Kahntinetta Pr’Out

1. Multi-scale Framework of the Morphological Evolution During Spin-Coating Process of Organic Solar CellsAnalyzing Morphology KahntinettaPr’Out Dr. Olga Wodo and Dr. BaskarGanapathysubramanian

2. Outline • Motivation & Objectives • Introduction • What are solar cells? • Organic vs. Traditional • Organic Solar Cells • Photovoltaic effect • Morphology • Approach & Methods • Current Status • Future Goals

3. Motivation and Objectives • Motivation: • The overall goal is to find an inexpensive renewable energy source that can sustain the world's energy requirements in place of fossil fuels. By improving the efficiency of organic solar cells, it could potentially alleviate this problem. • Objectives: • To accelerate the development of organic solar cells by way of computational analysis. • To characterize morphology and relate the metrics to the final efficiency and properties of the device.

4. Introduction: What are solar cells? • Solar Cells are devices that harvest the sun’s energy by way of the photovoltaic effect. • Photovoltaic effect • Sunlight emission • Photon absorption • Electron excitation • Free charges move about the crystal lattice to respective electrodes • Two types of solar cells: • Organic (OSC) • Traditional or Inorganic

5. Types of Solar Cells Organic Solar Cells Traditional Solar Cells Semiconducting metal Expensive High energy consumption during fabrication Rigid and Brittle About 20 year life span • Carbon based semiconducting material • Inexpensive • Low energy consumption during fabrication • Flexible • Short life span

6. Organic Vs. Traditional Solar Cells http://4.bp.blogspot.com/_Lg2EuzTdTSQ/SeghrfDEzbI/AAAAAAAAArc/9BzR2udG66U/s400/Organic+Solar+Cell.jpg http://averageguys.files.wordpress.com/2009/07/solar_cells.jpg

7. Organic Solar Cells • Photoactive layer consists of Electron Donor & Electron Acceptor Materials • Conjugated Polymer (Donor) • Fullerene (Acceptor) • P3HT/PCBM • Bulk Heterojunction (BHJ) is created as a result of the contact between the DA material • Morphology: how the two phases or materials interact and exist within each other • Morphology evolves during the fabrication process

8. Organic Solar Cells • Sunlight emission • Photon absorption • Exciton Creation • Exciton travels to interface (~20nm) • Exciton separation at interface ONLY • Charges travel to respective electrodes http://blog.disorderedmatter.eu/2008/03/07/how-do-organic-solar-cells-function-part-two/

9. Morphology: Ideal vs. Real 100 nm • Ideal Morphology: • Structured Pattern • Maximum Interface • Short pathways to electrodes • 20 nm to interface at any given point • Real Morphology: • Amorphous pattern • Isolated phases that do not reach electrodes • Various distances to interface 20 nm 20 nm C. M. Martin, V. M. Burlakov,a H. E. Assender, and D. A. R. Barkhouse http://www.ctcms.nist.gov/fipy/examples/cahnHilliard/CH.png

10. Cahn-Hilliard Equation: Used to model various morphologies. Approach and Methods • Where: • c is concentration • D is diffusion coefficient • γ is length of the transition region between phases • ∇2 is the Laplacian operator

11. Morphology Metrics • Power Spectral Density: • Auto Correlation Function: • Betti Number • b0, b1, and b2 http://www.sciencedirect.com/science?_ob=ArticleURL

12. Current Status • Learning C++ • Learning FFT, PSD, ACR, and Betti Number • Analyzing given morphologies provided by experimental results “Columnlike” Structure of theCross-Sectional Morphology of Bulk HeterojunctionMaterials Ji Sun Moon,† Jae Kwan Lee,† Shinuk Cho,† JiyunByun,‡ and Alan J. Heeger*,†

13. Future Goals • Run given program through super computer “CyStorm” • Analyze the morphology from this computational model

14. Questions?