Characterization and device performance of (AgCu)(InGa)Se2 absorber layers

The study of (AgCu)(InGa)Se₂ absorber layers is of interest in that Ag-chalcopyrites exhibit both wider bandgaps and lower melting points than their Cu counterparts. (AgCu)(InGa)Se₂ absorber layers were deposited over the composition range 0 < Ag/(Ag+Cu) < 1 and 0.3 < Ga/(In+Ga) < 1.0 using a variety of elemental co-evaporation processes. Films were found to be single-phase over the entire composition range, in contrast to prior studies. Devices with Ga content 0.3 < Ga/(In+Ga) < 0.5 tolerated Ag incorporation up to Ag/(Ag+Cu) = 0.5 without appreciable performance loss. Ag-containing films with Ga/(In+Ga) = 0.8 showed improved device characteristics over Cu-only control samples, in particular a 30-40% increase in short-circuit current. An absorber layer with composition Ag/(Ag+Cu) = 0.75 and Ga/(In+Ga) = 0.8 yielded a device with V_OC = 890 mV, J_SC = 20.5 mA/cm², fill factor = 71.3%, and ¿ = 13.0%.