Flexible Solar Cells A Major Qualifying Project Submitted to the Faculty Of Worcester Polytechnic Institute In Partial Fulfillment of the requirements for the Degree in Bachelor of Science In Mechanical Engineering By Francis LaRovere Edward Peglow Michael McMahon Project Advisor Professor Pratap Rao, Advisor This report represents work of WPI undergraduate students submitted to the faculty as evidence of a degree requirement. WPI routinely publishes these reports on its w ebsite without editorial or peer review. For more information about the projects program at WPI, see http://www.wpi.edu/Academics/Projects. 1 Table of Contents Table of Figures ............................................................................................................................................. 5 Table of Tables .............................................................................................................................................. 6 Acknowledgments ......................................................................................................................................... 7 Abstract ......................................................................................................................................................... 8 1. Introduction .............................................................................................................................................. 9 2. Scope ....................................................................................................................................................... 10 3. Background ............................................................................................................................................. 11 3.1 Working Principles of a Solar Cell ..................................................................................................... 11 3.2 State of the Art .................................................................................................................................. 11 3.3 Cell Types .......................................................................................................................................... 12 3.3.1 Crystalline Silicon Cells ............................................................................................................... 12 3.3.2 Copper Indium Gallium Selenide (CIGS) Cells ............................................................................ 12 3.3.3 Cadmium Telluride (CdTe) Cells ................................................................................................. 13 3.3.4 Perovskite Cells .......................................................................................................................... 14 3.3.5 Dye-sensitized Solar Cells (DSSC) ............................................................................................... 15 3.3.6 Bi2S3 Solar Cells ........................................................................................................................... 16 3.3.7 Bulk Heterojunction Solar Cells (BHJ) ........................................................................................ 17 3.4 Charge Collector Layers .................................................................................................................... 19 3.4.1 Transparent Conductive Oxides (TCOs) ..................................................................................... 19 3.4.2 ITO and Possible Substitutes ...................................................................................................... 19 3.4.3 Graphene ................................................................................................................................... 19 3.4.4 Carbon Nanotubes (CNTs) .......................................................................................................... 20 3.5 Nanowires ......................................................................................................................................... 20 3.5.1 Nanowires-Mat Electrodes ........................................................................................................ 20 3.5.2 Ag Nanowires ............................................................................................................................. 21 3.5.3 Alternative Nanostructures........................................................................................................ 23 3.6 Processing Methods .......................................................................................................................... 23 3.6.1 Roll to Roll Processing ................................................................................................................ 24 3.6.2 Chemical Bath Deposition .......................................................................................................... 24 3.6.3 Vapor Deposition ....................................................................................................................... 24 3.6.4 Dip Coating ................................................................................................................................. 24 3.6.5 Spin Coating ............................................................................................................................... 25 2 3.6.6 Drop Casting ............................................................................................................................... 25 3.6.7 Screen Printing ........................................................................................................................... 26 3.7 Cell Design and Laboratory Research ............................................................................................... 26 3.7.1 TiO2 Blocking Layer ..................................................................................................................... 26 3.7.2 Sb2S3 Solar Cells .......................................................................................................................... 26 3.7.3 CuSCN ......................................................................................................................................... 27 3.7.4 Zinc Oxide (ZnO) Nanowires....................................................................................................... 28 3.7.5 ZnO Performance and Construction .......................................................................................... 30 3.7.6 Gold/Palladium .......................................................................................................................... 30 4. Testing Methods ..................................................................................................................................... 32 4.1 Flexibility ........................................................................................................................................... 32 4.2 Efficiency ........................................................................................................................................... 32 5. Methods .................................................................................................................................................. 33 5.1 ITO/PET Substrate ............................................................................................................................. 33 5.2 TiO2 Blocking Layer ............................................................................................................................ 33 5.3 ZnO Nanowires .................................................................................................................................. 33 5.4 Sb2S3 Thin Film ................................................................................................................................... 34 5.5 CuSCN Thin Film ................................................................................................................................ 35 5.6 Au/Pd Back Contact .......................................................................................................................... 35 6. Results ..................................................................................................................................................... 36 6.1 Efficiency ........................................................................................................................................... 36 6.1.1 FTO Glass with High Temperature Annealing ............................................................................ 36 6.1.2 FTO Glass with Low Temperature Annealing ............................................................................. 37 6.1.3 ITO Plastic with Low Temperature Annealing ............................................................................ 37 6.1.4 Light Absorption of Sb2S3 ........................................................................................................... 40 6.2 Flexibility of Layers ............................................................................................................................ 42 6.2.1 ITO and Au/Pd Bending .............................................................................................................. 42 6.2.2 TiO2 Bending ............................................................................................................................... 44 6.2.3 Sb2S3 Bending ...........................................................................................................................