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

By

CHIDI CHUKWUEMEKA UHUEGBU MATRIC NO: CU03GP0037

Presented To

Department of Physics

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 
110     Introduction------------------------1 
120    Benefits of Thin Films--------------------2 
130    Aim and Objectives of the Study----------------3-4 
 
CHAPTER TWO   
210    Optical and Solid State Properties of Thin Film------------5 
211   Transmittance----------------------5-6 
212   Absorbance----------------------6 
213    Reflectance--------------------7 
214   Absorption Coefficient--------------------7-8 
215   Optical Density--------------------------8-9 
220    Band gap and Absorption Edge------------------9-12 
221 Absorption Edge  ------------------------12-13 
222   Optical Constants--------------------13-14 
223   Dielectric Constant----------------------14-15 
224   Optical Conductivity--------------------15 
225   Extinction Coefficient Factor----------------15 
230    Dispersion--------------------15-16 
2 40   Photoconductivity------------------------16-17 
250   Luminescence------------------17-18 
260   Electrical Conductivity--------------------18 
270 Thermal Conductivity------------------18-19 
280    Spectral Selective Surfaces Aspect of Solar Energy Application----------19 
281 Spectral Selectivity--------------------19-20 
282 Solar Spectral Selective Absorber Surfaces--------------20-21 
283 Semiconductor-Metal tandems----------------------21 
284   Heat Mirrors--------------------21-22 
285    Dark Mirrors--------------------------22 
286   Antireflection Coatings--------------------22-23 
287   Spectral Splitting and Cold Mirror Coatings--------------23 
288   Radiative Cooling Materials----------------23 
289   Window Coatings--------------------23-24 
290   Solar Control Coatings----------------24 
291    Low Thermal Transmittance----------------24 
292 Materials for Solar Control and Low Thermal Transmittance------------24-25 
293   Window Coatings with Dynamic Properties--------------------25-26 
 
CHAPTER THREE 
30     Methods for Thin Film Growth ----------------27 
311     Thermal Evaporation------------------27-29 
312     Epitaxial Growth----------------------29-30 
3121   Molecular Beam Epitaxial (MBE)----------------30-32 
3122 Liquid Phase Epitaxy ------------------32 
313   Sputtering--------------------------32-34
314   Chemical Vapour Deposition (CVD)--------------34-36 
315    Spray Pyrolysis ------------------37 
316     Plasma Technique----------------37-38 
317    Sol-gel Thin Film Formation------------------38 
318   Precursor Sol----------------------38-39 
3181   Sol-gel Dip Coating------------------39 
3182   Spin Coating--------------------39-40 
3183   Spin Deposition of Halide and Chalcogenide Films--------40-41 
319      The Solution Growth Technique----------------41-44 
3191    Thin Film Condensation Formation Mechanism----------44-45 
3192    Doping by Chemical Bath Deposition--------------45 
 
CHAPTER FOUR 
 The Measurement Techniques of Thin Film Characteristics and Materials--------46 
410    Measurement Techniques of Thin Film Characteristics--------46 
411      Film Thickness--------------------46 
4111    Micro balance (gravimetric ) Technique-------------- --47 
4112    Optical Technique--------------------47-48 
412      Absorbance/Transmittance Measurement----------48 
413      Method of Determining the Composition of Thin Films----------48-49 
4131    Atomic Absorption Spectroscopic (AAS) Method------------49 
4132    X-ray Fluorescence------------------49-50 
4133    Infrared Spectroscopy----------------50-51 
4134    Qualitative and Quantitative Chemical Analysis (QCA)------52 
420     Structural Characterization--------------52-53 
421    Crystallographic Structure and Topography--------------53-54 
421    Transmission Electron Microscopy (TEM)----------53-54 
422    Surface Structure------------------54 
4221   LEED Technique----------------------54 
4222    RHEED Technique------------------54-55 
4223    Photo Electron Spectroscopy (PES) --------------55
4224     Optical Microscopy------------------55-56 
430    Methodology--------------------------57-58 
431    Iron Copper Sulphide--------------------58-60 
432    Optical and Solid State Characterization------------60 
433    Film Thickness Measurement----------------60-61 
44   Morphological Analysis------------------------61 
 
