Lecture Solar Cells

8/10/2019 Lecture Solar Cells

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Renewable Energy Sources.

Solar Cells



2

Solar Energy



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Renewable Energy Sources

1. Wind Turbine:

• Converting the wind energy into electricity

• Wind, Propeller, Electric Generator, Current Flow (lights)

2. Solar Cells• Converting the Sun’s (light) energy directly into electricity

• Intensity of the sunlight

• Wavelength of the sunlight

• Type and surface area of the solar cell

3. Fuel Cells

• Producing electricity by combining Hydrogen and Oxygento produce H2O

4. Other: Solar Panels

• Heating: Cold water in – Hot water out

• Material



4

Interesting Estimates *

• Every hour, enough sunlight energy reaches the Earthto meet the world’s energy demand for a whole year.

• The amount of energy from the Sun that reaches the

Earth annually is 4 E18 Joules.***

• The amount of energy consumed annually by the

world's population is about 3 E14 Joules.



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Solar Cells: Basic Concepts• Photovoltaics

• Solar cells, (also called photovoltaics - PV), convert sunlight directly intoelectricity.

• They are made of semiconductor material- similar to those used in computerchips.

• When sunlight is absorbed by these cells, the solar energy knocks electronsloose from their atoms, allowing the electrons to flow through the material toproduce electricity. – movement of electrons.

• Sunlight contains packets of energy called photons that can be converteddirectly into electrical energy.

• This is referred to as the photovoltaic effect.

• Photo- means light and -voltaic means electrical current;

• Thin film solar cells use layers of semiconductor materials only a fewmicrometers thick.

• Thin film technology has made it possible for solar cells to double as rooftiles, rooftop shingles, building front elevation.



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Photovoltaic Cells Photovoltaic cells are made of at least two layers of semiconducting material. The

first layer has a positive charge; the next layer has a negative charge. When

sunlight strikes the cell, the semiconducting material absorbs photons from the

light. This process frees electrons from the negative layer, which move to the

positive layer. This flow of electrons constitutes an electric current, which can be

captured in a circuit connecting the two layers. The electricity generated by a

photovoltaic cell can be used directly, stored in batteries.

http://www.energyeducation.tx.gov/renewables/section_3/topics/photovoltaic_cells/d.html

http://www.energyeducation.tx.gov/renewables/section_3/topics/photovoltaic_cells/d.html



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Solar Panel collects and

utilizes heat energy.

Photovoltaic panels (Solar Cells)

transform light energy into electricity

Suns Light and Heat

http://www.makeitsolar.com/images/Solar_Panel_03C.GIF



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Atoms

An atom is composed of three different particles: (for now)

Nucleus - Center of the atom:

1. Protons (P+)-- positively charged.

.

2. Neutrons -- no charge.

3. Elec trons ( e-) -- negatively charged.

-- orbit the nucleus.

No of proto ns = No of electron s

Protons (P+)

Neutrons

(e-)



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Valence Electrons - Helium atom model

Two valence electrons (-)

Two protons (+)

Two neutrons

Outermos t energy level

An electron cell can be thought of

as the orbit of electrons around thenucleus.

The electrons in the outermost shell,

called the valence shell, are calledthe valence electrons.

Valence electrons determinethe chemical /electrical

properties of the atom.

http://upload.wikimedia.org/wikipedia/commons/a/a9/Atom.svg



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Example



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Valence Band-(oversimplified description)

E n e

r g y

l e v e l s

Valence band

Conduction band

Band gap

c o n d u c t o r

s e m i c o n d u c t o

r s

i n s u l a t o r



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Boron B5, Phosphorus P15 Silicon Si14

e-e-

e-e-

e-

e-

e-

e-

e-

N

e-

Si

e-

e-

e-

e-

e-

e-

e-

e-

e-e

-

e-

e-e-

B

e

-

e

e

e

e

e

e

e-

e

P

e

e

e

e

e

e

e

e

e

e e Si = 4 valence e-

S



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Semiconductor Doping• How can we change the electrical properties of the pure Semiconductor

material?

