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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 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. 

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 are promising semiconductor materials with attractive optoelectronic properties and appreciable stability, making them enticing candidates for photovoltaics and related electronic applications. Traditional synthesis methods for these materials have long suffered from high‐temperature requirements of 800–1000 °C. However, the recently developed solution processing route provides a way to circumvent this. By utilizing barium thiolate and ZrH₂, this method is capable of synthesizing BaZrS₃perovskite at modest temperatures (500–600 °C), generating crystalline domains on the order of hundreds of nanometers in size. Herein, a systematic study of this solution processing route is done to gain a mechanistic understanding of the process and to supplement the development of device quality fabrication methodologies. A barium polysulfide liquid flux is identified as playing a key role in the rapid synthesis of large‐grain BaZrS₃perovskite at modest temperatures. Additionally, this mechanism is successfully extended to the related BaHfS₃perovskite. The reported findings identify viable precursors, key temperature regimes, and reaction conditions that are likely to enable the large‐grain chalcogenide perovskite growth, essential toward the formation of device‐quality thin films. 

Abstract Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS₃and BaHfS₃chalcogenide perovskite films using single‐phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.