1. Applications of Photovoltaic Technologies
2017/4/17
Applications of Photovoltaic Technologies
Referenced website:

2. Why Solar Cells? Finite fossil fuel supply Less environmental damage
2017/4/17
Finite fossil fuel supply
Less environmental damage
No radiation risk (meltdown)
Nearly infinite supply of FREE energy
Sun gives us 32 x1024 joules a year,
Cover 0.1% of the Earth’s surface with 10% efficient solar cells with an efficiency of would satisfy our present needs.

3. Greenhouse Effect
2017/4/17
Human activities have now reached a scale where they are impacting on the planet's environment and its attractiveness to humans.

4. Spectrum of light h: Planck’s constant 6.626×10-34 (J-s)
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h: Planck’s constant 6.626×10-34 (J-s)
ν: frequency (s-1)
λ: wavelength (m)
c : light speed 3.0× 108 (m/s)

5. Atmospheric Effects
2017/4/17
Atmospheric effects have several impacts on the solar radiation at the Earth's surface. The major effects for photovoltaic applications are:
a reduction in the power of the solar radiation due to absorption, scattering and reflection in the atmosphere;
a change in the spectral content of the solar radiation due to greater absorption or scattering of some wavelengths;
the introduction of a diffuse or indirect component into the solar radiation; and
local variations in the atmosphere (such as water vapor, clouds and pollution) which have additional effects on the incident power, spectrum and directionality.
Hu, C. and White, R.M., "Solar Cells: From Basic to Advanced Systems", McGraw-Hill, New York, 1983.

6. Solar Radiation Power emitted from Sun =3.8×1023 (kw)
2017/4/17
Power emitted from Sun =3.8×1023 (kw)
Power direct to Earth=1.8×1014 (kW)
Solar constant=1353 W/m2
T=5762 K

7. Air Mass (AM) Intensity
2017/4/17
AM0 : The standard spectrum outside the Earth's atmosphere.
AM 1: Light incident with the angle of 0 degree.
AM 1.5: Light incident with the angle of 48 degree.
Intensity
Meinel A.B. and Meinel M.P., "Applied Solar Energy", Addison Wesley Publishing Co., 1976
ID : Direct beam intensity (W/m2)
IG : Global irradiance (W/m2)

8. Standard Solar Spectra
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9. Standard Solar Spectra-cont.
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The AM1.5 Global spectrum is designed for flat plate modules and has an integrated power of 1000 W/m2 (100 mW/cm2).
The AM1.5 Direct (+circumsolar) spectrum is defined for solar concentrator work. It includes the direct beam from the sun plus the circumsolar component in a disk 2.5 degrees around the sun. The direct plus circumsolar spectrum has an integrated power density of 900 W/m2.

10. Part of periodic table II III IV V VI B C(6) Al Si(14) P S Zn Ga
2017/4/17 II
III IV V VI B
C(6) Al
Si(14) P S Zn Ga
Ge(32) As Se Cd In Sb Te

11. Compound semiconductors
2017/4/17
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

12. Direct and indirect semiconductor
2017/4/17 Ev E P Ec
Indirect Semiconductor
phonon
photon Ev E P Ec
Direct Semiconductor
photon
High absorption probability
Low absorption probability
GaAs; InP etc.
c-Si

13. Crystal Structures Crystalline Amorphous Polycrystalline
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Crystalline
In a crystalline solid atoms making up the crystal are arranged in a periodic fashion
Amorphous
Commercial Si solar cells
Polycrystalline
Some solids are composed of small regions of single crystal material, known as polycrystalline.
In some solids there is no periodic structure of atoms at all and called amorphous solids

14. Commercial Si solar cells
2017/4/17
SINGLECRYSTAL
POLYCRYSTAL
AMORPHOUS

15. Metal-insulator-conductor
2017/4/17 Eg
Empty States (CB)
Filled States (VB)
metal
semiconductor
insulator
In metal conduction band (CB) and valence band (VB) overlap, in insulator and semiconductor CB and VB are separated by a energy band (Eg).
Eg for Si is eV (semiconductor) as compared to 5eV for diamond (Insulator)

16. Photon is a particle with energy E = hv
Photoelectric effect
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Electron
Photon
Semiconductor
Metal Eg
Photon
Photon is a particle with energy E = hv
Eph( hv)>Eg

17. Absorption of Light
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Eph < EG Photons with energy Eph less than the band gap energy EG interact only weakly with the semiconductor, passing through it as if it were transparent.
Eph = EG have just enough energy to create an electron hole pair and are efficiently absorbed.
Eph > EG Photons with energy much greater than the band gap are strongly absorbed

18. N- and P-type
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Addition of impurities with five valence electrons results an extra electron available current conduction
P, As, Sb (donor impurities
Addition of impurities with three valence electrons results in available empty energy state, a hole
B, Al, In, Ga (Acceptor impurities)

19. Physics of Photovoltaic Generation
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Physics of Photovoltaic Generation
If energy of inclined light (Ehp) > Energy band of material (EG).
Then, emit electron-hole pair (EHP) to produce the electric current.

20. Physics of Photovoltaic Generation
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Physics of Photovoltaic Generation
n-type semiconductor
Depletion Zone
p-type semiconductor

21. Solar Cell-structure A solar cell is a P-N junction device
2017/4/17
A solar cell is a P-N junction device
Light shining on the solar cell produces both a current and a voltage to generate electric power.
Busbar
Antireflection coating
Fingers
Emitter
Antireflection texturing
(grid pattern)
Base
Rear contact