• By adding foreign material to it, called dopants. (impurities)

• Boron, phosphorus, arsenic are common dopants.

• Rate of low :1 every 100,000,000 atoms

high: 1 every 10,000 atoms

Silicon (Si) with Phosphorus (P2,8,5) dopant : n-type(extra valence electrons are added)

Silicon (Si) with Boron (B2,3) dopant = p-type(missing fourth valence electron, holes)



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n - type

.e

e

e-

e

P

e

e

e

e

e

e

e

e

e

e e

e-

e-

e

-

e-

Phosphoru s w ith 5 valence gives - donor – n-type

Si-



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p- type

.

B

e-

e

e

e

e

e-

e-

e

-

e

-

Bo ron w ith 3 valence e - , accepts – acceptor

– p type

Si-



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p-n junction

e-

B

e-

e

e

e

e

e-

e-

e-

Si-

p-type

n-type

p-n Junct ion

e

e

e-

e

P

e

e

e

e

e

e

e

e

e

e e

e-e-

e-e-

Si-



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Photon Hits the Atom of a “Semi” Material

.

Hole is the “empty space” left behind as a result of the movement of the

free electron. Holes have + charge.



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Solar Cell Schematic. .

Protective Cover-Glass

Electrical Contact

Antireflective Layer

N

P-N Junction

PElectrical Contact

Load

current

P

Th P



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Sunlight is made of photons, small particles of energy.

These photons are absorbed by and pass through the material of a solar cell or solar

PV panel.The photons 'agitate' the electrons found in the material of the photovoltaic cell.

As they begin to move (or are removed), these are 'routed' into a current.

This, technically, is electricity - the movement of electrons along a path.

The Process



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In Summary

• Light breaks silicon bonds and creates “free”

electrons and holes, “missing electrons” • Holes are positive charges

• Built-in field separates electrons and holes

Step 1. Photogeneration of charge carriers,

electron (negative) and hole (positive).

Step 2. Separation of the charge carriers

through the medium.



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Q - What is a Circuit in Series ?

A – One where electricity travels on one path.

V = V1 + V2

I = Constant

V1

V2

V1=1.5

V2=1.5

I=1.7 A

P = (V1 +V2) (I)= (1.5+1.5) (1.7)

P ll l C ti M lti l P th



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Parallel Connection: Multiple Paths

Solar Cells vs. Equivalent Batteries

I2I1

(I)

I=I1+I2

I2

(I2 = I – I1)

V = Constant

I1 = 1.7 AI2 = 1.7 A

I = 1.7 + 1.7 = 3.4 A.

V1 = V2 = 1.5 V

Power = ?

http://www.makeitsolar.com/images/circuitcellparall.jpg




























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Factors affecting Solar Cell Performance

Light intensity (type of light)

Light wavelength (color of light) Angle of incident light

Surface condition of solar cells cleanness)

Temperature on solar cells



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Clicker - Q1

The drawing is a model of a carbon atom.

How many protons does its nucleus have?

A. 2

B. 4C. 6

D. 8

E. 10e-

e-

e-

e-

e-

e-



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Q2. Adding Impurities

• By adding impurities to silicon in order togenerate “holes” we are building __ ?__ type

material.

A. n - type

B. p - type



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Q3

• Name the junction that is created by dopingadjacent regions of a semiconductor

A n-type

B p-type

C valence junction

D p-n junction

E silicon



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Q4. Given the values and the set up bellow, what is the

total power generated?

I1 = 1.0 A

I2 = 1.0 A

V = 3.0 V

A. P = 3.0 W

B. P = 4.0 W

C. P = 5.0 WD. P = 6.0 W

E. P = 7.0 W

V = 3.0I1

I2

I









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Review Question (Q5)

A p-type semiconductor is a ___?_____carrier?

A. Photon

B. Electron

C. Hole

D. Ion

E. None of the above



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Review Question (Q6)

Which of the following will deteriorate asolar cell’s performance?

A. Thickness of the cell

B. A water stainC. Shape of the cell

D. All of the above

E. None of the above

Lecture Solar Cells

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