yes, I see this paper and other papers like this, but the papers just present the variation of contact resistance vs gate-source voltage in Fig and dont present any equation, Is it possible for me to have a math equation between Rc and Vgs ??I think the key to understand the background of this questions is this - "organic FET".
It looks like organic FETs have quite different physics than standard Si MOSFETs - see for example this paper:
In particular, contacts in organic FETs are not Ohmic, and their properties depend on channel condition (applied voltages, etc.).
I searched but I cant find any math equation for Rc vs Vgs :bang:Compact models in general and organic FETs in particular is not my area of expertise, but why don't you use Google search to find what you need: