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GROWTH AND CHARACTERIZATION OF TERNARY CHALCOGENIDE THIN FILMS FOR EFFICIENT SOLAR CELLS AND POSSIBLE INDUSTRIAL APPLICATIONS

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ABSTRACT 
 Ternary thin films of  Iron Copper Sulphide  (FeCuS), Iron Zinc Sulphide (FeZnS), Lead Silver Sulphide (PbAgS), Copper Silver Sulphide (CuAgS) and Copper Zinc Sulphide (CuZnS) were 
grown  using cheap and simple solution  growth technique with EDTA,  TEA and NH3  as 
complexing agents.  The deposited films were characterized using PYE-UNICO-UV-2102 PC 
spectrophotometer,  and  optical microscopy. The results suggest  that some of the films have 
crystal structures. From the spectral analysis of absorbance/transmittance, the optical and solid 
state properties were deduced. The other optical properties so obtained  include the reflectance, 
absorption coefficient, refractive index, extinction coefficient, optical conductivity and thickness, while the solid state properties are dielectric constant and band gap energy. 
 For all  the five categories of thin films grown (i.e. FeCuS, FeZnS, PbAgS, CuAgS and 
CuZnS), absorbance was high in UV and low in VIS-NIR-regions, while the 
transmittance were low in UV-region and high in VIS-NIR-regions. The reflectances 
were high in UV-region and low in the VIS-NIR-regions. 
 For FeCuS, FeZnS, PbAgS, CuAgS and CuZnS, the absorption coefficient ranged from 
0.1x106 m-1 to 1.65x106 m-1, 0.2x106 m-1 to 2.3x106 m-1, 0.5x106 m-1  to 0.9x106 m-1, 0.5x106 m-1 to 1.28x106 m-1 and 0.24x106 m-1 to 1.6x106 m-1, respectively. The real part of 
the refractive index ranged from 1.2 to 2.3, 0.72 to 2.3, 0.1 to 2.3, 1.94 to 2.28 and 1.6 to 
2.3, respectively. The corresponding values of optical conductivity ranged from 
0.03x1014 s-1  to 0.6x1014 s-1, 0.07x1014 s-1, 0.06x1014 s-1  to 0.6x1014 s-1, 0.24x1014 s-1 to 0.6x1014 s-1  and 0.12x1014 s-1  to 0.6x1014 s-1, respectively. The extinction coefficient, 
ranged from 0.005 to 0.038, 0.004 to 0.056, 0.010 to 0.140, 0.025 to 0.064 and 0.008 to 
0.082, respectively. The direct band gap ranged from  2.4eV to2.8eV for FeCuS, 2.9eV 
for FeZnS, 1.5eV to 2.1eV for PbAgS, 2.3eV for CuAgS and 2.2eV to 2.4eV for CuZnS. 
The values of the indirect band gap were in the range 0.6eV to 1.0eV for FeCuS, 1.9eV 
for FeZnS, 0.3eV to 0.8eV for PbAgS, 1.1eV for CuAgS and 0.4eV to 0.9eV for CuZnS. 
The real part of the dielectric constant ranged from 1.4 to 5.2, 0.7 to 5.2, 0.4 to 5.2, 3.8 to 
5.2 and 2.2 to 5.2, respectively, while the corresponding imaginary part of the dielectric 
constant ranged from 0.008 to 0.136, 0.008 to 0.164, 0.010 to 0.390, 0.100 to 0.290 and 
0.030 to 0.360, respectively. 
The range of band gaps,  1.5eV to 2.9eV makes the films suitable for solar cells 
fabrication; this is in agreement with the finding for the film FeCdS. 
