DYE-SENSITIZED SOLAR CELLS

Transcription

1 FUNDAMENTAL SCIENCES Chemistry DYE-SENSITIZED SOLAR CELLS Edited by K. Kalyanasundaram With contributions by: Michael Bertoz, Juan Bisquert, Filippo De Angelis, Hans Desilvestro, Francisco Fabregat-Santiago, Simona Fantacci, Anders Hagfeldt, Seigo Ito, Ke-jian Jiang, K. Kalyanasundaram, Prashant V. Kamat, Ladislav Kavan, Jacques-E. Moser, Md. К. Nazeeruddin, Laurence Peter, Henry J. Snaith, Gavin Tulloch, Sylvia Tulloch, Satoshi Uchida, Shozo Yanagida and Jun-ho Yum Forewords by: Michael Grätzel and Shozo Yanagida EPFL Press A Swiss academic publisher distributed by CRC Press

2 CONTENTS PREFACE xvii 1 PHOTOCHEMICAL AND PHOTOELECTROCHEMICAL APPROACHES TO ENERGY CONVERSION 1 K. Kalyanasundaram 1.1 The sun as an abundant energy resource Photochemical conversion and storage of solar energy (artificial photosynthesis) Photographic sensitization Photoelectrochemical conversion of solar energy Photogalvanic cells Generations of photovoltaic solar cells Photoelectrochemical solar cells with liquid junctions Photoredox reactions of colloidal semiconductors and particulates Dye sensitization of semiconductors Dye sensitization of bulk semiconductor electrodes Dye-sensitized solar cells - an overview Sequence of electron-transfer steps of a DSC Key efficiency parameters of a DSC Key components of the DSC Quasi-solid state DSCs with spiro-ometad Improvement in efficiency through the nanostructuring of materials Dye solar cells based on nanorods/nanotubes and nanowires Sensitization using quantum dots Semiconductor-sensitized ETA solar cells DSCs based on p-type semiconductor Conclusions References 38 2 TITANIA IN DIVERSE FORMS AS SUBSTRATES 45 Ladislav Kavan 2.1 Titania: fundamentals 45

3 x Dye-Sensitized Solar Cells 2.2 Electrochemistry of titania: depletion regime Photoelectrochemistry under band-gap excitation In-situ FTIR spectroelectrochemistry in the depletion regime Photoelectrochemistry under sub-band-gap excitation Electrochemistry of titania: accumulation regime Capacitive processes Li-insertion electrochemistry Spectroelectrochemistry of titania in the accumulation regime Titania photoanode for dye sensitized solar cells Non-organized titania made by decomposition of Ti(IV) alkoxides Electrochemical deposition of titania Aerosol pyrolysis Organized nanocrystalline titania Single-crystal anatase electrode Other methods of producing titania electrodes for DSC Multimodal structures Conclusion Acknowledgements References 76 3 MOLECULAR ENGINEERING OF SENSITIZERS FOR CONVERSION OF SOLAR ENERGY INTO ELECTRICITY 83 Jun-ho Yum and Md. K. Nazeeruddin 3.1 Introduction Ruthenium Sensitizers Effect of protons carried by the sensitizers on the performance Effect of cations in the ruthenium sensitizers on the performance Device stability Effect of alkyl chains in the sensitizer on the performance Effect of the ^-conjugation bridge between carboxylic acid groups and the ruthenium chromophore High Molar Extinction Coefficient Sensitizers Tuning spectral response by thiocyanato ligands Non-thiocyanato ruthenium complexes Organic sensitizers High efficiency organic sensitizers Near-IR absorbing sensitizers References 113