CHAPTER FIVE 
50   Results and Observations------------------62 
51   Optical Properties of Iron Copper Sulphide (FeCuS)--------------62 
511   Absorbance (A) ----------------------62 
512   Transmittance (T) --------------------62 
513    Reflectance (R ) ------------------------62-63 
514    Absorption Coefficient ( α ) ----------------63 
515    Refractive Index (n) ------------------63 
516    Optical Conductivity (Ïバ ) ------------------64 
517     Extinction Coefficient ( k) ----------------64 
52        Solid State Properties----------------64 
521     Band gap Energy (Eg) ----------------------64-65 
522    Dielectric Constant (real part) (ε r ) --------------65 
523     Dielectric Constant ( imaginary part ) (ε i ) ------------65 
53        Optical Properties of Iron Zinc Sulphide (FeZnS)----------65 
531      Absorbance (A) --------------------65 
532       Transmittance (T) ------------------66 
533        Reflectance (R) ------------------66 
534        Absorption Coefficient (α ) ------------------66 
535       Refractive Index (n) ----------------66-67 
536       Optical Conductivity (Ïバ) ----------------67 
537      Extinction Coefficient ( k) ----------------67 
54         Solid State Properties----------------67 
541      Band gap Energy ( Eg)----------------67 
542      Dielectric Constant (real ) (ε r) ------------------68 
543       Dielectric Constant (imaginary part ) (ε i )------------68 
55         Optical Properties of Lead Silver Sulphide ( PbAgS)------------68 
551       Absorbance (A) --------------------68 
552       Transmittance ( T )------------------69 
553      Reflectance ( R ) --------------------69 
554       Absorption Coefficient  (α ) ------------------69 
555        Refractive Index ( n) ------------------69-70 
556      Optical Conductivity (Ïバ ) --------------------70 
557        Extinction Coefficient ( k ) ------------------70 
56           Solid State Properties--------------------71 
561        Band gap Energy ( Eg ) ------------------71 
562       Dielectric Constant (real part ) (ε r ) ------------------71 
563        Dielectric Constant ( imaginary part ) (ε i )------------------71-72 
57            Optical Properties of Copper Silver Sulphide (CuAgS)----------72 
571         Absorbance (A) ------------------72 
572          Transmittance ( T ) --------------------72 
573            Reflectance ( R ) --------------------72 
574           Absorption Coefficient (α ) ----------------73 
575           Refractive Index (n ) ------------------73 
576          Optical Conductivity (Ïバ ) ------------------73 
577          Extinction Coefficient ( k) ------------------73 
58             Solid State Properties ------------------73 
581          Band gap Enegry ( Eg ) ----------------73-74 
582          Dielectric Constant (real part ) (ε r) --------------74 
583          Dielectric Constant (imaginary part ) (ε i )--------------74 
59            Optical Properties of Copper Zinc Sulphide (CuZnS)----------74 
591          Absorbance ( A ) ----------------74 
592          Transmittance ( T ) --------------------75 
593          Reflectance ( R ) --------------------75 
594         Absorption Coefficient (α ) ------------------75-76 
595          Refractive Index ( n) ------------------76 
596          Optical Conductivity (Ïバ) --------------76 
597          Extinction Coefficient ( k ) ----------------77 
510           Solid State Properties------------------77 
5101      Band gap Energy ( Eg) ------------------77-78 
5102       Dielectric Constant (real part ) (ε r ) --------------78 
5103      Dielectric Constant ( imaginary part ) (ε i ) ----------78 
 
CHAPTER SIX 
60 Analysis and Discussion----------------------80 
61 The Spectral Analysis--------------------80 
62 Other Optical Properties------------------80 
63 Solid State Properties--------------------80-81 
 
