AgBiS2 Nanocrystal Synthesis from Molecular Precursors: Insights into the Acid-Catalyzed Decomposition of Dialkyldithiocarbamate Ligands

Nanocrystals of mixed metal chalcogenides such as silver bismuth sulfide (AgBiS2) offer a potential route to low-cost, environmentally friendly solar absorbers. Although a number of methods for the preparation of AgBiS2 nanocrystals have been reported, there remains an ongoing need to develop improved controllable routes to size-tunable AgBiS2 nanomaterials without the presence of impurity phases. Here, we have expanded on the development of AgBiS2 nanocrystal synthesis using N,N-diethyldithiocarbamate complexes of Ag+ and Bi3+ as single-source precursors in oleylamine (OLA), establishing it as a reliable approach to high-purity and highly crystalline AgBiS2 nanomaterials. While a degree of size tunability could be achieved by tuning the reaction temperature, we found that adding dodecanethiol (DDT) to the reaction mixture dramatically decreased the precursor decomposition temperature and resulting nanocrystalline domain size. To understand the mechanism by which addition of thiol affects the precursor decomposition, in situ variable temperature NMR was employed in combination with DFT calculations, finding that the combination of DDT and OLA turns on acid-catalyzed pathways for dithiocarbamate transamidation with OLA, ultimately inducing low-temperature C-S bond cleavage. In addition to providing new routes to size-tunable AgBiS2 nanocrystals, these studies therefore provide potentially general insights regarding how the decomposition of dialkyldithiocarbamate complexes can be controlled and tuned.