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A facile method to prepare flexible n‐type Ag2Se/Se/polypyrrole (PPy) composite films is developed. First, Ag2Se nanostructures (NSs) are wet chemically synthesized; PPy is then in situ polymerized at the surface of the Ag2Se NSs; and finally, the Ag2Se/Se/PPy composite film on a porous nylon membrane is fabricated by a vacuum‐assisted filtration process followed by hot pressing. An optimal composite film shows an exceptionally high power factor of ≈2240 µW m−1 K−2 at 300 K, mainly because of the synergistic effect between well‐developed crystalline Ag2Se grains and a small amount of Se and PPy. The film also possesses outstanding flexibility (only about 6.5% decrease in electrical conductivity after 1000 times bending along a rod with a radius of 4 mm). Moreover, a flexible thermoelectric generator composed of six legs of the film outputs a voltage of 21.2 mV and a maximum power of 4.04 µW (corresponding power density of 37.6 W m−2) at a temperature difference of 34.1 K, verifying exceptionally high thermoelectric properties. This work shows the promise of the as‐prepared composite film for practical applications in wearable devices and will surely promote the research and development of flexible TE generators. [ABSTRACT FROM AUTHOR]

Bi2S3‐based thermoelectric materials without toxic and expensive elements have a high Seebeck coefficient and intrinsic low thermal conductivity. However, Bi2S3 suffers from low electrical conductivity, which makes it a less‐than‐perfect thermoelectric material. In this work, halogen elements F, Cl, and Br from halogen acid are successfully introduced into the Bi2S3 lattice using a hydrothermal procedure to efficiently improve the carrier concentration. Compared with the pure sample, the electron concentration of the Bi2S3 sample treated with HCl is increased by two orders of magnitude. An optimal power factor of 470 µW m−1 K−2 for the Bi2S2.96Cl0.04 sample at 673 K is obtained. Density functional theory calculations reveal that an effective delocalized electron conductive network forms after Cl doping, which raises the Fermi level into the conduction bands, thus generating more free electrons and improving the conductivity of the Bi2S3‐based materials. Ultimately, an excellent ZT of ≈0.8 is achieved at 673 K for the Bi2S2.96Cl0.04 sample, which is one of the highest values reported for a state‐of‐the‐art Bi2S3 system. The energy conversion efficiency of the module reaches 2.3% at 673 K with a temperature difference of 373 K. This study offers a new method for enhancing the thermoelectric properties of Bi2S3 by adding halogen acid in the hydrothermal process for powder synthesis. [ABSTRACT FROM AUTHOR]