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Republic of Iraq
Ministry of Higher Education
And Scientific Research
University of Baghdad
College of Science
Preparation dye – Sensitized Solar Cell
with Tracking System
A Thesis
Submitted to the University of Baghdad,
College of Sciences, Department of Physics as
a Partial Fulfillment of the Requirements for the
Degree of Master of Science in Physics
By
Dheyaa Badri Alwan
Supervised by
Ass. Prof. DDrr.. WWeessaamm AA.. AA.. TTwweejj
Dr. Mohanad M. Azzwi
2013 AD 1434 AH
وح ) ويسألونك عن الر
وح من أمر قل الر
رب وما أوتيت من
لا قليلا (العل ا
سورة الإرساء
58الآية
DEDICATION
To:
My father and my mother
To my partner in my life ……ENAS.
And my kids
My country beloved Iraq
The martyrs of Iraq with all the love and
appreciation.
Dheyaa
2013
Supervisor Certification
We certify that this thesis titled “Preparation dye – Sensitized Solar Cell
with tracking system” was prepared by Mr. (Dheyaa. B Alwan ), under
our supervision at Department of Physics, College of Science, University
of Baghdad, as a partial fulfillment of the requirements for the degree of
Master of Science in Physics.
Signature
Name: Dr. Wesam A. A. Twej
Title: Assistant Professor
Date: / /2014
(Supervisor)
Signature:
Name: Dr. Mohanad M. Azzwi
Title: Scientific Researcher
Address: Ministry science and technology
Date: / /2014
(Supervisor)
In view of the available recommendation, I forward this thesis for debate
by the Examination Committee.
Signature:
Name: : Dr. Raad M.S.Al-Haddad
Title: Professor
Address: Head of Physics Department,
Collage of Science, University of Baghdad.
Date: / / 2014
Examination Committee Certification
We certify that we have read this thesis entitled “Preparation dye –
Sensitized Solar Cell with Tracking System” as an examine committee,
examined the student Mr. (Dheyaa. B Alwan) in its contents and that, in
our opinion meets the standard of thesis for the degree of Master of
Science in physics.
Signature: Signature:
Name: Nathera A.A. AL-Tememee Name: Dr. Thamir Abdul-Jabbar Jumah
Title: Professor Title: Assistant Professor
Address: University of Baghdad Address: Al-Nahrain University
Date: / / 2014 Date: / / 2014
(Chairman) (Member)
Signature: Signature:
Name: Dr. Falah A-H . Mutlak Name: Dr. Wesam A. A. Twej
Title: instructor . Dr Title: Assistance Professor
Address: University of Baghdad Address: University of Baghdad
Date: / / 2014 Date: / / 2014
(Member) (Supervisor)
Signature:
Name: Dr. Mohanad M. Azzwi
Title: Scientific Researcher
Address: Ministry science and technology
Date: / / 2014
(Supervisor)
Approved by the Council of the College of Science.
Signature:
Name: D. Salih. M. Ali
Title: Assistant Professor
Address: Dean of the Science College, University of Baghdad
Date: / / 2014
ACKNOWLEDGEMENTS
Praise is to ALLAH, his majesty for his uncountable blessings, and
best prayers and peace be unto his best messenger Mohammed, his pure
descendant, and his family and his noble companions.
First I would like to thank my family. Without their love and support over
the years none of this would have been possible. They have always been
there for me and I am thankful for everything they have helped me
achieve. Next, I would like to thank my supervisors ASST. Prof.Dr.
WWeessaamm AA.. AA.. TTwweejj and .Dr. Mohanad M. Azzwi .I appreciate all what
they have done for me.
I wish to express my deep appreciation to all members of my group
(Molecular and Laser group) especially to Prof. Dr. Baha T. Al-Khafaji,
Prof. Dr. Nathera A. AL-Tememee and Dr.Firas J. AL-Maliki for
their valuable suggestions and for providing material study.
I would like to thank Mr. Mazin S. AL-Ansari (M.SC.senior
engineer of the physics department electronic lab) to help me in my
research. I would like to thank Distinguished High School - Harthiya,
Many thanks extended also to my friends Mr. Azal, Mr. Bilal, Mr. Wahid,
Mr. Ibrahim, Thanks to the chemistry lab service and thanks to everyone
who helped me.
Finally, I would like to express my extreme appreciation to my family
(especially my wife) for their moral support, long suffering and patience
during my study.
Abstract
As a new technology, in the solar cell field, the dye-sensitized solar
cell (DSSC) gives technically and economically practicable idea to
develop the solar cell technology.
Dye solar cells used natural dye (pomegranate, strawberry, black tea,
orange red, Grapefruit, Hibiscus sabdriffol, Borago officinalis) have been
studied. Pomegranate juice was chosen in this work as a natural dye
because of its high conversion efficiency. Furthermore ruthenium dye
was adopted in this work as industrial sensitize dye because of its high
efficiency over most industrial dyes. Basic components of the dye solar
cell which Studied, including electrodes types, type of dyes, electrolyte
concentration and thickness of titanium dioxide, In addition to several
improvers to increase the efficiency solar cell ,the best quality AgNO3.
The best conversion efficiencies obtained without any addition were
1.95% and 0.55% for ruthenium and pomegranate dye cells respectively
,while with addition of silver nitrate into the electrolyte, the conversion
efficiency improved and become 3.7% and 1.2% for ruthenium and
pomegranates dye respectively, the film thickness was (15 µm) and
ruthenium dye concentration used in all the results were (5×10-4
M). Three
types of experimental tests have been achieved (outdoor) using fixed,
one-axis and two-axis tracking system was adopted in this study and the
main difference among them is the ability to reduce the pointing error,
increasing the daily irradiation incident to increase the energy output. The
study was conducted in the region (Baghdad – Al Jadiriya), line latitude
(33.30) and longitude (44.14
0) .The two- axis system shows the best
systems and least loss of out power between the three systems.
List of Symbol
Description Symbol
Absorbance A
carbon C
Film thickness. D
Energy Consumption for Orienting the Panel EC
Energy gap Eg
Conduction band energy ECB
red- ox (Reduction-oxidation energy) E red-ox
Energy Produced by fixed mount EPF
Energy Produced by the Solar Panel with
Tracking
Ept
Current I
Iodide. I-
Tri-iodide I-3
Short-circuit current Isc
Current density J
Platinum Pt
Power of the incident light. Pin
Power at the maximum power point. PMAX
Resistance R
Sensitizer singlet state S
Difference between the net energy yield and the
consumption energy
Sd
Voltage at the maximum power point Vmax
Open-circuit voltage. Voc
Excited energy state of the sensitizer S*
Oxidized state of the sensitizer s+
Ground energy state of the sensitizer s°
Solar cell efficiency 𝜂
List of Abbreviations
The meaning of each character Abbreviations
Acetonitrile AC
Atomic force microscopy AFM
Conduction Band CB
Dye Sensitized Solar Cell DSSC
Energy gain EG
Fill Facto FF
Fluorine-Doped Tin Oxide FTO Fluorine-Doped Tin Oxide
Densities g/cm3
Photon energy 𝗁𝜈
Highest Occupied Molecular Orbital HOMO
Current-Voltage. I-V
Infrared IR
Ionic liquids ILS
Lowest Unoccupied Molecular LUMO
Light Emitting Diode LED
groups enhance the absorption of visible light NCS
Natural dye Sensitized Solar Cell NDSSC
Reduction – Oxidation Red-ox
Fluorine-Doped Tin Oxide Sno2:F
Power obtained by tracking mode PT
Power obtained by fixed mode PF
Photovoltaics PV
Transparent conductive oxide layer. TCO
Ultraviolet UV
Visible Vis
Valance band VB
X-Ray diffraction XRD
Solar cell energy SCE
Chapter One Theoretical CCoonncceeppttss
Number Title Page
1.1 Introduction 1
1.2 Energy sources 1
1.2.1 Solar radiation 2
1.3 Solar cell 3
1.3.1 A brief history of photovoltaic's 4
1.3.2 Developments of the Solar Cell 4
1.3.2.1 First Generation 4
1.3.2.2 Second Generation 5
1.3.2.3 Third generation 5
1.3.2.4 Four generation 5
1.4 First part :The dye sensitized solar cell 5
1.4.1 Operational principles of dye-sensitized solar cells 7
1.4.1.1 The kinetic processes in DSSCs 9
1.4.1.2 Life time Electron Transfer Processes in Dye Solar
cell
11
1.4.1.3 The stability of the dye sensitized solar cells 12
1.4.1.4 Conversion efficiencies of DSSC 13
1.4.2 Part of dye-sensitized solar cells 13
1.4.2.1 Titanium Dioxide (TiO2) 14
1.4.2.2 Dyes 14
1.4.2.2.1 Industrial Dyes 15
1.4.2.2.2 Natural dyes 16
1.4.2.3 Conductive Glass Substrates 17
1.4.2.3.1 The Photo electrode (Anode) 18
1.4.2.3.2 The counter electrode (cathode) 18
1.4.2.4 The Electrolyte 19
1.4.3 Mechanism and factors affecting on DSSC 19
1.4.3.1 Semiconductor (TiO2) 20
1.4.3.2 The sensitizing Dye 21
1.4.3.3 The effect of electrolyte 22
1.4.3.4 Additives in the Electrolytes 24
1.4.3.5 The sealing cells 24
1.5 Secand part :The solar tracker system design 24
1.5.1 Fundamentals Types of Solar Tracker 25
1.5.1.1 Active Tracker 25
1.5.1.2 Passive Tracker 26
1.5.2 Basic Types of Solar Tracker 26
1.5.2.1 Single Axis Trackers 26
1.5.2.2 Two Axis Trackers 27
1.5.2.3 Fixed Trackers 28
1.5.3 Light sensor for tracking 29
1.5.4 The energy gain 29
1.6 Literature Survey 30
1.7 Aim of the work 32
Chapter Two Experimental Par
Number Title Page
2.1 Introduction 33
2.2 Key components of a dye-sensitized solar cell 33
2.3 Materials 33
2.4 Measurement Techniques 35
2.5 Implementation and Assembly of Dye Solar Cells 35
2.5.1 Preparation of TiO2 Paste 36
2.5.2 Deposition of TiO2 Film 37
2.5.3 Dye solution preparation 39
2.5.4 Electrolyte Preparation 40
2.5.5 Counter Electrode Preparation 40
2.6 Cell Assembly 41
2.7 Effect of TiO2 past parameters on efficiency 43
2.7.1 Effect of thickness on efficiency 43
2.7.2 Effect of paste drying temperature on efficiency 44
2.7.3 Effect of the pH value on efficiency 44
2.7.4 Effect of electrolytes type on efficiency 45
2.7.5 Effect of solvent of electrolyte on efficiency 45
2.8 Test the efficiency of the solar cell 46
2.9 Part two Track the sun 47
2.10 Design of tracking system 47
2.10.1 Mechanical part 49
2.10.2 Optical part 49
2.10.2.1 LED-sensor 49
2.10.3 Electrical part 51
2.11 procedure solar tracker 52
Chapter Three Results and Discussion
rumbeN Title Page
3.1 Introduction 54
3.2 Result for first part 54
3.2.1 Absorption spectrum of ruthenium (N719) 54
3.2.2 Absorption spectrum of pomegranate 55
3.2.3 Absorbance of electrolyte solution 56
3.3 X-Ray measurement 56
3.4 The surface morphology of tio2 film using AFM 57
3.5 Effect of potassium iodide concentration 60
3.6 Effect of dye Concentration 61
3.7 Effect of time immersion 63
3.8 Effect of additive 64
3.8.1 Effect of additive concentration 65
3.8.2 Effect of additive type 67
3.8.3 Type of dyes 68
3.9 Effect of electrode type 69
3.10 Result for second part 70
3.10.1 Relationship of Single-Axis Tracking System with
Fixed Mount
71
3.10.2 Comparison of Dual-Axis Tracking System over
Fixed Mount
72
3.10.3 Comparison between global and direct solar
radiation
73
3.10.4 Comparison between global and direct solar
radiation by TES
75
3.10.5 The effect of dust on the solar tracker 77
3.10.6 Comparison between two-axis, one axis and fixed 78
3.11 Conclusion 81
3.12 Suggestion for future work
81
List of Figures
Chapter one Page
(1-1)…………… The spectrum of solar radiation 2
(1-2)…………… p-n junction of solar cell 3
(1-3)….. ………..Dye Solar Cell Structure 7
(1-4) ……………Principle of operation of DSSC 8
(1-5)….. ………..kinetic processes in DSSC 10
(1-6)…………… life time Electron Transfer Processes 12
N719Chemical structure 7) ……………-(1 15
(1-8)…………… Ainthocyanins from Pomegranate
pigment
17
(1-9)………… Schematic diagram of the process from the
dye to the conduction band of TiO2
20
(1-10)…… … Absorbance of ruthenium (N719) with
wavelength
22
(1-11)…………. single axis solar tracker 27
(1-12)………….Two axis solar tracking system 28
Chapter two Page
(2-1)………… The fabrication steps of the DSSC 36
(2-2)………. . Steps of TiO2 film deposition 37
(2-3)………… Masking of the deposition area 38
(2-4)………… Deposition of TiO2 Film 39
(2-5)………… Deposition of the dye on TiO2 film 40
( 2-6)…………Deposition carbon layer on the glass
conductive
41
(2-7)………… Dye solar cell assembly 42
(2-8)………… Model for dye solar cell 42
(2-9)………..The device for measuring the voltage and the
electric current
46
(2-10)…………structure of the two-axis 48
