Investigating Chemistry of Metal Dissolution in Amine-Thiol Mixtures & Exploiting it towards Benign Ink Formulations for

<p>Dissolution of metallic species in amine-thiol solvent mixtures has recently received attention for the deposition of metal chalcogenide semiconductor films for optoelectronic applications. However, little is known about the dissolution pathway for metallic precursors in an amine-thiol solvent mixture. To exploit the full potential of this method, it is essential that a detailed understanding of the dissolution chemistry be developed. In this study, we use several characterization techniques to examine metal dissolution and then propose overall mechanisms when In and Cu metals are dissolved in a hexylamine/1,2-ethanedithiol mixture. These dissolutions are found to be reactions leading to metal oxidation with co-evolution of H<sub>2,</sub> forming bis(1,2-ethanedithiolate) indium (III) in the case of indium dissolution and high nuclearity Cu(I) thiolate compounds in the case of copper dissolution. This understanding enables issues of toxicity and corrosivity associated with the amine-thiol system to be addressed by utilizing it as a mixture of reactants rather than a bulk solvent for ink formulation. Here, we demonstrate that metal complexes formed by dissolving a range of metals relevant to chalcogenide optoelectronics including Cu, In, Zn, Sn, Se and Ga with Se in amine-thiol solution can first be isolated by evaporation of the precursor solution and then dissolved in  weakly coordinating organic solvents to provide benign and stable solutions free of unreacted amine and thiol for film fabrication. We utilize this approach for the fabrication of CuIn(S,Se)<sub>2</sub> solar cells using DMSO as a fabrication solvent producing preliminary devices with a promising power conversion efficiency of 9.03%.</p> <nb:citations></nb:citations>