Incompletely Decomposed In₄SnSe₄ Leads to High‐Ranged Thermoelectric Performance in n‐Type PbTe

Abstract Additives in thermoelectric materials are conventionally considered as either extrinsic defects or second phases regardless of their dynamic processes. Herein, In₄SnSe₄, with inherent low thermal conductivity, is introduced into n‐type PbTe. It is revealed that In₄SnSe₄ decomposes incompletely at high temperatures, in which around 80% of In₄SnSe₄ dissolves into InSe and Sn, while 20% forms as nano‐precipitates. Benefiting from the incomplete decomposition, PbTe‐0.1%In₄SnSe₄ presents superior thermoelectric performance compared to the stepwise and compositionally identical PbTe‐0.4%InSe‐0.1%Sn. The residual In₄SnSe₄ along with Sn and InSe jointly contribute to the synergetic optimization of carrier mobility and lattice thermal conductivity in PbTe‐0.1%In₄SnSe₄. As a result, the room‐temperature dimensionless figure of merit (ZT) of ≈0.4 and the ZT_ave of ≈0.83 at 300–573 K are obtained, and an experimental maximum thermoelectric conversion efficiency (η) of ≈2.5% (ΔT ≈ 400 K) is obtained, demonstrating significant research progress in n‐type PbTe. This work indicates that the In₄SnSe₄ incomplete decomposition effectively decouples the electron and phonon transports in n‐type PbTe and the strategy of utilizing the unstable additives is proven feasible. Additionally, more dynamic behaviors of additives are worth expecting and may promote more achievements for other thermoelectric systems.