The effect of the addition of benzotriazol on the passive behaviour of copper in borax solutions was analyzed in the potential region - 0.32 to 0.71 V vs. RHE using voltammetric, photocurrent and ellipsometric techniques. Oxide formation can be explained as a sequence of Cu2O growth tinner layer ippl) and dissolution precipitation of Cu(II), (outer hydrated oxide layer (oppl)). The resulting photocurrent was proportional to the thickness of the ipp]. However, significant variations in the amplitude and phase of the photocurrent were detected as a function of the potential region and the composition of the electrolyte. These effects are related to changes in the excess of cations accumulated in the ippl.