Hello PF Let's say I have a device with three layers, A, B, and C, where layers A and C are the anode and cathode. I can measure the IV curves from that device easily. Now lets say I added a fourth layer, D, in between A and B. Layer D interacts with layer B such that it increases it's conductivity. So if I measure the IV curves again, I should get an increase in I for a given V. From looking up some equations on mobility, I know I can characterize the mobility as *sigma* = n e *mu*. Now I would normally say that if I get a doubling of conductivity, I would get a doubling of mobility, but the charge carrier density, n, is different since I added the fourth layer D. So how could I figure out my exact increase in mobility?