Solar TechnologyIn 2008

Daniel Ayoub

The University of Texas at AustinDepartment of Chemical Engineering

Introduction

Photovoltaic Cells Derived from Greek Language: φώς

“Phos” meaning light, and “voltaic” meaning electric

Brittanica

Introduction

First discovered in 1839 by French physicist A.E. Becquerel.

First “solar cell” build in 1883 by Charles Fritts with gold on selenium. Produced a current.

But why did this work?

Light

Initially Maxwell’s wave theory of light predicted energy would be proportional to light intensity

Einstein described light as composed of discrete quanta – photons.

E=hν

Light

A photon above a certain threshold frequency (energy) is able to eject a single electron.

= The Photovoltaic Effect

Light

1921 Albert Einstein Nobel Prize in Physics

Quantum Revolution

Solar Cells – General

Source: How stuff works

Solar Cells – P-n Junction

What is a p-n junction?

Materials – P-type

Addition of trivalent impurities usually from group IIIA.

“Hole”-rich material

Boron, Aluminum, Gallium, etc..

E.g.: Diffuse B2H6 gas into silicon

Source: Hyperphysics

Materials – N-type

Addition of pentavalent impurities usually from group 5A.

“Electron”-rich material

Phosphorus, Arsenic, Antimony, etc..

E.g.: Diffuse PH3 gas into silicon

Source: Hyperphysics

Solar Cells – Band Gap

△E between Valance band and Conduction band Available carriers only in conduction band

Source: Wikipedia

Materials – P-n Junction

Carrier Diffusion Depletion Region

at interface E-Field

Source: Wikipedia

Solar Cells

Photons above band gap energy create free electron-hole pairs.

E-Field will send free electron from P to N side

Solar Cells

Disrupts electrical neutrality Collect electrons. Pass through external circuit

to do work. Recombine with respective holes back in P-

type

Solar Cells – General

Source: How stuff works

Solar Cells Today

First Generation Single Junction Expensive Theoretical max efficiency 33%

(average 15%) $1/Watt

Solar Cells Today

Second Generation (Now) Alternative manufacturing techniques

Thin-Films CVD Electroplating

Defects reduce efficiency=>Use Multi-layer

CdTe, CIGS, etc Typical layer efficiency of 7-10% Replace 80cents of Si with 1 cent of

thin-film material

Solar Cells – HelioVolt (Austin, TX)

FASST Process = cheaper 10-14% power conversion efficiency

Solar Cells – Power Generation

Solar Cells – Power Generation

Solar Cells – Cool Stuff

Solyndra Cylindrical Tubes Thin-film CIGS coating Paint roof white Collect 20% more light 2x energy density claim Low installation cost

(1/2)

Source: Scientific American

Solar Cells – The Future

Third Generation Solar Cells Current Research targeting 30-60%

efficiencies! July 2007, U Delaware set 42.8%

efficiency record (1994 previous record of 24.7%)

Exploit other frequencies of light Multi-junction cells Cheaper manufacturing processes

References

• Hyperphyisics “The Doping of Semiconductors” http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/dope.html Retrieved Nov. 10th, 2008.

•Wikipedia. “Solar Cell”. http://en.wikipedia.org/wiki/Solar_cells/. Retrieved Nov. 10, 2008•Scott Aldous, How Stuff Works. “How Solar Cells Work”. http://

science.howstuffworks.com/solar-cell4.htm. Retrieved Nov. 10, 2008. • David Biello, Scientific American. “Cylindrical Solar Cells Give a Whole New Meaning to Sunroof”

http://www.sciam.com/article.cfm?id=cylindrical-solar-cells-give-new-meaning-to-sunroof• Carl Gutierrez, Forbes Magazine, Market Scan, “First Solar Goes Supernova” November, 2008 • Ed. P. Capper, “Properties of Narrow-Gap Cadmium-Based Compounds” INSPEC, IEE, London, UK, 1994. • Kim J et al. “Efficient Tandem Polymer Solar Cells Fabricated by All-Solution Processing.” Science, 2008. • Antonio Luque and Steven Hegedus. “Handbook of Photovoltaic Science and Engineering.” John Wiley and Sons. 2003 • M.A. Green et al. “Crystalline Silicon Thin-Film Solar cell Modules.” Solar Energy, 2004. • Fthenakis, “Renewable & Sustainable Energy Reviews," Vol. 8, 2004 • V M “Life Cycle Impact Analysis of Cadmium in CdTe PV Production” pp 303 – 334, • “Plastics: Background Information for Teachers.” American Plastics Council, 2006. • Stefan Lovgren, National Geographic News, “Spray-On Solar-Power Cells Are True Breakthrough” January, 2005. • "New Ways to Catch Rays" NOVA Website, November, 2008. • Steven Latham "Saved by the Sun", NOVA on PBS. Courtesy of SCHOTT. April 2007. • Kevin Bullis, “Making Cheaper Solar Cells” MIT Technology Review, September 12, 2008. • Peter Fairley, “Fixing the Power Grid” MIT Technology Review, October 17, 2007. • Reuters on 2007 “Abu Dhabi to build $350m solar power plant” • Reuters on 2007 “Egypt invests $109mn in solar power”