Dissertationen online der Freien Universität Berlin


Spray ILGAR growth and Raman spectroscopy of CuInS2 thin films
Camus, Christian

HaupttitelSpray ILGAR growth and Raman spectroscopy of CuInS2 thin films
TitelvarianteSpray ILGAR Wachstum und Raman-Spektroskopie an CuInS2 Dünnschichten
AutorCamus, Christian
Geburtsort: Frankfurt am Main
GutachterLux-Steiner, Prof. Dr. M. Ch.
weitere GutachterBrewer, Prof. W. D., PhD
Freie SchlagwörterChalcopyrite, ILGAR, Raman, Phononen, Confinement, Diffusion, Thin Film, Growth
DDC530 Physik
ZusammenfassungThis thesis focuses on the development of a Spray ILGAR process for the vacuum-free deposition of CuInS2 thin films for photovoltaic applications. The CuInS2 thin films were deposited by the cyclic repetition of spraying of a precursor layer of In2O3 and Cu and its subsequent sulfurization by H2S. The sulfurization of In2O3 was observed to be incomplete. Therefore, the films were annealed in an Ar/H2S atmosphere in order to complete the sulfurization.
The characterization of the Spray ILGAR CuInS2 films revealed that they consist of two differently crystallized regions: The lower part of the films at the substrate was composed of numerous thin CuInS2 layers separated by carbon-containing interlayers (layered bottom layer), whilst the upper part was formed by a well-crystallized top layer with grain sizes of 100-1000 nm.
The first part of the thesis focused on the investigation of the growth mechanism. Therefore, the phases formed at each step of the Spray ILGAR process were characterized separately by XPS, XAS, XRF, ERDA, TEM and SEM. In combination thes results of these measurements allowed the deduction of a complete growth model. The existence of the carbon-containing interlayers could thereby be explained by the incorporation of organic groups originating from the Cu precursor compund used in the spraying solution. The formation of the well-crystallized top layer could be explained by the diffusion of In into Cu(2-x)S agglomerates on the film surface, which have been formed previously due to the fast diffusion of Cu in Cu(2-x)S and CuInS2.
The degree of crystalline order and phase purity in the CuInS2 thin films were investigated by means of Micro-Raman spectroscopy in the second part of this thesis. These measurements revealed that the layered bottom layer contained two phases of CuInS2; the chalcopyrite and the cation-ordered phase of type CuAu I. In contrast, the well-crystallized top layer solely contained chalcopyrite-type CuInS2.
Raman spectroscopy also revealed that the carbon-containing interlayers in the CuInS2 films consisted of a blend of (nanocrystalline) graphite and amorphous carbon.
Additionally, the asymmetric peak shape of the Raman A1 mode of chalcopyrite-type CuInS2 thin films was analyzed. The peak shape was simulated numerically according to the phonon confinement model. These simulations yielded values for the average distances between crystallographic defects in the probed material, which confine phonons into nanocrystalline domains. Complimentary TEM studies suggested that the confinement may be caused by planar defects in the films.
Finally, Spray ILGAR CuInS2 thin films could be applied as absorber layers in thin-film solar cells, reaching efficiencies of up to 4.1 %.
Inhaltsverzeichnis001 Contents
005 1.: Introduction
009 2.: Material Properties and Deposition Methods
009 2.1.: Material Properties
009 2.1.1.: Structural Properties of CuInS2
011 2.1.2.: Phase Relations and Defects
013 2.1.3.: Secondary Phases
015 2.2.: Deposition Methods for Chalcopyrite Thin Films
017 2.3.: The “Ion Layer Gas Reaction”
025 3.: Process Design
026 3.1.: Deposition of Spray ILGAR Copper Sulfide Thin Films
026 3.1.1.: Choice of a Copper-Containing Precursor Compound
028 3.1.2.: Choice of a Solvent
030 3.1.3.: Modifications of the Spray ILGAR Setup
033 3.1.4.: Characterization of Spray ILGAR Copper Sulfide Thin Films
035 3.2.: Deposition of Spray ILGAR Indium Oxide Sulfide Thin Films
