Trace Cu–Te Co-regulation Decouples Charge and Phonon Transport in High-Performance n-Type Polycrystalline SnSe

Abstract High-performance n-type SnSe single crystals have been realized through extensive carrier and band-structure engineering, whereas n-type polycrystalline SnSe remains comparatively underdeveloped because native Sn vacancies favor p-type conduction and microstructural disorder further impedes electron transport. Here, we show that the co-incorporation of trace Cu and Te effectively decouples electronic and phonon transport in n-type polycrystalline SnSe. Trace Cu doping produces an acceptor-like perturbation but does not severely deplete the electron concentration; instead, it enhances mobility-related transport while concurrently suppressing lattice thermal conductivity. Subsequent Te alloying compensates for the unfavorable carrier-concentration change induced by Cu, improves high-temperature electrical conductivity, and preserves a large Seebeck coefficient. This cooperative electronic modulation yields a maximum power factor of ∼9.3 μW cm–1 K–2 at 873 K, which is, to our knowledge, the highest value reported for n-type polycrystalline SnSe-based materials. Meanwhile, Cu and Te co-incorporation further reduces the lattice thermal conductivity to ∼0.27 W m–1 K–1 at 873 K. Raman spectroscopy reveals mode-dependent peak broadening and shortened apparent phonon lifetimes, supporting enhanced phonon scattering through local vibrational modulation. Owing to the simultaneous enhancement of the power factor and suppression of lattice heat transport, the optimized Cu/Te-containing sample attains a peak thermoelectric figure of merit, ZT, of ∼2.2 at 873 K, one of the highest among all polycrystalline n-type thermoelectric systems. These results establish trace cation–anion co-incorporation as an effective route to high-performance n-type polycrystalline SnSe through complementary control of carrier and phonon transport.