Ribbons of Light: Emerging (Sb,Bi)(S,Se)(Br,I) Van der Waals Chalcohalides for Next-Generation Energy Applications

(Sb,Bi)(S,Se)(Br,I) pnictogen chalcohalides constitute an emerging family of Van der Waals (VdW) semiconductors with remarkable potential for energy-related applications, including photovoltaics (PV), photocatalysis (PC), and photoelectrocatalysis (PEC). These ternary compounds exhibit a quasi-1D orthorhombic crystalline phase, and an electronic structure analogous to lead-halide perovskites, making them promising candidates for sustainable and high-performance energy devices. This study introduces a new versatile and adaptable synthesis methodology, which combines co-evaporation of binary chalcogenides with reactive annealing under high-pressure halide atmospheres, to fabricate the eight (Sb,Bi)(S,Se)(Br,I) chalcohalides. Comprehensive structural, compositional, and optoelectronic analyses reveal a wide bandgap range (1.2-2.2 eV), high absorption coefficients, and anisotropic properties driven by unique ribbon-like morphology. Theoretical and experimental results highlight their high stability, versatile chemical adaptability, and defect-tolerant characteristics. Moreover, the distinct differences in morphology and crystallization between Sb and Bi-based compounds, as well as the influence of chalcogen and halogen elements on the optical and structural properties are discussed. Demonstrations of functional devices, including photocatalytic systems, underscore the practical viability of these materials. This work establishes a foundation for the development of pnictogen chalcohalides as scalable and eco-friendly alternatives for advanced energy applications.