Search for: All records

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. 

Tolerance factor analysis has been widely used to predict suitable compositions for oxide and halide perovskites. However, in the case of the emerging chalcogenide perovskites, the predictions from the tolerance factor have failed to align with experimental observations. In this work, we reconsider how tolerance factor is being applied, specifically adjusting for the effect of increased covalency of bonding on the ionic radii. Further, we propose a series of screening steps based on the octahedral factor, tolerance factor, and electronegativity difference to better predict the formation of sulfide perovskites. 

Chalcogenide perovskites are gaining prominence as earth-abundant and non-toxic solar absorber materials, crystallizing in a distorted perovskite structure. Among these, BaZrS3 has attracted the most attention due to its optimal bandgap and its ability to be synthesized at relatively low temperatures. BaZrS3 exhibits a high light absorption coefficient, excellent stability under exposure to air, moisture, and heat, and is composed of earth-abundant elements. These properties collectively position BaZrS3 as a promising candidate for a wide range of applications, although traditional high-temperature synthesis has primarily been a significant challenge. In this review, we provide a critical discussion of the various synthesis methods employed to fabricate BaZrS3, including solid-state synthesis, nanoparticle synthesis, and vacuum-based as well as solution-based approaches to synthesize thin films. We also comprehensively examine the experimentally measured and theoretically calculated optical, optoelectronic, electronic, and defect properties of BaZrS3. Furthermore, this review highlights the functional devices based on BaZrS3, showcasing applications spanning photovoltaics, photodetection, thermoelectrics, photoelectrochemical water splitting, piezoelectricity, and spintronics. Lastly, we propose a future roadmap to maximize the potential of this material. Additionally, this review extends its focus to BaHfS3 and BaTiS3, discussing their synthesis methods, properties, and explored applications, thereby offering a comparative perspective on this emerging family of chalcogenide perovskites. 

Chalcogenide perovskites represent a prominent class of emerging semiconductor materials for photovoltaic applications, boasting excellent optoelectronic properties, appropriate bandgaps, and remarkable stability. Among these, BaZrS3 is one of the most extensively studied chalcogenide perovskites. However, its synthesis typically demands high temperatures exceeding 900 °C. While recent advancements in solution-processing techniques have mitigated this challenge, they often rely on costly and difficult-to-find organometallic precursors. Furthermore, there is a notable gap in research regarding the influence of the Ba/Zr ratio on phase purity. Thus, our study explores solid-state reactions to investigate the impact of metal ratios and sulfur pressure on the phase purity of BaZrS3. Expanding upon this investigation, we aim to leverage cost-effective metal halide and metal sulfide precursors for the solution-based synthesis of BaMS3 (M=Ti, Zr, Hf) compounds. Additionally, we have devised a bilayer stacking approach to address the halide affinity of alkaline earth metals. Moreover, we introduce a novel solution-chemistry capable of dissolving alkaline earth metal sulfides, enabling the synthesis of BaMS3 compounds from metal sulfide precursors. While the BaSx liquid flux has shown promise, we identify the selenium liquid flux as an alternative method for synthesizing BaMS3 compounds. 

Oxide perovskites would provide a convenient precursor for the synthesis of chalcogenide perovskites. However, the stability of oxide perovskites means that there is no driving force for sulfurization or selenization with conventional chalcogen sources. In this work, we show that sulfurization and selenization of highly stable early transition metal oxides are possible by heating in the presence of HfH2 and S or Se, thereby creating HfS3 or HfSe3 as an oxygen sink and producing an oxygen shuttle in the form of H2O/H2S or H2O/H2Se. The conversion of ZrO2 into ZrS3 or ZrSe3 is supported with thermodynamic calculations and demonstrated experimentally as a proof-of-concept. Subsequently, we demonstrate that BaZrO3 can be converted to BaZrS3 at 575 °C, several hundred degrees below previous methods relying on conventional sulfur sources. 

AgInSe2 is a promising direct bandgap thin-film material with a rare n-type conductivity. Similar to thin film photovoltaic materials such as Cu(In,Ga)Se2 (CIGSe), which have achieved efficiencies as high as ~23%, AgInSe2 also crystallizes in a chalcopyrite phase while also being more tolerant to antisite defects due to higher defect formation energies resulting from more significant variations in cation sizes. AgInSe2 has a suitable bandgap of 1.24 eV, which lies in the high-efficiency region of the detailed balance limit. In this work, we have utilized a Dimethyl Formamide-Thiourea-Chloride-based solution-processed route to deposit a thin film of AgInS2 which is converted into AgInSe2 after a heat-treatment step in a selenium environment. AgInSe2 optoelectronic properties depend on the Ag/In ratio and the selenium heat-treatment conditions. Significant improvements in photoluminescence yield and lifetime are observed for Ag-poor films in selenium-rich conditions. X-ray Photoelectron Spectroscopy (XPS) measurements confirm a higher amount of selenium on the surface of films with improved optoelectronic properties. Furthermore, a high minority carrier lifetime of 9.2 ns and a Photoluminescence Quantum Yield (PLQY) of 0.013% is obtained without any passivating layer, which improved to 0.03% after CdS passivation. Hall effect measurements confirm that AgInSe2 has n-type conductivity with a moderate carrier concentration (10-14 cm-3), more suitable for a p-i-n architecture. XPS has further confirmed the moderate n-type conductivity. 

Chalcogenide semiconductors, such as BaMS3 (M = Zr and Hf) and Cu2BaSnS4, have attracted growing interest due to the constituent elements’ abundance and reported promising properties. However, the synthesis of these alkaline earth-containing chalcogenides from commonly available metal halides has generally been unsuccessful and has traditionally relied on expensive organometallic precursors or vacuum processing techniques, which hinder widespread research on these materials. In this study, we conducted thermodynamic calculations and developed chloriphilicity and iodiphilicity scales for various metals, leveraging their relative affinities for chlorine and iodine, respectively, compared to their corresponding metal sulfides. Utilizing these scales, we introduced a K2S–H2S system to address the affinity of alkaline earth metals for chlorine and iodine. This approach enables the synthesis of these intriguing chalcogenide materials through solution-based methods using metal chloride and metal iodide precursors. This system demonstrates remarkable efficacy for both sulfide and selenide semiconductors. 

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.