Synergistic tuning of electrical and thermal transport properties in Bi2SeS2 thermoelectric material via Ti/Cu co-doping

Herein, a Ti/Cu co-doping strategy is employed in Bi 2 SeS 2 to optimize its electrical and thermal transport properties through carrier regulation and microstructure modulation. The Ti/Cu co-doped Bi 2 SeS 2 samples were synthesized by mechanical alloying followed by spark plasma sintering. It is found that the co-doping boosts electrical conductivity while preserving a moderate Seebeck coefficient of 150–200 μV K −1 . This yields a high power factor of 5.5 μW cm −1 K −2 at 773 K. Moreover, the lattice thermal conductivity is reduced to ∼0.25 W m −1 K −1 , primarily due to effective phonon scattering induced by lattice strain and point defects. Finally, a peak zT of ∼0.80 is achieved at 773 K in Bi 1.96 Ti 0.04 SeS 2 -1 %Cu, surpassing the solely Cu-doped and Ti-doped counterparts by ∼22 % and 40 %, respectively. These findings reveal that multi-element doping is an effective approach for tailoring both charge and phonon transport, providing valuable insights for the design of advanced thermoelectric materials.