High Thermoelectric Power Factors in Plastic/Ductile Bulk SnSe₂‐Based Crystals

Abstract The recently discovered plastic/ductile inorganic thermoelectric (TE) materials open a new avenue for the fabrication of high‐efficiently flexible TE devices, which can utilize the small temperature difference between human body and environment to generate electricity. However, the maximum power factor (PF) of current plastic/ductile TE materials is usually around or less than 10 µW cm⁻¹ K⁻², much lower than the classic brittle TE materials. In this work, a record‐high PF of 18.0 µW cm⁻¹ K⁻² at 375 K in plastic/ductile bulk SnSe₂‐based crystals is reported, superior to all the plastic inorganic TE materials and flexible organic TE materials reported before. The origin of such high PF is from the modulation of material's stacking forms and polymorph crystal structures via simultaneously doping Cl/Br at Se‐site and intercalating Cu inside the van der Waals gap, leading to the significantly enhanced carrier concentrations and mobilities. An in‐plane fully flexible TE device made of the plastic/ductile SnSe₂‐based crystals is successfully developed to show a record‐high normalized maximum power density to 0.18 W m⁻¹ under a temperature difference of 30 K. This work indicates that the plastic/ductile material can realize high TE power factor to achieve large output electric power density in flexible TE technology.