An Investigation of the Surface Properties of (Ag,Cu)(In,Ga)Se $_{\bf 2}$ Thin Films

(Ag,Cu)(In,Ga)Se₂ alloy absorber layers with various Ga/(Ga+In) and Ag/(Ag+Cu) ratios were deposited using multisource elemental evaporation and analyzed by glancing incidence X-ray diffraction and energy dispersive X-ray spectroscopy. All films exhibit chalcopyrite reflections in the X-ray diffraction pattern and films with 0.5 ≤ Ga/(Ga+In) <; 1 and Ag/(Ag+Cu) >; 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 measurements show that all films studied have low (Ag+Cu)/Se and (Ag+Cu)/(Ga+In) ratios near the surface relative to the bulk composition, consistent with an ordered defect compound identified as (Ag,Cu)(In,Ga)₅Se₈. Additionally, the near-surface region of (Ag,Cu)(In,Ga)Se₂ films contains a higher Ag/(Ag+Cu) ratio than the bulk and the Ag(In,Ga)Se₂ film contains excess Ag near the surface.