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Solution-chemistry fabrication of semiconductor materials is an attractive synthesis method that allows for easy post-synthesis use in various applications. In this work, we investigate the solution-phase synthesis of a lesser-studied class of semiconductor materials, the binary sulfides of alkaline-earth (AE) metals and their potential for forming polysulfides. Studies have shown that metal polysulfides are widely applied as cathode materials in metal–sulfur batteries and isolated metal polysulfides outside of sulfur-containing solutions are quite rare. Other studies have shown that this material system has the potential to be a wide-bandgap semiconductor or superconducting electride and can also be used as an AESn precursor to access certain AE-M-S ternary materials. We show that the synthesis of Ba and Sr polysulfides is strongly correlated to the reaction temperature and that the length of the Sn2− oligomer chain is the dependent variable. To the best of our knowledge, we also report the synthesis of a previously unreported polymorph of SrS2. With bandgaps estimated via UV-vis spectroscopy, spanning the upper energy range of the visible spectrum (2.4–3.0 eV), the AE polysulfides have potential for semiconducting applications, such as displays, transparent conducting oxides, or tandem photovoltaics, among others. Paired with their high crystal abundance and relatively low toxicity, these materials make good candidates for future studies as wide-bandgap semiconductors. 

The chalcogenide perovskite family has been steadily gaining increasing attention from the research community due to its optoelectronic properties and potential for diverse applications. While BaZrS3 and BaTiS3 have been the most extensively studied, other promising compounds in this family, such as SrxTiS3 (1.05 < x < 1.22), are now being explored for various optical, optoelectronic, and energy storage applications. However, challenges remain in achieving the low-temperature synthesis of SrxTiS3. In this study, we report, for the first time, the synthesis of SrxTiS3 nanocrystals at temperatures below 400 °C. The synthesized nanocrystals exhibit a rod-like morphology. Additionally, we have developed solution-processing routes to synthesize phase-pure SrxTiS3 thin films, marking the first reported instance of such films, at temperatures below 600 °C. We also demonstrate the solid-state synthesis of SrxTiS3 powder below 600 °C. Our work paves the way for new and exciting application avenues for SrxTiS3. 

Chalcogenide perovskites have increasingly garnered attention in recent years for various optoelectronic applications. While distorted perovskites such as BaZrS3 are primarily being explored for photovoltaic applications, hexagonal ABS3 compounds such as BaTiS3 have been proposed for optical devices and thermoelectrics due to their intriguing properties arising from their quasi-1D structure, which imparts anisotropy in properties. However, other members of the hexagonal family remain largely unexplored, likely due to their harsh synthesis conditions. In this report, we synthesize nanocrystals of relatively unexplored members of the hexagonal ABX3 chalcogenides family, which also possess a similar rod-like morphology and could be useful for polarized photodetection applications. Specifically, we modified our previously reported sulfide perovskite nanoparticle synthesis route to produce BaNbS3 and BaTaS3 nanocrystals. Furthermore, we explored selenium and selenourea as precursors to synthesize selenide hexagonal nanocrystals such as BaTiSe3 and BaZrSe3, as well as other selenide analogues like Ba3Nb2Se9 and Ba3Ta2Se9. This marks the first report of nanocrystal synthesis for the BaMSe3 family, where M is an early transition metal. 

Recently, chalcogenide perovskites, of the form ABX3, where typically A = alkaline earth metals Ca, Sr, or Ba; B = group IV transition metals Zr or Hf; and X = chalcogens S or Se, have become of interest for their potential optoelectronic properties. In this work, we build upon recent studies and show a general synthesis protocol, involving the use of carbon disulfide insertion chemistry, to generate highly reactive precursors that can be used towards the colloidal synthesis of numerous ABS3 nanomaterials, including BaTiS3, BaZrS3, BaHfS3, α-SrZrS3 and α-SrHfS3. We overcome the shortcomings in the current literature where BaZrS3 nanoparticles are synthesized in separate phases via colloidal methods and lack a reproducible protocol for orthorhombic perovskite nanoparticles. We present a high-temperature, hot-injection method that reliably controls the formation of the colloidal BaZrS3 nanoparticles with the Pnma orthorhombic distorted perovskite structure. We show that the alternate phase, most notably denoted by its extra peaks in the pXRD pattern, is distinct from the distorted perovskite phase as it has a different bandgap value obtained via UV-vis measurements. We also show that the reaction byproducts, resulting from the use of oleylamine and CS2, have their own photoluminescence (PL), and their residual presence on the surface of the nanoparticles complicates the interpretation of PL from the nanoparticles. The utility of these nanomaterials is also assessed via the measurement of their absorption properties and in the form of highly stable colloidal inks for the fabrication of homogeneous, crack-free thin films of BaZrS3 nanoparticles. 