(2-11) ……….Parts of a sun tracker 48
(2-12)………. Photo of the Green led 50
(2-13)……….. modified designs of the four LED-sensors 50
(2-14)….. ……Circle for one-axis sun tracker 51
(2-15)………… Circle for two-axis sun tracker 52
(2-16)……….. Photo of direct solar tracker only 53
Chapter three Page
(3-1)………...The absorption spectrum of ruthenium
N719 dye
55
(3-2)………... Absorbance of pomegranate pigment 55
(3-3)………... Absorbance of electrolyte solution 56
(3-4)………... X-Ray spectrum of TiO2 past after
annealing
57
(3-5)….. …….Surface morphology of TiO2 paste film, 2
D view,
a) before b) after annealing at 450 oC
58
(3-6)…………. Surface morphology of TiO2 paste film, 3
D
view, a) before b) after annealing at
450 oC
59
(3-7)….. …….Granularity accumulation distribution
report before annealing
59
(3-8)……….. Granularity accumulation
distribution report after
annealing at 450 oC
60
(3-9)……….. concentration of KI and efficiency 61
(3-10)……… Concentration of dye 62
(3-11)…….. .time immersion 63
(3-12)……... concentration of dye with and without
additive
65
(3-13) …….. Effect of additive concentration 66
(3-14)……… Comparison between global and direct
solar radiation
75
(3-15)…….... Comparision global and direct solar
radiation
76
(3-16)……… Comporison between clear and dust day 77
(3-17)……… Comparison between two-axis, one axis and
fixed
80
List of table Page
(1-1)………. Life time Electron 11
(2-1)………. Material
(2-2)………. Plant origin 34
34
(2-3)………..origin, function and specification devices 35
(3-1)….. …...Time immersion 64
(3-2)………. Concentration of AgNO3 and efficiency 66
(3-3)………. Ruthenium and type additive 67
(3-4)….. …...The efficiency for natural dyes with and
without additive
68
(3-5)………. For best results after additive 69
(3-6)………. Electrode type 70
(3-7 )……….Comparison of fixed mount with single axis
tracker
system
71
(3-8)………. two-Axis Tracking System over Fixed Mount 73
(3-9)……....Comparision global and direct solar radiation
74
(3-10)……....Comparison between global and direct solar
radiation by (solar power meter)
77
(3-11)……... Comparision global and direct solar radiation
of clear and dust day
78
(3-12) ……… Comparison between two-axis, one axis and
fixed
79
CHAPTER ONE
Introduction and theoretical
part
Chapter One
1.1. Introduction
This chapter presents an introduction to the thesis includes two
parts:
The first Part article (1.4) describes the operating principle of dye
sensitized solar cell and the fundamental physical and chemical processes
of the cell operation, as well as, the materials which were utilized in the
dye sensitized solar cell with their properties. The general
implementation procedure for solar cell based on organic natural and
industrial dyes is also presented in this part. While the second part article
(1.5) deals with types of solar cell tracking system and there affected
parameters.
1.2. Energy sources
For all practical purposes energy supplies can be divided into two
classes:
1- Renewable energy is the energy obtained from natural and persistent
flow occurring in the immediate environment. Such energy may
also be called green energy or sustainable energy [1]. The field of
photovoltaics is the most important among the renewable energy
sources, as solar energy is largely abundant [2].
2- Non-renewable energy is the energy obtained from static stores of
energy that remain under the earth unless released by human
interaction. Examples are nuclear fuels and fossil fuels of coal, oil
and natural gas [1].
1.2.1. Solar radiation
The sun is a sphere of intensely hot gaseous matter with a diameter of
1.39 million km and is on the average 149.6 million km from the earth. The
solar radiation can be divided into two types: extraterrestrial and terrestrial
[3]. The energy from the sun in the form of photon energy is used by solar
cells to generate electricity. The solar irradiation has a broad energy
spectrum which is distributed into wavelengths. [4]. Figure (1-1) shows the
spectrum of solar radiation. [5]
Figure (1-1) the spectrum of solar radiation [5
1.3. Solar cell
A solar cell device converts the sunlight directly into electricity
through the photovoltaic. In principle it depends on two parameters. The
generation of current by absorbed incident illumination and the loss of
charge carriers via so-called recombination mechanisms [6].
Conventional semiconductor solar cells are based on p-n junctions. In a p-
n junction, two semiconductors with different majority charge carriers and
doping concentrations an n - doped and a p - doped material are in close
contact, as show in figure (1-2) [7].
Fig (1-2) p-n junction of solar cell [7]
1.3.1. A brief history of photovoltaic's
The process of converting sunlight directly into electricity is
referred to as the photovoltaic effect. It was first observed by Becquerel
in 1839, his theory then sparked the idea of using semiconductor material
as a source to convert solar power to electrical energy. The 20th century
witnessed the discovery of the photoelectric effect by Albert Einstein and
others [8]. The first silicon solar cell was thereafter developed by Chapin
et al. also from Bell laboratories, in 1954.The cell, using silicon as its raw
material, initially yield an efficiency of 6%, which was rapidly increased
to 10%. [9].
In 1941, Russell Ohl invented the silicon solar cell. With his
discovery the efficiency of solar cells began to increase [10].
Furthermore, the first photovoltaic effect in an organic crystal was
observed by Kallman and Pope in 1959 [11]. Dewald’s (1959, 1960a)
lucid expositions of the principles of semiconductor electrochemistry laid
the foundation for rapid experimental advances in the sixties, when many
important concepts were established: the relation between the sign of the
photopotential and the conductivity type of the electrode (Williams,
1960) [12].
1.3.2. Developments of the solar cell
The progress in solar cells can be divided into four generations:
1.3.2.1. First generation
First generation solar cells are the dominant technology in the
commercial production of solar cells. These cells are made using a
crystalline silicon wafer; they consist of large area, single layer p-n
junction devices. They are characterized by broad spectral absorption
range and high carrier motilities, but they require expensive
manufacturing technologies [13].
1.3.2.2. Second generation
Second generation of thin-film solar cell devices are based on low
energy preparation techniques such as vapor deposition and electroplating
[13]. Thin-film solar cells are cheaper but less efficient [14].
1.3.2.3. Third generation
Third generation photovoltaic refers to cell concepts that overcome the
31% theoretical upper limit of a single junction solar cell as defined by
Shockley and Queisser [15]. Third generation PV technologies may
overcome the fundamental limitations of photon to electron conversion in
single-junction devices and, thus, improve both their efficiency and cost
[16]. The third generation photovoltaics are very different from
semiconductor devices. These new devices include photo-
electrochemical cells, polymer solar cells, and nano-crystal solar cells.
[17]
1.3.2.4. Fourth generation
In the fourth generation composite photovoltaic technology with
the use of polymers with nanoparticles can be mixed together to make a
single multi-spectrum layer. Then the thin multi-spectrum layers can be
stacked to make multi-spectrum solar cells more efficient and cheaper
based on polymer solar cell and multi-junction technology [17].
1.4. First part: the dye sensitized solar cell
(DSSC) is a device for the conversion of visible light into
electricity and its performance is based on the sensitization of wide band
gap semiconductors [18]. The dye-sensitized solar cells (DSSC) are
attractive because they are made from cheap materials that do not need to
be highly purified and can be printed at low cost. DSSC are unique
compared with almost all other kinds of solar cells in that electron
transport, light absorption and hole transport are each handled by
different materials in the cell [19].
The DSSC resembles more electrochemical cell than a
conventional p-n junction solar cell. They offer a low-cost alternative to
conventional photovoltaic devices based on semiconductors such as
silicon or compound semiconductors [20].
The advantages of DSSC include simple processing methods, light
weight, mechanically robust, bifacial illumination and transparent which
can be used as windows. Outdoor measurements indicate that light
capture by the DSSC is less sensitive to the angle of incidence [18].
DSSC can work in low illumination conditions such as cloudy skies and
non-direct sunlight. The cutoff is low, therefore they are being proposed
for indoor use collecting energy for small devices the lights in the house.
DSSC can be made flexible using conductive plastic substrates.
The major disadvantage to the DSSC design is the use of the liquid
electrolyte. Electrolyte solution contains volatile organic solvents and
must be carefully sealed. The dyes in DSSC tend to degrade over time
especially when exposed to ultraviolet radiation, leading to a decreased
efficiency and a limited cell lifetime. DSSC have efficiencies of about 1-
11% which is lower than other solar cell technologies [18].In figure (1-3)
the basic configuration of a dye solar cell (DSSC) [21].When (TCO) is
transparent conductive oxide layer.
Fig (1-3) Dye Solar Cell Structure [21]
1.4.1. Operational principles of dye-sensitized solar cells
In typical DSSC architectures, the photon-induced oxidation of a
dye occurs at a TiO2 photoanode, while the reduction of the redox species
used to regenerate the dye occurs at the counter electrode. The standard
redox couple used for dye regeneration, iodide/triiodide (I-/I
-3), has
unmatched performance but typically requires a platinum catalyst in
DSSC operation.
Platinum has high catalytic activity toward I-3 reduction and is
sufficiently corrosion-resistant to iodide species present in the electrolyte.
However, since platinum is a precious metal, much incentive exists to
develop DSSC counter electrodes using cheaper, abundant materials, as
shown in Fig (1-4) [22].
Fig (1-4) Principle of operation of DSSC [22]
Extensive research has, for example, been performed on using
carbonaceous materials for the counter electrode because they are low
cost, corrosion resistant, and electrically conductive [23]. The light-to-
electricity conversion in a DSSC is based on the injection of electron
from the photo-excited state of the sensitized dye into the conduction
band of TiO2. The dye is regenerated by electron donation from iodide in
the electrolyte. The iodide is restored, in turn, by the reduction of tri-
iodide at the cathode, with the circuit being completed via electron
migration through the external load.
The voltage generated under illumination corresponds to the
difference between the Fermi level of the electron in the TiO2 and the
red- ox potential of the electrolyte.
The device generates electric power from light without suffering
any permanent chemical transformation [24].
1.4 .1.1.The kinetic processes in DSSC [25]
It is obvious that several issues have to be simultaneously satisfied in
order to achieve an efficient solar cell based on nanostructure dye
sensitized semiconductors. As described in the following equation:
[TiO2|S +hν → TiO2|S* (dye excitation) …………………… (1-
1)TiO2|S* → TiO2|S+ + e
- (CB) (electron injection in ps scale)
...………... (1-2)
TiO2|S* +3I- → TiO2|S + I3
- (dye regeneration in μs scale)
……………….. (1-3)
I3- +2e
-(Pt) → 3I
- (reduction)……………………….......... (1-4)
While the dark reactions which may also occur are:
I3- +2e
-(CB) → 3I
- (recombination to electrolyte from ms to s scale) …..
(1-5)
TiO2|S+ + e
-(CB) →TiO2|S (recombination from μs to ms scale) ………...
(1-6)
From the equations (1-1) - (1- 6) it is obvious that several issues
have to be simultaneously satisfied in order to achieve an efficient solar
cell based on nanostructure dye sensitized semiconductors. As a first
issue, the dye has to be rapidly reduced to its ground state after it is
oxidized, as shown in figure (1-5)[27].