4 Dye-Sensitized Solar Cells xi 4 OPTIMIZATION OF REDOX MEDIATORS AND ELECTROLYTES..117 Ke-jian Jiang and Shozo Yanagida* 4.1 Introduction Charge transfer processes in DSCs Electrolyte components and their roles in the DSCs Organic solvents Cations Additives Electron mediators Ionic liquid, quasi-solid and solid electrolytes Ionic liquid electrolyte Active iodide molten salts Nonactive iodide molten salts Additives in ILEs Quasi-solid electrolyte Remarks and prospects References PHOTOSENSITIZATION OF Sn0 2 AND OTHER OXIDES 145 Prashant V. Kamat 5.1 Dependence of the Sensitization Efficiency on the Energy Difference Coupled Semiconductor Systems SnO 2 -C 60 -Ru(bpy)3 + System Probing the Interaction of an Excited State Sensitizer with the Redox Couple Sensitization of Nanotube Arrays Charge Separation of Organic Clusters at an Sn0 2 Electrode Surface Concluding Remarks Acknowledgements References SOLID-STATE DYE-SENSITIZED SOLAR CELLS INCORPORATING MOLECULAR HOLE-TRANSPORTERS 163 Henry J. Snaith 6.1 Introduction Spiro-OMeTAD-based solid-state dye-sensitized solar cell The influence of additives upon the solar cell performance Charge generation: Electron Transfer Reductive quenching Charge generation: Hole-transfer Charge transport in molecular hole-transporters Hole mobility in spiro-ometad 175

5 xii Dye-Sensitized Solar Cells 6.9 Influence of charge density on the hole-mobility in molecular semiconductors The influence of chemical p-doping upon conductivity and hole-mobility The influence of ionic salts on conductivity and hole-mobility Current collection ТЮ 2 pore filling with molecular hole-transporters Charge recombination: The influence of additives Charge recombination: Ion solvation and immobilization Charge recombination: Controlling the spatial separation of electrons and holes at the heteroj unction Enhancing light capture in solid-state DSCs Alternative structures for mesoporous and nanostructured electrodes in solid-state DSCs Outlook for hole-transporter based solid-state DSCs References PACKAGING, SCALE-UP AND COMMERCIALIZATION OF DYE SOLAR CELLS 207 Hans Desilvestro, Michael Bertoz*, Sylvia Tulloch and Gavin Tulloch 7.1 Introduction From cells to panels Definitions Designs Materials Module performance - experiment vs. modeling Long-term stability - the key to industrial success Single cells Modules Panels Scaling up to commercial production levels Material costs and availability Manufacturing Commercial applications Conclusions Acknowledgements References HOW TO MAKE HIGH-EFFICIENCY DYE-SENSITIZED SOLAR CELLS 251 Seigo Ito 8.1 Introduction Experimental considerations Preparation of screen-printing pastes Synthesis of Ru-dye 253

6 Dye-Sensitized Solar Cells xiii Porous-Ti0 2 electrodes Counter-Pt electrodes DSC assembling Measurements Results and discussion TiCl 4 treatments Effect of the light-scattering ТЮ 2 layer Thickness of the nanocrystalline Ti0 2 layer Anti-reflecting film Reproducibility of DSC photovoltaics Conclusion Acknowledgements References SCALE-UP AND PRODUCT-DEVELOPMENT STUDIES OF DYE-SENSITIZED SOLAR CELLS IN ASIA AND EUROPE 267 K. Kalyanasundaram, Seigo Ito, Shozo Yanagida and Satoshi Uchida 9.1 Introduction Scaling up of laboratory cells to modules and panels DSC development studies in various European laboratories Energy Research Centre of the Netherlands (ECN) Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) G24 Innovation GSolar, Israel DSC development studies in various laboratories of Japan Aisin Seiki Co. Ltd. and Toyota Central R&D Laboratories Fujikura Ltd. (Japan) Peccell Technologies, Inc. (Japan) Sharp Co. Ltd. (Japan) Sony Corporation Ltd. (Japan) Shimane Institute for Industrial Technology (Japan) TDK Co., Ltd. (Japan) Eneos Co. Ltd. (Japan) NGK Spark Plug Co., Ltd. (Japan) Panasonic Denko Co. Ltd. (Japan) Taiyo Yuden Co., Ltd. (Japan) Dai Nippon Printing Company Mitsubhishi Paper Mills and Sekisui Jushi Corporation J-Power Co. Ltd. (Japan) DSC Development Work in Korea and Taiwan Korean Institute of Science and Technology (KIST) Electronics and Telecommunications Research

