Investigation On The Thermoelectric Performance Of Flexible Bi₂Te₃/SWCNT Hybrids And Devices

Thermoelectric materials?TEs?are kinds of new-type functional material that realize the mutual conversion of thermal energy and electrical energy.TEs can realize the reversible conversion between electric energy and heat energy,they show broad application prospects in many fields.TE devices composed of TEs have attracted great attention due to its unique advantages of their solid-state structure,consistent properties,no moving parts,compactness,and low maintenance.And it behaves amazing applications in temperature sensing,generating electricity and precise temperature controlling by Peltier cooling.They have attracted great attention due to the application in the renewable energy technology,intelligent micro-nano electronic equipment in recent years.Thus,TE materials have attracted intensive studies in the field of materials science and technology.The active cooling efficiency is determined by the figure-of-merit ZT.Passive cooling involves cooling a surface by emitting?8-13 ?m infrared?IR?light into the surroundings,achieving passive cooling of the heat source without consuming any external energy.The cooling efficiency could be improved with both efficient active and passive cooling performance.However,traditional high-performance inorganic TEs have a low thermal conductivity and are non-transparent in the IR wavelength range.Therefore,such TEs block the passive cooling of the heat source and accumulate heat quickly when they are not powered.Extra energy is therefore needed to drive the TEs to remove the accumulated heat.In order to utilizing and transporting the thermal energy totally,the TEs/device needs to keep close contact with the heat source and the cold source in actual applications.Moreover,both the heat source and the cold source behave curved surface.The conventional bulk TEs are inorganic semiconductors composed of covalent bond,ionic bond and van der Waals force with inherent brittleness and rigidity.They cannot closely contact curved heat sources and have difficulty in maintaining temperature differences,which decreases the efficiency of energy conversion and cooling ability due to the poor thermal contact within interface.The heat energy loss caused by poor contact among the heat source,the cold source and the TEs has also become one of the key factors restricting the development of the TE technology.Therefore,it remains a big challenge to fabricate high-performance and IR-transparent TEs and devices with good flexibility and high efficiency.We report a TE hybrid comprised of weak?000l?-textured n-type Bi₂Te₃ nanocrystals anchored on a carbon nanotube?SWCNT?network by a magnetron sputtering technique as above.The unique structure could improve both electrical conductivity and flexibility with an in-plane direction power factor of?265 ?W m^-1 K^-2.Because of its nanoporous structure and the multiscale defects lead to the ultralow thermal conductivity,which is as low as?0.34 W m^-1 K^-1,and the in-plane ZT value is?0.23 at room temperature.The hybrids show maximum transmittance values ranging from?16%to?95%,which can be attributed to the thickness and porous structure.Compared with non-IR transparent TEs with similar ZT values,our material would allow an extra passive cooling thermal flux that is?22%of the total cooling ability.Our results open a new way for the development of flexible and IR-transparent TEs with both efficient active and passive cooling performance.The Bi₂Te₃/SWCNT hybrid is assembled on a polyimide substrate by laser processing technology.An in-plane thin-film TE device is fabricated accordingly.The prototype TE device gives a maximum output power density of?0.93 mW/cm² under a temperature difference of?25 K at ambient temperature and shows good flexibility under bending.Our results play a positive role to the development of flexible TEs and their application in self-powered portable devices.