Fig (1-5) kinetic processes in DSSC [27]
while the electrons are injected into the conduction band of the TiO2
otherwise the solar cell performance will be low. This means that the
chemical potential of the iodide/tri-iodide red-ox electrolyte should be
positioned in more negative values than the oxidized form of the dye.
Furthermore the nanocrystalline TiO2 film must be able to permit
fast diffusion of charge carriers to the conductive substrate and then to
external circuit avoiding recombination losses, while good interfacial
contact between electrolyte and semiconductor has to be ensured [26].
1.4.1.2. Life time electron transfer processes in dye solar cell
The kinetics is sensitive to many subtle factors such as excitation
wavelength and dye loading conditions. Since the kinetics are
complicated and don’t always conform to a simple rate law, rate constants
aren’t strictly meaningful.
Table (1-1) shows examples of the electron life times during the
operation inside the DSSC [27].
The convention of reporting half-life times is followed in table (1-
1), in order to appreciate the different time scales of the relevant
processes that span nine orders of magnitude. A schematic description of
this time processing is illustrated in figure (1-6). Knowing that potential
vs. solar cell energy its (potential vs.SCE) .
Table (1-1) Life time Electron [27]
Process Half-life (second)
Injection 150 ps
Relaxation 12 ns
Regeneration 1 µs
Recombination 3 µs
Charge Transport 100 µs
Charge Interception 1 ms
Fig (1-6) Life time electron transfer processes [27]
1.4.1.3. The stability of the dye sensitized solar cells
h stability of the dye cells may be affected by the following issues
[28].
1- Chemical stability of the sensitizer dye attached to the TiO2 electrode
and in interaction with the surrounding electrolyte.
2- Chemical stability of the electrolyte.
3- Stability of the graphite or platinum -coating of the counter-electrode
in the electrolyte environment.
4- Quality of the sealing of the cell against oxygen and water from the
ambient air, and against loss of electrolyte solvent evaporation from
the cell.
1.4.1.4. Conversion efficiencies of DSSC (𝜂)
The overall conversion efficiency of the dye-sensitized solar cell is
determined by the photocurrent density measured at short circuit current
(Isc
), the photovoltage open-circuit (Voc
), the filling factor of the cell (FF)
and the input optical power (Pin ).
𝜂 =
..........................................................................................
(1-7)
Where Pin is the input optical power, and Isc
, Voc
are determined from the
photocurrent-photovoltage curve of the cell. The fill factor was calculated
from the following equation:
FF=
…………………………………………………… (1-8)
Where I, V were determined from the point of the curve the product of I
and V have maximum values. [29]
1.4.2. Part of the dye-sensitized solar cells
DSSC include substrate of conducting glass (TCO), porous
nanocrystalline semiconductor oxide film, sensitized dye for absorbing
visible sun light, a red-ox electrolyte (usually an organic solvent
containing a red-ox system, such as iodide/triiodide couple), graphite or
platinized cathode to collect electrons and catalyze the red-ox couple
regeneration reaction [25].
1.4.2.1. Titanium Dioxide (TiO2)
Semiconductor oxides are used in photo-electrochemistry because
of their stability against corrosion and their large band gap (˃ 3ev) [28].
This large band gap is needed in dye-sensitized solar cell for the
transparency of the semiconductor electrode for the wide range of the
solar spectrum. Semiconductor oxides used in dye- sensitized solar cell
include TiO2, ZnO and SnO2.
The role of the nanocrystalline porous oxide is to act as a host for
the monolayer of the sensitizing dye molecules using their large surface
area and a medium for electron transport to the conducting substrate [18].
The main reason for carrying out studies on TiO2 , because it deals
with many possible future applications and interesting properties of this
material. To a very large extent it is used as a pigment in paint, food and
candy due to its very high refractive index and non-toxicity, and it is the
native oxide surface layer on titanium based biocompatible implants [30].
TiO2 exists in three crystalline forms, anatase, rutile and brookite. The
densities are 3.89 g/cm3
and 4.26 g/cm3, 4.123 g/cm
3 for anatase, rutile
and brookite respectively [28].
The anatase structure is the most suitable for DSSC applications
because of it’s large band gap (3.2 eV) and high conduction band edge
energy and it’s interesting physical and chemical properties (such as
chemical stability, optical properties, photo-sensitivity and dielectric
properties [31].
1.4.2.2. Dyes
There are two types of pigments used in the manufacturing of solar
cells. They are different in their ability to absorb visible light; including
industrial and natural dye.
1.4.2.2.1. Industrial dyes
N719 dye is one of the most common Ru-based dyes and
considered a reference dye for DSSC.
The molecular formula of N719 is C58H86O8N8S2Ru with a
molecular weight of 1188.7 g/mole [32]. As show in fig (1-7). The
carboxyl ate groups allow dye to anchor onto the TiO2 surface via
formation of bide date and ester linkage, and –NCS groups enhance
the absorption of visible light.
N719 [33]Chemical structure 7) -Fig (1
N719 is commercially available from solar- nix as a dark purple
powder and is hygroscopic. Thus, it needs to be stored in a dark and
dry place. Sensitizer uptake to the mesoporous TiO2 film is achieved
by simply immersing the electrode into a 0.5 mM N-719 dye ethanol
solution or a mixture solution of acetonitrile and tert-butyl alcohol
(volume ration 1:1) and keeping at room temperature for 24 hours.
This process allows for a monolayer of dye to be chime adsorbed on
the film surface. After, the dye electrode should be stored in the dark
until use [34].
A key aspect of optimizing the sensitizer used for solar ener
conversion is to increase the ratio of the rates of forward (injection)
and reverse (recombination) electron transfer [35].
In a dye-sensitized photo electrode, dye molecules play a critically
important role in absorbing the incident photons and then generating
photo excited electrons, which finally transfer to the oxide through an
electron injection. To well fulfill these functions, the dye molecules
must simultaneously meet several requirements, including (1) forming
chemisorptions bonds with the oxide, (2) large extinction coefficient
and broad absorption spectrum in the visible region, (3) suitable
excited state energy level relative to the conduction band of the oxide,
(4) sufficient life-time at excited state so as to allow for effective
electron transfer, and (5) long term stability for many million cycles
[34].
1.4.2.2.2. Natural dyes
The advantages of natural dyes include their availability and low
cost. Pomegranate fruit (Punica granatum) has taken great attention for its
health benefits in the last years. In the past decade, numerous studies on
the antioxidant activity have shown that pomegranate juice contains high
levels of antioxidants - higher than most other fruit juices and beverages
[36]. Nature dyes can be used as an alternative for synthetic dyes. It
contain a diverse range of chemical compositions including 85.4% water
,10.6% total sugars , 1.4 % pectin and 0.2 -1% polyphenols other minor
compounds include fatty acids (conjugated and non-conjugated), aromatic
compounds, amino acids, anthocyanins, flavonoids, water-soluble
vitamins and minerals. The chemical composition of fruits differs
depending on the growing region, climate, maturity, cultural practice and
storage [37]
Fig (1-8): Ainthocyanins from pomegranate pigment [37]
The sensitization of wide band gap semiconductors using natural
pigments is attributed to anthocyanins.
The anthocyanins belong to the group of natural dyes responsible
for several colors in the red-blue range, found in fruits, flowers and leaves
of plants. Carbony1 and hydroxy1 groups present in the anthocyanin
molecules. [38]
1.4.2.3. Conductive glass substrates
Transparent conductive oxide (TCO) layer used for DSSC is an
important component in their construction; the most commonly used for
DSSC is fluorine-doped tin-oxide (FTO). However, FTO glass for DSSC
is not suitable in terms of cost effectiveness [39]. It is important to
heating the coated substrate (working electrode) at 450 oC for 30 min,
considering that the sheet resistance of FTO glass is in the range of 10-30
Ω/cm2 [40]. The anode –or working electrode is TCO and the cathode
also referred to as the counter –electrode, is composed of finely divide
particles of platinum deposited into another TCO [41]. The TCO glass at
the counter electrode is coated with few atomic layers of carbon or
platinum, in order to catalyze the red-ox reaction with the electrolyte
[42].
1. 4.2.3.1. The photo electrode (Anode)
To obtain optimal adhesive with the TCO substrate, suitable
binders are added to the colloidal solution of TiO2 prior to film deposition
by doctor-blade techniques. Sintering of the oxide layers at 450 - 520 0C
gives the film two important properties, the individual particles come into
close contact so that the conductance and charge collection properties are
improved, and the aerial oxidation at higher temperatures removes
organic matter from the mesoporous film that could act as potential trap
sites [43].
1.4.2.3.2. The counter electrode (cathode)
The counter-electrode consists of the conducting glass, SnO2: F,
covered on one side with a catalytic quantity of platinum metal [44]. In
the case of the iodide/iodine red-ox couple, the oxidized form
corresponds to triiodide and its reduction involves two electrons, equation
(1-4). The counter electrode must be catalytically active to ensure rapid
reaction and low overpotential.To avoid such problem, alternatives to
platinum are needed. A prospective candidate is carbon [45]. But
platinum is the better catalyst for iodide/tri-iodide couple. Because (Pt) is
rare metal, therefore carbon (graphite) is used as a cheap alternative to
platinum [46].
1.4.2.4 .The electrolyte
The electrolyte serves to regenerate the dye which has been
oxidized by electron injection into the semiconductor, and to transfer the
reduced charge to the counter electrode, where the reduction-oxidization
couple (iodide/tri-iodide) is regenerated by an electron flowing back
through the external circuit with the help of carbon layer.
The electrolyte consists of red- ox couple (iodide/tri-iodide) in an
organic solvent [45].The electrolyte in a dye-sensitized solar cell has a
redox potential that determines the potential of the cell's positive
electrode [47]. I-/I3
- system is still the best electrolyte for DSSC [48].
The efficiency of DSSC using these electrolytes is usually lower
than that based on the electrolytes in acetonitrile because of slow physical
mass transfer due to the high viscosity through nano-porous TiO2
electrode [49]. Recently, room temperature ionic liquids (ILs) have
attracted considerable interests as a potential candidate for replacing the
volatile organic solvents due to their negligible vapor pressure and high
ionic conductivity [50]. Reduction-oxidation (red-ox) reaction describe
all chemical reaction in which atoms have their oxidation number
(oxidation state) changed.
The two processes can be explained as follows:
1- Oxidation is the loss of electrons and an increase in oxidation state
by a molecule, atom, or ion.
2- Reduction is the gain of electrons and a decrease in oxidation state
by a molecule, atom, or ion [28].
1.4.3. Mechanism and factors affecting on DSSC
There are several factors that affect the efficiency of the solar cell,
such as:
1.4.3.1. Semiconductor (TiO2)
One of the crucial aspects that determine cell performance is the
formulation of the paste used for deposition of the nanocrystalline TiO2
films and the subsequent sintering procedure. The latter should guarantee
good electromechanical bonding between nanoparticles (maximizing
electron diffusion length) and a large surface area (maximizing dye
sensitization and light harvesting). This tradeoff is conventionally
obtained by subjecting the film to a temperature ∼ 30 min step at ∼
450 °C in a furnace or hotplate [51]. This is a colloidal suspension and
should resemble latex paint. Store the titanium dioxide suspension in a
small plastic capped bottle and allow it to equilibrate for at least 15
minutes for the best results [52].
Fig (1-9) Schematic diagram of the light-induced electron excitation and
injection process from the dye to the conduction band of TiO2 [32].
It is noted that current density increases with increasing film
thickness. While fill factor decreases with increasing film thickness. The
current density increase is related to the increase in electron injection from
excited dyes to the conduction band of TiO2, arising from the increased
surface area [53].
1.4.3.2. The sensitizing dye
In DSSC, the photosensitizer is one of the most important
components influencing solar cell performance, because the choice of
sensitizer determines the photo-response of the DSSC and initiates the
primary steps of photon absorption and the subsequent electron transfer
process. [54].
The most successful dye species used is ruthenium based dye,
mainly because of broad absorption spectra and rapid charge injection
rates [55].The absorption spectrum of the optimum dye for DSSC should
cover the whole visible region and even part of the near-infrared. In
addition, the dye must have suitable anchoring groups, which firmly
attach the molecule to the semiconductor oxide [56].
