Surface characterization of (AgCu)(InGa)Se 2 thin films for solar cells

AgCu(InGa)Se 2 alloy absorber layers with various Ga/(Ga+In) and Ag/(Ag+Cu) ratios were deposited using multi-source elemental evaporation and analyzed by glancing incidence x-ray diffraction and energy dispersive x-ray spectroscopy. All films exhibit satellite chalcopyrite reflections in the x-ray diffraction pattern and films with 0.5 ≤ Ga 0.5 have additional reflections consistent with an ordered defect phase which is limited to the near-surface region of the film. X-ray photoelectron spectroscopy results show that all films have low (Ag+Cu)/Se ratios near the surface, consistent with an ordered defect compound. Films with 0 5 Se 8 ordered defect phases. Additionally the near-surface region of (AgCu)(InGa)Se 2 films contains a higher Ag/(Ag+Cu) ratio than the bulk and the Ag(InGa)Se 2 film contains excess Ag near the surface.