TABLE OF CONTENTS 
Title------------------------ii 
Certification--------------------------.iii 
Dedication------------------------iv 
Acknowledgement----------------------.v 
Table of Contents----------------------.vi-xiii 
List of Figures ------------.------------xiv-xvi 
List of Plates------------------------xvii 
List of Slides------------------------.xviii 
List of Set Ups ----------------------xvii 
Abstract------------------------xviii-xix 
CHAPTER ONE 
1.1.0     Introduction------------------------1 
1.2.0    Benefits of Thin Films--------------------.2 
1.3.0    Aim and Objectives of the Study--.--------------.3-4 
CHAPTER TWO   
2.1.0    Optical and Solid State Properties of Thin Film--.----------5 
2.1.1   Transmittance----------------------5-6 
2.1.2   Absorbance----------------------.6 
2.1.3    Reflectance--------------------.7 
2.1.4   Absorption Coefficient--------------------7-8 
2.1.5   Optical Density------------------------.--8-9 
2.2.0    Band gap and Absorption Edge--------.----------9-12 
2.2.1 Absorption Edge  --------------------.----12-13 
2.2.2   Optical Constants--------------------13-14 
2.2.3   Dielectric Constant----------------.------14-15 
2.2.4   Optical Conductivity--------------------15 
2.2.5   Extinction Coefficient Factor----------------.15 
2.3.0    Dispersion----.----------------.15-16 
2.4.0   Photoconductivity----.--------------------16-17 
2.5.0   Luminescence--.----------------17-18 
2.6.0   Electrical Conductivity--.------------------18 
2.7.0 Thermal Conductivity------------------.18-19 
2.8.0    Spectral Selective Surfaces Aspect of Solar Energy Application----------19 
2.8.1 Spectral Selectivity--------------.------.19-20 
2.8.2 Solar Spectral Selective Absorber Surfaces--------------.20-21 
2.8.3 Semiconductor-Metal tandems----------------------21 
2.8.4   Heat Mirrors--------------------21-22 
2.8.5    Dark Mirrors--------------------------22 
2.8.6   Antireflection Coatings--------------------22-23 
2.8.7   Spectral Splitting and Cold Mirror Coatings--------------23 
2.8.8   Radiative Cooling Materials----------------23 
2.8.9   Window Coatings--------------------23-24 
2.9.0   Solar Control Coatings----------------24 
2.9.1    Low Thermal Transmittance----------------24 
2.9.2 Materials for Solar Control and Low Thermal Transmittance------------24-25 
2.9.3   Window Coatings with Dynamic Properties--------------------25-26 
CHAPTER THREE 
3.0     Methods for Thin Film Growth --.--------------.27 
3.1.1     Thermal Evaporation--.----------------27-29 
3.1.2     Epitaxial Growth--.--------------------29-30 
3.1.2.1   Molecular Beam Epitaxial (MBE)----------------.30-32 
3.1.2.2 Liquid Phase Epitaxy ------------------32 
3.1.3   Sputtering--------------------------32-34
3.1.4   Chemical Vapour Deposition (CVD)--------------34-36 
3.1.5    Spray Pyrolysis ------------------.37 
3.1.6     Plasma Technique----------------37-38 
3.1.7    Sol-gel Thin Film Formation------------------.38 
3.1.8   Precursor Sol----------------------38-39 
3.1.8.1   Sol-gel Dip Coating------------------.39 
3.1.8.2   Spin Coating--------------------39-40 
3.1.8.3   Spin Deposition of Halide and Chalcogenide Films--------.40-41 
3.1.9      The Solution Growth Technique------------.----41-44 
3.1.9.1    Thin Film Condensation Formation Mechanism------.----.44-45 
3.1.9.2    Doping by Chemical Bath Deposition--------------.45 
CHAPTER FOUR 
 The Measurement Techniques of Thin Film Characteristics and Materials--------46 
4.1.0    Measurement Techniques of Thin Film Characteristics--------.46 
4.1.1      Film Thickness--------------------.46 
4.1.1.1    Micro balance (gravimetric ) Technique-------------- --47 
4.1.1.2    Optical Technique--------------------.47-48 
4.1.2      Absorbance/Transmittance Measurement----------48 