The absorption spectrum of N719 dye is shown in figure (1-10)
[57]. The dye sensitizer absorbs the solar radiation and transfers the
photoexcited electron to a wide band gap semiconductor electrode
consisting of a mesoporous oxide layer composed of nanometer-sized
particles, while the concomitant hole is transferred to the redox
electrolyte [58]
Fig (1-10) Absorbance of ruthenium (N719) with wavelength [57]
1.4.3.3. The effect of electrolyte
The electrolyte solution was prepared by taking the proportionate
quantity of KI and iodine in acetonitrile solvent [59]. The efficient
electrolyte solutions have the following requirements [28]:
1- The electrolyte must regenerate the oxidized dye molecule quickly.
2- The electrolyte used in DSSC should have high solubility and high
diffusion coefficients in DSSC to ensure efficient charge carriers
transport.
3- It should not absorb light strongly at wavelengths in visible region
which cause decomposition and unwanted products.
4- It should have high stability to ensure long operating life.
5- It must be highly reversible for fast electron transfer at the counter
electrode and be chemically inert toward all other components in the
DSSC.
6- It should not quench the excited state of the sensitizer.
7- The chemical potential level of the iodide/tri-iodide in the electrolyte
should be higher than high occupied molecular orbit (HOMO) level of the
organic dye to develop a driving force for fast reduction of the dye ions
before recombination with the injected electron.
The (I2) reacts with the disassociated iodide ion (I ˉ), to produce tri-
iodide (I ˉ3) via the reaction [28].
I ˉ + I2 = I
ˉ3…..……………………………………………………………. (1-9)
Under operation, the counter electrode coated with carbon returns charge
to the solution via the reaction, mentioned in equation (1-4).
The iodide ions (I ˉ) diffuse through the solution and reduce the
oxidized dye molecules via the electron returning reaction, mentioned in
equation (1-3).
A reaction between the electrolyte and semiconductor can occurs
locations where the defects TiO2 is not completely covered in dye. This
produces a loss mechanism within the DSSC, described by the net
oxidation- reduction reaction where an electron in the conduction band of
the semiconductor reduces the (I ⁻3) ion; mentioned in equation (1-5).
Iodide/tri-iodide ion has been found to affect many parameters that
influence solar cell performance including the strength of sensitizer
surface attachment, the charge transport rate, and the dynamics of
interfacial electron transfer and the rate of iodide oxidation. There are
problems with the iodide/tri-iodide based electrolyte. They are highly
corrosive, low viscosity solvents and usually volatile which complicated
the sealing [60].
1.4.3.4. Additives in the electrolytes
It has been observed from literature that generally a distinct group of
single additives is used to enhance the performance of electrolytes and
the additive resulting in optimum properties is then used in DSSC.
However, after optimizing the performance of the electrolytes containing
a single additive, binary additive mixtures were also used to study their
effect on the performance of DSSC [61].
The position of the CB in the TiO2 depends strongly on the surface
charges and adsorbed dipolar molecules. These additives in the
electrolytes are expected to be adsorbed onto the TiO2 surface, thus
affecting the CB in the TiO2 strongly associated with the photocurrent
and photovoltage. Therefore, the introductions of additives into the liquid
electrolytes have been effective strategies to enhance the photovoltaic
performances of DSSC [62].The difference is that the function of electric
additive for optimizing the photovoltaic performance of DSSCs is more
efficient than that of the donor number of solvent [25].
1.4.3.5. The sealing cells
Sealing the cell is crucial for long-term performance, since it
prevents loss of electrolyte and the intrusion of water [44]. Several
sealing materials have been used, such as epoxy and silicon [30].
1.5. Second part: The solar tracker system design
The solar tracker, a device that keeps PV (photovoltaic) or photo-
thermal panels in an optimum position perpendicular to the solar radiation
during daylight hours, to increase the collected energy. The first tracker
introduced by Finster in 1962, was completely mechanical. One year
later, Saavedra presented a mechanism with an automatic electronic
control [63]. The sun's position in the sky varies both with the season
(altitude) and time of day as the sun moves across the sky. Although
trackers are not a necessary part of a PV system, their implementation can
dramatically improve a systems power output by keeping the sun in focus
throughout the day [64].
The orientation principle of the photovoltaic panels is based on the
input data referring to the position of the sun on the sky. For the highest
conversion efficiency, the sunrays have to fall normal on the receiver by
the use of mechanical systems for the orientation of the panels in
accordance with the path of the sun. Basically, the tracking systems are
mechanical systems driven by electrical motors, which are controlled in
order to ensure the optimal positioning of the panel relatively to the sun
position on the sky dome [65]. The PV system with tracking is efficient if
the following condition is achieved
𝖲d = (EPT - EPF) - EC>> 0…………………………………………………..
(1-10)
Where Sd is the difference between the net energy yield due to using
tracking system and the consumption energy used for tracking. EPT is the
electric energy produced by the photovoltaic panel with tracking, EPF the
electric energy produced by the same panel without tracking (fixed), and
EC the energy consumption for tracking the panel [66].
1.5.1. Fundamentals types of solar tracker
There are several types of solar tracker in terms of its components and the
way it operates :
1.5.1.1. Active tracker
Firstly the light intensity from the sun should be measured to
determine where the solar panels should be pointing. Light sensors are
positioned on the tracker. If the sun is not facing the tracker directly,
there will be a difference in light intensity on one light sensor compared
to another and this difference can be used to determine in which direction
the tracker has to be tilted in order to be facing the sun [64].
1.5.1.2. Passive tracker
Passive tracker: the passive trackers use a boiling point from a
compressed fluid that is driven from one side to other by the solar heat
which creates a gas pressure that may cause the tracker movement. As
this process presents a bad quality of orientation precision, it turns out to
be unsuitable for certain types of photovoltaic collectors [64].
1.5.2. Basic types of
solar tracker
There are many different types of solar tracker which can be
grouped into single axis and two- axis models:
1.5.2.1. Single axis trackers:
Single axis solar trackers can either have a horizontal or a vertical
axis. The horizontal type is used in tropical regions where the sun gets
very high at noon. The vertical type is used in high latitudes where the
sun does not get very high [64]. The single axis tracker is pivot on their
axis to track the sun, facing east in the morning and west in the afternoon,
as show in figure (1-11) [69].
The tilt angle of the system is equal to the latitude angle of the
location because the revolution axis has to be always parallel to the polar
axis [67]. Generally one-axis motion (east-west) is employed in the
tracking system while two- axis Tracking systems are used occasionally
[68] .
Fig (1-11) Single axis solar tracker [69]
1.5.2.2. Two axis trackers
Two- axis sun trackers have both a horizontal and a vertical axis so
that they can track the sun's apparent motion exactly anywhere in the
world. So, they are able to follow very precisely the sun path along the
period of one year. That's why two axis tracking systems are more
efficient than the single axis, but also more expensive because they are
using more electrical and mechanical parts [70]. On other hand, some
solar systems require only two axis tracking system such as point focus
concentrator. Two axis sun tracking system can be applied in all types of
solar systems to increase their efficiency [71]. Two axis trackers track
the sun both east to west and north to south for adding power output
(approximately 40% gain) [70]. Depending on the relative position of the
revolute axes, there are two types of dual-axis systems: azimuth, and
polar. For the polar trackers, there are two independent motions, because
the daily motion is made by rotating the panel around the polar axis. For
the azimuth trackers, the daily motion is made by rotating the panel
around the vertical axis, so that it is necessary to continuously combine
the vertical rotation with the elevation motion around the horizontal axis
[66], as shown in figure (1-12) [72].
Fig
(1-12): Two axis solar tracking system [72]
1.5.2.3. Fixed tracker
It is used for a comparison of sun tracking options of the yearly
energy output of a PV system mounted in a fixed position in a rack facing
north and inclined at an optimum tilt, i.e. an angle at which the annual
sum of global tilted irradiation received by PV modules is maximum.
This type of mounting is very common and provides a robust solution
with minimum maintenance effort. However, it may not be effective in
terms of harvesting maximum possible solar energy. [73]
1.5.3. Light sensor for tracking
A sensor is a device that measures a physical quantity and converts
it into a signal which can be read by an observer or by an instrument.
Sensor can also be defined as a device which receives a signal and
converts it into electrical form which can be further used for electronic
devices. [74]. There are many types of sensor, the detectors of the solar
radiation are solar cells, thermo resistors or thermistors, Phototransistors,
and green light emitting diodes (LED) [75].
1.5.4. The energy gain
The simplest method to obtain an I-V characteristic is to load the
module with a variable resistor, and measure the voltage and current
through digital multimeter. Fixed panel was kept tilted at a latitude angle
where the tracking panel is tracked through changing the azimuth and
elevation position so that it was always remained perpendicular to the
solar beam radiation. Also surplus energy of tracking module with
respect to fixed module of PV panel was obtained by the following
equation: [76].
EG=( )
⨯100 %…………………………………………………….
(1-11)
That's where:
EG= Energy gain. PT= power obtained by tracking mode. PF= Power
obtained by fixed mode.
1.6. Literature Survey
Researches on wide band gap oxide semiconductors sensitized with
dyes began in the 19th century, when photography was invented. The
work of Vogel in Berlin after 1873 can be considered the first study of
dye-sensitization of semiconductors, where silver halide were
sensitized by dyes to produce black and white photographic films. [46].
In (1988) G. Hlengiwe, showed that the nanocrystalline dye sensitized
solar cells, were based on a wide band gap «3.0-3.2eV»
semiconductor TiO2 [77].
In (1991) O, Regan and Grätzel solved the issue by employing nano-
porous Tio2electrode. a solar cell was called the dye sensitized
nanostructured solar or the Gratzel cells after its inventor The
developments have continued since then to increase dye solar cell
efficiency. [46].
In (2000) Helwa et.al studied the solar energy captured by different solar
tracking systems. They calculated the solar energy collected by using
measured global, beam and diffused radiations on a horizontal surface
[78].
In (2002) J. Halme proved That Titanium dioxide (TiO2) became the
semiconductor of choice for the photoelectrode because of its many
advantages such as low-cost, availability and non-toxicity [28].
In (2003) a group of researchers at the Swiss Federal Institute of
Technology had increased the thermo-stability of DSSC by using
ruthenium sensitizer in conjunction with quasi-solid state gel
electrolyte. [18].
In (2006) F. Lenzmann et.al reported the first successful solid-hybrid dye-
sensitized solar cell. Two researchers had designed alternate
semiconductor morphologies, a combination of nanowires and
nanoparticles, to provide a direct path to the electrode via the
semiconductor conduction band [20].
In (2008) M. Gratzel et.al demonstrated cell efficiencies of 8.2% using a
new solvent-free liquid red-ox electrolyte consisting of a melt of three
salts, as an alternative to using organic solvents as an electrolyte
solution. The efficiency with this electrolyte is less than the 11%
being delivered using the iodine-based solutions [18].
In (2009) Su. YH et.al used the natural act as an inexpensive and
biologically-friendly dye, which was fabricated on a TiO2/FTO
substrate. The efficiency of the photoelectric conversion in water-
based DSSC of natural pigment was up to 0.131% [79].
In (2010) M. Hossein Bazargan et.al used a new type counter electrode
for flexible dye-sensitized solar cells (DSSC) has been fabricated
using an industrial flexible copper (Cu) sheet as substrate and graphite
hich applied by spraying method [42].as the catalytic material w
In (2011) M.H. Bazergan et.al used natural dyes extracted from
pomegranate juiced as a sensitizer for nanocrystalline TiO2. Platinum
coated electrodes and result the semiconductor sensitizer enabled a
faster and simpler production of cheaper and environmentally friendly
solar cells [80].
At the same years, K. Kiong Chai et.al examined the use of a solar
photovoltaic system with a sun tracker [81].
In (2012) K. Ebrahim Jasim, used Natural Dye-Sensitized Solar Cell
(NDSSC) Based on TiO2 using local dyes extracted from Henna,
pomegranate, cherries and Bahraini raspberries [82].
In (2012) G. Deb et.al used single axis solar tracker device to ensure the
optimization of the conversion of solar energy into electricity by
properly orienting the PV panel in accordance with the real position of
the sun. [83].
In (2012) U. Adithi, et.al studied the electrical characterization of Dye
Sensitized Solar Cell using natural dye, extracted from the
pomegranate as a photo sensitizer [84].
