TABLE OF CONTENTS Abstract……………………I Acknowledgements…………III Table of Contents………IV List of Figures…………VII List of Tables…………XII List of Schemes………XIII CHAPTER 1 AN INTRODUCTION TO TERNARY I–III–VI2 SEMICONDUCTORS 1-1 CIS-based solar cell 1 1-2 Ternary I–III–VI2 Semiconductors 3 1-3 Methods of Preparation of CuInS2 5 1-3.1 Hydrothermal Method 5 1-3.2 Solvothermal Method 6 1-3.3 Single Source Decomposition 8 1-3.4 Thermolysis Method 9 1-3.5 Hot-injection Method 10 1-4 References 13 CHAPTER 2 HYDROTHERMAL SYNTHESIS OF CuInS2 HOLLOW SPHERES AND CROSS-PLATE-LIKE MICROSTRUCTURES 2-1 Abstract 16 2-2 Introduction 17 2-3 Experimental Section 19 2-3.1 Chemicals 19 2-3.2 Synthesis of CuInS2 Hollow Microspheres by Hydrothermal Method 19 2-3.3 Synthesis of CuInS2 Cross-Plate-Like Microstructures by Hydrothermal Method 20 2-3.4 Instrumentation 20 2-4 Results and Discussion 22 2-4.1 Characterization of CuInS2 Hollow Microspheres and Their Optical Properties 22 2-4.2 Characterization of CuInS2 Cross-Plate-Like Microstructures and Their Optical Properties 28 2-4.3 The Proposed Growth Pathway 33 2-5 Conclusion 38 2-6 References 39 CHAPTER 3 SOLVOTHERMAL CO-SYNTHESIS OF CuInS2 CHALCOPYRITE NANOPARTICLES AND HEXAGONAL WURTZITE CRYSTALS 3-1 Abstract 41 3-2 Introduction 43 3-3 Experimental Section 45 3-3.1 Chemicals 45 3-3.2 Synthesis of CH- and WZ-CuInS2 45 3-3.3 Instrumentation 47 3-4 Results and Discussion 48 3-4.1 Structure Model of CH-CuInS2 and WZ-CuInS¬2 48 3-4.2 Characterization of CH- and WZ-CuInS2 Nanoparticles 52 3-4.3 Importance of Ethylenediamine and the Proposed Growth Mechanism 68 3-5 Conclusion 72 3-6 References 73 LIST OF FIGURES CHAPTER 1 AN INTRODUCTION TO TERNARY I–III–VI2 SEMICONDUCTORS Figure 1.1 A typical configuration for a CIS-based solar cell and a SEM image from the cleaved cross-section of a CIS-based solar cell. 2 Figure 1.2 Band gap distribution of ternary I–III–VI2 semiconductors for use as absorbers. 4 Figure 1.3 Typical solar spectrum and the spectral response of CuGaSe2, CuInS2, and CuInSe2. 4 Figure 1.4 TEM image, SAED pattern, and UV–vis absorption spectrum of CuInS2 nanorods under hydrothermal synthesis. 6 Figure 1.5 SEM images of CuInS2 microspheres by varying sulfur source and solvent under solvothermal synthesis. 7 Figure 1.6 Color transition of CuInS2 nanoparticles from irradiation for 0, 2, 4, 6, 8, 11, 21, 30, 50, 74, 124, and 218 h. 8 Figure 1.7 HRTEM images, XRD pattern, and UV–vis absorption spectra of CuInS2 nanoparticles formed from single source decomposition. 9 Figure 1.8 TEM images of the Cu-In sulfide nanocorns, nanobottles, and nanolarvas at different magnification. 10 Figure 1.9 XRD patterns and UV–vis absorption spectrum of the CuInS2 nanocrystals synthesized by hot-injection method. 12 Figure 1.10 TEM images of Cu1.0In2.0S3.5, Cu1.0In1.0S2.0, Cu2.0In1.0S2.5, and Cu3.0In1.0S3.0 nanocrystals. 12 CHAPTER 2 HYDROTHERMAL SYNTHESIS OF CuInS2 HOLLOW SPHERES AND CROSS-PLATE-LIKE MICROSTRUCTURES Figure 2.1 XRD patterns of the CuInS2 hollow microspheres. 