Progress of thiol-amine ‘alkahest’ solutions for thin film deposition

Binary thiol-amine mixtures termed ‘alkahests’ possess high solvent power for an assortment of bulk solids, such as metals and metal chalcogenides, under mild conditions. The resulting inks are used in the solution deposition of metal chalcogenide thin films for a variety of applications. The molecular solutes resulting from the dissolution of bulk solid precursors affect film quality; it is therefore important to identify them to effectively tailor ink compositions for thin film optimization. Thiol-amine solutions have closed the gap with hydrazine-processed devices, with favorable efficiencies in solar cells and thermoelectric devices. Thiol-amine solutions have been leveraged in other areas, such as engineering the surfaces of nanocrystals. Solution deposition of thin films has garnered interest as a replacement for vacuum deposition techniques due to its scalability and lower cost. While hydrazine processing offered an alternative to vacuum deposition, its commercialization is limited due to its toxicity and explosive nature. Binary thiol-amine mixtures (‘alkahests’) have proven usage in the dissolution of a wide range of inexpensive bulk solids to give inks. Intensive studies of dissolution, solute speciation, and decomposition mechanisms have bridged the quality gap between hydrazine-processed and vacuum-deposited thin films, but analogous studies for thiol-amine mixtures are nascent. Here, we outline recent progress made in identifying the molecular solutes from bulk solid dissolution in thiol-amine solutions. New applications and potential areas of future study are highlighted. Solution deposition of thin films has garnered interest as a replacement for vacuum deposition techniques due to its scalability and lower cost. While hydrazine processing offered an alternative to vacuum deposition, its commercialization is limited due to its toxicity and explosive nature. Binary thiol-amine mixtures (‘alkahests’) have proven usage in the dissolution of a wide range of inexpensive bulk solids to give inks. Intensive studies of dissolution, solute speciation, and decomposition mechanisms have bridged the quality gap between hydrazine-processed and vacuum-deposited thin films, but analogous studies for thiol-amine mixtures are nascent. Here, we outline recent progress made in identifying the molecular solutes from bulk solid dissolution in thiol-amine solutions. New applications and potential areas of future study are highlighted.