Realizing Remarkable Improvement of Electrical Performance in N‐Type BiSbSe₃ via In Situ Compositing

Abstract BiSbSe₃ is a Te‐free thermoelectric material with intrinsically low thermal conductivity. Its thermoelectric performance is limited by poor electrical conductivity. To optimize electrical conductivity, Bi₂SbSe₃ with high carrier concentration and mobility is introduced to BiSbSe₃ matrix through in situ reaction and conventional mechanical mixing. In both methods, carrier concentrations are improved by carrier injection and redistribution. Carrier mobility is manipulated based on microstructure. In the conventional method, isolated flake‐shaped Bi₂SbSe₃ grains with weak‐bonding phase boundaries restrict carrier mobility. For the in situ method, irregular Bi₂SbSe₃ connects into conductive networks inducing a percolation effect, and in situ formed small‐angle phase boundaries barely impede carriers. Thus, the carrier mobilities of in situ composites are significantly improved and higher than that of conventional composites. Simultaneously optimized carrier concentration and mobility remarkably enhance electrical conductivity over the whole working temperature. Maximum electrical conductivity of 378 S cm⁻¹ is achieved in BiSbSe₃‐38 vol% Bi₂SbSe₃ in situ composites at 300 K, obtaining more than 300% improvement compared with 124 S cm⁻¹ in BiSbSe₃ matrix. Lattice thermal conductivity is reduced at a low compositing fraction. Ultimately, a record‐breaking average ZT of 0.65 (300–750 K) is attained in BiSbSe₃‐13 vol% Bi₂SbSe₃ in situ composite. The in situ compositing method in this work effectively optimizes electrical performance, anticipated to be applied in other thermoelectric materials.