solarna celija (1)

8/13/2019 solarna celija (1)

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Instead of introduction

ber Halbleiter sollte man nicht arbeiten, das isteine Schweinerei; wer wei, ob es berhauptHalbleiter gibt.

Wolfgang Pauli, 1931

Nitko se ne bi trebao baviti poluvodiima, to je

obina pizdarija, ne znamo postoje li uope.Wolfgang Pauli, 1931


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p-n photovoltaic effect

If ordinary p-n junction is short circuited in absence of light, no

steday current will flow in external circuit inspite of p-n potential(first low of thermodynamics)

If light is allowed to fall on pn junction, measurable voltagesand currents may be observed


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Optical generation


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Absorption coefficient


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Short circuited and open circuited p-n junction 1) open circuit:

falling light creates excess electron-hole pairs

electrons created in the p-region diffuse to the junction and descend potential barries

to n-side (simillar reasoning may be applied for hoels) These charge densities lower potential barrier for V0

Phenomenon is called p-n photovoltaic effect and output voltage photovoltage

2) Short circuit:

If external circuit connecting p and n regions is closed, electrical current will flow as

long as there is diffusion current of optically created excess electrons the n-regionand current of optically created hoes from p-region to maintain barrier at heightother than 0


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I-V characteristics of the illuminated p-n junction (1)


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after tedious but straightforward calculation , we obtain:

which can be reorganised as follows:


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J0stands for saturation current (dark current) and it should be kep as lowas possible

It is function of material and dimensional parameters of the device,independent of the illumination level

JLis generation current, independent on the junction voltage Vbutdirectly proportional to illumination intensity. This comes from thefact that generation G = Ne-x, and N is proportional to illumination

If the circuit resistance is infinite (open circuit), J vanishes and the open-circuit voltage Vocis given by:

Vocis maximum obtainable volatge for given irradiance. AssumingJL>> J0, Vocincreases exponentially with ILand thus irradiance(illumination). Note: Maximum Voc is of order of !!


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If the circuit resistance (including internal deviceresistance) is zero, generated photovoltage V0= 0 and

maximal current, so called short circuit currentflows:

Jsc= -JL

In case of both Vocand Jsc, delivered power is 0.


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Sollar cell efficiency (1)


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Sollar cell efficiency (2)


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Task

1. Set 9 voltagelevels on variac,ranging from 0V,in steps of 30 V

2. For each voltagelevel, measureIscand solarirradiance (SI)

3. Plot Iscvs SIpoints

4. Using MS Excel,

find Isc= f(SI),includingcorrespondingstatisticalanalysis(LINEST)

Uv(V) SI (W/m2) Isc(mA)

0

30

6090

120

150

180210

240

Repeat procedure for LED and incandescent bulb

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