4.1.3      Method of Determining the Composition of Thin Films--------.--48-49 
4.1.3.1    Atomic Absorption Spectroscopic (AAS) Method------------.49 
4.1.3.2    X-ray Fluorescence------------------.49-50 
4.1.3.3    Infrared Spectroscopy----------------50-51 
4.1.3.4    Qualitative and Quantitative Chemical Analysis (QCA)------52 
4.2.0     Structural Characterization--------------52-53 
4.2.1    Crystallographic Structure and Topography--------------.53-54 
4.2.1    Transmission Electron Microscopy (TEM)----------53-54 
4.2.2    Surface Structure------------------54 
4.2.2.1   LEED Technique----------------------.54 
4.2.2.2    RHEED Technique------------------.54-55 
4.2.2.3    Photo Electron Spectroscopy (PES) --------------.55
4.2.2.4     Optical Microscopy------------------.55-56 
4.3.0    Methodology----------.----------------.57-58 
4.3.1    Iron Copper Sulphide--.------------------58-60 
4.3.2    Optical and Solid State Characterization------------60 
4.3.3    Film Thickness Measurement----------------60-61 
4.4.   Morphological Analysis----------------.------.--61 
CHAPTER FIVE 
5.0   Results and Observations--------------.----62 
5.1   Optical Properties of Iron Copper Sulphide (FeCuS)--------.--.----62 
5.1.1   Absorbance (A) ----------------------62 
5.1.2   Transmittance (T) --------------------.62 
5.1.3    Reflectance (R ) ------------------------62-63 
5.1.4    Absorption Coefficient ( α ) ----------------63 
5.1.5    Refractive Index (n) ------------------63 
5.1.6    Optical Conductivity (σo ) ------------------64 
5.1.7     Extinction Coefficient ( k) ----------------64 
5.2        Solid State Properties----------------.64 
5.2.1     Band gap Energy (Eg) ----------------------64-65 
5.2.2    Dielectric Constant (real part) (ε r ) --------------65 
5.2.3     Dielectric Constant ( imaginary part ) (ε i ) ------------65 
5.3        Optical Properties of Iron Zinc Sulphide (FeZnS)----------65 
5.3.1      Absorbance (A) --------------------.65 
5.3.2       Transmittance (T) ------------------.66 
5.3.3        Reflectance (R) ------------------.66 
5.3.4        Absorption Coefficient (α ) ------------------.66 
5.3.5       Refractive Index (n) ----------------66-67 
5.3.6       Optical Conductivity (σo) ----------------67 
5.3.7      Extinction Coefficient ( k) ----------------.67 
5.4         Solid State Properties----------------67 
5.4.1      Band gap Energy ( Eg)----------------67 
5.4.2      Dielectric Constant (real ) (ε r) ------------------.68 
5.4.3       Dielectric Constant (imaginary part ) (ε i )------------.68 
5.5         Optical Properties of Lead Silver Sulphide ( PbAgS)------------68 
5.5.1       Absorbance (A) .--------------------68 
5.5.2       Transmittance ( T )------------------69 
5.5.3      Reflectance ( R ) --------------------69 
5.5.4       Absorption Coefficient  (α ) ------------------.69 
5.5.5        Refractive Index ( n) ------------------.69-70 
5.5.6      Optical Conductivity (σo ) ------------------.--70 
5.5.7        Extinction Coefficient ( k ) ------------------.70 
5.6           Solid State Properties--------------------71 
5.6.1        Band gap Energy ( Eg ) ------------------71 
5.6.2       Dielectric Constant (real part ) (ε r ) ------------------.71 
5.6.3        Dielectric Constant ( imaginary part ) (ε i )------------------71-72 
5.7            Optical Properties of Copper Silver Sulphide (CuAgS)----------72 
5.7.1         Absorbance (A) ------------------.72 
5.7.2          Transmittance ( T ) --------------------72 
5.7.3            Reflectance ( R ) --------------------.72 
5.7.4           Absorption Coefficient (α ) ----------------73 
5.7.5           Refractive Index (n ) ------------------73 
5.7.6          Optical Conductivity (σo ) ------------------.73 
5.7.7          Extinction Coefficient ( k) ------------------73 