In (2013) S. Zhang, et.al improved the energy conversion efficiency of
DSSC which could be used for future applications [85].
In the same year (2013), S. Deepthi, et.al studied the comparison of single
axis solar tracking system and two- axis solar tracking system with a
fixed mount solar system [86].
1.7. Aim of the work
This work deals with dye solar cells implementation and examination
using both natural and synthetic dyes. The effect of addition chemical
substances was investigated in order to enhance the value of both voltage
and current and consequently solar cell efficiency. The effect of three
types of solar tracking system (fixed, one axis and two- axis) was studied
on the solar cell efficiency from sunrise until sunset.
CHAPTER TWO
Experimental Part
Materials and equipments
Chapter two
2.1. Introduction
This chapter presents the implementation of solar cells based on
organic dyes. Two types of organic dyes were used; ruthenium as
industrial dye and pomegranates juice pigment as natural dye. The
absorption spectra for ruthenium and pomegranate natural pigment were
recorded using UV-VIS spectrophotometer. The photovoltaic performance
of the constructed ruthenium and pomegranate DSSC were calculated with
and without solar tracker. In order to keep the solar cell in an optimum
position perpendicularly to the solar radiation during daylight hours,
single- axis and two axis tracking system have been designed and
implemented.
2.2. Part one: Basic components of a dye-sensitized solar cell
Dye-sensitized solar cells consist of a variety of components that
have to be optimized both individually and as a component of the whole
assembly. This includes the glass substrate with the transparent conducting
oxide (TCO) layer, a mesoporous titanium dioxide (TiO2) layer, dye,
electrolyte (organic) solvent, red-ox couple, and a counter electrode.
Ultimately, individual cells have to be interconnected (in an optimized
way) in a solar module to guarantee the highest active area for power
generation.
2.3. Materials
Table (2-1) shows the list of materials used in processing the
(DSSC). In this table the chemical name with its formula, some of their
characteristics and the suppliers of the material are listed. The purity of
these materials are listed also in this table. Some of the plant materials
and the origin for the natural dyes are listed in table (2-2).
Table (2-1) list of materials used in processing the (DSSC) .
Purity% MW
(g/m)
supplier Basic description of the
materials Formula Chemical
materials
99.9%
80 MK nano
Canada
Very thin and white
powder To make the
conducting film
TiO2
(titanium
dioxide
powder)
anatase (10 nm)
95% 60.05 SCR-china transparent Volatility
liquid (solvent) CH3COOH ( acetic acid
solution )
18
Al Mansour
Company
Pure water (solvent) H2O deionizer
water
99 .9 % 46.o7 Fluka Pure ethanol (solvent) CH3CH2OH Ethanol
99% 166.0028 Erftstadt
.Germany
White powder (used for
making the electrolyte)
(KI ) potassium
iodide
99.5% 126.9 G.P.R
England
Black crystal (used for
making the electrolyte) (I ) Iodine
99%
1188.55 Solaronix-
Switzerland
Dark purple crystal (the
dye used for the
professional modal)
C58H86O8N8S2Ru N719 dye
Ruthenium
dye
99% 62.079 GCC
England
Volatility liquid (solvent) C2H6O2 Ethylene
glycol
Transmission
80%
Solaronix-
Switzerland
Transparent electron
(solid)
(FTO)
Glass
conductive (7
Ohm/sq-
resistivity)thic
kness(2.2mm)
99.9%
41.05 SCR-china Volatility liquid (solvent) AC Acetonitrile
Table (2-2)The plant origin
Type
of
plant
Pomegranate Hibiscus
sabdriffol
Raspberry Red
orange
Grapefruit Black
tea
Borago
officinalis
Origin Iraq –
Diyala
Egypt Syrian Iran Indian Srilanc Egypt
2.4. Measurement Techniques
Many measurements were accomplished in this study using
different devices and equipments.
Table (2-3) Origin, function and specification devices
Item Function Device type Original Specification
1 Absorbance
measurement Abs
USA
Sp-3000
190 nm-1100nm
220 V
2 Measurement of (
Voltage, Current digital multimeter China -86 C
400mv-1000V
400 uA-10A
3
Voltage, Current
and Resistance
measurement
Avometer A- 830 L - China 500v-200mv
10A-20uA
4 Analysis and
characterization
AFM
AA3000, Angstrom
Advanced Inc.
USA
220V, Resolution:
0.26nm lateral,
0.1nm vertical
precision of 50nm
XRD
Philips pw 1050 with
Cu-Kα (1.5406 A)
40 kV, 30 mA
5
the intensity of
radiation
measurement
Calculate the
average energy per
hour automatically.
TES-1333
China
Solar Power Meter
22000W/m
2.5. Implementation and Assembly of Dye Solar Cells:
Fluorine-doped tin oxide glass was supplied by (Solaronix-
Switzerland), with dimensions (25 x 25 x 2.2 mm), and an effective area
(1 cm2) was used
Fig (2-1): The fabrication steps of the DSSC
with a sheet resistance (7 /cm2) and transmittance > 80 % in visible light.
The conductive glass plates were used as electrodes for electron collection.
Before preparation of the electrodes, the glass substrates were washed with
ethanol, then wiped and let it dry in air.
2.5.1. Preparation of TiO2 Paste:
The TiO2 powder has been grinding by using mortar and pestle for
20 minute in order to prevent powder aggregation. A diluted acetic acid
was prepared by mixing it with de-ionized water to obtain a solution with
pH = 3. PH was measured using a pH-meter. The diluted acetic acid is
used to prevent aggregation of TiO2 particles, ensure good adhesion onto
the TCO substrate and avoid cracking of the deposited film. The TiO2
preparation 0f TiO2 paste
Film Deposition
Sintering Staining Dye
Catalyst coating
Addition of Electrolyte
Electrical contacts
Cell Assembly
Sealing
solution was prepared by blending of 6ml of diluted acetic acid gradually
to 6g of TiO2powder. 1 drop of a surfactant is then added (dish washing
detergent). The solution was mixed until it became uniform and lump-
free. Suspension is then stored and allows equilibrating for 15 minutes.
2.5.2. Deposition of TiO2 film:
The basic step for film deposition is described in the following
paragraphs. The tape casting method was used to deposit TiO2 paste onto
the conducting glass plate as shown in fig (2-2), first, a multi-meter was
used to check which side of the glass is conductive, and the resistances
reading were above (7 – 20 ohm). Then, the conductive side of FTO
(fluorine-doped tin oxide) substrates was covered on two parallel edges
with adhesive tape to control the thickness of the TiO2 film and to provide
non-coated areas for electrical contact.
Fig (2-2): Steps of TiO2 film deposition.
Fig (2-3) Masking of the deposition area
The TiO2 paste was distributed in the masked area quickly by
sliding a glass rod. The deposited TiO2 film was dried in air.
The sintering of TiO2 electrodes was performed at 450 °C for 30
minutes in an electric furnace in order to remove the organic binders and to
establish a good electrical contact between adjacent TiO2 particles in the
porous layer as well as between TiO2 film and the conducting SnO2: F
layer. Sintering temperature also affect particles size and porosity. Then,
the electrodes were taken out of the furnace to cool at room temperature.
The resulting TiO2 films were porous without cracks
Fig (2-4): Deposition of TIO2film.
The final thickness of TiO2 film was (15 μ m), which was measured
according to the tape thickness using micrometers. This thickness found to
be suitable thickness for acceptable results.
2.5.3. Dye solution preparation
Initially, ruthenium powder (0.06g) was weighed using balance.
Then, the synthetic dye was prepared by dissolving the ruthenium powder
to 100 ml of ethanol. The solution concentration became 0.5 x 10-3
(mol/L). The natural dye was obtained by fresh pomegranate fruit. Were
used two TiO2 films, one was coated with ruthenium dye and the other
with pomegranate pigment by immersing them into the dye solution for
20 minute of pomegranate, as shown in fig (2-5). But immersion time
with ruthenium dye was 5.5 hours so that the dye molecules filled the
pores and chemically attached to the TiO2 particles.
Fig (2-5) Deposition of the dye on TiO2 film
2.5.4. Electrolyte preparation
The electrolyte solution was prepared by dissolving 0.127g of
iodine (I2) and 0.83g of potassium iodide (KI) in 10 ml of ethanol and was
stored in an opaque container to avoid absorption of light. These
concentrations were optimized to reduce recombination current and to
minimize light absorption by tri-iodide ions which cause decomposition.
2.5.5. Counter electrode preparation
The counter electrode (cathode) was prepared by applying a thin
carbon layer on the entire surface of the conductive side of another
conductive substrate using a soft pencil, but the operation failed. While
the method by candle soot yielded acceptable results. The carbon
(graphite) serves to accelerate the chemical reactions which transform the
tri-iodide ions back to iodide ions at the counter electrode by electron
donation, with Note the sides of the glass electrodes are carefully handled
avoiding touching the faces of the electrodes, as shown in fig (2-6).
Fig (2-6) Deposition carbon layer on the glass conductive substrate
2.6. Cell Assembly
The immersed TiO2 electrodes in ruthenium and in pomegranate
juice were removed and washed with ethanol and was dried in air. A drop
of 1ml electrolyte solution was added on TiO2 electrode, as shown in fig
(2-7). After adding the electrolyte on the TiO2 electrode, the cell was
assembled by putting the two electrodes on one another shifted about 1cm.
The shift between the two electrodes is needed for the electrical contact.
The cell has to be sealed, otherwise the electrolyte would evaporate. The
dye solar cells were isolated using glue around the masked area, as shown
in fig (2-8), two clamps were used to press the two electrodes together
until the sealant became dry.
Fig (2-7): Dye solar cell assembly
Fig (2-8) Model for dye solar cell
2.7. Effect of TiO2 past parameters on efficiency
The reason for choosing (TiO2) is that TiO2 has a high electrical
conductivity, high refractive index and optical catalyst in the regions (UV).
Great radiations resistance in this region supported two main functions,
firstly transfer the charge to the electrode and secondly as a platform to
carry the organic dye molecules. The parameter that had been influenced in
this process can be summarized in the following points:
2.7.1. Effect of thickness on efficiency
1. Experimentally the use of thickness more than 15 microns and less than
5 microns cause disintegration of titanium dioxide layer after very short
time period in the case of thicker recipes. As well as it cannot get
harmony between the material itself and between the materials with the
glass. While the thinner recipes, leads to insufficient saturation of the
dye layer due to thickness lack.
2- Increasing the thickness of the cell increases the volatile compounds
drops and thus increase the number of class cycles because of increasing
the amount of absorbed dye.
3- Cell thickness affects the light scattering and optical density along the
optical path. Therefore, it is necessary to have TiO2 layer thickness
between (10-15) microns. It is favorable to fix the thickness at 15
microns to overcome all the problems of thickness.
4- During the preparation; the water amount is very important, where the
increase of titanium dioxide powder can absorb a large amount of
water in the middle of molecules and thus the structure of the film is
not fully formed (ie disintegrate). In other word the layer decreases the
ability to carry the dye and thus reduce the efficiency because of the
low of film thickness.
5-The relationship between film thickness and the filling factor (FF) is
inversely proportional. So the film thickness should be carefully selected
to get the best fill factor (0.78), this value lead to the highest DSSC
efficiency.
2.7.2. Effect of paste drying temperature on efficiency
1. The layer of TiO2 must be heated to 450-500 degrees for consolidating
the glass and layer. Further increasing in the temperature above this level
causes damage to the paste layer. As well as long drying time cause
robust affection on the paste layer homogeneity, yielding brittle slabs.
Therefore; the time of drying must not exceed half an hour.
2- After 5.5 hours of immersing the slide in dye solution, the slide should
be kept in oven at 70 oC for ten minutes.
3- At lab test, the sun simulator optical sources should be shielded by
glass barrier in order to prevent the high temperature affection on
2.7.3. Effect of the pH value on efficiency
The basic or acidic environment of the paste plays an important role in
sensitizing the dyes. Where, the rate of recombination between the TiO2
electron and the oxidized dye was depending on PH. The suitable PH value
in this work was found to be about (3-4), for achieving output from the
DSSC.
2.7.4. Effect of electrolytes type on efficiency
In this work the solute electrolyte was adopted instead of solid for
the following reasons
1- Solid state holes conductors are more robust, but the efficiencies are
lower.
2- Difficulties in filling tortuous pore network limits thickness and the
efficiency.
