from the valence bands to conduction bands) within the material, resulting in

the buildup of voltage between two electrodes.(Brabec & et al, 2001) In solar cell, the

primary energy source is sunlight.

Fig 2.1a Band Diagram of Solar Cell

The first step in solar cell function always involves photon absorption by a semiconducting

material. When the photon is absorbed, the energy of photon will be transferred to valence

electrons in crystal, which excite an electron to another band, called the conduction band, in

which, electrons can freely move. Figure 4 shows different band gap in conducting materials.

Then, the free electrons can move to one single direction because of the special composition

of solar cells, which then generates current.

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STRUCTURE OF SOLAR CELL:

Figure 2.1b: Mechanism of Solar Cell

A. Encapsulate – Encapsulate which is made of glass or other clear material such clear plastic

seals the cell from the external environment.

B. Contact Grid- The contact grid is made of a good conductor, such as a metal, and it serves

as a collector of electrons.

C. The Antireflective Coating (AR Coating) - Through a combination of a favourable

refractive index, and thickness, this layer serves to guide light into the solar cell. Without this

layer, much of the light would simply bounce off the surface.

D. N-Type Silicon - N-type silicon is created by doping (contaminating) the Si with

compounds that contain one more valence electrons than Si does, such as with either

Phosphorus or Arsenic.

Since only four electrons are required to bond with the four adjacent silicon atoms, the fifth

valence electron is available for conduction.

E. P-Type Silicon- P-type silicon is created by doping with compounds containing one less

valence electrons than Si does, such as with Boron. When silicon (four valence electrons) is

doped with atoms that have one less valence electrons (three valence electrons), only three

electrons are available for bonding with four adjacent silicon atoms, therefore an incomplete

bond (hole) exists which can attract an electron from a nearby atom. Filling one hole creates

another hole in a different Si atom. This movement of holes is available for conduction.

F. Back Contact - The back contact, made out of a metal, covers the entire back surface of

the solar cell and acts as a conductor. (Specmat, 2009).

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2.2 Titanium Dioxide (TIO2)

The material choice is mainly TiO2 (Anatase), crystal structure but alternatives such as ZnO

and Nb2O5 have been investigated as well. (Tennakone et al, 1999) Titanium dioxide was

recognized as semiconductor of choice due to its great properties in photochemistry and

photo-electrochemistry; it is a low-cost, widely available, non-toxic and biocompatible

semiconductor material. Besides, experimental results showed meso-porous TiO2 layer has a

highly efficient charge transport. (Nelson, 1999)

Figure 2.2a: Titanium (IV) Oxide Lattice Structure (Web Elements)

2.3 Construction and Mode of Operation

Typical design of a dye-sensitized solar cell the support substrate can be glass, although it is

possible to use a flexible plastic substrate. The support substrate must be transparent in

visible and near UV region because light is coupled into the cell through it. The anode

electrode is made of a thin film of a transparent, conducting material, which is deposited on

the inner side of the support substrate. For this purpose indium thin oxide (ITO)

semiconductor is widely used. Although other semiconductors such as fluorine-doped thin

oxide can be used as well. The real photo anode is formed by a porous film of nanocrystalline

semiconductor (TiO2). These films are usually few micrometers thick (between 1- 10 μm)

and can be fabricated in different ways. The most widely used method for fabrication of thin

films is casting slurry of the nanocrystals using spray, or drag coating and then calcine the

film at 400-450ºC. Thus structural stability can be created.

Key components in our DSSC:

(1) Semi –conductor: TiO2

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(2) Sensitizer (dye): ruthenium dye

(3) Counter electrode: Carbon coating

(4) Mechanical support: ITO glass coated with TiO2

Electron flow in the DSSC:

1. Dye becomes excited by light.

2. Dye injects an electron very rapidly to the TiO2* (the conduction band), dye is oxidized in

the process.

3. Electrons are transported through the semi-conducting TiO2, move through the load, and

eventually reach the counter electrode.

4. At counter electrode, normally platinum, the electrons reduce the redox mediator located in

the electrolyte of the DSSC.

5. Redox mediator diffuses to meet and regenerate oxidized dye molecules. * The TiO2 (or

other semiconductor used in the DSSC) promotes directional flow of electrons in the solar

cell. This is due to kinetics of electron movement. Once injected quickly to the TiO2 (10^-12

seconds), electrons are not as easily recombined with the sensitizer or redox mediator

(which occurs on a 10^-2, 10^-3second time frame). If instead, the electrons entered a

metal, recombination events would be much more frequent.

Fig 2.3a Operation of DSSC

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CHAPTER 3: EXPERIMENT METHODOLOGY

The experiments were carried out under the meteorological conditions of Ranchi (latitude of

23.35° N; longitude of 85.33° E) in India. Based on the scientific references found in earlier

literature chapter, the prototype of “hybrid dye sensitized solar cell based on TiO2” was

constructed. In this chapter, details of procedures to conduct the experiments will be

presented.

3.1 Assembling the Dye-Sensitized Solar Cell

1. Determine the conductive side of glass in the model kit by touching both of protruding

leads of the multi-meter with one side of the glass. The conductive side could be identified

with average resistance from 20-38 ohms.

2. Fix three sides of the plate using tape with the conductive sides facing up.

Fig 3.1a Etching the ITO glass

3. Etching the ITO glass conducting side by HCL and Zn paste.

4. Add 2-3 drops of the TiO2 the suspension onto the conductive side and spread out The

TiO2 evenly on the surface of the plate with glass rod. Carefully remove the tape without

perturbing the TiO2 layer.

