Colloidal metal chalcogenide nanoparticles have emerged as a promising hydrazine-free route for the fabrication of solution processed electronic devices. While a wide variety of synthetic pathways have been developed for these nanomaterials, typical colloidal syntheses rely on the use of metal salts as precursors, which contain anionic impurities such as halides, nitrates, acetates, and so forth, that may incorporate and alter the electrical properties of the targeted nanoparticles. In this report, the recent advances in aminethiol chemistry and its unique ability to dissolve pure metals, chalcogens, and metal chalcogenides is expanded upon for the fabrication of metal chalcogenide nanoparticles. Alkylammonium metal thiolate species are easily formed upon addition of monoamine and dithiol to elemental Cu, In, Ga, Sn, Zn, Se, or metal chalcogenides such as Cu 2 S and Ag 2 S. These species were then used directly for the synthesis of colloidal nanoparticles without the need for any additional purification. The thermal decomposition pathway of one such representative alkylammonium metal thiolate species was studied, verifying that only metal chalcogenides and volatile byproducts are formed, providing a flexible route to compositionally uniform, phase pure, and anionic impurity-free colloidal nanoparticles. Synthetic methods were developed from these precursors to yield pure phase colloidal nanoparticles of binary, ternary, and quaternary materials and their alloys including In 2 S 3 , (In x Ga 1−x ) 2 S 3 , CuInS 2 , CuIn(S x Se 1−x ) 2 , Cu(In x Ga 1−x )S 2 , Cu 2 ZnSnS 4 , and AgInS 2 . Successful synthesis with various experimental methods such as heat up, hot injection, and microwave assisted solvothermal reactions were also demonstrated, showing the flexibility and greater scope for this new synthesis route.

Colloidal nanoparticles have demonstrated significant promise in the fabrication of solution-processed Cu(In,Ga)(S,Se) 2 photovoltaics. However, carbonaceous impurities from long-chain native ligands retained in the films during and after heat treatments have necessitated the exploration of postsynthetic ligand-exchange procedures, which increases process complexity and solvent usage and could potentially reduce the cost advantages that solution processing aims to deliver over conventional vacuum processing. In this report, a new method to directly synthesize anion impurityfree CuInS 2 (CIS) nanoparticles with both inorganic and thermally degradable thioacetamide (TAA) ligands is developed to bypass the need for ligand exchange completely. Metal thiolate complexes were isolated from solutions of Cu 2 S or Cu and In precursors in amine−thiol mixtures. The isolated metal thiolate complexes were solubilized in the readily available and low-toxicity solvent sulfolane and thermally decomposed to CIS nanoparticles in the presence of TAA. H 2 S formed during thiolate decomposition was used in conjunction with TAA as ligands for nanoparticles. High-mass-concentration ink in the low-toxicity polar solvent dimethyl sulfoxide was used to easily deposit thin films using scalable blade coating. A CuInSe 2 photovoltaic device with a total area power conversion efficiency of 7.1% was prepared from a carbon-free CIS nanoparticle film. Further, synthetic methods were successfully adapted to the more complex quaternary material Cu 2 ZnSnS 4 , where phase-pure material synthesis was observed. The developed methods represent a paradigm shift in the synthesis of metal sulfide nanomaterials and the subsequent solution processing of photovoltaics without the need for ligand exchange.