Identification of the Molecular Precursors for Hydrazine Solution Processed CuIn(Se,S)₂ Films and Their Interactions

We investigate the molecular species present in hydrazine CuIn(Se,S) 2 precursor solutions, their interactions, and phase formation in solution processed CuIn(Se,S) 2 thin films through Raman spectroscopy. The reaction between Cu 2 S and sulfur yields [Cu 6 S 4 ] 2− ions, while [In 2 Se 4 ] 2− ions are formed by the reaction of In 2 Se 3 with selenium within their respective solutions. Once combined to prepare a CuIn(Se,S) 2 precursor solution, these two species appear to be bridged via newly formed In−S bonds. The creation of the In−S bonds in the CuIn(Se,S) 2 precursor solution provides strong evidence for the mixing of copper, indium, sulfur, and selenium at a molecular level even prior to deposition. From this configuration, relatively little atomic diffusion is required to reach the chalcopyrite structure, which enables the formation of highly uniform polycrystalline CuIn(Se,S) 2 films at relatively low temperatures.