Design And Performance Optimization Of Flexible Film-type Metal Selenide Thermoelectric Generators

Wearable thermoelectric generators can convert the temperature difference between the human skin and the environment into electricity without imposing strict requirements on human motion states or environmental conditions.In recent years,they have been considered a very promising self-powered wearable electronic device.The output performance of such devices is mainly determined by the performance of thermoelectric materials and the design of device structures.Among various room-temperature thermoelectric materials,selenium-based materials,due to their low cost,low toxicity,and rich element content,are increasingly receiving attention.Their excellent thermoelectric properties at room temperature make them promising for application in wearable electronic devices.To address the practical application requirements of wearable thermoelectric devices,there are still two significant challenges that need to be overcome in research on flexible thermoelectric film devices.First,the power factor of thermoelectric films is still lower than that of bulk materials.Second,due to the lack of device structure optimization,most flexible film devices cannot effectively utilize the temperature difference established between the human skin and the environment,thereby limiting their output performance.To address these issues,this paper uses two kinds of selenides,Ag₂Se and Cu₂Se,as the object of research and uses the solvent thermal method and spark plasma sintering process to prepare to obtain flexible thermoelectric film materials.The microscopic morphology,crystal structure,elemental content and distribution of Cu2Se and Ag2Se films were finely controlled by component modulation and sintering processes to optimize their thermoelectric properties.A novel wearable flexible film device combining Cu₂Se-Ag₂Se with photothermal materials and hydrogels is designed by Comsol multiphysics simulation software.The effect of the size of the Cu₂Se and Ag₂Se thermoelectric legs on the output performance of the device was analyzed,and the power generation performance of the film device under different sun illuminations was investigated.The output performance is significantly improved by increasing the actual temperature difference between the two sides of the device.The main research works are as follows:The nylon-based Cu_2+xSe（x=0～0.25）films with excellent flexibility were prepared by a spark plasma sintering process,which successfully filled the Cu vacancies in the system by the over-introduction of Cu and regulated the carrier concentration,resulting in a power factor of 856.59±119.92μW m^-1 K^-2 at room temperature for the Cu_2.20Se film.In addition,the optimum length of Cu_2.20Se film at different hot side temperatures was obtained by simulation.At a hot side temperature of 310.15 K and an ambient temperature of 300.15 K,the measured temperature difference between the two sides of a 2 mm length of Cu_2.20Se film was 6.6 K.The output power density of the film was 2.918μW cm^-2 K^-2,which is at a high level among similar film materials.The same process was used to prepare flexible nylon-based Ag_2+xSe（x=0.1～0.5）films,and the composition control was used to optimize the Seebeck coefficient and conductivity of the Ag_2+xSe films and to determine the optimum ratio of Ag_2+xSe to Ag_2.3Se.By fine-tuning the spark plasma sintering process,the Ag agglomeration at the micron level was eliminated and the Se vacancy content was controlled.This improved the carrier transport state in the system,ultimately achieving a significant increase in power factor.The power factor of the Ag_2.3Se film reached 3933.07±550.63μW m^-1 K^-2 at a sintering temperature and time of 200°C and 5 min,respectively,and the optimum length of the Ag_2.3Se film at different hot side temperatures under natural convection conditions was confirmed by simulation.When the hot side temperature is 308.15 K and the ambient temperature is 298.15K,the actual temperature difference between the two sides of the film with a length of 2 mm is 6.35 K.The optimum output power density is 19.38μW cm^-2 K^-2,which is extremely competitive among similar materials.A wearable Cu₂Se-Ag₂Se thermoelectric film device was designed that can collect thermal energy using a photothermal film at the hot side and dissipate heat using a hydrogel at the cold side.The output performance of the device was tested using a self-built test system.The results show that the output power of the device gradually increases with increasing solar illumination,and the actual temperature difference between the hot and cold sides of the device reaches 35.5 K at one solar illumination,corresponding to an output power of 85.67μW.This work provides a new idea for the development of wearable thermoelectric generators with practical application potential.