Electrical and optical characterization of CdxZn1-xS and PbS thin films for photovoltaic applications

Thin film characterization for solar cells

Masterarbeit , 2011 , 112 Seiten , Note: A

Physik - Angewandte Physik

In this research an n-type CdxZn1-xS and p-type PbS thin films were optimised for solar cell applications employing chemical bath deposition technique. The thin films were prepared using thiourea and nitrates of cadmium, zinc and lead. Deposition of optimised CdxZn1-xS was done by CBD at 820 C and in alkaline conditions while that of PbS was done at room temperature and both films at normal atmospheric pressure utilizing aqueous conditions. This study concentrated on optimising optical and electrical characterization of the films. Optical constant suitable for photovoltaic applications were sort for and for this purpose a UV VIS IR spectrophotometer 3700 DUV was utilised while the electrical properties were investigated using a four point probe connected to a Keithley 2400 source meter interfaced with computer. The optical band gap of the as deposited CdxZn1-xS films varied from 2.47eV (x =0.6) to 2.72 eV (x =1.0), and transmittance above 79% in the VIS - NIR region for the concentration range of x = 0.6 to 1.0, that is, the band gap increased with increasing Zn concentration of the alloy and Cd06Zn0.4S sample showed the widest band gap. It was obtained that the presence of zinc increased optical band gap. The average extinction coefficients for the as deposited CdxZn1-xS samples were very low revealing that they absorb very little radiation hence a good window layer material. As measured by the four point probe connected to a Keithley 2400 source meter, electrical resistivity increased with increase in Zn in the bath in CdxZn1-xS and a resistivity range of 9.5×101 – 1.22× 102 Ω-cm was obtained. These properties are appropriate for window layers used for photovoltaic cell applications. PbS thin films had a band gap of 0.89 eV and a transmittance of below 55% appropriate for absorber layers of photovoltaic cells and a resistivity range of 6.78 × 103 to 1.26 × 104 Ω-cm. The fabricated photovoltaic cell had a short circuit current, Isc = 0.031 A, open voltage, Voc = 0.37V, efficiency, η = 0.9% and a fill factor, FF = 0.66 implying that the two materials are appropriate for photovoltaic applications especially in the VIS and IR light spectrum.

Inhaltsverzeichnis (Table of Contents)

• DEDICATION
• ACKNOWLEDGMENT
• DECLARATION
• TABLE OF CONTENT
• LIST OF TABLES
• LIST OF FIGURES
• ABBREVIATIONS AND ACRONYMS
• ABSTRACT
• CHAPTER ONE
  • INTRODUCTION
  • 1.1 Background of the study
  • 1.2 Problem statement for the study
  • 1.3 Objectives
    • 1.3.1 Main objective
    • 1.3.2 Specific objectives
  • 1.4 Rationale of the study
  • 1.5 Structure of thesis
  • CHAPTER TWO
    • LITERATURE REVIEW
    • 2.1 Survey on Cadmium Sulphide (CdS) thin films
      • 2.1.1 Electrical properties of CdS thin films
      • 2.1.2 Optical properties of CdS thin films
    • 2.2 Survey on lead sulphide (PbS) thin films
    • 2.3 CdS-PbS based photovoltaic Cells
    • CHAPTER THREE
      • THEORETICAL CONSIDERATIONS
      • 3.1 Semiconductor thin films
      • 3.2 Energy bands in solids
      • 3.3 Energy band structure in semiconductors
        • 3.3.1 Intrinsic semiconductors
        • 3.3.2 Extrinsic Semiconductors
      • 3.4 Semiconductor transport carriers
      • 3.5 Optical phenomena in thin films
        • 3.5.1 Photoconductivity in thin films
      • 3.6 Thin film applications
        • 3.6.1 The p-n junction
        • 3.6.2 Photovoltaic cells
          • 3.6.2.2 Photovoltaic cell operation
        • 3.7 Strengths and limitation of thin films for photovoltaic cells
        • 3.8 Thin film deposition techniques
          • 3.8.1 Chemical Deposition Techniques
      • CHAPTER FOUR
        • EXPERIMENTAL PROCEDURES
        • 4.1 Materials and reagents
        • 4.2 Preparation of CdS thin films
        • 4.3 Preparation of PbS thin films
        • 4.4 Characterization techniques
        • 4.4.1 X-ray Diffraction (XRD)
        • 4.4.2 Scanning Electron Microscopy (SEM)
        • 4.4.3 Energy Dispersive X-ray Spectroscopy (EDX)
        • 4.4.4 UV-Vis Spectroscopy
        • 4.4.5 Four-point probe method
        • 4.5 Fabrication of CdS-PbS heterojunction photovoltaic cells
      • CHAPTER FIVE
        • RESULTS AND DISCUSSION
        • 5.1 Structural characterization of CdS thin films
        • 5.2 Morphological characterization of CdS thin films
        • 5.3 Compositional characterization of CdS thin films
        • 5.4 Optical characterization of CdS thin films
        • 5.5 Electrical characterization of CdS thin films
        • 5.6 Structural characterization of PbS thin films
        • 5.7 Morphological characterization of PbS thin films
        • 5.8 Compositional characterization of PbS thin films
        • 5.9 Optical characterization of PbS thin films
        • 5.10 Electrical characterization of PbS thin films
        • 5.11 Characterization of CdS-PbS heterojunction photovoltaic cells
        • 5.11.1 Current-Voltage (I-V) characteristics
        • 5.11.2 Quantum efficiency
      • CHAPTER SIX
        • CONCLUSION AND RECOMMENDATIONS
        • 6.1 Conclusion
        • 6.2 Recommendations
      • REFERENCES
      • APPENDICES

      Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)

      This thesis aims to investigate the electrical and optical properties of CdxZn1-xS and PbS thin films for photovoltaic applications. The study focuses on the fabrication and characterization of these thin films using various techniques, including chemical deposition, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, UV-Vis spectroscopy, and four-point probe method. The research also explores the potential of CdS-PbS heterojunctions for photovoltaic cell applications.

      • Electrical and optical properties of CdxZn1-xS and PbS thin films
      • Fabrication and characterization of thin films using various techniques
      • Potential of CdS-PbS heterojunctions for photovoltaic cell applications
      • Performance evaluation of CdS-PbS heterojunction photovoltaic cells
      • Optimization of thin film properties for enhanced photovoltaic efficiency

      Zusammenfassung der Kapitel (Chapter Summaries)

      Chapter One introduces the background of the study, outlining the importance of thin films in photovoltaic applications. It also defines the problem statement, objectives, rationale, and structure of the thesis. Chapter Two provides a comprehensive literature review on the electrical and optical properties of CdS and PbS thin films, highlighting their potential for photovoltaic applications. It also discusses the fabrication and characterization of CdS-PbS heterojunction photovoltaic cells. Chapter Three delves into the theoretical considerations of semiconductor thin films, including energy bands, transport carriers, optical phenomena, and thin film deposition techniques. It also explains the principles of p-n junctions and photovoltaic cell operation. Chapter Four details the experimental procedures employed in the study, including materials and reagents, thin film preparation techniques, and characterization methods. Chapter Five presents the results and discussion of the study, analyzing the structural, morphological, compositional, optical, and electrical properties of the fabricated thin films. It also evaluates the performance of the CdS-PbS heterojunction photovoltaic cells. Chapter Six concludes the thesis by summarizing the findings, highlighting the significance of the research, and providing recommendations for future work.

      Schlüsselwörter (Keywords)

      The keywords and focus themes of the text include CdxZn1-xS, PbS, thin films, photovoltaic applications, heterojunction, chemical deposition, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, UV-Vis spectroscopy, four-point probe method, electrical properties, optical properties, current-voltage characteristics, quantum efficiency, and photovoltaic cell performance.

• Hochschule: Kenyatta University
• Veranstaltung: Master of Science ( Physics)
• Note: A
• Autor: Cliff Orori Mosiori (Autor:in)
• Erscheinungsjahr: 2011
• Seiten: 112
• Katalognummer: V278908
• ISBN (eBook): 9783656718406
• ISBN (Buch): 9783656718390
• Sprache: Englisch
• Schlagworte: electrical, cdxzn1-xs, thin