In this work, a photoelectrochemical approach is applied to the characterization of oxide layers grown on copper in 0.5 M NaCl solutions, under open circuit corrosion conditions. Cathodic photocurrents are observed from the beginning of the immersion, but an additional anodic component of the photocurrent appears for longer immersion times. In the presence of benzotriazole, a corrosion inhibitor for copper, the oxide layer thickness is much lower and simultaneous n-type and p-type responses can be measured at the rest potential from the beginning of the immersion. These results, supported by a theoretical modelling of the spectral responses as a function of oxide layer thickness, provide new information about interface energetics with thin passivating oxide layers.