The chemical bath deposition of cubic copper (I) selenide (Cu2-xSe) thin films has been achieved on an inert Pt substrate from a selenosulfite-containing bath at 75 degrees C. The electrochemical polarisation of this film at -0.78 V vs. SCE leads to the transformation of the compound into the orthorhombic phase. The lattice parameter of the face-centered cubic copper (I) selenide increases from 5.742 Angstrom to 5.761 Angstrom due to the decrease of the concentration of Cu vacancies upon electrochemical polarisation. The transformation of the cubic to an orthorhombic phase starts to occur when copper vacancies reach a critical value of x < 0.15. This transformation seems to be induced by a Cu3Se2 impurity in the cubic Cu2-xSe phase.