Effect of sputtering sequence on the properties of Ag-Cu-In-Ga metal precursors and reacted (Ag,Cu)(In,Ga)Se2 films

The addition of Ag to Cu-Ga-In precursors for reaction to form (AgCu)(InGa)Se₂ has shown benefits including improved adhesion, greater process tolerance and potential for improved device performance. In this study, sequential layer sputtering of Ag-Ga, Cu-Ga, and In targets with different layer sequences is characterized. Ag/(Cu+Ag) and (Ag+Cu)/(Ga+In) ratios were fixed at 0.25 and 0.9, respectively. The most uniform morphology is achieved in Ag-Ga/Cu-In-Ga co-sputtered precursors. No metallic In phase was found in this case, and only the Ag(In,Ga)₂ phase was detected. Varying the sputtering sequence for stacked layers results in dissimilar morphologies and structural phases. X-ray diffraction (XRD) analyses reveal that the Ag-Ga and In layers intermix when they are in contact, forming a Ag(In,Ga)₂ phase. Incorporating a Cu-Ga layer between the Ag-Ga and In layers prevents the formation of such a phase. Finally, solar cells fabricated from the Cu-Ga/In/Ag-Ga metal precursor sequence showed the highest overall performance.