5.8             Solid State Properties ------------------73 
5.8.1          Band gap Enegry ( Eg ) ----------------73-74 
5.8.2          Dielectric Constant (real part ) (ε r) --------------.74 
5.8.3          Dielectric Constant (imaginary part ) (ε i )--------------.74 
5.9            Optical Properties of Copper Zinc Sulphide (CuZnS)----------74 
5.9.1          Absorbance ( A ) ----------------.74 
5.9.2          Transmittance ( T ) --------------------75 
5.9.3          Reflectance ( R ) ------------------.--.75 
5.9.4         Absorption Coefficient (α ) ------------------75-76 
5.9.5          Refractive Index ( n) ------------------.76 
5.9.6          Optical Conductivity (σo) --------------76 
5.9.7          Extinction Coefficient ( k ) ----.------------77 
5.10           Solid State Properties------------------.77 
5.10.1      Band gap Energy ( Eg) ------------------77-78 
5.10.2       Dielectric Constant (real part ) (ε r ) --------------.78 
5.10.3      Dielectric Constant ( imaginary part ) (ε i ) ----------78 
CHAPTER SIX 
6.0 Analysis and Discussion----------------------.80 
6.1 The Spectral Analysis--.------------------80 
6.2 Other Optical Properties------------------80 
6.3 Solid State Properties--------------------.80-81 
CHAPTER SEVEN 
Conclusion and Recommendations ----------------82 
7.0 Conclusion----------------------82-84 
7.1 Recommendation--------------------.85 
REFERENCES------------------------.86-99 
Appendix A. Figures------------------.100-154 
Appendix B  Plates----.----------------155-157 
Appendix C Slides--------------------158-159 
Appendix D Set Ups ------------------160-161 
LIST OF FIGURES 
Figure 5.1 Graph of absorbance (A) versus wavelength for FeCuS thin film------100 
Figure 5.2 Graph of transmittance (T) versus wavelength for FeCuS thin film--------.101 
Figure 5.3 Graph of reflectance (R) versus wavelength for FeCuS thin film------.102 
Figure 5.4 Graph of absorption coefficient versus photon energy for FeCuS thin film------.103 
Figure 5.5 Graph of refractive index versus photon energy for FeCuS thin film------.104 
Figure 5.6 Graph of optical conductivity versus photon energy for FeCuS  thin film--.105 
Figure 5.7 Graph of extinction coefficient versus photon energy for FeCuS thin film--106 
Figure 5.8 Graph of α2
 versus photon energy for FeCuS thin film--.------.107 
Figure 5.9 Graph of α1/2 
versus photon energy for FeCuS thin film------------------108 
Figure 5.10 Graph of dielectric constant (real part) versus photon energy for FeCuS thin film.109 
Figure 5.11 Graph of dielectric constant (imaginary part) versus photon energy for FeCuS thin 
film----------------------------.110 
Figure 5.12 Graph of absorbance (A) versus wavelength for FeZnS thin film------.111 
Figure 5.13 Graph of transmittance (T) versus wavelength for FeZnS thin film----112 
Figure 5.14 Graph of reflectance (R ) versus wavelength for FeZnS thin film------113 
Figure 5.15 Graph of absorption coefficient versus photon energy for FeZnS thin film--114 
Figure 5.16 Graph of refractive index versus photon energy for FeZnS thin film--------115 
Figure 5.17 Graph of optical conductivity versus photon energy for FeZnS thin film----.116 
Figure 5.18 Graph of extinction coefficient versus photon energy for FeZnS thin film--.117 
Figure 5.19 Graph of α2
 versus photon energy for FeZnS thin film----.--------------.118 
Figure 5.20 Graph of α1/2
 versus photon energy for FeZnS thin film--.--------.119 
Figure 5.21 Graph of dielectric constant (real part) versus photon energy for FeZnS thin film.120 
Figure 5.22 Graph of dielectric constant (imaginary part) versus photon energy for FeZnS thin 
film----------------------------.121 
Figure 5.23 Graph of absorbance (A) versus wavelength for PbAgS thin film------.122 
