Photovoltaic and Photoelectrochemical Solar Energy Conversion

ISBN-13: 9781461592358 / Angielski / Miękka / 2012 / 422 str.

F. Cardon

Opis

In recent years there has been an increasing interest in syscems which enable the conversion of solar energy into electri calor chemical energy. Many types of systems have been proposed and studied experimenta11y, the fundamentals of which extend from solid state physics to photo- and electrochemistry. For most of the systems considered excitation of an electron by absorption of a photon is fo1lowed by charge separation at an interface. It follows that the different fields involved (photovo1taics, photo electrochemistry, photogalvanics, etc.) have several essential aspects in common. It was the main purpose with the NATO Advanced Study Insti tute held at Gent, Belgium, from August 25 to September 5, 1980, to bring together research workers specializing in one of these fields in order to enab1e them not only to extend their knowledge into their own field but also to promote the interdisciplinary exchange of ideas. The scope of the A.S.I. has been 1imited to systems which have not or have hardly reached the stage of prac tica1 development. As a consequence, no lectures on economica1 aspects of solar energy conversion have been included. The topics covered in this volume are the fundamentals of recombination in solar ce1ls (P. Landsberg), theoretical and experimental aspects of heterojunctions and semiconductor/metal Schottky barriers (J.J. Loferski, W.H. Bloss and W.G. Townsend), photoelectrochemica1 ce11s (H. Gerischer and A.J. Nozik), pho- v PREFACE vi ga1vanic ce11s (W.J. Albery) and fina11y, surfactant assemb1ies (M. Gratzel).

