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 BiSbSe2.52S0.45Br0.03 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.