Colloidal semiconductor nanoparticles (NPs) have long been used as a reliable method for depositing thin films of semiconductor materials for applications, such as photovoltaics via solution-processed means. Traditional methods for synthesizing colloidal NPs often utilize heavy, long-chain organic species to serve as surface ligands, which, during the fabrication of selenized chalcogenide films, leaves behind an undesirable carbonaceous residue in the film. In an effort to minimize these residues, this work looks at using N-methyl-2-pyrrolidone (NMP) as an alternative to the traditional species used as surface ligands. In addition to serving as a primary ligand, NMP also serves as the reaction medium and coating solvent for fabricating CuInS2 (CIS) NPs and thin-film solar cells. Through the use of the NMP-based synthesis, a substantial reduction in the number of carbonaceous residues was observed in selenized films. Additionally, the resulting fine-grain layer at the bottom of the film was observed to exhibit a larger average grain size and increased chalcopyrite character over those of traditionally prepared films, presumably as a result of the reduced carbon content. As a result, a gallium-free CuIn(S,Se)2 device was shown to achieve power-conversion efficiencies of over 11% as well as possessing exceptional carrier generation capabilities with a short-circuit current density (JSC) of 41.6 mA/cm2, which is among the highest for the CIGSSe family of devices fabricated from solution-processed methods. 

Synthesis of homoleptic zirconium and hafnium dithiocarbamate via carbon disulfide insertion into zirconium and hafnium amides were investigated for their utility as soluble molecular precursors for chalcogenide perovskites and binary metal sulfides. Treating M(NEtR)4 (M= Zr, Hf and R= Me, Et) with CS2 resulted in quantitative yields of homoleptic Group IV dithiocarbamates. Zr(2-S2CNMeEt) (1), Zr(2-S2CNEt2)4 (2), and Hf(2-S2CNEt2)4 (4), a rare example of a crystal of a homoleptic hafnium CS2 inserted amide species, were characterized. A computational analysis confirmed assignments for IR spectroscopy. To exemplify the utility of the Group IV dithiocarbamates, a solution-phase nanoparticle synthesis was performed to obtain ZrS3 via the thermal decomposition of Zr(S2CNMeEt)4. 

Chalcogenide perovskites have recently attracted significant attention for renewable energy applications due to their predicted combination of air, moisture, and thermal stability, which has been experimentally validated, along with their excellent optoelectronic properties, which are still under experimental investigation. While historically requiring high synthesis temperatures, some solution-processed routes have recently emerged for synthesizing chalcogenide perovskites, such as BaZrS3 and BaHfS3, at temperatures below 600 °C. This study discusses several experimental challenges associated with the moderate-temperature synthesis of solution-deposited chalcogenide perovskites. Firstly, we identify Ruddlesden–Popper (RP) phases as thermodynamically stable competing secondary phases in perovskite synthesis. High sulfur pressures favor the formation of BaZrS3 or BaHfS3, whereas lower sulfur pressures result in a mixture of perovskite and RP phases. Additionally, we briefly discuss the mechanism of moderate-temperature synthesis of chalcogenide perovskites, including some of the morphological and optoelectronic challenges it presents, such as grain overgrowth, secondary phase contamination entrapment, and the presence of mid-band gap emissions. Finally, we address the importance of substrate selection and the potential presence of Ca- and Na-based impurities originating from cation out-diffusion from glass substrates. Addressing these challenges will be crucial as these unique materials continue to be investigated for applications in optoelectronic devices.