Spis treści

Recombination in Solar Cells: Theoretical Aspects.- 1. Introduction.- 2. Conventions Usually Made for p-n Junctions and Solar Cells.- 3. Three Laws of Photovoltaics.- 4. Maximum Power, Recombination and the Ideality Factor.- 5. Junction Currents as Recombination Currents.- 6. Steady-State Recombination Rates at a Given Plane X.- 7. Junction Model and Space-Dependences.- 8. Transition Region Recombination Current Density.- 9. The Bulk-Regions Recombination Current Density.- 10. Summery of p-n Junction Current Densities from Sections 8 and 9.- 11. Configuration and Electrostatics of the Schottky Barrier Solar Cell.- 12. The Place of Recombination Effects in (p-type) Schottky Barrier Solar Cells.- 13. Recombination Currents and Voltage Drops in (p-type) Schottky Barrier Solar Cells.- 14. Conclusion.- A Few More General Topics.- (I) Thermodynamic Efficiency.- (II) Simple Theory to See that an Optimum Energy Gap Exists.- (III) Is Dollars per Peak Watt a Good Unit?.- (IV) Energy Unit for Global Use.- (V) When will Solar Conversion be Economically Viable?.- References.- Schottky Barrier Solar Cells.- 1. Introduction.- 2. The Schottky Barrier Cell Principle.- 2.1. Principle of SBSC Operation.- 2.2. Current Transport Mechanism in Schottky Barriers.- 2.3. Effect of the MIS Potential Distribution upon the Diode Quality Factor n.- 2.4. The MIS SBSC under Illumination.- 2.5. The Minority Carrier MIS SB Cell.- 3. Solar Cell Parameters and Design Considerations.- 3.1. Metal-Semiconductor Barrier Height.- 3.2. Diode Quality Factor n.- 3.3. Interfacial Oxide Thickness.- 3.4. Transmission Properties of the Metal.- 3.5. Spectral Response.- 3.6. Substrate Resistivity.- 3.7. Substrate Thickness.- 3.8. Series Resistance.- 4. Results and Discussion of Typical Silicon MIS Cells.- 4.1. Open Circuit Voltage.- 4.2. Short Circuit Current Density.- 4.3. Fill Factor.- 4.4. Efficiency.- 4.5. The Min MIS Cell.- 4.6. The MIS Inversion Layer Cell.- 4.7. Stability of MIS Solar Cells.- 4.8. The Future for MIS Cells — Cheaper Substrates?.- Acknowledgement.- References.- CdS-Cux S Thin Film Solar Cells.- 1. Introduction.- 2. CdS Thin Film Technology.- 2.1. Vacuum Vapor Deposition of CdS Films.- 2.2. Sputtering.- 2.3. Spray Deposition.- 2.4. Sintering.- 3. CuxS Thin Film Technology.- 3.1. Dipping Process (Wet Process).- 3.2. Evaporation of CuCl.- 3.3. Evaporation of CuxS.- 3.4. Sputtering of CuxS.- 4. Properties of the CdS Layer.- 4.1. Crystallography and Grain Size of CdS Films.- 4.2. Optical Properties of the CdS Films.- 4.3. Luminescence.- 4.4. Electrical Properties of CdS Films.- 5. Properties of CuxS Films.- 5.1. Stoichiometry.- 5.2. Coulometric Titration.- 5.3. Optical Properties.- 5.4. Electrical Properties.- 6. Properties of the Heterojunction.- 6.1. Structure of the Heterojunction.- 6.2. Surface Effects of the CuxS Film.- 6.3. Capacitance Measurements.- 6.4. Diffusion Length in CuxS and CdS.- 6.5. Spectral Response.- 6.6. Band Diagram.- 7. Technology of CdS-CuxS Photovoltaic Generators.- 7.1. Cell Structures.- 7.2. Fabrication Process of CdS-CuxS Cells.- 8. Performance Characteristics of Solar Cells and Generators.- References.- Conversion of Solar Energy Using Tandem Photovoltaic Cells Made from Multi-Element Semiconductors.- I. Introduction.- II. Increasing Efficiency by Recourse to Tandem PV Cell Systems.- III. Design of an Optimized Solar Cell Structure for Tandem Cell Systems.- IV. Selection of Semiconductors for Tandem Solar Cell Systems.- V. Optimized Design of Direct Gap Photovoltaic Cells.- VI. Monolothic and Split Spectrum Tandem Cell Systems.- VII. Synthesis and Properties of Ternary Alloy Chalcopyrite Semiconductors.- VIII. Thin Films of CuInSe2 and Solar Cells Made from Them.- IX. Summary and Conclusions.- References.- The Principles of Photoelectrochemical Energy Conversion.- I. Sunlight Conversion into Chemical Energy.- Photoredox Reactions.- Redox Energies and the Scales of Redox Potentials.- Photosynthesis as an Example.- Artificial Systems for Energy Conversion.- References to Lecture for Further Reading.- II. Fundamentals of Semiconductor Electrochemistry.- The Space Charge Layer.- Kinetics of Electron Transfer Reactions.- References.- III. The Semiconductor Electrolyte Contact under Illumination and Photodecomposition Reactions.- Distribution of Electrons and Holes under Illumination.- Photodecomposition of Semiconductors.- References.- IV. Photoelectrochemical Cells and their Problems.- Regenerative Cells.- Storage Cells.- Energy Conversion Efficiency.- References.- Photoelectrochemical Devices for Solar Energy Conversion.- General Discussion of Photoelectrochemical Devices.- Semiconductor Electrolyte Junctions — Conventional Picture.- Photo-Induced Charge Transfer Reactions.- Semiconductor Electrode Stability.- Electrochemical Photovoltaic Cells.- Photoelectrosynthetic Cells.- Photoelectrolysis Cells.- Photocatalytic Cells.- General Considerations.- Effects and Importance of Surface States.- Unpinned Band Edges.- Hot Carriers.- Surface Modification.- Electrochemical Photovoltaic Cells.- Reduced Surface and Grain Boundary Recombination.- Non-aqueous Electrolytes.- Storage Systems.- General Status and Prognosis for Electrochemical Photovoltaic Cells.- Photoelectrosynthetic Cells.- Derivatized Electrodes.- Photo-Oxidation and Photo-Reduction on the same Surface and in Particulate System.- Dye Sensitization.- Layered Compounds and other New Materials.- General Status and Prognosis for Photoelectrosynthesis.- Acknowledgement.- References.- The Iron Thionine Photogalvanic Cell.- The Reaction Scheme.- The Differential Equation.- The Characteristic Lengths.- The Kinetic Length.- Bleaching and the Generation Length.- The Recipe for Success.- The Electrode Kinetics.- Current Voltage Characteristics.- Homogeneous Kinetics.- The Iron Thionine System.- The Reaction Scheme.- Quantum Efficiencies.- The Parameters.- Rotating Transparent Disc Electrodes.- The Thionine System.- The Synthesis of Modified Thiazine Dyes.- The Properties of the Modified Dyes.- Self Quenching.- Summary of Progress to Date.- Electrode Selectivity.- The Problem.- The Manufacture of the Thionine Coated Electrode.- Properties of the Thionine Coated Electrode.- Electrode Kinetics.- Application to Photogalvanic Systems.- The Efficiencies of Photogalvanic Cells.- The Concentration of Fe(II).- The Concentration of Ee(III).- The Variation of Power with ?E? and k-2.- Variation with pH.- Final Summary.- Acknowledgements.- References.- Charge Separation and Redox Catalysis in Solar Energy Conversion Processes.- 1. Introduction.- 2. Design of Photoredox Reactions for Photodissociation of Water.- 2.1. Photodecomposition of Water in Homogeneous Solutions.- 2.2. Photoproduction of H2 from Water.- 2.2.1. Photolysis of Simple Ions in Acid Media.- 2.2.2. Photolysis of Metal Hydrides.- 2.2.3. H2 Production via Dye-Sensitized Redox Reactions.- 2.2.4. Photochemistry of Selected Redox Systems for H2 Evolution.- 2.3. Redox Systems for O2-Evolution from Water.- 2.3.1. Photo-Induced Oxygen Evolution from Water.- 3. Stabilization of Redox Intermediates through the Use of Multiphase Systems.- 3.1. Micelles.- 3.1.1. Photoionisation.- 3.1.2. Light Induced Electron Transfer in the Micelle.- 3.1.3. Solution and Spatial Separation of Reactants in Micelles.- 3.1.4. Functional Micellar Systems.- a) Redox Reactions in Transition Metal Ion Micelles.- b) Micelles Formed with Crown Ether Surfactants.- c) Micelles with Long Chain Derivatives of Sensitizer or Acceptor Relays.- 3.2. Light-Induced Charge Separation in Vesicles.- 3.3. Charge Separation Phenimena in Other Multiphase Systems.- 4. Redox Catalysis.- 4.1. Concept of Redox Catalysis.- 4.2. Redox Catalysis in the H2 -Evolution Reaction from Water.- 4.3. Redox Catalysis in the O2Evolution Reaction from Water.- 4.4. Coupled Redox Catalysts for Water Decomposition.- 5. Photoelectrochemical Cells Based on Redox Reactions.- References.- Author Index.