Silver Selenide Flexible Thermoelectric Composite Film Preparation And Its Thermoelectric Properties

In recent years,with the increasing popularity of smart wearable electronic devices such as wireless earphones,smart glasses,and smart watches in lives,the traditional battery power supply have been unable to be satisfied with the long-term use of people,resulting in an urgent need for the market to develop a renewable and sustainable power supply technology.Among the many emerging energy generation methods,thermoelectric generators(TEGs),which can directly convert the temperature difference between the human body and the external environment into electrical energy,is gradually coming into view as an ideal self-powered technology that is easy to wear and integrate without mechanical vibration,and can be continuously powered without maintenance.In the field of thermoelectric materials,p-type thermoelectric materials are basically more researched,and relatively more researches in n-type thermoelectric materials are some toxic Te-containing materials,such as bismuth telluride and silver telluride,which are not suitable for flexible wearable devices,so it is necessary to explore Te-free thermoelectric materials.Silver selenide(Ag₂Se),as an“electron crystal,phonon liquid”n-type material with high electrical conductivity and low thermal conductivity at room temperature,it has rich crustal reserves and is an environmentally friendly material.In this thesis,we first prepared pure-Ag₂Se powder using the template method,prepared thermoelectric films and thermoelectric units by vacuum-assisted filtration and screen printing,and later prepared thermoelectric films by magnetron sputtering,as follows:(1)Firstly,pure-Ag₂Se nanorods were synthesized by the template method,and then the Ag₂Se/Polyvinylpyrrolidone(PVP)composite thermoelectric films with different Ag₂Se contents were prepared by vacuum-assisted filtration method.Among them,the 0.15 wt%Ag₂Se/PVP film has the best thermoelectric properties with the maximum power factor of16.18?W?m^-1?K^-2at 320 K.The thermoelectric unit prepared from this film have an open-circuit voltage of 10.9 m V and an output power of 55.57 n W at a temperature difference of 40 K.The film conductivity changed to 89.8%of the initial value when it has been bent500 times.In addition,the thermoelectric performance of the film can remain stable within 40days when it is placed in air,and its electrical conductivity drops only to 89%of the initial value after 50 days.We proposed to cold-press the films on the basis of the above experiment.Among them,the best thermoelectric properties were obtained by cold pressing treatment only without PVP thermoelectric films with a maximum power factor of 136?W?m^-1?K^-2at380 K and the best flexibility reliability,its electrical conductivity only changed to 91.48%of the original after bending 1500 times.The thermoelectric unit composed of this film has an open-circuit voltage of 17 m V and an output power of 391 n W at a temperature difference of40 K.(2)The preparation of the Ag₂Se/PVP thermoelectric unit using screen printing was proposed.Three unit were prepared by adjusting the ratio of Ag₂Se to PVP.Among them,the PI30 thermoelectric unit with the least PVP content has the largest power factor of 4.3?W?m^-1?K^-2at room temperature,but its flexibility reliability is the worst,its electrical conductivity is reduced to 81%of the initial value after 1500 bending cycles.The PI30thermoelectric unit output performance was tested with an open circuit voltage of 21.6 m V and a maximum output power of 233.3 n W at a temperature difference of 40 K.Based on the preparation of the Ag₂Se/PVP thermoelectric unit,we propose a fan-shaped Ag₂Se-Cu₂S thermoelectric unit,and four units are prepared by adjusting the ratio of Cu₂S to PEDOT:PSS.Among them,the PI1.2 thermoelectric unit has the best performance,with a power factor of6.39?W?m^-1?K^-2at 300 K.Its electrical conductivity drops to 75%of the initial value after1500 bending cycles.The PI1.2 Cu₂S/PEDOT:PSS thermoelectric unit and PI30 Ag₂Se/PVP thermoelectric unit were selected to prepare a fan-shaped Ag₂Se-Cu₂S thermoelectric unit,which was tested for output performance with an open-circuit voltage of 33.5 m V and an output power of 163.20 n W at a temperature difference of 20 K.(3)The Ag₂Se flexible thermoelectric films are prepared by magnetron sputtering,and the effects of different annealing temperature,sputtering power and sputtering time on the thermoelectric properties of the films are systematically investigated.Controlling the remaining experimental variables,six annealing temperatures were set under vacuum atmosphere,among which the best thermoelectric properties were obtained for the films annealed at 623 K with a power factor of 526.86?W?m^-1?K^-2at 300 K.Controlling the remaining experimental variables,five sputtering powers were set,where the best thermoelectric properties were obtained for the 80 W film with a power factor of 526.86?W?m^-1?K^-2at 300 K(the 80 W film was the 623 K film).Controlling the remaining experimental variables,five sputtering times were set,with the best thermoelectric properties of 25 min films and 555.55?W?m^-1?K^-2at 300 K.In a flexibility test on 573 K film,the conductivity of the film dropping to only 87%of its initial value after 1000 bends,and remaining essentially constant with increasing bends.