Enhanced Lattice Symmetry via Mn Doping Boosts Electrical Transport Performance in Rhombohedral GeSe Thermoelectric Materials

Low-symmetry thermoelectric material GeSe exhibits inherently low thermal conductivity but suppressed electrical transport properties. Here, we demonstrate that Mn doping in AgBiTe2-alloyed rhombohedral GeSe introduces band engineering and further significantly enhances lattice symmetry. Mn-induced resonant energy levels enhance the density of states effective mass and significantly optimize the Seebeck coefficient. Crucially, elevated lattice symmetry reduces deformation potential and weakens phonon-electron coupling, triggering a 185% surge in carrier mobility despite a ~1.2-fold increase in the effective mass. The synergistically optimized Seebeck coefficient and electrical conductivity enable the high-symmetry (GeMn0.005Se)0.9(AgBiTe2)0.1 sample to achieve a record average power factor of ~17 μW cm−1 K−2 over 300–673 K while retaining low lattice thermal conductivity. Consequently, a maximum ZT of ~1.50 at 673 K and an average ZT of ~0.94 (300–673 K) are achieved, yielding a single-leg thermoelectric conversion efficiency of ~6.1% under a temperature difference of 325 K. This lattice symmetry manipulation through rational doping provides a universal pathway to promote phonon-electron decoupling and enhances thermoelectric performance in low-symmetry thermoelectric materials. This work demonstrates that Mn doping in rhombohedral GeSe enhances carrier mobility by optimizing lattice symmetry, which also creates beneficial resonant levels and synergistically improves the overall electrical and thermoelectric performance.