036 3.3.: The Spray ILGAR Deposition Process for CuInS2 Thin Films
036 3.3.1.: Sequential Deposition of Spray ILGAR CuInS2 Thin Films
040 3.3.2.: Simultaneous Deposition of Spray ILGAR CuInS2 Thin Films
045 3.4.: Summary of Chapter 3
047 4.: Growth Mechanism Analysis
048 4.1.: Chemical Reactions and Phase Transformations in Solids
051 4.2.: Precursor Layer Deposition
051 4.2.1.: Deposition of a Copper-Containing Precursor Compound
055 4.2.2.: Deposition of an Indium-Containing Precursor Compound
057 4.2.3.: Interactions between the Deposition Processes of Copper and In2O3
062 4.3.: Precursor Layer Sulfurization
068 4.4.: Composition and Morphology of Spray ILGAR CuInS2 Thin Films
069 4.4.1.: Compositional Analysis of Spray ILGAR CuInS2 Thin Films
073 4.4.2.: Correlation of Composition and Morphology
074 Distribution of Cu(2-x)S in As-Deposited Spray ILGAR CuInS2 Thin Films
074 Distribution of In2O3 in As-Deposited Spray ILGAR CuInS2 Thin Films
075 Surface Composition of Spray ILGAR CuInS2 Thin Films
076 Carbon in the Layered Bottom Layer of Spray ILGAR CuInS2 Thin Films
077 Formation of the Well-Crystallized Top Layer in Spray ILGAR CuInS2 Thin Films
079 4.5.: Growth Mechanism of Spray ILGAR CuInS2 Thin Films
079 4.5.1.: Formation of As-Deposited Spray ILGAR CuInS2 Thin Films
081 4.5.2.: Diffusion Processes during the Post-Deposition H2S annealing
086 4.6.: Consequences of the Growth Model for the Spray ILGAR Process
087 4.7.: Summary of Chapter 4
089 5.: Raman Spectroscopy of Spray ILGAR CuInS2 Thin Films
090 5.1.: Introduction to Raman Spectroscopy
090 5.1.1.: Lattice Vibrations in Solids
091 5.1.2.: Inelastic Light Scattering by Phonons in Solids
093 5.1.3.: Vibrational Properties of CuInS2
095 5.1.4.: Experimental Setup
097 5.2.: CuAu-Order and Secondary Phases in Spray ILGAR CuInS2 Thin Films
097 5.2.1.: Influences of Secondary Phases on the CuInS2 Raman Spectrum
100 5.2.2.: Raman Spectroscopy of As-Deposited Spray ILGAR CuInS2 Thin Films
106 5.2.3.: Raman Spectroscopy of H2S treated Spray ILGAR CuInS2 Thin Films
112 5.3.: Carbon in Spray ILGAR CuInS2 Thin Films
117 5.4.: Origin of the Spectral Shape of the Chalcopyrite A1 Mode in CuInS2 Thin Films
118 5.4.1.: Influence of Strain on the A1 Mode of CuInS2
119 5.4.2.: Asymmetry of the A1 Mode in CuInS2 Thin Films
121 5.4.3.: The Phonon Confinement Model
123 5.4.4.: Modifications of the Phonon Confinement Model Formalism
126 5.4.5.: Modeling of Raman Spectra of the A1 Mode of CuInS2
132 5.4.6.: Correlation of Crystal Structure and Phonon Confinement
134 5.5.: Summary of Chapter 5
135 6.: Effect of the Absorber Morphology on the Solar Cell Performance
135 6.1.: Solar Cells Based on CuInS2
140 6.2.: Spray ILGAR CuInS2/CdS/i-ZnO/n+-ZnO Heterojunctions
151 7.: Summary and Outlook
155 Appendix
155 I: Summary of Preparation Parameters
155 I.i: Preparation of the Spraying Solution
156 I.ii: Preparation Parameters of the Spray ILGAR Process
157 I.iii: Parameters of the Post-Deposition Treatments
159 II: List of Abbreviations
160 III: List of Symbols
162 IV: Phase Diagrams
165 V: Diffusion Constants
167 VI: Mathcad Fitting Routine
172 VII: Analysis Techniques
172 VII.i: X-ray Photoelectron and Auger Spectroscopy
173 VII.ii: X-ray Diffraction
174 VII.iii: X-ray Fluorescence and Energy Dispersive X-ray Spectroscopy
176 VII.iv: Scanning and Transmission Electron Microscopy
176 VII.v: Elastic Recoil Detection Analysis
178 IIX: Input Parameters for QE-Simulations
179 IX: AM 1.5 Solar Spectrum
180 X: Thermodynamic Data of Relevant Compounds
181 XI: Vibrations of the A1, B21LO and E1LO Modes of Chalcopyrite-Type CuInS2
182 XII: Publications
185 Bibliography
199 Acknowledgements
203 Statement
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Seitenzahl200 S.
Fachbereich/EinrichtungFB Physik
Rechte Nutzungsbedingungen
Tag der Disputation22.10.2008
Erstellt am10.11.2008 - 11:27:36
Letzte Änderung19.02.2010 - 10:05:49
Statische URLhttp://www.diss.fu-berlin.de/diss/receive/FUDISS_thesis_000000006014