Some of the fundamental problems concerning nanocryst. film electrodes such as photocurrent and photovoltage generation, the effect of an external bias, and the importance of surface states were discussed. The problems were described from a mol. perspective and for example quantum chem. calcns. on small TiO2 clusters can be used to describe local surface states. Nanocryst. semiconductor electrodes exhibit properties which differ strongly from those of bulk solids.