THE INVESTIGATION OF ALTERNATIVE METALS OF Au, Ag, Al AND Cu FOR BACK CONTACT USED IN FABRICATED ZnS/SnS HETEROJUNCTION FOR SOLAR CELL APPLICATION

In this research, we examined metallic back contacts effects on the electrical characteristics of heterojunctions in the context of solar cells. Gold, silver, aluminum and copper were selected as substitutes for the conventional molybdenum. Heterojunctions with SnS and ZnS as an absorber and buffer layers, respectively, were fabricated using spray pyrolysis. The characterization revealed the formation of SnS in an orthorhombic structure and ZnS in a cubic structure, displaying preferential orientations along (120) and (222) planes, respectively. These structures exhibited excellent crystallinity, evidenced by large crystallite sizes and phase purity, as confirmed by morphological study. Optical measurements indicated the band gap for SnS and ZnS as 1.5 and 3.1eV, respectively. Additionally, through Hall Effect and Mott–Schottky analysis, it was observed that the SnS and ZnS films displayed p-type and n-type conductivity, with corresponding carrier concentrations of 1.87×1018 and 1.41×1019cm−3, respectively. The electrical characteristics of the n-ZnS/p-SnS heterojunction were explored through forward I–V analysis. Photocurrent measurements revealed that the constructed structures demonstrated rectifying behavior. The resistance series and ideality factor values obtained were observed to be relatively high. The unusual ideality factor can be attributed to the formation of Schottky contact between contacts (Ag, Al, Cu) and SnS film, possibly due to defects at the interface state of ZnS/SnS. This study’s findings indicate that, among the tested FTO/ZnS/SnS heterojunction structures, with Au metal contact exhibited superior performance. It suggests that Au could serve as a viable alternative to Mo as the back metal contact for SnS-based solar cells.