Defect-mediated carrier type transition and thermoelectric transport in Fe-substituted Sb2S3

Thermoelectric materials that efficiently convert waste heat into electricity are gaining attention for their potential in next-generation energy harvesting technologies. In this study, we investigate Fe-doped antimony trisulfide (Sb₂S₃), a structurally anisotropic and abundant compound, as a promising candidate for thermoelectric applications. Fe was introduced via a chemical precipitation route (2, 6, 10, and 12%) and annealed under argon atmosphere. Structural analysis confirmed the orthorhombic Sb₂S₃ phase, with XRD revealing a minor Sb₂O₃ secondary phase at higher Fe concentrations, indicating dopant-induced oxidation and structural reordering. SEM and TEM analyses revealed dense grains and improved interconnectivity at optimal doping levels, while UV–Vis absorption showed band gap modulation from 1.79 eV to 1.60 eV due to Fe incorporation. Seebeck coefficient, electrical conductivity, and Hall measurements revealed a doping-induced conduction-type reversal from intrinsic n-type to p-type (2–10% Fe) and to n-type at 12% Fe accompanied by tunable carrier concentration. Thermal conductivity was suppressed at higher doping levels, attributed to enhanced phonon scattering, aided by grain boundaries and the secondary phases. The combined effects led to improved power factor and overall thermoelectric performance, demonstrating the critical role of Fe doping in tuning transport behavior. This study reports for the first time, that Fe incorporation alters the dominant carrier-type in Sb₂S₃, shifting its conduction mechanism. Such carrier-type modulation provides an effective strategy to optimize the Seebeck coefficient and electrical conductivity simultaneously, thereby offering new opportunities to engineer defect chemistry for improved thermoelectric applications.