Lecture 9B - Solar Photovoltaics - Part 2

Lecture 9B - Solar Photovoltaics - Part 2 - 2/28/11 ECE...

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2/28/11 1 ECE 4364/5374G-9B (c) Saifur Rahman 1 Professor Saifur Rahman Electrical & Computer Engineering Dept. Virginia Tech ECE 4364/5374G: Alternate Energy Systems Lecture 9B – Photovoltaic Systems Part 2 ECE 4364/5374G-9B (c) Saifur Rahman 2 We will assume a single crystal silicon material. Silicon is representative of diamond crystal structure. Each atom is covalently bonded to four nearest ones. Each atom shares its four valence electrons with four neighboring atoms. Core electrons are tightly bonded and do not contribute to electrical conductivity. At absolute zero, the semiconductor is a perfect insulator. Basic opera+on of a solar cell
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2/28/11 2 ECE 4364/5374G-9B (c) Saifur Rahman 3 Figure 9.1 – Two dimensional representa+on of intrinsic silicon crystal ECE 4364/5374G-9B (c) Saifur Rahman 4 Figure 9.2 – Silicon crystal with a broken covalent bond
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3 ECE 4364/5374G-9B (c) Saifur Rahman 5 As temp is raised above zero deg Kelvin, energy is transferred to valence electrons. Some electrons begin to conduct electrical charge in the conduction band. These electrons are called intrinsic carriers. Amount of energy needed to bridge valence and conduction bands is called the energy gap which is 1.12 eV for silicon. At 300 deg K there are 1.6 x 10e10 intrinsic carriers per cubic centimeter. Metal has 10e22 such carriers. Basic opera+on – contd. ECE 4364/5374G-9B (c) Saifur Rahman 6 Silicon needs to be doped to increase conductivity. Boron, aluminum, gallium or indium doping results in p-type semiconductor. Phosphorus, arsenic or antimony doping results in n-type semiconductor. The action of metallurgically joining uniform p- and n-type samples produces a p-n junction. There positive and negative charges redistribute establishing internal electric fields. Basic opera+on – contd.
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This note was uploaded on 03/16/2012 for the course ECE 5374G taught by Professor Srahman during the Spring '12 term at Virginia Tech.

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Lecture 9B - Solar Photovoltaics - Part 2 - 2/28/11 ECE...

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