The composition and solar cell behaviour of CuInS2/ZnSe junctions have been studied with XPS and electroreflectance (ER) techniques. Quite stoichiometric ZnSe thin films grow on CuInS2, substrates by chemical bath deposition (CBD), even if using different concentration of Zn and Se precursors. This result contrasts with those of films grown on conducting SnO2, which present a higher concentration of Zn not bonded to Se. mainly as Zn(O,OH) and metallic Zn-0. ER at different incidence angles (angle resolved electroreflectance, ARER) shows two signals from the CuInS2, surface in contact with ZnSe. The signal with increasing intensity at lower incidence is assigned to an interfacial CuInS2, phase with higher energy gap. A lower conversion efficiency was found on those cells where this signal is more intense. XPS results at the CuInS2/ZnSe interface seem to indicate that such interfacial ARER signal is associated with an interfacial In excess.