Dear Fatemeh,

Professor Ruediger gave you the relevant relation. For an example of calculating the ideality factor n of a single diode model please follow the procedure given in my paper: Article A distributed SPICE-model of a solar cell

In order to determine n you have to choose the part of the I-V curve where the effect of the shunt and series resistance are negligible.

Best wishes

Dear Fatameh,

we have the I-V-relationship

I = IS*(exp(V/(nVT))-1) with n the ideal factor.

Now you plot the logarithm of the current I as a function of the voltage V:

ln I = f(V)

For sufficient high V, that you can neglect the -1you must find a linear function with the slope 1/(n*UT) with UT the thermal voltage kT/e. At room temperature UT nearly 25 mV. So, the inverse slope is nearly n*25mV.

With Regard

R. Mitdank

Dear Dr Rüdiger Mitdank

Thank you so much for reply. I ploted the liogarithm of the current i as a function of the V and i fund the slop for one graph:( y = 3/4295x - 12/31 )

but i didn't undrestand how unfortunately. can you help me and i send for you my graph (Excel or word File)? just i have 2 graph and i need ideal factor.

Thank you so much

Can you send an excel table with 2 rows with i and v-values?

R. Mitdank

Dear Dr Rüdiger Mitdank

What is your openion?. acording my results, is it good as diod (Schottky diode)?

Fatemeh

Dear Fatemeh,

Professor Ruediger gave you the relevant relation. For an example of calculating the ideality factor n of a single diode model please follow the procedure given in my paper: Article A distributed SPICE-model of a solar cell

In order to determine n you have to choose the part of the I-V curve where the effect of the shunt and series resistance are negligible.

Best wishes

I agree with Abdelhalim zekry sir

Following

Dear Fatemeh,

Welcome again,

Here an extended answer which i introduced before on a similar question:

I will introduce a physically based method.

Assuming that  the polymer hetero junction diode follows the diode shockley equation, I = Is ( exp [ V- I Rs]/nVt + V/ Rsh,then all you need to plot I versus V on a semilogarithmic scale. That is Log10 I versus V.

You will observe a straight line in the middle current ranges, the slope of this straight line  Log10 I2/I1 = Delta V/ nVt * log10 exp, with Delta V corresponds to the voltage change from I2 to I1. At low currents. the current through the shunting resistance will be dominant and Rsh= I / slope of the I-V characteristics near the zero diode voltage.

In order to determine Rs you extrapolate the straight line at the middle currents to the higher current range and see how much the I-V curve deviates from the extrapolated straight line . At certain current I, the voltage deviation the extrapolated line is Delta V, then Rs= Delta V / I.

Is is determined by extrapolating the straight line to the Zero voltage. The intercept current is Is.

For more information and to see an example please follow the Link:https://www.researchgate.net/publication/3062547_A_distributed_SPICE-model_of_a_solar_cell

There are other methods based on curve fitting and numerical techniques.

You can find this method in our book chapter in Elsevier: Chapter Solar cells and arrays: Principles, analysis and design

wish you success

Thank you all