Note on copper-cuprous oxide photocells

In a recent paper (Mott 1939) the author has given a theory of the copper oxide rectifier which explains successfully the direction of rectification. The purpose of this note is to account for the electromotive force observed when the contact is illuminated. Cuprous oxide is an oxidation semi-conductor, whose conductivity depends on excess oxygen; moreover, at and below room temperature it shows a positive Hall coefficient (Engelhardt 1933). It follows that the current is normally carried by positive holes in a full band. The conductivity is given by δ = δ0e-Є/kTЄ ~ 0.3 eV, and 2Є will represent the work required to lift an electron from the full band to a normally empty “ impurity” level, i.e. a level due to excess oxygen.