While the center of action in a nano-PV device is often taken to be the heterojunction where the excitons split to yield charges, most other parts of the device directly govern the transport and collection of the generated charges. This is particularly true for the electrodes used to collect the charges. A simple model predicts that the open-circuit voltage of these devices would depend directly on the difference in work-functions between the cathode and the anode. However, for many  devices either this result does not hold or the dependence is unclear. The actual performance depends upon the nature of the contact formed between the metal electrode and the photoactive material in question. This brings in a crucial dependece of the device performace on the geometry and electronic structure of, what is very often just the metal-semiconductor interface.