Dear Dennish

Welcome,

You have a thin film CZTS with two metal layers contacted to it to access it electrically.

You expect that the I-V characteristics of such Metal semiconductor metal MSM are straight lines but you get some nonlinear curve somewhere between the ohmic behavior of straight line and a rectifier like I-V curve. 

It is well known among the semiconductor device literature that the metal semiconductor contacts may be either ohmic or rectifying according to the metal the semiconductor work functions and the doping concentration of the semiconductor.

So, it is clear that your metal semiconductor contacts behave nonohmic and approaching that of the rectifiers. 

To get ohmic MS contacts one has to make the recombination of the carries at the interface of the MS contact very large approaching the thermal velocity

The other technique is to raise the doping concentration to sufficiently large values such that a tunnel MS contact is formed.

On the other side it seems that your specimen is sensitive to the illumination as at any applied voltage the magnitude of the current increases due to the photogenerated carriers.

For more information  please see the link:https://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_1988

wish you success

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

 These (nice) I-V-curves are typically for rectifying (non-Ohmic) contacts. The forward direction is for positive voltages, the reverse direction can be observed at negative voltages. If you illuminate for reverse voltages the contacts, a photocurrent flows. The increase in the current due to electron hole separation in the space charge region is observed. The breakdown near -3V can have different origin but generally this photoelement is a nice success.

Prof. Zekry and Prof. Rudiger : thank you for the suggestions and discussion.

Is it applicable for Photovoltaic applications?.  

Dear Dennish,

I believe, principially you have shown - it is applicable. Nevertheless, the parameter are still insufficient, especially the ratio of reverse current and photocurrent. The diode characteristic has to be improved. Furthermore, the quantum efficiency has to be determined as a function of wavelength. But the potential for this material is high due to the low cost materials used.

Yes Prof.

Currently, i am working on making these material for potential use of Photovoltaic applications. Your answers interesting me. Thank you for that. I will let you know my results. 

thank you for the answers, Prof.

Dear Dennish,

I would like to greet Prof. Mitdank from Berlin

Your device shows photo electric effect. It does not show photo voltaic effect. It is merely a semiconductor film supplied by two nonlinear metal contacts. It acts as a photo constructor with nonohmic contacts. To get a photovoltaic effect you have to produce a p-n heterojunction structure or rectifying M-S junction to the whole illuminated surface while allowing the solar radiation to penetrate to the underlying semiconductor.

For more basic information about the solar cells please follow the link:https://www.researchgate.net/publication/236002879_A_course_on_photo-voltaic_array_systems

Best wishes

Book A course on photo-voltaic array systems

There is certainly an interfacial layer between the metal and the semiconductors or between the n and p region of your device (probably due to oxydation or to gas adsorption).

fully agree with Rüdiger Mitdank