Emerging chalcogenide perovskites represent a promising class of semiconductor materials with distinct properties that set them apart from halide perovskites and oxide-based alternatives. These materials, primarily composed of group IV or group II cations paired with chalcogen anions (S, Se, Te), exhibit unique electronic and structural characteristics that make them attractive for optoelectronic applications, particularly photovoltaics.

One of the most notable differences between chalcogenide and halide perovskites lies in their stability. Halide perovskites, while achieving remarkable photovoltaic efficiencies, suffer from degradation under moisture, heat, and prolonged illumination. In contrast, chalcogenide perovskites demonstrate superior thermodynamic and environmental stability due to their stronger ionic-covalent bonding. For example, BaZrS3, a prototypical chalcogenide perovskite, remains stable in ambient conditions without encapsulation, unlike methylammonium lead iodide (MAPbI3), which degrades rapidly in humid environments. Thermal stability is also significantly higher, with many chalcogenide perovskites maintaining structural integrity at temperatures exceeding 600°C, compared to halide perovskites that decompose below 300°C.

Bandgap engineering is another critical distinction. Halide perovskites typically exhibit direct bandgaps in the range of 1.5 to 2.2 eV, making them suitable for single-junction solar cells. Chalcogenide perovskites, however, often possess wider bandgaps, ranging from 1.7 to 2.5 eV for materials like BaZrS3 and CaZrSe3. While this may limit their absorption in the visible spectrum, their higher absorption coefficients and superior charge carrier mobilities compensate for this drawback. Additionally, alloying or strain engineering can be employed to fine-tune their bandgaps, potentially improving their photovoltaic performance.

Synthesis challenges remain a significant hurdle for chalcogenide perovskites. Unlike halide perovskites, which can be solution-processed at low temperatures, chalcogenide perovskites typically require high-temperature solid-state reactions or chemical vapor transport methods. For instance, BaZrS3 synthesis often involves heating precursors above 1000°C in sulfur-rich atmospheres, complicating large-scale production and integration with flexible substrates. Thin-film deposition techniques, such as pulsed laser deposition or sputtering, have been explored but struggle with stoichiometric control and phase purity. Recent advances in mechanochemical synthesis and low-temperature routes offer potential solutions, though reproducibility and scalability remain unresolved.

Photovoltaic efficiency potential is an area of active investigation. Theoretical calculations suggest that chalcogenide perovskites could achieve power conversion efficiencies exceeding 20% due to their high absorption coefficients, long carrier diffusion lengths, and low defect densities. Experimental results, however, lag behind, with reported efficiencies still below 5% for prototype devices. The primary limiting factors include interfacial recombination, incomplete light absorption, and challenges in forming high-quality p-n junctions. Optimizing device architectures, such as tandem configurations with narrower-bandgap materials, could unlock higher efficiencies.

Defect physics in chalcogenide perovskites differs markedly from halide perovskites. Halide perovskites exhibit benign defect tolerance, where intrinsic point defects (e.g., vacancies, interstitials) do not severely impair carrier lifetimes. Chalcogenide perovskites, while possessing lower intrinsic defect densities, are more susceptible to deep-level traps arising from anion vacancies or antisite defects. For example, sulfur vacancies in BaZrS3 can introduce mid-gap states that act as recombination centers. Passivation strategies, such as post-synthesis annealing in chalcogen atmospheres or doping with aliovalent elements, have shown promise in mitigating these effects.

Another advantage of chalcogenide perovskites is their compatibility with existing semiconductor processing technologies. Unlike halide perovskites, which are incompatible with standard lithography due to solvent sensitivity, chalcogenide perovskites can withstand conventional fabrication steps, enabling easier integration into multi-junction devices or silicon-based tandems. Their robustness also makes them suitable for harsh-environment applications, such as space photovoltaics or high-temperature electronics.

Despite these advantages, several challenges must be addressed before chalcogenide perovskites can compete with halide perovskites or silicon photovoltaics. The high synthesis temperatures limit substrate choices and increase manufacturing costs. Additionally, the lack of high-quality single crystals or epitaxial thin films hinders fundamental studies of their electronic properties. Further research into alternative synthesis routes, such as solvothermal methods or atomic layer deposition, could alleviate these issues.

In summary, chalcogenide perovskites offer a compelling combination of stability, tunable bandgaps, and defect-resistant properties that distinguish them from halide perovskites. While their current photovoltaic performance is modest, their inherent advantages in durability and process compatibility position them as viable candidates for next-generation optoelectronic devices. Overcoming synthesis and defect-related challenges will be crucial to unlocking their full potential in solar energy conversion and beyond.