3- Solute electrolyte has faster recombination ability than liquid.
2.7.5. Effect of solvent of electrolyte on efficiency
The electrolyte is one of the key components for dye sensitized solar
cells and its properties have high affection on the conversion efficiency and
stability of solar cells. The DSSC efficiency depends completely on the
type of solvent, i.e. solvents specification, viscosity and vapor pressure.
Therefore, the most important point in the preparation of the solution is the
choice of the solvent type. Firstly, acetone trail has been chosen. The
achieved results are fruitless. This result may be due to stored or to the
undesired density of the solvent. Then ethylene glycol had been used, in
spite of its high density it was used.
The high viscosity of the solvent can be reduced by dilution with
water, alcohol and addition of a few acetone trail drops to the final mixture
the output of the cell can be enhanced.
2.8. Testing the solar cell:
Fig (2-9) device for measuring the voltage and the electric current .
Photo-response of the ruthenium (N719) and pomegranate pigment
solar cells was evaluated by recording Voltage (V) and current (I), as
shown in fig (2-9). Illuminating the solar cell with 40-mW/cm2 tungsten
halogen lamp, using a glass for protecting the cell in order to remove
most of the heat from the light source, and the rheostat, effective area was
(1 cm2).
The current–voltage characteristics of a cell in the dark and
illumination permit an evaluation of most of its photovoltaic
performances as well as its electrical behavior. The short circuit current
(Isc) is the one which crosses the cell at zero applied voltage and is a
function of illumination. Charges travel under an internal potential
difference typically equal to open circuit voltage (Voc).
The Voc is measured when current in the cell is zero, corresponding
to almost flat valence and conduction bands; Imax and Vmax values are
defined in order to maximize the power |Imax ×Vmax|. This is the maximum
power Pmax delivered by the cell. The filln factor FF is the ratio of the
maximum power to the product of short circuit current and open circuit
voltage. To calculate the efficiency the following steps are followed
1- Key S1 switched on and key S2 was off to record open circuit voltage
(Voc), keeping the current equal zero.
2- S1 switched off and S2 was on to record ( Isc ) , keeping the voltage and
resistance equal zero.
3- S1 and S2 were switched on, the resistance was increased slowly
every time then the voltage and the current value were recorded. At
highest value of resistance, the voltage is maximum (Vmax) , and the of
the FF and eff.was calculated by using equations (1-7) and (1-8)
Previously reported.
2.9. Part two: Tracker the sun
To maintain the sustainability and efficiency of the solar cell
during the day a system to track the sun from sunrise until the sunset
automatically was used. During the day the sun appears to move across the
sky from left to right and up and down above the horizon from sunrise to
sunset. Using the green LED as a sensor.
2.10. Design of tracking system
The Scheme in fig (2-10) explains a simplified format of the solar
tracker in all its types.
Fig ( 2-10 ) Structure of the two - axis solar tracking system
The solar tracking system was designed and built to maintain
the efficiency of the solar cell throughout the day, as shown in fig (2-11).
The system is consisted of three parts:
Fig (2-11) Parts of a sun tracker 1-Umbrella. 2- LED. 3- Solar cell (6.5×
7.5) cm. 4- Platform. 5- Motor (1). 6- Motor (2). 7- Battery (6 v) .8-
Distributor box. 9- Digital multimeter. 10- Wires.
2.10.1 Mechanical part:
The mechanical part includes the animated base with motor (no.5
in fig 2-11) to regulate the movement (right – left), which (motor no. 6 in
fig 2-11) is used to regulate the movement (north – south).
The advantages of this motor are its low cost, high torque at low
velocities. Platform no.4 in figure (2-11) that carry the solar cell, and
movement (3600) .
2.10.2. Optical part
This part consists of four LEDS (called quadruple) is sensitive to
light, with an umbrella to prevent the arrival of light to LEDS. Because of
movement of the earth during the day, the device should be moved to keep
the balance and make the solar radiation vertical always on the cell.
2.10.2.1. LED-sensor
LED (green light emitting diodes) can be used as an optical sensor,
when an optical power incident on it, electrical signal can be generated.
its properties The sun sensor is made using clear lens 5mm GaP , a
semiconductor device, Cheap , available in the market and 1.7 volts uses
voltage as an input to a circuit and turn the LED into a solar sensor, as
shown in fig (2-12) is used in normal circumstances, (called cross-
shaped).
Fig (2-12) green led (1- Right movement.2- The movement of the left.
3- South movement 4- Movement of the North.
While the shape illustrated it has been laboratory, as shown in fig
(2-13) is used in case of expecting the exits of clouds.
Fig (2-13) Modified designs of the four LED-sensors (1,2) The Sunrise period
until midday.(3,4) The Period after midday until sunset
2.10.3. Electrical part
This part includes an electrical circuit for the solar tracker, as shown
in fig (2-14). Which contains of the sun tracker circuit (one - axis), will
the fig (2-15) shows the circuit (two-axis) . These circuits consist of the
following parts:
1- Tow led. 2- Two D.C motor. 3- Eight transistors. 4- Power supply
(6 volt).
The LED as (photodiode) is utilized to capture the optical signal and
converted it to electrical signal, act as detector. This amplified is sending
to the motor after using three stage transistors.
Fig (2-14) circuit for one-axis sun tracker
Fig (2-15) circuit for two-axis sun tracker
2.11. Procedure of solar tracker
In the case of diffuse radiation measurement the setup is illustrated
in fig (2-16). In this figure it is clear that there is a cover on the cell in
order to allow entering direct light only, and preventing the scattered and
reflected light. From the recorded voltage and current, the performance of
cell with direct irradiation could be estimated.
Fig (2-16) direct solar tracker only
CHAPTER THREE
Results and Discussion
Chapter three
3.1. Introduction
In this chapter; the results utilized from the experimental part of the
work are presented and discussed. The discussion includes, natural and
industrial dyes experiment, with and without addition of different additives,
compares the efficiencies in each case as well as the spectral measurements.
The gain achieved from the tracking system operation has been analyzed in
the two cases, direct radiation and global radiation.
3.2. Result for first part: The optical measurement
Based on spectroscopic measurement, it was found that both
ruthenium dye in ethanol solution and pomegranate have absorption peaks
in the visible region, while electrolyte solution has not any peak.
3.2.1. Absorption spectrum of ruthenium (N719)
The absorption spectrum of ruthenium dye in ethanol solvent is
shown in fig (3-1(. There are three absorption peaks at (355 nm, 385nm,
535 nm), therefore these bands cover a part of the visible region. The
ruthenium N719 dye has absorption spectrum extends only to 700 nm; so
that it has nearly no absorption band in the infrared region which cause
limited solar cell efficiency. The thiocyanate ion ligand is the most
sensitive part of the dye (N719), when adsorbed onto TiO2 in DSSC [87].
Fig (3-1) the absorption spectrum of ruthenium N719 dye
3.2.2. Absorption spectrum of pomegranate
Pomegranate juice dye has an intense absorption band at 310 nm,
and a low intensity at 375, both of them are in the UV portion of the solar
spectrum. Furthermore, there is another one fixed at 520 nm but its
intensity is lower than that of ruthenium N719 dye. The interested
absorption peak of the natural dye is that at 520 nm because of its big
Fig (3-2) Absorbance of pomegranate pigment
3.2.3. Absorbance of electrolyte solution
The electrolyte solution contains iodide and tri-iodide ions, so that
it shows a little absorption in the visible range, as shown in fig (3-3).
This unwanted little absorption can cause Losses efficiently cell.
Decomposition of electrolyte ions would lower the solar cell efficiency,
and reduce the cell operational lifetime and has proven to be one of the
most versatile re-dox couples. For these reasons there is combining high
overall conversion efficiency, at the same time, good long-term
stability. It is important to remember that; the UV radiation on the dye
solar cell is efficiently blocked by the wide bandgap FTO glass (3 eV)
which acts as a filter for UV and a window for the visible portion,
which reduces the decomposition of dyes and electrolyte induced by
UV absorption.
Fig (3-3) Absorbance of electrolyte solution
3.3. X-Ray measurement
The crystalline and structural composition of TiO2 paste sample after
annealing at (450 0C) was investigated using X-ray diffraction. as
shown in fig (3-4).
The utilized TiO2 Nano-particles are of anatase crystal structure
with grain size of 10 nm. The TiO2 paste kept its anatase structure even
when is annealed at 450 oC ,
Fig (3-4) the X-Ray spectrum of TiO2 past after annealing
3.4. The surface morphology of TiO2 paste film using AFM
The AFM images of TiO2 sample was shown in fig (3-7). Analysis
of the AFM images confirmed that the TiO2 films consist of
interconnected grain particles with an average diameter of 94.86 nm.
It can be seen from fig (3-7), the TiO2 particles are stuck together
forming large cluster. The TiO2 particles nano size caused increasing in
the surface area, yielding to enhance the dye adsorption capacity on
TiO2.
The aggregates generate an effective light scattering and, thus,
significantly increasing the traveling distance of the light within the
photo electrode film. This leads to an increasing in the opportunity for
the photons to interact with the dye molecules adsorbed on
nanocrystalline, and as such, enhancing the light harvesting efficiency
of photoelectrode. Therefore, the aggregation that occurs in the nano
particle here is not absolutely unfavorable.
Fig (3-7, 3- 8) presents the granularity accumulation
distribution report for TiO2 film before and after annealing at 450 oC.
From these figures it can be seen that in both cases the average
clustering diameter is still under 100 nm, where it reach about 96,59 nm
before annealing while this diameter transform to 94.86 nm after
annealing as a result of shrinkage.
Fig (3-5 a, b) presents the image surface morphology of TiO2 nano paste
film before and after annealing at 450oC respectively. It is clear that,
from fig (3-6, a) the porosity is more obvious than that in fig (3-6, b),
which may be attributed to the same reason mentioned before
Figure (3-5) surface morphology of TiO2 paste film, 2 D view, a) before b) after
annealing at 450 oC
(a) ( b)
Figure (3-6) surface morphology of TiO2 paste film, 3D view, a) before
b) After annealing at 450 oC
Sample:1 Code:Sample Code
Line No.:lineno Grain No.:105
Instrument:CSPM Date:2013-05-15
Avg. Diameter:96.59 nm
Diameter(nm)<
Volume(%)
Cumulation(%)
Diameter(nm)<
Volume(%)
Cumulation(%)
Diameter(nm)<
Volume(%)
Cumulation(%)
50.00
55.00
60.00
70.00
75.00
80.00
0.95
2.86
2.86
2.86
4.76
5.71
0.95
3.81
6.67
9.52
14.29
20.00
85.00
90.00
95.00
100.00
105.00
110.00
6.67
8.57
6.67
14.29
8.57
5.71
26.67
35.24
41.90
56.19
64.76
70.48
115.00
120.00
125.00
130.00
8.57
8.57
6.67
5.71
79.05
87.62
94.29
100.00
Fig (3-7) Granularity accumulation distribution report before annealing
Sample:2 Code:Sample Code
Line No.:lineno Grain No.:132
Instrument:CSPM Date:2013-05-15
Avg. Diameter:94.86 nm
Diameter(nm
)<
Volume(
%)
Cumulation(
%)
Diameter(nm
)<
Volume(
%)
Cumulation(
%)
Diameter(nm
)<
Volume(
%)
Cumulation(
%)
60.00
65.00
70.00
75.00
80.00
85.00
3.03
10.61
6.06
4.55
4.55
14.39
3.03
13.64
19.70
24.24
28.79
43.18
90.00
95.00
100.00
105.00
110.00
115.00
7.58
6.06
2.27
6.82
5.30
3.79
50.76
56.82
59.09
65.91
71.21
75.00
120.00
125.00
130.00
135.00
140.00
145.00
3.79
2.27
8.33
4.55
4.55
1.52
78.79
81.06
89.39
93.94
98.48
100.00
3.5. Effect of potassium iodide concentration on efficiency
Potassium iodide KI is Compound white hygroscopic, low and high
concentration of KI reduce the solar cell efficiency so that a moderated
amount of KI must be selected to be (0.83 gm. / ℓ) as shown in fig (3-
9).This red-ox has good solubility, low absorbance in the visible region,
and provides rapid dye regeneration. At high iodine concentration
reductive quenching might deactivate the excited state representing losses
in the channel. The rate of back reaction is much smaller, typically τ ≈ 1
μs. Another recombination process is the reduction of tri-iodide in
electrolyte by conduction band electrons. The selected as (0.83 gm. / ℓ).
