Optimizing Thermoelectric Performance in Phase-Stabilized n-Type BiSbSe₃

Orthorhombic n-type BiSbSe₃ possesses a theoretically promising thermoelectric performance in single-crystalline form. However, orthorhombic BiSbSe₃ is stable only at high temperatures but thermodynamically unstable at room temperature. While orthorhombic BiSbSe₃ polycrystals can be synthesized via rapid quenching to kinetically preserve this metastable phase, single-crystal growth demands slow cooling to enable near-equilibrium atomic incorporation at the growth front. Resolving the room-temperature thermodynamic instability of orthorhombic BiSbSe₃ is an essential precondition for unlocking its thermoelectric potential. In this work, we successfully realized thermodynamic stabilization of the orthorhombic BiSbSe₃ at room temperature through chemical composition optimization. Alloying with 15% sulfur (S) enables reproducible, quench-free synthesis of pure orthorhombic BiSbSe₃, opening a viable pathway toward single-crystal growth and full realization of its thermoelectric potential. Building on this, we conducted a systematic investigation into the effects of halogen (Cl, Br, and I) doping on thermoelectric transport of n-type phase-stabilized orthorhombic BiSbSe₃ polycrystals. The optimized BiSbSe_2.52S_0.45Br_0.03 achieves a peak ZT of ∼1.0 at 773 K and a single-leg conversion efficiency of ∼6.1% at a temperature difference of ∼474 K, demonstrating that our phase-stabilization approach does not compromise the promising thermoelectric properties of orthorhombic BiSbSe₃, thereby paving the way for anticipated high performance in high-quality single crystals.