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Abstract Chalcogenide perovskites, particularly BaZrS₃, hold promise for optoelectronic devices owing to their exceptional light absorption and inherent stability. However, thin films obtained at lower processing temperatures typically result in small grain sizes and inferior transport properties. Here we introduce an approach employing co-sputtering elemental Ba and Zr targets followed by CS₂sulfurization, with a judiciously applied NaF capping layer. NaF acts as a flux agent during sulfurization, leading to marked increase in grain size and improved crystallinity. This process results in near-stoichiometric films with enhanced photoresponse. Terahertz spectroscopy further reveals a carrier mobility more than two orders of magnitude higher than those obtained from field-effect transistor measurements, suggesting that bulk transport is limited by grain boundary scattering. Our results demonstrate flux-assisted sulfurization as an effective strategy to improve the crystallinity of chalcogenide perovskite thin films for optoelectronic applications. Graphical abstract 

Abstract Chalcogenide perovskites have emerged as promising semiconductor materials due to their appealing properties, including tunable bandgaps, high absorption coefficients, reasonable carrier lifetimes and mobilities, excellent chemical stability, and environmentally benign nature. However, beyond the well‐studied BaZrS₃, reports on chalcogenide perovskite thin films with diverse compositions are scarce. In this study, the realization of four different types of chalcogenide perovskite thin films with controlled phases, through CS₂annealing of amorphous chalcogenide precursor films deposited by pulsed laser deposition (PLD), is reported. This achievement is guided by a thorough theoretical investigation of the phase stability of chalcogenide perovskites. Upon crystallization in the distorted perovskite phase, all materials exhibit photoluminescence (PL) with peak positions in the visible range, consistent with their expected bandgap values. However, the full‐width‐at‐half‐maximum (FWHM) of the PL spectra varies significantly across these materials, ranging from 99 meV for SrHfS₃to 231 meV for BaHfS₃. The difference is attributed to the difference in kinetic barriers between local structural motifs for the Sr and Ba compounds. The findings underscore the promise of chalcogenide perovskite thin films as an alternative to traditional halide perovskites for optoelectronic applications, while highlighting the challenges in optimizing their synthesis and performance. 

Abstract Realizing van der Waals (vdW) epitaxy in the 1980s represents a breakthrough that circumvents the stringent lattice matching and processing compatibility requirements in conventional covalent heteroepitaxy. However, due to the weak vdW interactions, there is little control over film qualities by the substrate. Typically, discrete domains with a spread of misorientation angles are formed, limiting the applicability of vdW epitaxy. Here, the epitaxial growth of monocrystalline, covalent Cr₅Te₈2D crystals on monolayer vdW WSe₂by chemical vapor deposition is reported, driven by interfacial dative bond formation. The lattice of Cr₅Te₈, with a lateral dimension of a few tens of micrometers, is fully commensurate with that of WSe₂via 3 × 3 (Cr₅Te₈)/7 × 7 (WSe₂) supercell matching, forming a single‐crystalline moiré superlattice. This work establishes a conceptually distinct paradigm of thin‐film epitaxy, termed “dative epitaxy”, which takes full advantage of covalent epitaxy with chemical bonding for fixing the atomic registry and crystal orientation, while circumventing its stringent lattice matching and processing compatibility requirements; conversely, it ensures the full flexibility of vdW epitaxy, while avoiding its poor orientation control. Cr₅Te₈2D crystals grown by dative epitaxy exhibit square magnetic hysteresis, suggesting minimized interfacial defects that can serve as pinning sites. 

Chalcogenide perovskite semiconductors, with their excellent optical absorption, chemical stability, and lack of toxicity, have emerged as a promising alternative to traditional halide perovskites. Through first-principles density functional theory, we show that despite the large lattice mismatch between the prototypical BaZrS3 and BaZrO3 chalcogenide perovskites, BaZr(S1−xOx)3 can form low-energy ordered lattices that significantly reduce strain. The bandgap dependence of the resulting ordered compound on x is found to exhibit double Vegard's law behavior, having two distinct linear regions, associated with an underlying distorted or undistorted perovskite structures. 

The prototypical chalcogenide perovskite, BaZrS3 (BZS), with its direct bandgap of 1.7–1.8 eV, high chemical stability, and strong light–matter interactions, has garnered significant interest over the past few years. So far, attempts to grow BaZrS3 films have been limited mainly to physical vapor deposition techniques. Here, we report the fabrication of BZS thin films via a facile aqueous solution route of polymer-assisted deposition (PAD), where the polymer-chelated cation precursor films were sulfurized in a mixed CS2 and Ar atmosphere. The formation of a single-phase polycrystalline BZS thin film at a processing temperature of 900 °C was confirmed by X-ray diffraction and Raman spectroscopy. The stoichiometry of the films was verified by Rutherford Backscattering spectrometry and energy-dispersive X-ray spectroscopy. The BZS films showed a photoluminescence peak at around 1.8 eV and exhibited a photogenerated current under light illumination at a wavelength of 530 nm. Temperature-dependent resistivity analysis revealed that the conduction of BaZrS3 films under the dark condition could be described by the Efros–Shklovskii variable range hopping model in the temperature range of 60–300 K, with an activation energy of about 44 meV.