22 Figure 2.2 SEM images of the CuInS2 hollow microspheres. 23 Figure 2.3 TEM images, SAED pattern and high-resolution TEM image of the CuInS2 hollow microspheres. 24 Figure 2.4 EDS spectrum of the CuInS2 hollow microspheres. 25 Figure 2.5 Photographs of the as-prepared CuInS2 product after centifugation and the final CuInS2 product dispersed in ethanol. 26 Figure 2.6 UV□vis absorption spectra of the CuInS2 hollow microspheres and a plot of (αhν)2 vs hν for the determination of the direct band gap value. 27 Figure 2.7 UV□vis absorption spectra of the directly formed CuS plates before solvothermal synthesis. 27 Figure 2.8 XRD patterns of the cross-plate-like CuInS2 microstructures. 28 Figure 2.9 SEM images of the cross-plate-like CuInS2 microstructures. 29 Figure 2.10 TEM images, SAED pattern and high-resolution TEM image of the cross-plate-like CuInS2 microstructures. 30 Figure 2.11 EDS spectrum of the cross-plate-like CuInS2 microstructures. 31 Figure 2.12 UV□vis absorption spectra of the cross-plate-like CuInS2 microstructures and a plot of (αhν)2 vs hν for the determination of the direct band gap value. 32 Figure 2.13 UV□vis absorption spectra of the CuInS2 hollow microspheres and cross-plate-like microstructures. 33 Figure 2.14 XRD patterns of the precipitated CuS before CuInS¬2 synthesis. 34 Figure 2.15 XRD patterns of the CuS precipitate without heating and the CuInS2 hollow microspheres prepared by the hydrothermal synthesis. 35 Figure 2.16 XRD patterns of the CuS precipitate without heating and the cross-plate-like CuInS2 microstructures prepared by hydrothermal synthesis. 35 Figure 2.17 SEM images of the CuS precipitate made without heating and the as-synthesized CuInS2 microstructures grown under hydrothermal synthesis at 180 oC for 12 h. 36 CHAPTER 3 SOLVOTHERMAL CO-SYNTHESIS OF CuInS2 CHALCOPYRITE NANOPARTICLES AND HEXAGONAL WURTZITE CRYSTALS Figure 3.1 Schematic diagrams of the Cu and In atom arrangement and structure conversion. 49 Figure 3.2 Crystal structures of zinc blende, wurtzite, and chalcopyrite CuInS2. 49 Figure 3.3 XRD pattern of chalcopyrite CuInS2 and wurtzite CuInS2. 50 Figure 3.4 XRD patterns of the chalcopyrite and wurtzite CuInS2 mixtures. 53 Figure 3.5 XRD patterns of the CuInS2 nanocrystals synthesized by changing the amount of capping agent oleylamine (OM) added from 2 to 8 ml. 53 Figure 3.6 Comparison of an experimental XRD pattern with several other possible crystal phases. 54 Figure 3.7 SEM images of the as-prepared CuInS2 nanoparticles under the solvothermal condition at 180 oC for 12 h by using ethylenediamine as solvent. 56 Figure 3.8 SEM images of the CuInS2 nanocrystals synthesized by changing the amount of capping agent oleylamine (OM) added from 2 to 8 ml. 56 Figure 3.9 SEM images of the small-sized CuInS2 nanoparticles with morphologies of triangular plates and prisms. 57 Figure 3.10 SEM images of the large-sized CuInS2 nanoparticles with morphologies of regular/distorted hexagonal rods and prisms. 