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  • Electrodeposition and

    Characterisation of

    Semiconductor Materials

    Charles Yianni Cummings

    A thesis submitted for the degree of Doctor of Philosophy

    University of Bath

    Department of Chemistry

    May 2012

    Copyright

    Attention is drawn to the fact that copyright of this thesis rests with its author. A copy of this thesis has been

    supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the

    author and they must not copy it or use the material from it except as permitted by law or with the consent of the

    author.

    This thesis maybe available for consultation within the University Library and maybe photocopied or lent to

    other libraries for the purposes of consultation.

    ________________

    Charles Yianni Cummings

  • Electrodeposition and Characterisation of Semiconductor Materials

    ii

    Table of Contents ii

    Abstract vii

    Acknowledgments ix

    1. Introduction 1

    1.1. Introduction to Photovoltaics 2

    1.1.1. Photovoltaics commodity or necessity 2

    1.1.2. History of photovoltaics 4

    1.1.3. Types of solar cell 5

    1.1.4. 1st Generation photovoltaic devices: Silicon based solar

    cells

    6

    1.1.5. 2nd Generation photovoltaic devices: Thin film based

    solar cells.

    6

    1.1.6. Introduction to photo-electrochemical systems 7

    1.1.7. Introduction to the topics of the thesis 8

    1.2. Photovoltaic Device Physics 9

    1.2.1. Semiconductors 9

    1.2.2. Electrons and holes 11

    1.2.3. Semiconductor type and doping 13

    1.3. Semiconductor Photo-Electrochemistry 15

    1.3.1. Semiconductor electrochemistry 15

    1.3.2. Photo-effects of semiconductor electrodes 20

    1.3.3. Reported photo-electrochemical effects at the

    semiconductor | electrolyte interface

    22

    1.4. Introduction to the topics of the thesis 23

    1.5. References 25

    2. CuInSe2 (CISe) via Electrodeposition onto Mo/MoSe2 Film Electrodes

    27

    2.1. Abstract 28

    2.2. Introduction 29

    2.2.1. Introduction to CISe based solar cells 29

    2.2.2. Introduction to MoSe2 32

    2.3. Experimental Methods 34

    2.3.1. Reagents 34

    2.3.2. Instrumentation 34

    2.3.3. Selenisation of molybdenum films 35

    2.3.4. Electrodeposition of InCu films and CISe formation 35

  • Electrodeposition and Characterisation of Semiconductor Materials

    iii

    2.3.5. Photo-electrochemical characterisation of CISe films 36

    2.4. Results and Discussion 37

    2.4.1. Voltammetric characterisation of Mo/MoSe2 electrodes:

    Ru(NH3)6 3+

    reduction and Fe-(CpMeOH)2 oxidation

    37

    2.4.2. Voltammetric characterisation of Mo/MoSe2 electrodes:

    Cu 2+

    electrodeposition

    40

    2.4.3. Voltammetric characterisation of Mo/MoSe2 electrodes:

    In 3+

    electrodeposition

    42

    2.4.4. Voltammetric characterisation of Mo/MoSe2 electrodes:

    CuIn alloy electrodeposition and photo-electrochemistry

    43

    2.5. Conclusions 47

    2.6. References 48

    3. Rocking Disc Electrodeposition of Copper Films on Mo/MoSe2 Photovoltaic Substrates

    51

    3.1. Abstract 52

    3.2. Introduction 53

    3.2.1. Introduction to uniformity issues in electrodeposition 53

    3.2.2. The rotating disc electrode 55

    3.2.3. The rocking disc electrode 57

    3.3. Experimental Methods 58

    3.3.1. Reagents 58

    3.3.2. Instrumentation 58

    3.3.3. Design and operation of the rocking disc electrode 59

    3.3.4. Formation and characterisation of Mo/MoSe2 electrodes 60

    3.3.5. Cu plating procedure 62

    3.4. Results and Discussion 63

    3.4.1. Voltammetric characterisation of the rocking disc

    electrode: Ru(NH3)6 3+

    reduction at the calibration

    electrode

    63

    3.4.2. Voltammetric characterisation of the rocking disc

    electrode: Cu reduction on Mo/MoSe2 electrodes

    69

    3.5. Conclusions 74

    3.6. References 75

    4. Rocking Disc Electrodeposition of CuIn Alloys and Subsequent Selenisation for Large Area CISe Solar Cells

    77

    4.1. Abstract 78

    4.2. Introduction 79

  • Electrodeposition and Characterisation of Semiconductor Materials

    iv

    4.2.1. Introduction to semiconductor formation 79

    4.2.2. Electrodeposition of binary systems 79

    4.2.3. Introduction to wet chemical semiconductor processing 80

    4.2.4. Etches used for CISe films 82

    4.3. Experimental Methods 84

    4.3.1. Reagents 84

    4.3.2. Instrumentation 84

    4.3.3. Composition of the CuIn plating solution 85

    4.3.4. Selenisation of the CuIn films and re-anneal treatments 85

    4.3.5. Photo-electrochemical mapping of large area CISe films

    (ca. 12.1 cm 2 )

