Internal field produced by the junction separates some of the positive charges ("holes") from the negative charges (electrons) within the photovoltaic device.   The holes are swept into the positive or p-layer and the electrons are swept into the negative or n-layer.

  Although these opposite charges are attracted to each other, most of them can only recombine by passing through an external circuit outside the material because of the internal potential energy barrier.

  Therefore if a circuit is made power can be produced from the cells under illumination, since the free electrons have to pass through the load recombine with the positive holes.