Semiconductor–Semimetal Composite Engineering Enabling Record-High Thermoelectric Power Density for Low-Temperature Energy Harvesting

Sustained thermoelectric efforts have concentrated on the enhancement of conversion efficiency of power generators, while simultaneously achieving high output power continues to lag. Specifically, the highest output power density of emerging Mg-based modules reported so far is only half of that of commercial Bi₂Te₃-based, mainly due to the low power factor of MgAgSb. Herein, homogenously distributed MgCuSb in situ nanoprecipitates in the MgAgSb matrix effectively optimized carrier concentration due to the effect of carrier injection from the metal–semiconductor Ohmic contact. As a result, a record-high average power factor of 27.2 µW cm⁻¹ K⁻² is obtained in MgCu_0.1Ag_0.87Sb_0.99 composite within the temperature range of 300–550 K, which is much higher than ever reported values of MgAgSb system. Benefiting from the combination of the optimized average power factor of p-leg and low interface resistivity, a fabricated eight-pair MgCu_0.1Ag_0.87Sb_0.99/Mg_3.2Bi_1.5Sb_0.5 module demonstrates an unprecedently high output power density of 2.9 W cm⁻² under a temperature difference of 300 K, outperforming all low-temperature advanced thermoelectric modules. Meanwhile, a competitive conversion efficiency of 7.65% is obtained simultaneously. The work significantly advances high-power thermoelectric applications of Mg-based modules in the field of low-temperature sustainable energy harvesting.