57 Figure 3.11 TEM image, SEM image, SAED pattern and high-resolution TEM image of the CH-CuInS2 nanocrystals. 59 Figure 3.12 TEM image and high-resolution TEM image of a CuInS2 triangular plate. 59 Figure 3.13 TEM images, SAED pattern and high-resolution TEM image of a CuInS2 triangular prism. 60 Figure 3.14 TEM image, SAED patterns and high-resolution TEM image of a regular hexagonal CuInS2 crystal sample made by microtomy. 61 Figure 3.15 Cross-section TEM image of a hexagonal CuInS2 crystal sample made by microtomy. 61 Figure 3.16 EDS spectrum of chalcopyrite and wurtzite CuInS2 nanoparticles. 63 Figure 3.17 Large-area EDS mapping of CuInS2 with the TEM sample made by microtomy. 64 Figure 3.18 Large-area EDS spectrum of CuInS2 with the TEM sample made by microtomy. 64 Figure 3.19 UV–vis spectra of the CuInS2 nanocrystals synthesized at 180 oC for 12 h by adding different volumes of capping agent oleylamine (OM) from 2 to 8 ml and a photograph of the as-prepared CuInS2 products dispersed in ethanol. 66 Figure 3.20 A plot of (αhν)2 vs hν for the determination of the direct band gap value of the mixed CuInS¬2 crystals. 66 Figure 3.21 UV□vis absorption spectra of the CuInS2 nanoparticles synthesized at 180 oC for 12 h by changing the amount oleylamine added from 2 to 8 ml. 67 Figure 3.22 XRD patterns of the as-prepared CuInS2 nanoparticles by using oleylamine as solvent under solvothermal treatment at 180 oC for 12 h. 70 Figure 3.23 SEM images of the as-prepared CuInS2 nanoparticles by using oleylamine as solvent under solvothermal treatment at 180 oC for 12 h. 70 LIST OF TABLES CHAPTER 2 HYDROTHERMAL SYNTHESIS OF CuInS2 HOLLOW SPHERES AND CROSS-PLATE-LIKE MICROSTRUCTURES Table 2.1 Elemental composition of the CuInS2 hollow microspheres. 25 Table 2.2 Elemental composition of the cross-plate-like CuInS2 microstructures. 31 CHAPTER 3 SOLVOTHERMAL CO-SYNTHESIS OF CuInS2 CHALCOPYRITE NANOPARTICLES AND HEXAGONAL WURTZITE CRYSTALS Table 3.1 Crystal data of chalcopyrite CuInS2 and wurtzite CuInS2. 50 Table 3.2 Diffraction angles, miller indices, and d-spacings of chalcopyrite and wurtzite CuInS2. 51 Table 3.3 Elemental composition of the chalcopyrite CuInS2 nanoparticles. 63 Table 3.4 Elemental composition of a haxagonal wurtzite CuInS2 crystal. 63 Table 3.5 Elemental composition of CuInS2 with the TEM sample made by microtomy. 64 LIST OF SCHEMES CHAPTER 2 HYDROTHERMAL SYNTHESIS OF CuInS2 HOLLOW SPHERES AND CROSS-PLATE-LIKE MICROSTRUCTURES Scheme 2.1 Synthetic route for preparing CuInS2 microstructures via a hydrothermal method. 21 Scheme 2.2 Proposed mechanism and morphology evolution of the CuInS2 microstructures formed by using the hydrothermal synthesis approach. 36 CHAPTER 3 SOLVOTHERMAL CO-SYNTHESIS OF CuInS2 CHALCOPYRITE NANOPARTICLES AND HEXAGONAL WURTZITE CRYSTALS Scheme 3.1 Synthetic route for preparing mixed CH- and WZ-CuInS2 nanoparticles. 46 Scheme 3.2 Proposed mechanism and morphology evolution of chalcopyrite and wurtzite CuInS2 nanoparticles under the solvothermal condition. 71