The rearrangement of charges and holes at the junction forms a potential barrier with a negative charge layer on one side and a positive charge layer on the other side.⁷  If the two sides are connected via a circuit, light striking the n-type semiconductor will knock electrons into the conduction band, which are repulsed from the potential barrier, and thus will flow into the circuit through a load to do useful work, in order to recombine with holes in the p-type material. But the process of electrons flowing out of the n-type material creates holes, which are then filled by electrons flowing across the junction, which also creates holes in the p-type material, which are filled by electrons flowing in from the circuit.  In this way electron hole combinations are continually forming and disappearing which results in a net charge flow or current through the system.  Remember that this flow is being driven by the energy in the incident sunlight, with out it the system is static.  So now that our solar cell is on line, how much juice can we squeeze out of it, or more appropriately, how much power can we harvest from the sun?