First Stages of CuInSe[sub 2] Electrodeposition from Cu(II)-In(III)-Se(IV) Acidic Solutions on Polycrystalline Mo Films

The first stages of the electrochemical deposition of a Cu-In-Se compound on molybdenum-coated glass were investigated. The surface morphology was examined after various deposition times by a field emission gun-scanning electron microscope. The surface composition and chemical environment analysis were characterized by X-ray photoelectron spectroscopy (XPS). Raman spectroscopy, X-ray diffraction, and X-ray fluorescence were also performed. This enabled the growth steps to be evidenced. A quasi-instantaneous three-dimensional nucleation occurs. The first nuclei are made of a copper-rich Cu-Se phase without indium. Codeposition of indium starts when the Se/Cu surface ratio reaches a value close to 1, which confirms that the formation of a Cu-Se phase is a prerequisite for indium incorporation. With increasing the deposition time, the In/Cu surface ratio increases and tends to a constant value close to 0.5, smaller than the bulk value. The Se/Cu ratio increases first rapidly and then more slowly, when coalescence of the nuclei has occurred. XPS analysis shows that this two-step behavior corresponds to an evolution of the chemical environment of the Se species, indicating the presence of several Se compounds in the film. X-ray diffraction and Raman spectroscopy confirm the presence of a Cu-Se phase and elemental Se, in addition to the predominant chalcopyrite phase.