👤 Axel G Medaille

Selenium is experiencing renewed interest as a elemental semiconductor for a range of optoelectronic and energy applications due to its irresistibly simple composition and favorable wide bandgap. However, its high volatility and low radiative efficiency make it challenging to assess structural and optoelectronic quality, calling for advanced, non-destructive characterization methods. In this work, we employ a closed-space encapsulation strategy to prevent degradation during measurement and enable sensitive probing of vibrational and optoelectronic properties. Using temperature-dependent Raman and photoluminescence spectroscopy, we investigate grown-in stress, vibrational dynamics, and electron-phonon interactions in selenium thin films synthesized under nominally identical conditions across different laboratories. Our results reveal that short-range structural disorder is not intrinsic to the material, but highly sensitive to subtle processing variations, which strongly influence electron-phonon coupling and non-radiative recombination. We find that such structural disorder and grown-in stress likely promote the formation of extended defects, which act as dominant non-radiative recombination centers limiting carrier lifetime and open-circuit voltage in photovoltaic devices. These findings demonstrate that the optoelectronic quality of selenium thin films can be significantly improved through precise control of synthesis and post-deposition treatments, outlining a clear pathway toward optimizing selenium-based thin film technologies through targeted control of crystallization dynamics and microstructural disorder. Show less

(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. Show less