This work investigates the structural, electronic, thermoelectric, and optoelectric properties of a solid solution of BiSb( \(Te_{1-x}Se_x)_3\) . The properties of this alloy were calculated using Density Functional Theory within the GGA and TB-mBJ for the exchange-correlation potential. The formation energy, bulk modulus, band structure, density of states (DOS), energy band gap, real and imaginary dielectric constants, absorption coefficient, Seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit are obtained. The calculated formation energies confirm the stability and potential synthesis of these alloys. The band gap in the band structure and DOS shows that the alloys are semiconductors. The band curvatures of these alloys reveal a mixture of heavy and light effective masses, accounting for the good thermoelectric behaviour observed. Notably, BiSb \((Te_{0.25}Se_{0.75})_3\) exhibits a figure of merit (ZT) of 1.10 at 900 K for n-type doping-additionally. The results obtained in this work indicate that BiSb \((Te_{1-x}Se_x)_3\) is a promising candidate for optoelectronic and thermoelectric applications.