7 xiv Dye-Sensitized Solar Cells Institute(ETRI), Korea Samsung SDI, Korea Industrial Technology Research Institute of Taiwan (ITRI) J Touch Taiwan DSC development work in Australia and China Dyesol, Australia Institute of Plasma Physics, Chinese Academy of Sciences Conclusion Acknowledgement References CHARACTERIZATION AND MODELING OF DYE-SENSITIZED SOLAR CELLS: A TOOLBOX APPROACH 323 Anders Hagfeldt and Laurence Peter 10.1 Introduction Theoretical background Interfacial electron transfer processes in the DSC Electron trapping in the DSC Electron transport in the DSC The toolbox Determination of injection efficiency and electron diffusion length under steady-state conditions Electrochemical and spectrolectrochemical techniques to study the energetics of the oxide/dye/electrolyte interface Electrochemical measurements with thin layer cells Small-amplitude time-resolved methods Methods based on frequency response analysis Photovoltage decay Determination of density of trapped electrons in DSCs Measuring the internal electron quasi Fermi level in the DSC Determining the electron diffusion length using IMVS and IMPS Photoinduced absorption spectroscopy (PIA) Conclusions Acknowledgments Appendix 1 Analytical IMPS solutions Appendix 2 Numerical solutions of the continuity equation [10.115] References 399

8 Dye-Sensitized Solar Cells xv 11 DYNAMICS OF INTERFACIAL AND SURFACE ELECTRON TRANSFER PROCESSES 403 Jacques-E. Moser 11.1 Introduction Energetics of charge transfer reactions Mesoscopic metal oxide semiconductors Dye sensitizer Kinetics of interfacial electron transfer Charge injection dynamics Charge recombination Electron transfer dynamics involving the redox mediator Kinetics of interception of dye cations by a redox mediator Conduction band electron - oxidized mediator recombination Electron transport in nanocrystalline ТЮ 2 films References IMPEDANCE SPECTROSCOPY: A GENERAL INTRODUCTION AND APPLICATION TO DYE-SENSITIZED SOLAR CELLS 457 Juan Bisquert and Francisco Fabregat-Santiago 12.1 Introduction A basic solar cell model The ideal diode model Physical origin of the diode equation for a solar cell Introduction to IS methods Steady state and small perturbation quantities The frequency domain Simple equivalent circuits Basic physical model and parameters of IS in solar cells Simplest impedance model of a solar cell Measurements of electron lifetimes Basic physical models and parameters of IS in dye-sensitized solar cells Electronic processes in a DSC The capacitance of electron accumulation in a DSC Recombination resistance The transport resistance Transmission line models General structure of transmission lines General diffusion transmission lines Diffusion-recombination transmission line Parameters of the diffusion-recombination model Effect of boundaries on the transmission line 520

9 xvi Dye-Sensitized Solar Cells 12.7 Applications Liquid electrolyte cells Experimental IS parameters of DSCs Nanotubes Effects of the impedance parameters on the j-v curves Acknowledgments Appendix: properties of measured DSCs References THEORETICAL AND MODEL SYSTEM CALCULATIONS 555 Filippo De Angelis and Simona Fantacci 13.1 Introduction Theoretical and computational methods Density Functional Theory (DFT) Basis sets The Car-Parrinello method Solvation effects Excited states Nonadiabatic method Dye sensitizers Ruthenium(II)-polypyridyl sensitizers Calculations on N Calculations on other Ru(II)-dye sensitizers Trans-complexes Organic sensitizers Squaraine dyes Studies of the Ti0 2 substrate ТЮ 2 models Dye sensitizers on Ti Organic dyes on Ti0 2 : adsorption and electron dynamics Inorganic dyes on Ti0 2 : adsorption and excited states Conclusions and perspective References 589 INDEX 593