CHAPTER SEVEN 
Conclusion and Recommendations ----------------82 
70 Conclusion----------------------82-84 
71 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 51 Graph of absorbance (A) versus wavelength for FeCuS thin film------100 
Figure 52 Graph of transmittance (T) versus wavelength for FeCuS thin film--------101 
Figure 53 Graph of reflectance (R) versus wavelength for FeCuS thin film------102 
Figure 54 Graph of absorption coefficient versus photon energy for FeCuS thin film------103 
Figure 55 Graph of refractive index versus photon energy for FeCuS thin film------104 
Figure 56 Graph of optical conductivity versus photon energy for FeCuS  thin film--105 
Figure 57 Graph of extinction coefficient versus photon energy for FeCuS thin film--106 
Figure 58 Graph of α2
 versus photon energy for FeCuS thin film--------107 
Figure 59 Graph of α1/2 
versus photon energy for FeCuS thin film------------------108 
Figure 510 Graph of dielectric constant (real part) versus photon energy for FeCuS thin film109 
Figure 511 Graph of dielectric constant (imaginary part) versus photon energy for FeCuS thin 
film----------------------------110 
Figure 512 Graph of absorbance (A) versus wavelength for FeZnS thin film------111 
Figure 513 Graph of transmittance (T) versus wavelength for FeZnS thin film----112 
Figure 514 Graph of reflectance (R ) versus wavelength for FeZnS thin film------113 
Figure 515 Graph of absorption coefficient versus photon energy for FeZnS thin film--114 
Figure 516 Graph of refractive index versus photon energy for FeZnS thin film--------115 
Figure 517 Graph of optical conductivity versus photon energy for FeZnS thin film----116 
Figure 518 Graph of extinction coefficient versus photon energy for FeZnS thin film--117 
Figure 519 Graph of α2
 versus photon energy for FeZnS thin film------------------118 
Figure 520 Graph of α1/2
 versus photon energy for FeZnS thin film----------119 
Figure 521 Graph of dielectric constant (real part) versus photon energy for FeZnS thin film120 
Figure 522 Graph of dielectric constant (imaginary part) versus photon energy for FeZnS thin 
film----------------------------121 
Figure 523 Graph of absorbance (A) versus wavelength for PbAgS thin film------122 
Figure 524 Graph of transmittance (T) versus wavelength for PbAgS thin film------------123 
Figure 525 Graph of reflectance (R ) versus wavelength for PbAgS thin film------------124 
Figure 526 Graph of absorption coefficient versus photon energy for PbAgS thin film--125 
 Figure 527 Graph of refractive index versus photon energy for PbAgS thin film------126
Figure 528 Graph of optical conductivity versus photon energy for PbAgS thin film--127 
Figure 529 Graph of extinction coefficient versus photon energy for PbAgS thin film------128 
Figure 530 Graph of α2
 versus photon energy for PbAgS thin film--------129 
Figure 531 Graph of α1/2
 versus photon energy for PbAgS thin film--------130 
Figure 532 Graph of dielectric constant (real part) versus photon energy for PbAgS thin film131 
Figure 533 Graph of dielectric constant (imaginary part) versus photon energy for PbAgS thin 
film----------------------------132 
Figure 534 Graph of absorbance (A) versus wavelength for CuAgS thin film------------133 
Figure 535 Graph of transmittance (T) versus wavelength for CuAgS thin film--------134 
Figure 536 Graph of reflectance (R ) versus wavelength for CuAgS thin film------------135 
Figure 537 Graph of absorption coefficient versus photon energy for CuAgS thin film------136 
Figure 538 Graph of refractive index versus photon energy for CuAgS thin film------137 
Figure 539 Graph of optical conductivity versus photon energy for CuAgS thin film----------138 
Figure 540 Graph of extinction coefficient versus photon energy for CuAgS thin film--139 
Figure 541 Graph of α2
 versus photon energy for CuAgS thin film----------140 
Figure 542 Graph of α1/2
 versus photon energy for CuAgS thin film--------------------141 
Figure 543 Graph of dielectric constant (real part) versus photon energy for CuAgS thin 
film----------------------------142 
Figure 544 Graph of dielectric constant (imaginary part) versus photon energy for CuAgS thin 
film----------------------------143 
Figure 545 Graph of absorbance (A) versus wavelength for CuZnS thin film------144 
Figure 546 Graph of transmittance versus wavelength for CuZnS thin film--------145 
Figure 547 Graph of reflectance (R ) versus wavelength for CuZnS thin film------------146 
Figure 548 Graph of absorption coefficient versus photon energy for CuZnS thin film--147 
Figure 549 Graph of refractive index versus photon energy for CuZnS thin film------148 
Figure 550 Graph of optical conductivity versus photon energy for CuZnS thin film----149 
Figure 551 Graph of extinction coefficient versus photon energy for CuZnS thin film--150 
Figure 552 Graph of α2
 versus photon energy for CuZnS thin film----------151 
Figure 553 Graph of α1/2
 versus photon energy for CuZnS thin film------------------152 
Figure 554 Graph of dielectric constant (real part) versus photon energy for CuZnS thin film153 

Figure 555 Graph of dielectric constant (imaginary part) versus photon energy for CuZnS thin 
film----------------------------154 
 
LIST OF PLATES 
Plate 51 Photomicrograph of FeCuS------------------155 
Plate 52 Photomicrograph of FeZnS------------------156 
Plate 53 Photomicrograph of PbAgS------------------156 
Plate 54 Photomicrograph of CuAgS------------------157 
Plate 55 Photomicrograph of CuZnS------------------157 

LIST OF SLIDES 
Slide 51 Picture of FeCuS thin film------------------158 
Slide 52 Picture of FeZnS thin film------------------158 
Slide 53 Picture of PbAgS thin film------------------159 
Slide 54 Picture of CuAgS thin film------------------159 
Slide 55 Picture of CuZnS thin film------------------159 

 
LIST OF SET UPS 
Set Up 31 Experimental Set Up ----------------------160 
Set up 41 Flow Chart for the Growth Process ------------------161

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