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 (GeMn_0.005Se)_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.