Hi Indudhar,

This depends on the voltage range where you are going to calculate the ideality factor. Within very low bias voltage region both the TE and Cheung's model can deliver almost similar results. However, at higher voltages, the series resistance effect dominates. Therefore, you have to use Cheung's model. 

Hi Avishek,

From the literature I see that, one has to use the data points in the downward curvature region of I-V plot in Cheung's model. When I followed the said procedure I see more no. of data points (voltage range) in Cheung's model than in TE model. Does this a wrong way compare the models when the voltage ranges are different?

Dear Indudhar,

From the conceptual point of view the ideality factor depends on the effect of the series resistance on the terminal i-v characteristics. Therefore to avoid the effect of the series resistance one has to choose the current range such that the voltage drop on the series resistance IRs is negligible compared to the junction voltage drop. 

You may find useful information about this issue in the paper at the linhttps://www.researchgate.net/publication/232710923_A_Zekry_and_G_El-Dllal_effect_of_MS_contact_on_the_electrical_behavior_of_solar_cells_Journal_of_solid-state_Electronics_Vol31_No1_1988k:

Best wishes

Article A. Zekry and G. El-Dllal, “ effect of MS contact on the elec...