Nanotechnology for Solar Module Applications: Zinc Oxide Nanostructures and Anti-Reflective Coating Modeling, Deposition, Analysis, and Model Fitting
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AN ABSTRACT OF THE DISSERTATION OF Katherine M. Han for the degree of Doctor of Philosophy in Chemical Engineering presented on March 19, 2014. Title: Nanotechnology for Solar Module Applications: Zinc Oxide Nanostructures and Anti-Reflective Coating Modeling, Deposition, Analysis, and Model Fitting Abstract approved: ______________________________________________________ Chih-Hung Chang To become a competitor for fossil fuels such as coal, solar installations will need to be produced and installed at a price equal to or below grid parity. This price can be approached by either reducing the overall system cost or increasing system efficiency. The focus of this paper is on increasing both cell and module efficiency through application of nanotechnology and by numeral modeling. The first portion of this dissertation will focus on the production and characterization of zinc oxide urchin-like nanostructures. These nanostructures have a very high surface area to volume ratio. Such nanostructures could be appropriate for dye sensitized solar cells, an emergent PV technology. The second portion focuses on improving a solar module’s anti- reflective properties. In a traditional glass-encapsulated solar module at least 4% of the incoming light is lost to reflections off of the first optical interface alone. This in turn lower system efficiency and increases the levelized cost of energy. The power loss can be reduced greatly by thin film or gradient index anti-reflective coatings. An in-depth review of the current options for mathematical modeling of the optics of anti- reflective coatings is presented. The following chapter describes a numerical approach to anti-reflective interface design and a comparison between the finite- difference time-domain and the transfer matrix method of optical modeling. The last chapter describes several approaches to applying anti-reflective coatings to solar module lamination materials, including glass and a flexible substrate, fluorinated ethylene polymer. Scale up deposition of the anti-reflective coating on the flexible substrate is discussed. ©Copyright by Katherine M. Han March 19, 2014 All Rights Reserved Nanotechnology for Solar Module Applications: Zinc Oxide Nanostructures and Anti- Reflective Coating Modeling, Deposition, Analysis, and Model Fitting by Katherine M. Han A DISSERTATION Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented March 19, 2014 Commencement June 2014 Doctor of Philosophy dissertation of Katherine M. Han presented on March 19, 2014 APPROVED: Major Professor, representing Chemical Engineering Head of the School of Chemical, Biological, and Environmental Engineering Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Katherine M. Han, Author ACKNOWLEDGEMENTS The author expresses sincere appreciation to her loving partner, Hai-Yue Han, to her parents, Carl and Sunnye VanWormer, to her sisters, Becky and Andrea VanWormer, to the Chang lab group and to Dr. Chih-hung Chang. Special thanks to Dr. John Loeser, Dr. Steven Strauss, and Dr. Rat for their support throughout all of the many undergraduate and graduate years. Financial support came from Oregon BEST, the National Science Foundation STTR Phase II Grant with CSD Nano Inc., the Microproducts Breakthrough Institute, the Rickert Engineering Fellowship, ONAMI, Remcom, Inc., the P.F. Nellie Buck Yerex Graduate Fellowship, and the Oregon Lottery Scholarship. TABLE OF CONTENTS Page 1 INTRODUCTION....................................................................................................... 1 1.1 Background ........................................................................................................ 1 1.2 Dissertation Structure ......................................................................................... 6 1.3 Works Cited ....................................................................................................... 7 2 HIGH ASPECT RATIO ZNO NANO-URCHINS USING CHEMICAL VAPOUR DEPOSITION GROWTH OF ZINC ACETYLACETONATE .................................... 8 2.1 Introduction ........................................................................................................ 8 2.2 Experimental ...................................................................................................... 9 2.2.1 ZnO nano-urchin growth by CVD ............................................................ 9 2.2.2 ZnO Nanostructure analysis ...................................................................... 9 2.3 Results and discussion ..................................................................................... 10 2.4 Conclusions ...................................................................................................... 16 2.5 Acknowledgements .......................................................................................... 17 2.6 References ........................................................................................................ 17 3 NUMERICAL MODELING OF SUB-WAVELENGTH ANTI-REFLECTIVE STRUCTURES FOR SOLAR MODULE APPLICATIONS ...................................... 20 3.1 Introduction ...................................................................................................... 21 3.1.1 Scope ....................................................................................................... 21 3.1.2 Background on anti-reflective sub-wavelength structures ...................... 22 3.1.3 Ideal anti-reflective sub-wavelength structures and gradient indexes .... 26 TABLE OF CONTENTS (Continued) Page 3.1.4 Properties of ARSWS models................................................................. 26 3.1.5 Commercial EM modeling software packages ....................................... 28 3.1.6 Utility of modeling ARSWS ................................................................... 28 3.2 Overview of Optical Modeling Methods ......................................................... 29 3.3 Effective Medium Theory ................................................................................ 29 3.3.1 Effective Medium Approximations ........................................................ 32 3.4 Time-Based Optical Modeling Methods .......................................................... 38 3.4.1 Finite-Difference Time-Domain ............................................................. 38 3.5 Frequency-Based Optical Modeling Methods ................................................. 50 3.5.1 Transfer matrix method .......................................................................... 50 3.5.2 Rigorous coupled wave analysis, Fourier modal method, and coordinate transfer method ................................................................................................... 54 3.5.3 Finite Element Method ........................................................................... 67 3.6 Conclusion ....................................................................................................... 71 3.7 Acknowledgments ............................................................................................ 73 3.8 References ........................................................................................................ 73 4 FINITE DIFFERENCE TIME DOMAIN MODELING OF SUBWAVELENGTH- STRUCTURED ANTI-REFLECTIVE COATINGS .................................................. 88 4.1 INTRODUCTION ........................................................................................... 88 4.2 METHODS ...................................................................................................... 89 4.3 RESULTS ........................................................................................................ 91 4.4 CONCLUSION ................................................................................................ 97 TABLE OF CONTENTS (Continued) Page 4.5 ACKNOWLEDGEMENT ............................................................................... 99 4.6 REFERENCES ................................................................................................. 99 5 EXPERIMENTAL ANTI-REFLECTIVE COATINGS ......................................... 102 5.1 Introduction to sources of reflection in solar modules ................................... 102 5.2 Anti-reflective sub-wavelength and light trapping texturing of silicon ......... 103 5.2.1 Introduction ........................................................................................... 103 5.2.2 Methods ................................................................................................ 104 5.2.3 Results ................................................................................................... 105 5.2.4 Discussion ............................................................................................. 108 5.3 Hollow and Solid/Hollow Silica NP ARCs ................................................... 110 5.3.1 Introduction ........................................................................................... 110 5.3.2 Methods ................................................................................................ 110 5.3.3 Results ................................................................................................... 111 5.3.4 Discussion 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