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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 MgCu0.1Ag0.87Sb0.99 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 MgCu0.1Ag0.87Sb0.99/Mg3.2Bi1.5Sb0.5 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. [ABSTRACT FROM AUTHOR]

A solar thermoelectric generator (STEG) that harvests solar energy and converts it into electricity based on the fundamentals of the Seebeck effect is a promising alternative to photovoltaic technologies. The combination of a phase change material (PCM) with STEG further enables stable and durable energy output despite the variations of solar radiation flux. However, the widespread promotion of STEG is still impeded by its restricted output electricity (<50 W m−2), attributed to the undesirable thermal management in PCMs. Herein, an ingenious phase change composite, with the typical conformation of circular truncated cone and embedded with the actinomorphic arrangement of polybenzobisoxazole fibers, is tailored by a mold processing strategy. The fibrous crystals in organic fibers offer temperature‐resistance thermal highways during the charging/discharging processes, while their actinomorphic configuration facilitates a controllable thermo‐conductive behavior. These structural features render concentrated thermal energy to be efficiently stored in the PCM and maximally discharged into the thermoelectric system. A record‐breaking power density as high as 198.70 W m−2 can be achieved in this powerful STEG via real‐environment solar‐thermal‐electric conversion, a value comparable to that of some commercial photovoltaic devices. This work opens up opportunities for durable and giant electricity supply from clean solar energy during real‐time STEG applications. [ABSTRACT FROM AUTHOR]