Sulfurization of Cu–In electrodeposited precursors for CuInS2-based solar cells

Cu–In electrodeposited layers were annealed using rapid thermal processing (RTP) in a reactive atmosphere containing sulfur vapors. The CuInS₂ formation mechanism during sulfurization of electrodeposited precursors proceeds mainly through direct sulfurization of the metallic Cu–In alloy, forming spinel CuIn₅S₈ and chalcopyrite CuInS₂ ternary phases. During the heating step, the Cu–In metallic alloy gets richer in copper as the temperature increases and transforms from CuIn₂ to Cu₁₁In₉, then Cu₁₆In₉ and finally to Cu₇In₃. The use of rapidly cooled samples stopped after different durations of the process along with ex-situ XRD analysis enabled us to differentiate the Cu₁₆In₉ and Cu₇In₃ phases. Finally, the efficiency of the solar cells made with the two-step electrodeposition and RTP low-cost process reaches 11% (active area 0.421 cm²), which is close to the results obtained for cells made with PVD precursors.