Fabrication Of Bi₂Te₃-Based Thermoelectric Thin Films And Devices On Flexible Substrates

Thermoelectric materials can directly convert thermal energy into electrical energy,which is a unique advantage that other materials cannot match.Secondly,thermoelectric materials will not produce harmful substances to the environment,and are a clean energy material.In today’s increasingly serious energy crisis,it provides a new idea for researchers to find new energy.Thermoelectric materials can be divided into four categories by operating temperature,namely low temperature,room temperature,medium temperature and high temperature thermoelectric materials.Bi₂Te₃ based thermoelectric materials are favored by researchers because their best room temperature thermoelectric performance.However,they are limited in the wearable field due to their inherent brittleness,stiffness,and non-scalable fabrication techniques.In recent years,the development of wearable technology and the urgent need for wearable and self-powered devices has led to the development of flexible thermoelectric materials as an emerging trend.The Bi₂Te₃ based thermoelectric films on flexible polyimide substrates have the advantages of low cost and easy commercial batch manufacturing,which are the keys to promote the commercial application of thermoelectric devices in wearable devices.In this paper,a high vacuum magnetron sputtering deposition system was used to prepare p-type Bi_0.5Sb_1.5Te₃ thin films with excellent room temperature thermoelectric properties on polyimide（PI）substrates,and a series of experiments were conducted to explore their optimal deposition process parameters.Firstly,the effect of coating deposition power on the open circuit voltage of the prepared thin film devices was investigated,and the optimal deposition power was determined from the experimentally collected data;Secondly,the influence of deposition temperature on the open-circuit voltage of the thin film device was studied on the basis of the optimal deposition power.Finally,the effect of deposition time on the open-circuit voltage of the thin film device was studied on the basis of the former two.Thus,the best process parameters for depositing p-type Bi_0.5Sb_1.5Te₃ films were found,and the corresponding films and devices were prepared under the best process parameter conditions.Its device composed of four Bi_0.5Sb_1.5Te₃ films obtained an open-circuit voltage of 38.6 m V with a power factor of 5.98μW cm^-1K^-2（300K）at a small temperature difference ofΔT=60 K.Secondly,this paper also studies the deposition of W-doped Bi_0.5Sb_1.5Te3films on polyimide substrates by magnetron sputtering to prepare flexible thermoelectric films and generators,and the optimal process parameters for depositing the films were investigated.At room temperature,the power factor（PF）of the W-doped Bi_0.5Sb_1.5Te₃ film reaches 13.75μWcm^-1K^-2,which is twice that of the pure Bi_0.5Sb_1.5Te₃film.Theoretical calculations show that the W doping can effectively reduce the power function and increase the carrier concentration and mobility of Bi_0.5Sb_1.5Te₃ films,thus enhancing the thermoelectric performance.The flexible TEG composed of four W-doped Bi_0.5Sb_1.5Te₃ films can provide an output voltage of 46.9 m V and a power density of 6.91 m Wcm^-2 at a temperature difference ofΔT=60 K.Due to the superior flexibility of the polyimide substrate,the prepared W-doped Bi_0.5Sb_1.5Te₃ films have good mechanical flexibility and can withstand high-frequency elastic bending（more than 1000 times）,while maintaining their intrinsic electrical properties.These results demonstrate that Bi_0.5Sb_1.5Te₃-based materials have great potential for self-powered wearable electronics.