The theory of MIS‐Schottky barriers and their electrical characteristics is examined for its application to solar cells. It is found that the interface behavior of contacts forward‐biased by illumination is qualitatively different from that of the same contacts biased in the dark by an applied forward voltage. Observed increases due to the interfacial layer in the open‐circuit voltage of the solar cell cannot therefore be associated with increases in the ’’nvalue’’ measured for the dark current, but rather are due to the different effects of this layer on the transport properties of majority and minority carriers. The theory predicts an optimum thickness for the interfacial layer above which the short‐circuit (minority‐carrier) current decreases, and the efficiency (fill factor) is degraded.