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

摘要

The addition of Ag to Cu-Ga-In precursors for reaction to form (AgCu)(InGa)Se 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) 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) 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.