Role of irreducible occupancy sites on thermoelectric performance of Te-doped BiSbSe3

Doping can effectively modulate electron and phonon transport. However, the impact of symmetry-governed irreducible site occupancy remains unclear. In this work, we theoretically investigate the thermoelectric transport properties of Te-doped BiSbSe3 by considering phonon–phonon and electron–phonon scattering. Three irreducible Te-doping sites (S1–S3) are identified via the tree search algorithm. The results show that the three irreducible Te-doped sites have only a slight influence on the bandgap. However, the electron–phonon coupling exhibits site-selective modulation, resulting in up to twofold variations in electrical conductivity and electronic thermal conductivity. Additionally, lattice thermal conductivity decreases by 21%, 41%, and 54% along the c axis when Te atoms are doped at S1, S2, and S3, respectively. Notably, the optical phonon modes contribute over 50% to lattice thermal conductivity along the a axis in both pristine and doped structures, compared to 30% along other axes. Although all doping sites reduce lattice thermal conductivity, only S2 and S3 enhance thermoelectric performance. Specifically, zT values peak at 1.92 (S2) and 2.07 (S3), whereas S1 doping causes a 20%zT reduction due to carrier mobility loss. Our findings suggest that specific crystallographic doping site is essential for optimizing thermoelectric efficiency.