ABSTRACT

Tin selenide-telluride (Sn[SexTe1‒x]) alloys are promising candidates for next-generation solar cell applications; however, their structural characteristics are still not fully understood. This study investigates the effect of selenium (Se) and tellurium (Te) composition on the structural properties of bulk-derived Sn(SexTe1‒x) thin films with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0. The bulk alloys were synthesised using the Bridgman method and subsequently employed as source materials for the thin-film fabrication via vacuum evaporation. Energy-dispersive X-ray spectroscopy analysis revealed increasing deviations from ideal stoichiometry with higher Se content, particularly in the bulk samples. In contrast, the thin films exhibited compositions closer to the intended Se-to-Te ratios, attributed to more controlled deposition and reduced segregation during film growth. Scanning electron microscopy analysis showed that bulk samples exhibited significant grain structure variation with increasing Se content, whereas thin films displayed a more uniform morphology—transitioning from granular to nanostructured features. X-ray diffraction analysis revealed a structural transition from a cubic phase (SnTe, x = 0.0) to an orthorhombic phase at higher Se concentrations (x ≥ 0.6), accompanied by corresponding changes in lattice parameters. At x = 1.0 (SnSe), both the bulk and thin-film samples exhibited identical lattice parameters (a = 11.470 Å, b = 4.152 Å and c = 4.439 Å), confirming the formation of a pure orthorhombic phase. These findings emphasise the importance of compositional control in tuning the structural phases of Sn(SexTe1‒x) alloys and demonstrate the viability of fabricating high-quality thin films from bulk-derived source materials. The successful transfer of structural integrity from bulk to thin-film form opens new avenues for optimising these materials for photovoltaic device applications. 

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