Surface chemistry of electrodeposited Cu₂O films studied by XPS

The surfaces of electrodeposited Cu₂ O films grown using a variety of solution conditions have been examined using X-ray photoelectron spectroscopy (XPS). Sodium and carbon are identified as impurities in certain films. Cu₂ O films deposited from basic solutions using lactate or citrate ligands contain more impurities than films deposited from acidic lactate or acetate solutions. Depth proiling reveals that sodium is located as deep as 100 nm below the surface of one film in the form of Na-O-Cu bonds. Sodium content can be correlated with preferred orientation of the polycrystalline films, with strongly (111) orientated films containing the largest amounts of sodium. Prior to ion sputtering, Cu₂O/eutectic gallium-indium junctions display rectifying current-voltage behavior, with films containing larger amounts of impurities displaying lower photocurrent and open circuit voltage values. After sputtering the Cu₂O surface to remove the impurities, symmetric current-voltage behavior is observed.