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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 Cu2S and sulfur yields [Cu6S4]2- ions, while [In2Se4]2- ions are formed by the reaction of In2Se3 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.