Is there any mathematical formula there for the ideality factor of the diodes?
I will be very much thankful for the above. Please send the mathematical expression for it.
Dear Manoj,
I would like to somewhat elaborate the answer of the the colleagues Andres and Dreher. At first, there is analytical formula fro the ideality factor. You can find them by following the link:http://journals.tubitak.gov.tr/physics/issues/fiz-07-31-1/fiz-31-1-2-0609-3.pdf.
However, the ideality factor is best estimated from the dark i-v characteristics at the intermediate current range where the both Rsh and Rs are negligible. In this current range the the diode equation follows the equation:
I= I0 exp V/nVt, with the symbols have their usual meaning.
In this region one selects two points I1,V1 and I2,V2. and substite these value in the equation one gets;
V2-V1 = n ln I2/I1,
n =( V2-V1)/ ln I2/I1,
This may be the best approach to estimate a most probable value for the ideality factor n.
Best wishes
The ideality factor is derived from the slope of the dark-IV, Suns-Voc and ocassionally the Light-IV curve.
The basic cell equation in the dark is:
,
where I is the current through the diode, V is the voltage across the diode, I0 is the dark saturartion current, n is the ideality factor and T is the temperature in kelvin. q and k are both constants. for V > 50 - 100 mV the -1 term can be ignored and so the above equation reduces to:
taking the log of both sides of the equation gives:
When plotting the natural log of the current against the voltage, the slope gives q/nkT and the intercept gives ln(I0). In real cells the ideality factor depends on the voltage across the cell. The ideality factor can either be plotted as a function of voltage or it can be given as a single value. Since the ideality factor varies with voltage, if given as a single value the voltage range also needs to be given.
Deviations in the ideality factor from one indicate that either there are unusual recombination mechanisms taking place or that the recombination is changing in magnitude. Thus the ideality factor is a powerful tool for examining the recombination in a device. The measurement of I0 is only valid when the ideality factor is stable.
Evening dear Manoj,
I would like to somewhat elaborate the answer of the the colleagues Andres and Dreher. At first, there is analytical formula fro the ideality factor. You can find them by following the link:
:http://journals.tubitak.gov.tr/physics/issues/fiz-07-31-1/fiz-31-1-2-0609-3.pdf
You can also find methods to determine the ideality factor of the solar cell by following our chapter: Chapter Solar cells and arrays: Principles, analysis and design
There is also simplified practical methods to calculate the ideality factor n:
please follow the original paper: Article A distributed SPICE-model of a solar cell
Best wishes
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