Flexible Thermoelectric Devices Based On Tunable Low Dimensional Chalcogenide Metal Compounds

As a clean energy material,thermoelectric(TE)materials can directly realize the mutual conversion between thermal energy and electric energy,which is expected to improve the utilization rate of energy,alleviate the increasingly serious energy crisis,environmental pollution and other problems.In recent years,with the development of wearable technology,TE materials and devices must not only have higher power output,but also have good flexibility to meet the requirements of curved surface fitting and integration.Therefore,there is an urgent need to develop high-performance flexible TE materials and devices.The construction of high-performance flexible TE devices has been facing various challenges.As an important class of TE materials,chalcogenide compounds have the advantages of good Seebeck coefficient and adjustable conductivity,as well as low intrinsic thermal conductivity.However,chalcogen compounds(such as Ag₂Te,Cu_1.75Te,etc.)cannot couple high conductivity and high Seebeck coefficient,resulting in a lower power factor.In addition,the macroscopic films assembled by pure inorganic compounds are poor in flexibility and cannot adapt to the application environment of wearable electronics.Most of the flexible film/device construction methods are highly manual,unable to carry out the large-scale preparation of TE module units and precise process control,which limits the integration and application of thin film TE devices and wearable electronic devices.To solve the above problems,this paper is based on low-dimensional chalcogenide metal compounds(Ag_xTe,Cu_xTe,Ag₂Se)nanomaterials.Aiming at the performance control of materials and the construction of flexible devices,the metallization doping of chalcogen compounds and composite material modification and 3D printing of flexible thin film devices are studied,the main contents include:The hexagonal phase Te nanowires with uniform and controllable length was prepared by the hydrothermal-solvothermal method as the template for the subsequent reaction.The Te nanowires template was metallized and doped to obtain Ag_xTe and Cu_xTe nanowires with different nominal molar ratios,the conductivity of Ag_xTe and the Seebeck coefficient of Cu_xTe are greatly improved,and p-n type TE materials with the best TE properties are obtained.The power factor of p-type Cu_1.5Te and n-type Ag₄Te are 64.3?W m^-1 K^-2 and 101?W m^-1 K^-2.A p-n type Te-based metal compound TE device is constructed and the output voltage of 5 pairs of TE modules is 24.5 m V at a temperature difference of 50 K.Se@Ag₂Se core-shell structure nanorods were prepared by reduction using Se nanorods as templates.Using single-walled carbon nanotubes(SWCNT)with high flexibility and high conductivity as a mechanical-electrical enhancement material,supplemented by a low-temperature hot pressing process,a highly flexible Ag₂Se/SWCNT composite film is constructed.The nano-bridge structure between SWCNT and Ag₂Se significantly improves the flexibility.After 1000bendings,it can still maintain 94%performance,and the composite film exhibits excellent TE properties(PF?1030.7?W m^-1 K^-2,300 K).The high flexibility TE device composed of 6 composite material modules,the largest output power is 2.36?W at a temperature difference of 50 K.Using low-dimensional chalcogenide metal compounds(Ag_xTe,Cu_xTe and Ag₂Se)and lignocellulose nanofibers,TE hydrogels that meet the printing requirements were prepared,and flexible TE devices were constructed through bio-3D printers.The gel module can be cured by shrinkage at low temperature(<353K)and loaded on a variety of substrates(nylon,copy paper,polyimide,polyvinylidene fluoride film,etc.).Through the adjustment of parameters such as print head diameter,pneumatic pressure,printing speed and distance,the printing of low-dimensional TE materials of different sizes can be completed,and flexible TE generators of different structures can be constructed.The highly integrated density device composed of 70 pairs of p-n type TE modules exhibits an output voltage of 360.5 m V and a power density of 1.278 W m^-2 under a temperature difference of 50 K.