5. Dry the glass with TiO2 under room temperature over 4 hours and then heat to 420C for

another 20 min, until the dried TiO2 turns brown.

6. Then both the ITO pieces were kept in the acetone for ultrasonic bath for 15minute.

7. After 15minute the ITO was 10 times in distilled water then it is again kept in distilled

water for ultrasonic bath, this process is done two times for 15 minute each. Now again the

ITO is surge in the distilled water and then kept in the ethanol for ultrasonic bath for 15

minute.

8. Now both the ITO were taken to dry it properly using the dryer.

9. While heating, light the candle and coat the conductive side of the other piece of glass with

graphite over 45 sec.

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CHAPTER 4. RESULTS AND DISCUSSION

In this section, results from each experiment mentioned in the methodology chapter are

presented and analyzed. Explanations are proposed for each result. If not mentioned

specifically, all of the results were measured under 298K, 1 atm pressure with the

illumination of fluorescent light.

The efficiency Ƞ of the DSSC is given by:

Ƞ = 𝐼𝑆𝐶 𝑉𝑂𝐶 𝐹𝐹

𝑃𝑖𝑛

Where

Isc= short circuit current density

Voc=open circuit voltage

Pin= input power (radiation falling on the surface of the solar cell)

FF= fill factor

Open circuit voltage (Voc): Open circuit voltage V is the maximum voltage that can be

Obtained from a solar cell when its terminals are left open.

Short circuit current (Isc): Short circuit current is the maximum current produced by a solar

cell when its terminals are shorted.

Fill factor (FF): The fill factor (FF) is defined as the ratio of the maximum power from the

solar

Cell to the product of Voc and Isc. Graphically, the FF is a measure of the "squareness" of the

I-V curve and mainly related to the resistive losses in a solar cell [13].

Therefore,

FF = 𝑉𝑚 𝐼𝑚

𝑉𝑜𝑐 𝐼𝑠𝑐

Where

Vm= maximum voltage

Im= maximum current

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Fig4.1a I-V characteristics of a solar cell

Thus we have,

Area = 0.6 * 0.7 = 0.42cm2

Voc = 0.49458 V

Isc = 83.4699 µA

Vm = 0.239 V

Im = 56.421 µA

Pin = 100mW/cm2

Therefore

Fill Factor (FF) = 56.421∗0.239

83.4699∗0.49458 = 0.3266 or 32.66%

And

Efficiency (Ƞ) = 0.49458∗83.4699∗10−6

0.42∗100∗10−3 × 32.66 = 0.0321%

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CHAPTER 5. FUTUREWORK

Control Experiment I: Graphite Layer Thickness Dependence

Provided in protocol and other literatures (Grazel, 2005, etc), coating graphite onto the

conductive side is one of crucial steps for making the DSSC. However, few literatures went

into details in the potential influence of graphite layer on the efficiency of the solar cell. So, I

have decided to test the dependence of the thickness of graphite layer with the performance

of the cell.

Control Experiment II: TiO2 Layer Thickness Dependence

TiO2 layer is the carrier of electron after it is excited by the organic dye. As the thickness of

graphite was recognized, it is necessary to recognize the semiconductor layer thickness

dependency. This experiment is relatively easier to control than others, because the thickness

of TiO2 in this project was controlled by the tape thickness. Thus, by layering several pieces

of tape on one side and then following the same rolling procedure as used for a normal cell,

we can control the thickness of TiO2 in this simple way.

Control Experiment III: Temperature Dependence

Temperature dependence of the performance of DSSC was proposed in the paper by me

which will teste the dark current.

Control Experiment IV: Dye Solution dependence

I have decided to do the experiment by using different type of dye solution like Aniline blue,

Methyl orange and Ru complex etc.

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References

1. K. Tennakone, G.R.R. Kumara, I.R.M. Kottegoda, V.S.P. Perera, Chem. Commun.

15 (1999).

2. Exxon Mobil. "2007 Summary Anual Report." Exxon Mobil, 2007.Web. 13 Nov.

2011. <http://www.exxonmobil.com/corporate/files/ news_pub_sar_2007.pdf>.

3. Perlin, John (2004). "The Silicon Solar Cell Turns 50"

4. National Renewable Energy Laboratory. Retrieved 5 October 2010.

5. Michael Grätzel, Journal of photochemistry and photobiology, 2003

6. Brabec. C. J., Sariciftci. N. S., Hummelen J. C. (2001). Adv. Funct. Mater.

7. Ma, W.L, Yang. C.Y, Gong. X, Lee. K, Heeger. A. J. (2005), Adv. Funct. Mater.

8. Kohjiro Hara, Mitsuhiko Kurashige, Yasufumi Dan-oh, NJC letter, 2003

9. Gerd Löbbert "Phthalocyanines" in Ullmann's Encyclopedia of Industrial

Chemistry, 2002,Wiley-VCH,Weinheim.

10. J. Fang, L. Su, J. Wu, Y. Shen, Z. Lu, New J. Chem. 270 (1997) 145.

11. Carey, M. J, et al. Proceeding of SPIE, 2004 Vol. 5215, pp 32–40.

12. B. A. Gregg, S.-G. Chen and S. Ferrere, "Enhanced dye-sensitized photoconversion

efficiency via reversible production of UV-induced surface states

in nanoporous TiO2", J. Phys. Chem. B, 107, 3019-29, 2003.