Thermoelectric enhancement through structural phase transitions in 1T′–2H WS₂

Transition metal dichalcogenides (TMDs) offer transformative potential for thermoelectric (TE) applications owing to their tunable phase-dependent electronic properties. Yet, optimizing their thermoelectric performance remains challenging due to inherent trade-offs among electrical and thermal transport parameters. Here, we leverage controlled structural phase transitions in metastable 1T′-WS₂ through gradual in-situ thermal annealing at 400 K. We demonstrate control over the structural phase evolution from semi-metallic 1T′ to semiconducting 2H phases, revealing optimal thermoelectric performance in intermediate mixed-phase states. Notably, an impressive 350 % enhancement in power factor (up to 200 μWm⁻¹K⁻²) was achieved compared to pure-phase counterparts, attributed to the synergy of metallic-semiconducting interfaces through an energy-filtering effect. Our findings offer strategic insights into phase engineering for future low-dimensional TE materials.