Figure 5.24 Graph of transmittance (T) versus wavelength for PbAgS thin film------------123 
Figure 5.25 Graph of reflectance (R ) versus wavelength for PbAgS thin film------------124 
Figure 5.26 Graph of absorption coefficient versus photon energy for PbAgS thin film--125 
 Figure 5.27 Graph of refractive index versus photon energy for PbAgS thin film------126
Figure 5.28 Graph of optical conductivity versus photon energy for PbAgS thin film--127 
Figure 5.29 Graph of extinction coefficient versus photon energy for PbAgS thin film------128 
Figure 5.30 Graph of α2
 versus photon energy for PbAgS thin film--------.129 
Figure 5.31 Graph of α1/2
 versus photon energy for PbAgS thin film--------130 
Figure 5.32 Graph of dielectric constant (real part) versus photon energy for PbAgS thin film.131 
Figure 5.33 Graph of dielectric constant (imaginary part) versus photon energy for PbAgS thin 
film----------------------------.132 
Figure 5.34 Graph of absorbance (A) versus wavelength for CuAgS thin film------------133 
Figure 5.35 Graph of transmittance (T) versus wavelength for CuAgS thin film--------.134 
Figure 5.36 Graph of reflectance (R ) versus wavelength for CuAgS thin film------------135 
Figure 5.37 Graph of absorption coefficient versus photon energy for CuAgS thin film------.136 
Figure 5.38 Graph of refractive index versus photon energy for CuAgS thin film------.137 
Figure 5.39 Graph of optical conductivity versus photon energy for CuAgS thin film----------138 
Figure 5.40 Graph of extinction coefficient versus photon energy for CuAgS thin film--139 
Figure 5.41 Graph of α2
 versus photon energy for CuAgS thin film----------.140 
Figure 5.42 Graph of α1/2
 versus photon energy for CuAgS thin film--------------------.141 
Figure 5.43 Graph of dielectric constant (real part) versus photon energy for CuAgS thin 
film----------------------------142 
Figure 5.44 Graph of dielectric constant (imaginary part) versus photon energy for CuAgS thin 
film----------------------------143 
Figure 5.45 Graph of absorbance (A) versus wavelength for CuZnS thin film------144 
Figure 5.46 Graph of transmittance versus wavelength for CuZnS thin film--------.145 
Figure 5.47 Graph of reflectance (R ) versus wavelength for CuZnS thin film------------146 
Figure 5.48 Graph of absorption coefficient versus photon energy for CuZnS thin film--147 
Figure 5.49 Graph of refractive index versus photon energy for CuZnS thin film------.148 
Figure 5.50 Graph of optical conductivity versus photon energy for CuZnS thin film----149 
Figure 5.51 Graph of extinction coefficient versus photon energy for CuZnS thin film--150 
Figure 5.52 Graph of α2
 versus photon energy for CuZnS thin film----------.151 
Figure 5.53 Graph of α1/2
 versus photon energy for CuZnS thin film------------------.152 
Figure 5.54 Graph of dielectric constant (real part) versus photon energy for CuZnS thin film.153 
Figure 5.55 Graph of dielectric constant (imaginary part) versus photon energy for CuZnS thin 
film----------------------------.154 
LIST OF PLATES 
Plate 5.1 Photomicrograph of FeCuS------------------155 
Plate 5.2 Photomicrograph of FeZnS------------------156 
Plate 5.3 Photomicrograph of PbAgS------------------156 
Plate 5.4 Photomicrograph of CuAgS------------------157 
Plate 5.5 Photomicrograph of CuZnS------------------157 
LIST OF SLIDES 
Slide 5.1 Picture of FeCuS thin film------------------158 
Slide 5.2 Picture of FeZnS thin film------------------158 
Slide 5.3 Picture of PbAgS thin film------------------159 
Slide 5.4 Picture of CuAgS thin film------------------159 
Slide 5.5 Picture of CuZnS thin film------------------159 
LIST OF SET UPS 
Set Up 3.1 Experimental Set Up ----------------------160 
Set up 4.1 Flow Chart for the Growth Process --.--------.--------161

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