Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2020 Research project to study cadmium selenide (CdSe) solar cells Behrang Bagheri Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Recommended Citation Bagheri, Behrang, "Research project to study cadmium selenide (CdSe) solar cells" (2020). Graduate Theses and Dissertations. 17865. https://lib.dr.iastate.edu/etd/17865 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Research project to study cadmium selenide (CdSe) solar cells by Behrang Bagheri A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Electrical Engineering (Microelectronics and Photonics) Program of Study Committee: Vikram L. Dalal, Major Professor Mani Mina Rana Biswas Jaeyoun Kim Ruth Shinar The student author, whose presentation of the scholarship herein was approved by the program of study committee, is solely responsible for the content of this dissertation. The Graduate College will ensure this dissertation is globally accessible and will not permit alterations after a degree is conferred. Iowa State University Ames, Iowa 2020 Copyright © Behrang Bagheri, 2020. All rights reserved. ii DEDICATION I would like to dedicate this dissertation to my wife Seyedeh Shaghayegh Jalalian, for all her love and support. I also would like to dedicate this work to my mother Hajieh Khanom Esmailzadeh and my father Abasal Bagheri for their love, endless support and encouragement. Finally, I would like to thank to my sisters Khatere Bagheri and Azadeh Bagheri, also my brother Mohamad Bagher Bagheri. This work is not possible without their support and sacrifice and I won’t be the same person that I am today. Finally, this work is dedicated to my children Johnyar Bagheri. You have made me stronger, better and more fulfilled that I could have ever imagined. I love you to the moon and back. iii TABLE OF CONTENTS Page LIST OF FIGURES ....................................................................................................................... vi LIST OF TABLES ....................................................................................................................... xiii NOMENCLATURE ......................................................................................................................xv ACKNOWLEDGMENTS .......................................................................................................... xvii ABSTRACT …………………………………………………………………………………..xix CHAPTER 1. INTRODUCTION TO RENEWABLE ENERGY, SOLAR ENERGY AND SOLAR CELLS ...............................................................................................................................1 1-1 Thesis Structure ................................................................................................................. 1 1-2 Energy ............................................................................................................................... 1 1-3 Nonrenewable and Renewable Energy .............................................................................. 2 1-4 Solar Energy ...................................................................................................................... 3 1-5 Photovoltaic and Solar Cells ............................................................................................. 8 1-6 References ......................................................................................................................... 9 CHAPTER 2. DEVICE PHYSICS OF SOLAR CELLS ..............................................................10 2-1 Basic structure and working principle of solar cells ....................................................... 10 2-2 Absorption ....................................................................................................................... 14 2-3 Recombination ................................................................................................................. 20 2-3-1 Band-to-band recombination ................................................................................... 20 2-3-2 Trap-assisted or schottky read hall (SRH) recombination ....................................... 21 2-3-3 Auger recombination ............................................................................................... 23 2-3-4 Recombination through Shallow Levels .................................................................. 24 2-3-5 Recombination involving excitons .......................................................................... 25 2-4 Carrier collection ............................................................................................................. 26 2-4-1 Diffusion based collection ....................................................................................... 27 2-4-2 Drift assisted collection............................................................................................ 28 2-5 The Shockley-Queisser limit ........................................................................................... 30 2-6 References ....................................................................................................................... 32 CHAPTER 3. DEVICE CHARACTERIZATION TECHNIQUES OF SOLAR CELLS ............33 3-1 Introduction ..................................................................................................................... 33 3-2 Solar cell equivalent circuit ............................................................................................. 33 3-3 Current-Voltage (IV) measurement of solar cell ............................................................. 35 3-3-1 Light I-V measurement ............................................................................................ 36 3-3-2 Dark I-V measurement 22 Feb 2019 ....................................................................... 39 3-4 Quantum efficiency (QE) ................................................................................................ 41 3-5 Sub-gap quantum efficiency ............................................................................................ 45 3-6 Capacitance vs. voltage (C-V) spectroscopy ................................................................... 47 iv 3-7 Capacitance-Frequency vs Temperature (CFT) .............................................................. 49 3-8 Photoconductivity ............................................................................................................ 52 3-9 Space charge limited current (SCLC) ............................................................................. 54 3-10 Scanning electron microscope (SEM) ............................................................................. 55 3-11 Energy dispersive x-ray spectroscopy (EDS) .................................................................. 57 3-12 References ....................................................................................................................... 59 CHAPTER 4. CADMIUM SELENIDE THIN FILMS GROWTH, IMPROVEMENT AND CHARACTERIZATION FOR SOLAR CELL APPLICATION ..................................................62 4-1 Introduction ..................................................................................................................... 62 4-2 Cadmium selenide (CdSe) ............................................................................................... 65 4-3 Deposition techniques of CdSe ....................................................................................... 66 4-3-1 Close space vapor transport (CSVT) ....................................................................... 66 4-3-2 Thermal evaporation (TE) ........................................................................................ 67 4-3-3 E6 Thermal Evaporation system at Iowa State University (ISU), Microelectronic Research Center (MRC)........................................................................... 69 4-4 Experiments to improve CdSe ......................................................................................... 70 4-4-1 Cadmium Chloride (CdCl2) treatment..................................................................... 70 4-4-2 Post-deposition selenization..................................................................................... 71 4-4-3 CdSe deposition with selenium (Se) flux................................................................. 72 4-5 CdSe thin films preparation and characterization ........................................................... 73 4-5-1 Optical properties ..................................................................................................... 73 4-5-2 Grain enhancement on CdSe thin films ................................................................... 75 4-5-2-1 CdSe with Se flux (CdSe:Se) ........................................................................ 75 4-5-2-2 Effect of annealing temperature .................................................................... 76 4-5-2-3 Cross section SEM image of CdSe film .......................................................