PV Tutorial Allen Hermann, Ph. D. Professor of Physics Emeritus, and Professor of Music Adjunct, University of Colorado, Boulder, Colorado, USA and Vice-president, NanoTech Inc. Lexington, Kentucky, USA
Background and Cost Photovoltaics convert sunlight directly to electric power Carbon-neutral Highly abundant the earth receives 120 quadrillion watts of power from the sun, humans currently use about 13 trillion watts Costs Module cost Balance of system cost Power conditioning cost Lewis, et al. Basic Research Needs for Solar Energy Utilization. Currently about $0.30/kWh, a factor of 5-10 behind total cost of fossil fuel generation
Lecture 1 Semiconductors and Physics at the Nano-scale Electronic Properties of Solids: Free-electron Fermi gas Energy bands in solids Semiconductors and doping pn junctions Amorphous semiconductors Nano-scale Physics: Background Quantum confinement
Review of Electronic Properties of Solids Free Electron Fermi Gas
Energy Bands, Semiconductors, Doping
Hydrogen Molecule
energy-states energy-states in solids: Band-Pattern Atom Molecule/Solid 6.6.06-8.6.06 Clemson Summer School Dr. Karl Molter / FH Trier / molter@fhtrier.de 19
energy-states in solids: Insulator electron-energy conduction-band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fhtrier.de Fermilevel E F bandgap E G (> 5 ev) valence-band 6.6.06-8.6.06 20
Figure 7.1. Schematic plot of the single particle energy spectrum in a bulk semiconductor for both the electron and hole states on the left side of the panel with appropriate electron (e) and hole (h) discrete quantum states shown on the right. The upper parabolic band is the conduction band, the lower the valence.
Figure 9.12. A valence electron jumping across the energy gap in pure silicon resulting in the generation of a free electron and hole in the crystal: (a) energy band model, (b) bond model.
Figure 9.13. Extrinsic n-type silicon doped with P donor atoms. (a) Energy band diagram and (b) Bond model.
Figure 9.14. Extrinsic p-type silicon doped with B acceptor atoms. (a) Energy band diagram and (b) Bond model.
energy-states in solids : metal / conductor electron-energy Clemson Summer School Dr. Karl Molter / FH Trier / molter@fhtrier.de Fermilevel E F conduction-band 6.6.06-8.6.06 28
energy-states in solids: semiconductor electron-energy conduction-band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fhtrier.de Fermilevel E F bandgap E G ( 0,5 2 ev) valence-band 6.6.06-8.6.06 29
Introduction to pn Junctions
Amorphous Semiconductors
Nanoscale Physics Background
10,000 Kilometers
1000 Kilometers
100 Kilometers
10 Kilometers
10 Kilometers
1 Kilometer
Oak trees 100 Meters
What is Nanotechnology? Research and technology development at the atomic, molecular or macromolecular levels, in the length scale of approximately 1-100 nanometers. Creating and using structures, devices and systems that have novel properties and functions because of their small and/or intermediate size. Ability to control processes at a few nm-range for advanced material processing and manufacturing.
History of Nanotechnology As early as 500 AD, glass artisans were making stained glass windows with vibrant reds and yellows. These colours were much more luminous and durable than dyes could produce, and were the products of coinage metal nanoparticles imbedded in the glass. As these nanoparticles get smaller, the colours shift from red, through yellow and green, to blue. 58
Soft x-ray Nanoworld Microworld Ultraviolet Visible Infrared Microwave The Scale of Things Nanometers and More Things Natural 10-2 m 1 cm 10 mm Things Manmade Head of a pin 1-2 mm The Challenge Ant ~ 5 mm 10-3 m 1,000,000 nanometers = 1 millimeter (mm) Dust mite 200 mm 10-4 m 0.1 mm 100 mm MicroElectroMechanical (MEMS) devices 10-100 mm wide Human hair ~ 60-120 mm wide Red blood cells (~7-8 mm) Fly ash ~ 10-20 mm 10-5 m 10-6 m 0.01 mm 10 mm 1,000 nanometers = 1 micrometer (mm) Pollen grain Red blood cells Zone plate x-ray lens Outer ring spacing ~35 nm O O S P O O O O O O O O O O O O O O O O O O O O O S S S S S S S 10-7 m 0.1 mm 100 nm Fabricate and combine nanoscale building blocks to make useful devices, e.g., a photosynthetic reaction center with integral semiconductor storage. ~10 nm diameter ATP synthase 10-8 m 0.01 mm 10 nm Self-assembled, Nature-inspired structure Many 10s of nm Nanotube electrode DNA ~2-1/2 nm diameter Atoms of silicon spacing ~tenths of nm 10-9 m 10-10 m 1 nanometer (nm) 0.1 nm Quantum corral of 48 iron atoms on copper surface positioned one at a time with an STM tip Corral diameter 14 nm Carbon buckyball ~1 nm diameter Carbon nanotube ~1.3 nm diameter
20 nm nanorods of MnO 2 for positive electrodes in Li ion batteries
Quantum Confinement One Dimension
Quantum Confinement Three Dimensions
Figure 7.2. Solutions of quantum dots of varying size. Note the variation in color of each solution illustrating the particle size dependence of the optical absorption for each sample. Note that the smaller particles are in the red solution (absorbs blue), and that the larger ones are in the blue (absorbs red).