Fig (3-9) concentration of KI and efficiency
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Efficiency
%
concentration of KI (gm/ℓ ) on efficiency
Fig (3-8) Granularity accumulation distribution report after annealing at
450 oC
3.6. Effect of dye concentration on efficiency
To investigate the effect of dye concentration on the
performance of DSSC, ruthenium dye concentration effect on the
output efficiency was adopted. The dye immersion time, of FTO slide
coated TiO2 in dye solution was fixed for 5.5 hours and PH=3 . The
electrolyte concentrations were 0.83 gm/ℓ and 0.127 gm/ℓ for (KI)
and (I) respectively.
The concentrations of ruthenium dye were changed without any
additive. The maximum utilize efficiency was 1.9 %.The low dye
concentration samples produce higher efficiencies than that of the high
one, so that the utilized dye concentration do not exceed 5 × 10-2
M.
This may be attributing to that, the process of electrons transfer from
the ground state to the irritation state in the first excited state at low
dye concentration was done in a very fast time. In the first period the
dye is pervasive within the TiO2until it reaches the saturation after 5.5
hours, as shown in fig (3-10).
Fig (3-10) Concentration of dye
where the adsorption of dye is fully saturated and can receive all
photons of sunlight, absorbed them by the electrons and ascends to
higher levels shortly but slightly. At dye concentration of 5 × 10-5
M,
the output efficiency is very low; by increasing the dye concentration
the efficiency will be enhanced. The efficiency reached a maximum
value at dye concentration of 5 × 10-4
M. Higher than this
concentration, the dye molecules aggregation will occurs yielding
reduction in the efficiency.
3.7. Effect of immersion time on efficiency
The same conditions described in paragraph 3.4.5 were applied
here, but the TiO2-dye immersing times which extends from a few
seconds up to 8 h and the adopted dye concentration was 5 × 10-4
M,
as shown in fig (3-11).
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0.005000.001000.000500.000100.00005
Efficiency %
Concentration N719 without AgNO3 gm/L
Fig (3-11) Immersion time of TiO2 film
In particular for N719 under investigated conditions, it has been
demonstrated that the first hour is strategic for an effective uptake of
the dye by the TiO2 nanoparticles, with a saturation level reached
within the 5.5 h with Thickness (15µ). Suggesting that commonly
used longer dipping times, typically >24 h [88], are useless or even
undesirable when making DSSC devices. As shown in fig (3-11)
,the layer before and after this period got gradient efficiency due or
its little period saturation and dives either because of excess
(aggregated of dye molecules inside the TiO2nanoporous) which
leads to decline reverse efficient or inefficient dye adsorption by
TiO2 nanoporous. Further information of DSSC parameters are
illustrated in table (3-1) immersion time.
0
1
2
3
4
2.5 3.5
4.5 5.5
6.5 7.5
effi
cien
cy %
Immersion time (hour)
Table (3-1) immersion time of TiO2coating film in ruthenium dye
Time
(hours)
ISC
mA
Imax
mA
Voc
Volt
Vmax
Volt
FF% 𝜂%
2.5 1.3 1.2 0.57 0.33 53 0.9
3.5 2.3 2 0.62 0.42 59 2.1
4.5 4.2 2.9 0.57 0.47 60 3.4
5.5 4 3 0.55 0.5 68 3.7
6.5 2.2 1.83 0.47 0.35 62 1.6
7.5 1.85 1.5 0.55 0.37 54 1.4
3.8. Effect of additive on efficiency
Additives play an important role to enhance the photovoltaic
parameters in liquid electrolyte-based DSSC. The position of the CB in
the TiO2 depends strongly on the surface charges and adsorbed
molecules. These additives in the electrolytes are expected to be
adsorbed onto the TiO2 surface, thus affecting the CB in the TiO2
strongly associated with the photocurrent and photovoltage. . These
additives affect directly recombination reaction with the iodine mainly
devoted to the enhancement of short-circuit photocurrents (Jsc), as
shown in fig (3-12).
Fig (3-12) Concentration of dye with and without additive
In order to present the effect of additive on the performance of DSSC,
0.01 gm./ ℓ of AgNO3 had been added to the electrolyte solution. The
cell efficiency investigated at different dye concentration.
3.8.1. Effect of additive concentration on efficiency
In order to study the additive concentration on the performance
of DSSC, silver nitrate at different concentration was selected, for
enhance the efficiency of the cell as shown in fig (3-13), because most
of its results were enhancing the efficiency of the solar cell. The
enhancement in both current and voltage is due to the increase in the
electron transfer speed, where the silver solution adding will be
increasing the electrical conductivity of the electrolyte. The film
thickness was (15µ) and dye concentration (5×10-4
M).
0
0.5
1
1.5
2
2.5
3
3.5
4
0.005 0.001 0.0005 0.0001 8E-05 5E-05
Eff
icie
ncy
%
Dye concentration [M] with and without AgNO3 gm/ℓ
with
without
The best efficiency was 3.7% which corresponding to the sample of
adding 0.01% of AgNO3.
Figure (3-13) Effect of additive concentration
This sample presents the greatest fill factor 68% among the other
samples. The details parameters of the samples of different doping
additive concentration are shown in table (3-2).
Table (3-2) Concentration of AgNO3 and efficiency
AgNO3
(gm/ℓ)
ISC
mA
Imax
mA
Voc
Volt
Vmax
Volt
FF% 𝜂 %
0.005 1.3 1.2 0.57 0.33 50 0.9
0.001 1.9 1.6 0.64 0.4 52 1.6
0.01 4 3 0.55 0.5 68 3.7
0.03 2.3 2 0.62 0.42 59 2.1
0
1
2
3
4
0.001 0.005
0.01 0.03
0.2 0.4
effi
cien
cy
%
concentration of AgNO3 (gm / ℓ)
0.2 2.2 1.6 0.52 0.35 50 1.4
0.4 0.8 0.77 0.6 0.36 58 0.7
3.8.2. Effect of additive type on efficiency
The additive is important component in liquid electrolytes for
optimizing the photovoltaic performance of DSSC. Some of additives
showed voltage increase with drastic current decrease, while others kept
current at a certain level. Other additives reduce the volatile organic
compounds and found that the increase in these compounds due to the
suppression of the dark currents or negative shift to CB of TiO2, adding
the additive is intended to reduce the three-iodide at a fixed rate and
also added enhance current and thus increase the efficiency of the
delivery package for titanium dioxide to receive the electrons next from
the dye.
The effect of different additive types on the output efficiency of
DSSC is illustrated in (table 3-3).
Table (3-3) Ruthenium and type additive
Efficiency % Ruthenium and type additive
3.7 % AgNO3
1.7 % CuI
1.6 % AuCl3
1.35 % CaCO3
1.06 % AuCl3 +AgNO3
3.8.3. Type of dyes
The DSSC of industrial dye showed better efficiency rather than
natural dye because of its high stability. The absorption band of both
industrial and natural dye should be covers most of the solar spectrum.
Several natural sensitizing dyes such as; Pomegranate, raspberries ,red
orange, Hibiscus sabdriffol, Black tea, grapefruit and Borago
officinalis were selected with the effective area (1cm2 ) in this work.
These plants have high levels of anthocyanins molecules. In this work
the achieved voltages were within 0.7 volt, while the generated current
reaches 2Am. The best accepted results for the adopted natural dye
DSSC are illustrated in table (3-4).
Table (3-4) Natural dyes with and without additive
Dye Process Isc Voc Imax Vmax FF 𝜂 %
Pomegranate before 1.3 0.55 1.1 0.2 0.31 0.55 %
After 1.3 o.7 1.2 0.4 0.53 1.2 %
Hibiscus
sabdriffol
before 0.56 0.54 0.45 0.23 0.34 0.26 %
After 0.6 0.35 0.5 0.3 0.71 0.4 %
Raspberry before 0.7 0.52 0.59 0.2 0.32 0.3 %
After 0.75 0.5 0.7 0.2 0.37 0.34 %
Red orange
before 0.45 0.36 0.3 0.21 0.39 0.1 %
After 0.3 0.41 0.26 0.3 0.63 0.2 %
Grapefruit before 0.2 0.18 0.1 0.1 0.28 0.02 %
After 0.22 0.4 0.15 0.2 0.33 0.1 %
Black tea before 111µ 0.3 90 µ 0.1 2.4 0.0002 %
After 0.045 0.14 0.035 0.03 0.17 0.003 %
Borago
officinalis
after 5 µ 0.1 2 µ 0.07 0.28 0.000003%
before 23 µ 0.4 80 µ 0.35 0.75 0.0001 %
Multiplying the voltage and current produces power output in
watts. So in order to achieve better output power both values for
current and voltage must be appropriate. The values of the voltages
were suitable but the value of the currents was in the mille-ampere,
microampere range. Part the problem due to the uniform in the titanium
dioxide layer. Several attempts were done to enhance the generated
current in the prepared cells. The prepared cells were kept in dark
place; otherwise the strong light will terminate the stability of the cell.
The best result was in pomegranate sample, where the generated
current value (ISC) reached to 1.3 mA and (Imax) 1.1 mA without any
additive, while with additive reach 1.3 mA with adding 0.01 gm/ℓ of
AgNO3, but increase (Imax) it reach about 1.2 mA, therefore adopted a
research study on the dye pomegranate and ruthenium because they are
the most efficient as shown in table (3-5).
Table (3-5) For best results after additive
Efficiency % AgNO3 additive
3.7 % Ruthenium –N719
1.2 % Pomegranate
3.9. Effect of electrode type on efficiency
Two types of electrodes were adopted, to investigate the
electrode type affection on the performance of the DSSC, type (I) and
type (II):
Type (I) consist of two FTO glass electrodes; this type was adopted in
all the samples which was used in this work.
Type (II) consist of one FTO glass electrode, which should be in front
of the incident light, and the second pole was glass coated with thin
silver layer the resistance (10 /cm2) . Both samples were prepared
under the same condition.
The first sample of type (I) give filling factor equal to 53% and
efficiency of (1.2 %), while the second type (II) give filling factor of
(48%) and efficiency of (0.1%).The reduction in the values of the
filling factor and the efficiency in the second model than that in the
first model may be attributed to the iodine itching in the silver metals
coated. This abrasion destroys the homogeneity of the conducted
silver coating resistance yielding distortion in charge movement. As
well as this reduction may be due to that; the high reflectivity of the
silver coating may disturb the time schedule of the charge
regeneration and recombination, as shown in table (3-6) .
Pomegranate
Fresh
Counter
electrode
Anode
electrode FF% 𝜂 %
1cm2
FTO FTO 53 % 1.2 %
1cm2
Ag FTO 48 % 0.1 %
Table (3-6) different electrode types
3.5. Result for second part
In this work green LED is used as a sensor for the tracking
system. The implemented system is equipped with four LEDS (Green
color) to measure the global solar radiation. The CdS tracker is pretty
good but it lacks in accuracy and sensitivity. The LEDs generate
voltage had been experimented sunlight. The green LED generate
about 1.65V to 1.74V.
The generated voltage can act as an input to a circuit and convert
the LED to a solar sensor. As well as the sensitivity of green LED is
better than the other types, because of its spectral response with
respect to the visible sun light. In this work the utilizing of LEDS
instead of normal detector is due to its low cost, sensitive, simple to
use and peak spectral response. The green LEDS are made from
gallium Phosphide, a semiconductor with a much higher bandgap
voltage. The circuit is designed to bring the panel back to the east just
after sun rise.
3.10.1. Relationship of single-axis tracking system with
fixed mount
The single - axis system is more complicated than fixed system
(tilt angle 330). One-axis tracking systems is expensive require
concrete foundation, which adds farther cost. The recorded results of
both static panel in (5-June-2013) and single-axis tracker in (27-May-
2013 ) are taken for a two days from morning 7 am to evening 5 pm
for every hour in (Jadiriya - Baghdad), as listed in table
(3-7).
