Fabrication And Performance Analysis Of Flexible Thermoelectric Devices By Inkjet Printing Telluride Nanowires

As an all-solid-state and environmentally friendly energy conversion material,thermoelectric material provides a feasible new way for the increasing power supply demand of electronic equipment.However,traditional high-performance thermoelectric materials are usually rigid,which limits their use in wearable devices.How to decouple the thermoelectric and mechanical properties of thermoelectric materials and prepare flexible thermoelectric devices at low cost is a major challenge.In recent years,the rapid development of flexible thermoelectric devices has provided new opportunities for the application of wearable devices in consumer electronics,health care,human-computer interaction and other fields.Telluride materials（such as Bi₂Te₃,Pb Te,Ge Te,etc.）are one of the highest performance thermoelectric material systems,and have been widely studied and applied in the field of flexible thermoelectric devices in recent years.Low-dimensional telluride nanomaterials have attracted much attention due to their special optical and electrical properties.Many literatures have reported the synthesis methods of low-dimensional telluride nanomaterials,such as template method,hot injection method and hydrothermal method.Deposition of low-dimensional inorganic thermoelectric materials on flexible substrates has proven to be an effective way to prepare high-performance flexible thermoelectric devices.Based on this,a variety of methods for preparing high-performance flexible film thermoelectric devices have been developed,such as vacuum filtration,screen printing,magnetron sputtering,and inkjet printing.Among them,inkjet printing technology is considered to be a reliable solution for large-scale preparation of flexible thermoelectric devices due to its maskless,high resolution and low cost,which is expected to further promote the application of thermoelectric devices in the field of flexible electronics.However,how to synthesize inorganic thermoelectric material based ink suitable for inkjet printing is one of the main difficulties in the preparation of high performance thermoelectric devices by inkjet printing technology.To solve the above problems,a low-cost and universal scheme for fabricating high-performance flexible thermoelectric devices based on inkjet printing technology is developed in this paper.The main research contents are as follows:（1）In order to meet the requirements of inkjet printing technology for powder size（less than1/10 of nozzle diameter）,Te nanowires were first prepared by high temperature liquid phase synthesis.The diameter of nanowires was～30 nm and the length was<2μm.Subsequently,a variety of telluride nanowires were synthesized using Te nanowires as templates,and the effects of reaction conditions on the morphology and phase of the synthesized products were explored.The results show that the product retains the nanowire morphology of Te nanowire template and its surface ligand polyvinylpyrrolidone（PVP）,and exhibits good dispersion and stability in ethanol solvent.A stable ink was obtained by simple ultrasonic dispersion,and its Z value was about 20,which was inconsistent with the Z value range suitable for inkjet printing reported in the literature.However,by selecting the appropriate nozzle voltage and waveform,the ink droplets can still be smoothly ejected without satellite droplets.In order to optimize the quality of the printing film,the effect of different printing droplet spacing on the macroscopic morphology of the film was investigated.The study found that when the droplet spacing is 20μm,the quality of the printed film is the highest.In order to verify the universality of the scheme and the diversity of inkjet printing,we used Ag₂Te,Cu₇Te₄,Bi₂Te_2.7Se_0.3 three inks to print films with different patterns.（2）Based on the work of the previous chapter,we prepared Ag₂Te films by inkjet printing with polyimide as a flexible substrate,and prepared flexible thermoelectric film devices for research.The printed film was post-processed by glass fiber assisted heat treatment process.The effects of heat treatment temperature on the morphology,phase and thermoelectric properties of the films were studied.The experimental results show that when the temperature exceeds 573 K,the Ag₂Te film will undergo a phase transition,and the nanowire morphology will change into a porous network structure.Among them,the sample treated at 673 K has the best thermoelectric properties,and the power factor reaches 138.9μWm^-1K^-2 at room temperature.The effects of different stoichiometric ratios on the thermoelectric properties of the films were further studied.It was found that the thermoelectric properties of Ag_2.1Te films were the best,and the room temperature power factor reached 221.3μWm^-1K^-2,400 K The power factor reaches a maximum of 494.5μWm^-1K^-2.Finally,combined with commercial silver ink,a full inkjet printed film thermoelectric device was prepared.At a temperature difference of 30 K,the output power of the four-legged Ag_2.1Te thermoelectric device reached 101.3 n W,and the normalized power density reached 0.9μWcm^-2K^-2.Compared with the results reported in the literature,the prepared device is the highest output performance thermoelectric device prepared by inkjet printing.In addition,the device exhibits good flexibility,bending 400 times at a bending radius of 10 mm,and the device resistance increases by only 8%.In conclusion,the ink preparation scheme and thermoelectric material performance optimization strategy proposed in this paper have certain universality,which is expected to be extended to other chalcogenides and has great potential in the preparation of high-performance flexible thermoelectric devices.