Lattice expansion enables interstitial doping to achieve a high average <i>ZT</i> in <i>n</i> ‐type PbS

Lead sulfide (PbS) presents large potential in thermoelectric application due to its earth-abundant S element. However, inferior average ZT (ZTave) value makes PbS less competitive with analogs PbTe and PbSe. To promote performance, this study implements strategies of continuous Se alloying Cu interstitial doping synergistically tune thermal electrical transport properties n-type PbS. First, the lattice parameter 5.93 Å is linearly expanded 6.03 PbS0.5Se0.5 increasing content. This Se-alloyed not only intensifies phonon scattering but also facilitates formation interstitials. Based on PbS0.6Se0.4 content minimal conductivity, interstitials are introduced improve electron density, thus boosting peak power factor, from 3.88 μW cm−1 K−2 20.58 PbS0.6Se0.4−1%Cu. Meanwhile, conductivity PbS0.6Se0.4−x%Cu (x = 0–2) further suppressed strong strain field caused by Finally, lowered high properties, a ~1.1 ZTave ~0.82 can be achieved − 1%Cu at 300–773K, which outperforms previously reported