    86

    4.3.6. Etching and photo-electrochemistry of small CISe films

    (ca. 1 cm 2 )

    87

    4.4. Results and Discussion 88

    4.4.1. Photoactive CISe by rocking disc electrodeposition:

    voltammetric investigation of CuIn plating

    88

    4.4.2. Photoactive CISe by rocking disc electrodeposition:

    uniform electrodeposition onto Mo

    90

    4.4.3. Photoactive CISe by rocking disc electrodeposition:

    selenisation to form CISe

    93

    4.4.4. Photoactive CISe by rocking disc electrodeposition: effect

    of diluted KCN and re-annealed treatments

    95

    4.4.5. Photoactive CISe by rocking disc electrodeposition:

    Effect of HClO and KCN etchants

    97

    4.5. Conclusion 102

    4.6. References 103

    5. Surface Spectro-Electrochemistry of Mesoporous Fe2O3 for use in Water Splitting

    105

    5.1. Abstract 106

    5.2. Introduction 107

    5.2.1. Introduction to the photo-electrochemical splitting of

    water

    107

    5.2.2. The study of iron oxide photoanodes 110

    5.2.3. Theoretical basis for potential modulated transmission

    spectroscopy

    112

    5.2.4. Total impedance of mesoporous and spectroscopic active

    systems

    114

    5.3. Experimental Details 118

  • Electrodeposition and Characterisation of Semiconductor Materials

    v

    5.3.1. Reagents 118

    5.3.2. Instrumentation 118

    5.3.3. Potential modulated transmission measurements 118

    5.3.4. Light induced absorption spectroscopy 120

    5.3.5. Formation of Fe2O3 films of FTO coated glass substrates 120

    5.4. Results and discussion 121

    5.4.1. Mesoporous Fe2O3 films in 0.1 M NaOH: dark cyclic

    voltammetry

    121

    5.4.2. Mesoporous Fe2O3 films in 0.1 M NaOH: potential

    modulated transmittance spectrometry

    121

    5.4.3. Mesoporous Fe2O3 films in 0.1 M NaOH:. impedance

    spectroscopy

    125

    5.4.4. Mesoporous Fe2O3 films in 0.1 M NaOH: frequency

    response

    128

    5.4.5. Mesoporous Fe2O3 films in 0.1 M NaOH: light induced

    spectroscopy

    129

    5.5. Conclusion 133

    5.6. References 134

    6. Electron Hopping Rate Measurements in ITO Junctions: Charge Diffusion in a Ruthenium-Bipyridyl-Phosphonate – TiO2 Film

    136

    6.1. Abstract 137

    6.2. Introduction 138

    6.2.1. Nanotechnology and dye sensitised solar cells 138

    6.2.2. Introduction to focused ion beam technologies 140

    6.2.3. Introduction to the ruthenium based electrochemistry 142

    6.3. Experimental Details 144

    6.3.1. Reagents 144

    6.3.2. Instrumentation 144

    6.3.3. Layer-by-layer assembly of Ru2-TiO2 films 144

    6.3.4. Preparation for junction electrode experiments 145

    6.4. Results and Discussion 146

    6.4.1. Voltammeric characterisation of layer-by-layer films of

    Ru2 - TiO2: formation and characterisation

    146

    6.4.2. Voltammeric characterisation of layer-by-layer films of

    Ru2 - TiO2: ITO film electrodes

    147

    6.4.3. Voltammeric characterisation of layer-by-layer films of

    Ru2 - TiO2: ITO junction electrodes

    150

  • Electrodeposition and Characterisation of Semiconductor Materials

    vi

    6.5. Conclusions 152

    6.6. References 153

    7. Conclusion and Outlook 155

    7.1. Conclusion 156

    7.2. Further Work 157

    Appendix 159

    A. Theoretical Electrochemical Basis 160

    A.1. Introduction to electrochemistry 160

    A.2. Chemical equilibria and chemical potential: 161

    A.3. Electrostatic potential of particles 164

    A.4. Electric potential at interfaces 165

    A.5. Electrochemical potential 167

    A.6. The Nernst equation 170

    A.7. Diffusion 171

    A.8. Adsorption processes 175

    A.9. Electrode dynamics 175

    A.10. Non-faradic or capacitive currents 177

    A.11. Faradic currents and cyclic voltammetry 180

    A.12. Immobilised systems 185

    A.13. Sweep rate for diffusion and immobilised systems 188

    A.14. Electrodeposition 190

    A.15. Electrochemical impedance spectroscopy 192

  • Electrodeposition and Characterisation of Semiconductor Mate

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