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  • Islamic University of Gaza

    Deanery of Higher Studies

    Faculty of Science

    Department of Physics

    Dye Sensitized Solar Cells Based on Natural Dyes

    Extracted from Plant Roots

    By

    Islam Mahmoud Radwan

    B.Sc. in Physics, Islamic University of Gaza

    Supervisors

    Dr. Taher M. El-Agez Dr. Sofyan A. Taya

    Associate Professor of Physics Associate Professor of Physics

    Submitted to the Faculty of Science as a Partial Fulfillment of the Master Degree of

    Science (M. Sc.) in Physics

    1436 2015

  • ii

    Dedication

    I dedicate my thesis to:

    The sake of Allah, my greatest Creator,

    My beloved messenger, Mohammed (Peace be upon him),

    My beautiful homeland, Palestine,

    Our martyrs and prisoners who sacrificed their lives for the sake of Palestine,

    The Islamic University of Gaza (IUG),

    My loving parents who kept supporting me throughout the process,

    My dearest wife and son who stood by me in my difficult time,

    My dear brothers and sisters,

    My friends who encouraged and supported me.

    Islam M. Radwan

  • iii

    Acknowledgment

    In the Name of Allah, the Most Merciful, the Most compassionate, I must acknowledge my

    thanks to the greatest Allah, for His bless and guidance. I owe my university, IUG, the

    success of my work.

    I am very grateful to all people who never hesitated to give me a hand to complete my

    research, particularly Dr. Sofyan Taya and Dr. Taher El-Agez.

    I would like to thank the staff members in Physics department at IUG for their continued

    support. I would like to express my special thanks to my dear friends who helped me pursue

    my thesis.

  • iv

    Abstract

    The objectives of this thesis are to prepare dye sensitized solar cells (DSSCs) using titanium

    dioxide (TiO2) as a semiconducting layer based on six natural dyes extracted from plant roots

    which are purple carrot, carrot, beet, curcuma, kale and radish as sensitizers. Among the

    previous dyes, purple carrot showed the best efficiency.

    The performance of DSSCs sensitized by purple carrot is improved through: adjustment of

    the solution extraction temperature, studying the effect of pH on the extract solution, and

    finally the influence of pre and post-treatments of the fluorinated tin oxide (FTO) glass

    substrate and the TiO2 film using hydrochloric (HCl), phosphoric (H3PO4), and nitric (HNO3)

    acids.

    The results showed that an extracting temperature of 50C could be used as an optimal value.

    The treatment of the dye solutions with acetic acid resulted in better performance in

    comparison with the hydrochloric acid treatment. The pre-treatment of the FTO with H3PO4

    and the post-treatment of TiO2 with HNO3 resulted in improved efficiencies of 130% and

    250% respectively for the DSSCs sensitized by purple carrot.

  • v

    Abstract in Arabic

    6

    . .

    :

    ( (HCl 2TiO FTO

    (4PO3H) 3) (HNO.

    . 05

    )(

    .

    . %135

    .% 005 2TiO

  • vi

    CONTENTS

    Dedication .......................................................................................................................... ii

    Acknowledgment .............................................................................................................. iii

    Abstract ............................................................................................................................. iv

    Abstract in Arabic............................................................................................................. v

    List of Figures .................................................................................................................... x

    List of Tables .................................................................................................................. xiv

    List of Abbreviations ..................................................................................................... xvi

    1. INTRODUCTION ..................................................................................................... 1

    1.1. Global Energy Demand .................................................................................. 1

    1.2. Harvesting the Sun's Energy.......................................................................... 1

    1.3. Solar Radiation and Air Mass ....................................................................... 2

    1.4. Generations of Photovoltaic Solar Cells ....................................................... 3

    1.4.1. First Generation of Photovoltaics (1970s)..................................................... 4

    1.4.2. Second Generation of Photovoltaics (1980s)................................................. 5

    1.4.3. Third Generation of Photovoltaics (1990s) ................................................... 6

    1.4.3.1 Concentrating Photovoltaic Technology ....................................................... 6

    1.4.3.2 Dye Sensitized Solar Cells (DSSC) ................................................................ 6

    1.4.3.3 Organic Solar Cells ......................................................................................... 7

    1.4.3.4 Novel and Emerging Solar Cell Concepts ..................................................... 8

    1.5 Photovoltaic Processes in a Solar Cell ........................................................... 8

    1.6 State of the Art .............................................................................................. 10

    1.7 Gaza and Electricity Crisis .......................................................................... 11

    1.8 Research Aims ............................................................................................... 12

    1.9 Thesis Layout ................................................................................................ 13

  • vii

    2. DYE SENSITIZED SOLAR CELLS ..................................................................... 14

    2.1 Introduction ................................................................................................... 14

    2.2 The Architecture of a DSSC ......................................................................... 14

    2.3 Key Components of a Dye Sensitized Solar Cell ........................................ 15

    2.3.1 Substrates ....................................................................................................... 15

    2.3.2 TiO2 Semiconductor as the Photoelectrode ................................................. 16

    2.3.3 Dye as the Photosensitizer ............................................................................. 18

    2.3.4 The Electrolyte Redox ................................................................................... 19

    2.3.5 The Counter Electrode .................................................................................. 20

    2.4 Operating Principles of Dye Sensitized Solar Cells ................................... 21

    2.4.1 Light Absorption and Electron Injection ..................................................... 22

    2.4.2 Electron Transport and Collection ............................................................... 23

    2.4.3 Dye Regeneration........................................................................................... 23

    2.5 Key Efficiency Parameters of DSSC ........................................................... 24

    2.5.1 Incident Photon to Current Conversion Efficiency (IPCE) ........................ 24

    2.5.2 Short Circuit Photocurrent Density (Jsc) ..................................................... 25

    2.5.3 Open Circuit Photovoltage (Voc) ................................................................... 25

    2.5.4 Optimum Voltage (Vm) .................................................................................. 26

    2.5.5 Optimum Current (Im) .................................................................................. 26

    2.5.6 Output Power (Pout) ....................................................................................... 26

    2.5.7 Fill Factor (FF) .............................................................................................. 26

    2.5.8 Solar Energy to Electricity Conversion Efficiency () ................................ 27

    2.5.9 Standard Measurements ............................................................................... 27

    2.6 Electrochemical Impedance Spectroscopy ................................................. 28

    2.7 Nyquist Plot .................................................................................................... 30

    2.8 Bode Plot ........................................................................................................ 30

  • viii

    2.9 Equivalent Circuits ....................................................................................... 31

    3. RESEARCH TECHNIQUES ................................................................................. 33

    3.1 Experimental Techniques ............................................................................. 33

    3.1.1 UV-Vis Spectroscopy .................................................................................... 33

    3.1.2 Solar Cell I-V Measurement