Exceptionally high average power factor and thermoelectric figure of merit in n-type PbSe by the dual incorporation of Cu and Te

Thermoelectric materials with high average power factor and thermoelectric figure of merit (ZT) has been a sought-after goal. Here, we report new n-type thermoelectric system CuxPbSe0.99Te0.01 (x = 0.0025, 0.004, and 0.005) exhibiting record-high average ZT ∼1.3 over 400-773 K ever reported for n-type polycrystalline materials including the state-of-the-art PbTe. We concurrently alloy Te to the PbSe lattice and introduce excess Cu to its interstitial voids. Their resulting strong attraction facilitates charge transfer from Cu atoms to the crystal matrix significantly. It follows the increased carrier concentration without damaging its mobility and the consequently improved electrical conductivity. This interaction also increases effective mass of electron in the conduction band according to DFT calculations, thereby raising the magnitude of Seebeck coefficient without diminishing electrical conductivity. Resultantly, Cu0.005PbSe0.99Te0.01 attains an exceptionally high average power factor of ∼27 μW cm-1 K-2 from 400 to 773 K with a maximum of ∼30 μW cm-1 K-2 at 300 K, the highest among all n- and p-type PbSe-based materials. Its ∼23 μW cm-1 K-2 at 773 K is even higher than ∼21 μW cm-1 K-2 of the state-of-the-art n-type PbTe. Interstitial Cu atoms induce the formation of coherent nanostructures. They are highly mobile, displacing Pb atoms from the ideal octahedral center and severely distorting the local microstructure. This significantly depresses lattice thermal conductivity to ∼0.2 Wm-1 K-1 at 773 K below the theoretical lower bound. The multiple effects of the dual incorporation of Cu and Te synergistically boosts a ZT of Cu0.005PbSe0.99Te0.01 to ∼1.7 at 773 K.