Table (3-7) Comparison of fixed mount with single axis tracker
system
Time
(Hours)
fixed system Solar Tracking(single
axis)
V mA mW V mA Mw
7:00 4.01 4.98 20 4.11 20.7 85
8:00 4.12 31.3 129 4.21 42.7 180
9:00 4.10 45.1 185 4.15 60.2 250
10:00 4.10 66 270 4.10 80.5 330
11:00 4.07 81 330 4.02 92 370
12:00 4.12 93.5 385 4.20 95 400
13:00 4.02 74.6 300 4.21 77 324
14:00 4.21 58.2 245 4.10 70.7 290
15:00 4.20 40.5 170 4.20 52.4 220
16:00 4.25 25.9 110 4.10 35.9 147
17:00 4.1 15.6 64 4.10 21.7 89
Average Power 220 244
The main disadvantage of the single axis tracker is that; it can
only track the daily movement of the sun and not the yearly
movement. The efficiency of the single axis tracking system is also
reduced during cloudy days since it can only track the east-west
movement of the sun.
The surface area and type of surface must be taking into
consideration, in order to use of the reflected and scattered radiation.
The energy gain between the two systems can be calculated by using
equation (1-11).
The calculated efficiency of the single axis tracking system over
that of the one - axis was 10.90%.
3.10.2. Comparison of two-axis tracking system and fixed
mount
Two-axis system can be used and placed anywhere in the world
because it does not require a specific angle. It can work easily, while
the fixed system is complicated due to the tilt angle which varies
according to geographical location.
There is a difference between the energy gain of the tracking system
(two-axis) in (23-May-2013) and fixed system in (5-June-2013). The
difference is biggest for the first type from 7.00 am in the morning to
16.00 pm in the afternoon when the sun is high enough above the
horizon at the same time oriented away from south, as shown in table
(3-8).
The calculated efficiency of the two- axis tracking system over that
of the fixed amount equal to 36.4 % .
Will The calculated efficiency of the two- axis tracking system over that
of the one-axis equal to 22.9 % .
Table (3-8) two-Axis Tracking System over Fixed Mount
Time/Hours
Fixed Mount
Solar Tracking (two- axis)
V mA mW V mA Mw
7:00 4.1 4.89 20 4.10 29.3 120
8:00 4.13 31.2 129 4.11 60.8 250
9:00 4.10 45 185 4.11 79 325
10:00 4.20 64 270 4.20 92.8 390
11:00 4.10 80.5 330 4.10 102.4 420
12:00 4.11 93.7 385 4.10 103.6 425
13:00 4.10 73 300 4.11 93.7 385
14:00 4.10 59.7 245 4.11 90 370
15:00 4.11 41.7 170 4.12 70 289
16:00 4.11 26.8 110 4.11 48.7 200
17:00 4.00 16 64 4.10 30.7 126
Average Power
220 300
3.10.3. Comparison between global and direct solar
radiation
The calculation of the direct solar radiation was achieved in 6-
March-2013. The results which describe the above situation are
illustrated in table (3-9).
Table (3-9) Comparison between global and direct solar radiation
Time/
Hour
I mA
Global
Light
)(Global
Electric
power
radiation mW
I mA
direct light
Direct)(
Electric power
radiation
mW
7 34 136 26 104
8 55 220 40 160
9 66 264 51 204
10 80 320 63 252
11 89 356 71 284
12 98 392 80 320
13 90 360 63 252
14 75 300 54 216
15 57 228 43 172
16 35 140 23 92
17 22 88 11 44
This can be achieved by putting a cover to allowed direct light
only, and didn't allowed the reflected and scattered rays to enter inside
the cell. The highest generated current value at midday in this case
was 80 mA; while in the case of the total radiation without cover was
98 mA, as shown in table (3-9). This calculation was for good weather
condition. It is clear that there was noticeable difference between the
two measurements, with and without cover because of the reflected
and scattered radiation shown in fig (3-14). There are several factors
that can increase the received radiation such as large surface area, high
altitude Surface color, and type of the surface.
Fig (3-14) Comparison between global and direct solar radiation
3.10.4. Comparison between global and direct solar
radiation by solar power meter (TES-1333).
In order to calibrate our instrument, the measurements were
conducted on the same day at the same time. Achieved in (4 – June –
2013). Total radiation at midday with a device (TES-1333) was
recorded as 1200W/m2. The solar tracker after putting the cover on the
solar cell (6.5cm×7.5cm Standard)
to tap direct radiation only, after calibration between reading in the first
device and the second device was found to be in the record at 12:00 pm
960W/m2. As shown in fig (3-15), the difference between them is the
reflected and scattered radiation; this difference cannot be neglected in
research importance.
0
50
100
150
200
250
300
350
400
450
6 8 10 12 14 16 18
Ele
ctri
c p
ow
er (
mW
)
Time (Hour)
Global radiation
Direct radiation
Fig (3-15) Comparision global and direct solar radiation
The results are listed in table (3-10). Solar power meter was used
to measure the scattered and reflected radiation, first inside the building
in the shade which was (200W/m2), than outdoors, putting the device
lens towards the ground to prevent direct light from reaching the lens
which was (340W/m2). The two readings have to be taken into account
of the scattered and reflected radiation in this study; the increase
depends on the surface area of the building, the type and color of the
surface.
Table (3-10) Comparison between global and direct solar radiation by (solar power
meter)
Time/Hour
Global)(
Solar power
radiation
W/m2
Direct)(
Solar radiation
W/m2
Diffuse
W/m2
7 408 312 96
8 660 480 180
9 792 614 178
10 760 760 200
11 1074 856 218
12 1200 960 240
13 1080 756 324
14 900 655 245
15 686 522 164
16 420 285 135
17 266 135 131
3.10.5. The effect of dust on the solar tracker
There are different changes in the atmosphere conditions so that
different distribution sensors must be used. Result illustrated in fig (3-
16)
Fig (3-16) Comporison between clear and dust day
The work was examined in sunny day, in16-June-2013, and in
another day which was dusty, in 2-June-2013. In clear day, the output
power recorded at midday was 400 mW, while at dusty day was 250
mW. It is important to note that the recorded voltage was almost
unchanged and fixed at 4 volt. Table (3-11), summarized these results.
Table (3-11) comparision global and direct solar radiation of clear and dust day
Time
(Hours)
V volt
global
I mA
global
Direct solar
radiation
(clear)
mW
Direct
Solar radiation
(Dust)
mW
7 4.12 34 104 62
8 4.16 55 222 156
9 4.10 66 272 164
10 4.1 80 823 184
11 4.07 89.5 833 217
12 4.12 98.9 212 259
13 4.02 90 831 203
14 4.36 75 827 194
15 4.33 57.2 227 108
16 4.39 35 152 48
17 4.25 22.2 22 34
3.10.6. Comparison between two-axis, one axis and fixed
In the fig (3-17) the blue line represents the solar tracker (two-
axis). It is favorable, because it does not specify an angle, works easily
and free movement. It achieved the highest value of the current
(425mW), in 23-May-2013.
The color red is belongs to single axis system that is proven at the
angle of an annual work (330).This type of tracker work in daily
movement from east to west. The system is less efficient in cloudy and
dusty days. The recorded reading of this system which is done in
middle day was less than 400mW in27-May-2013. In table (3-12), the
latter system (fixed) of green color was less important than the other
types because it is of fixed angle and proven throughout the year at 33
degrees. The highest value obtained in the middle day (385mW),
which is less than the previous species, it is done in5-June-2013.
table (3-12) Comparison between two-axis, one axis and fixed
Time/Hour
Two –axis
mW
One –axis
mW
Fixed
mW
7 120 85 20
8 250 180 129
9 325 250 185
10 390 330 270
11 420 370 330
12 425 400 385
13 385 324 300
14 370 290 245
15 289 220 170
16 200 147 110
17 126 89 64
The differences between the three types are significant at around
7.00 am in the morning and at 17.00 pm in the afternoon when the sun
is high enough above the horizon, as shown in fig (3-17). This is
because the sun yields significantly greater amounts of energy when
the sun's energy is predominantly direct. Direct radiation comes
straight from the sun, rather than the entire sky.
Fig (3-17) Comparison between two-axis, one axis and fixed
0
20
40
60
80
100
120
6 7 8 9 10 11 12 13 14 15 16 17 18
Current mA
Time/hours
fixed two axis one axis
3.11. Conclusion
The following conclusions have been obtained from the analysis
of experimental work:
1- The ruthenium dye has higher absorption in visible range of the
solar spectrum than pomegranate pigment.
.
2- The fill factor of dye solar cells was found to be equal to 61%for
ruthenium (N719) and 45% for pomegranate solar cells. Low fill
factor suggests that there is a high resistive loss in the cell which
causes low efficiency.
3- The dye solar cells require efficient and compact sealing method.
4-It can be concluded that both single-axis and dual-axis are highly
affected on the electrical energy output when compared to the fixed
mount system. Dual-axis tracking system works well even during
cloudy days when compared with single- axis tracker.
5- Using DC motor instead of AC motor to enhance the speed control,
position and control and operating at low speed. In addition to that, the
AC motors are expensive than DC motors for most horsepower rating.
3.12. Suggestions for future work
1- Using other industrial and natural dyes, such as osmium in place of
ruthenium, which extended to more absorption of red and
strengthening the response of the cell to light relative to the
ruthenium.
2- Fabrication of dye solar cell using indium-tin oxide glass
electrodes.
3- The efficiency of the dual-axis tracking system can be increased
even more by placing a mirror or concave lens on top of the cell.
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الخالصة
الصبغية الشمسية والخاليا الشمسية الخاليا مجال في جديدة، تكنولوجيا بوصفها
الخاليا تكنولوجيا لتطوير و تقنيا اقتصاديا مجدية فكرة يعطي (DSSC) نوعية
.الشمسية
,الشاي االسود ,الفراولة تستخدم الخاليا الشمسية الصبغية صبغة طبيعية )الرمان،
ورد ماوي(،التي تم دراستها.اخترت ,شاي كوجرات,كريب فروت ,البرتقال االحمر
تحويل العالية، صبغة الرمان من بين الصبغات الطبيعية لدراستها بسبب كفاءة ال
ايضا بسبب وعالوة على ذلك اعتمد في هذا العمل صبغة الروثنيوم كصبغة صناعية
كفائتها العالية من بين معظم االصباغ الصناعية. المكونات االساسية للخلية الشمسية
الصبغية التي درست بما في ذلك انواع االقطاب،نوع الصبغات، تركيز
ي اوكسيد التيتانيوم اضافة الى عدة محسنات لزيادة االلكترواليت وسمك فيلم ثنائ
و كانت افضل كفاءة تحويل تحققت دون اي اضافة AgNO3كفاءة الخلية وافضلها
( للروثنيوم والرمان على التوالي، بينما مع اضافة نترات 0.55، )%(1.95)%
( و 3.7الفضة في المحلول االلكتروليتي كفاءة التحويل تحسنت واصبحت )%
15ثبت سمك الفيلم على ) ( للروثنيوم والرمان على التوالي.1.2)%
M 10 دم في كل النتائج كانتخ(،وتركيز الصبغة الصناعية المستمترمايكرو-4
×5.
تم اجراء ثالثة انواع من التجارب العملية لتصنيف اداء المنظومة من خالل تتبع
المحورين ، ذوالشمس االول نظام تتبع ثابتة ، ونظام ذوالمحور الواحد، ونظام
وتاثيرهم على مجمل الكفاءة اليومية . لقد بينت الدراسة ان ربح الطاقة بين نظام ذو
، ربح الطاقة بين النظام ذو المحورين 36.4% المحورين والنظام الثابت كانت
وربح الطاقة بين النظام ذو المحور الواحد 22والنظام ذو المحور الواحد كانت%
وهذا يعني ان النظام ذو المحورين هو االفضل واالقل 10.9والنظام الثابت كانت%
-قة الجادريةخسارة بالطاقة من بين االنظمة الثالثة. وقد اجريت الدراسة هذه في منط
N 33.3بغداد التي تقع عند خط عرض 0
E وخط طول0
44.14.
جمهورية العراق
وزارة التعليم العالي والبحث العلمي
جامعة بغداد
كلية العلوم
تحضيرخلية شمسية صبغية مع المتتبع الشمسي
مقدمة إلى رسالة
جامعة بغداد –كلية العلوم
الماجستيرجزء من متطلبات نيل درجة ك
في الفيزياء
من قبل
ضياء بدري علوان
(1991بكالوريوس علوم في الفيزياء )
أشراف
مهند موسى العزاوي. د وسام عبدعلي تويجد..م. أ
ھ1433 م2013
