Phase and surface modification by electrochemical post deposition treatments in ultrasonic-assisted CuInSe₂/Cu electrodeposited films

CuInSe₂ films were prepared onto Cu-cladded substrates by ultrasonic-assisted electrodeposition using different bath compositions and a fixed deposition potential of E=-1500 mV vs Ag/AgCl. In situ electrochemical treatments named selenization and electrocrystallization, in a Se⁴⁺ electrolyte were applied to modify the morphology, film structure and the phase composition. Films were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and photocurrent response. A Cu_2-xSe layer develops as the electrode is introduced into the electrolyte. The presence of Cu-In, In-Se, Cu-Se, cubic, hexagonal and tetragonal CuInSe₂ phases as well as elemental In and Se was observed. After selenization, partial phase dissolution and Se deposition is observed and after the electrocrystallization treatment the secondary phases such as Cu-Se, Cu-In, In and Se reduce substantially and the grain sizes increase, as well as the photocurrent response. Phase diagrams are constructed for each set of films and reaction mechanisms are proposed to explain the phase evolution.