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�’o ) ------------------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�’o) ----------------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�’o ) --------------------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�’o ) ------------------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�’o) --------------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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