4. solar photo-voltaic technology-1

7/28/2019 4. Solar Photo-Voltaic Technology-1

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Light energyElectricity

It is generated due to principle of

photoelectric effect

Lets look at the process in some

further detail:


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Photovoltaic energy is the directconversion of light into electricity at

the atomic level.

Some materials exhibit a

property known as thephotoelectric effect that causes

them to absorb photons of light

and release electrons.

When these free electrons arecaptured, an electric current

results that can be used as

electricity.


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Metal

Semi-conductor

Deciding factor is capacity of material to excite electron

Option of materials


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Electron is excited (by photon) from filled (valence band) to empty conduction

band and then it participate in electricity conduction

Eg

Metal Semiconductor Insulator

Eg


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Metal

Bandgap isoverlapping

Electric field willnot be created inmetals

Semi-conductor

Bandgap issignificant

Best materialand hence usedin manufacturing


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n-type Si

Ec

Ev

Eg

Ed

T = 0K T > 50K

Ed

e--

Si

Sb

Donation of electrons from donor level to the conduction band

Group V donoratomeg, P, As or Sb) in the

covalent bonding model

of a Si crystal


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p-type Si

Ec

Ev

Eg

Ea

T = 0K T 50K

Ea

h

+

Si

Al

Group III acceptoratom (e.g. B or Al)

in the covalent bonding model of a Sicrystal

Acceptance of a valence band electrons by an acceptor level and the

resulting creation of holes


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Elemental semiconductors: Si, Ge Compound semiconductors: GaAs, InP

Ternary semiconductors: AlGaAs, HgCdTe

Quaternary semiconductors: InGaAsP, InGaAlP

Elemental IV

Compounds

Binary III-V Binary II-VI

Si SiGe AlP CdTe

Ge SiC GaAs CdS

As InP ZnS

GaP CdSe


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Video


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Green

photon Blue photon

Valence band

Conduction band

Band gap, Eg

Red

photon

Wavelength () red green blue

4. solar photo-voltaic technology-1

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