The power factor (PF = S 2 σ) is a key parameter in thermoelectric performance (ZT ∝ PF), which can have a complex dependence on carrier concentration and temperature due to their competing effects on S and σ. As a result, a balanced carrier concentration, striking an equilibrium between the Seebeck coefficient and electrical conductivity, is necessary to maximise PF. The optimal PF is higher for p-type (8.16 mW m -1 K -2 ) rather than n-type (4.67 mW m -1 K -2 ) Sb2Si2Te6 (Figures and). In contrast, for Sc2Si2Te6, the highest PF of n-type is 19 mW m -1 K -2 , which significantly exceeds the value of 3.06 mW m -1 K -2 for p-type doping (Figures and). Moreover, this optimal PF for ntype Sc2Si2Te6 markedly exceeds the PF predicted for various layered thermoelectric materials, such as BiCuOSe (~1.71 mW m -1 K -2 ), while it still lags behind that predicted for monolayer SnSe (~28 mW m -1 K -2 ). This ultra-high PF in n-type Sc2Si2Te6 primarily originates from the enhanced Seebeck coefficient attributable to conduction band degeneracy, as discussed above. Using a band degeneracy strategy to enhance the PF has also been reported in other materials, such as PbTe, which achieves a band degeneracy of 16 by tuning the doping and composition. Thermal transport properties