Generated current typically flows perpendicular to the cell surface from the bulk of the cell and then laterally through the top doped layer until it is collected at a top surface contact.
The resistance and current of the base is assumed to be constant. The resistance to the current of the bulk component of the cell, or the "bulk resistance", Rb, is defined as:
taking into account the thickness of the material. Where:
l = length of conducting (resistive) path
ρb= "bulk resistivity" (inverse of conductivity) of the bulk cell material (0.5 - 5.0 Ω cm for a typical silicon solar cell)
A = cell area, and
w = width of bulk region of cell.