A monoamine–dithiol mixture is used to prepare homogeneous Cu(In, Ga)Se2 (CIGSe) molecular precursor solution, which yields a highly sulfur depleted CIGSe thin-film solar cell with a power conversion efficiency of 12.2%.
Solution
processing of metal chalcogenides using elemental metals
dissolved in an amine–thiol solvent mixture has recently received
a great deal of attention for the fabrication of thin-film optoelectronic
devices. However, little is known about the dissolution pathway for
metallic precursors in such mixtures. 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 these solutions and then propose
reaction mechanisms for In and Cu dissolutions in a hexylamine/1,2-ethanedithiol
mixture. These dissolutions are rather found to be reactions resulting
in metal oxidation with coevolution of H2 forming bis(1,2-ethanedithiolate)indium(III)
in the case of indium dissolution and high nuclearity Cu(I) thiolate
compounds in case of copper dissolution. This understanding allowed
us to address the issue of toxicity and corrosivity associated with
amine–thiol solvent by utilizing it as a reactant rather than
a solvent for ink formulation. Here, we demonstrate a new approach
whereby metal complexes formed by dissolving a range of metals 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 a variety of weakly coordinating organic solvents
to provide a benign and stable solution free of unreacted amine and
thiol for thin-film fabrication of various chalcogenide semiconductors.
We utilize this new approach to demonstrate the fabrication of CuIn(S,Se)2 solar cells using dimethyl sulfoxide as a fabrication solvent.
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