( for last layer ) The increase in the surface roughness is useful for

collecting more radiation in solar cell application, where due to light

scattering at surface roughness, it may lead to better light trapping and

higher conversion efficiency of the thin film solar cells, but on the other

hand this roughness may incur a higher contact resistance of the front

electric contact grid

for the junction between two layer, the increase in the surface roughens lead to increase the combination of the hole and electron (reverse saturation current ) through the junction,this lead to decrease the efficiency of thin film solar cell

I agree with Slewa. Surface roughess may improve the light absorption at the expense of increasing contact resistance. Surface roughess may also improve charge separation.

Thank you Slewa and Gupta. Do you have any papers related to this. Can you send the link.

you welcome .......... read my thesis