【作者】 张林；

【导师】 韩广；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2024， 硕士

【摘要】 热电转换技术能将体热或环境中的热量直接转换成电能,具有性能稳定、持续供能等优点,在废热回收发电、柔性电子设备持续供能等方面具有重要潜力。碲化铋（Bi₂Te₃）基材料在近室温区具有优异的热电性能,然而传统Bi₂Te₃基块体材料因其本征刚脆性,难与形状复杂的热源表面贴合,导致热能利用率较低。发展一种高效、快速且可控的Bi₂Te₃柔性热电膜制备策略,对促进Bi₂Te₃柔性热电器件的实际应用至关重要。本文采用真空辅助抽滤和丝网印刷,将材料与柔性衬底相结合制备成柔性热电膜,通过热处理及热压工艺调节,提升了Bi₂Te₃膜的功率因子,最后对热电膜进行连接与封装,构筑了具有较高输出功率密度的柔性热电器件。本文主要研究内容如下。（1）采用热注射法合成了Bi₂Te₃纳米管,系统研究了还原剂的注射温度对产物纯度的影响规律;基于合成的Bi₂Te₃粉末,通过真空辅助抽滤获得了Bi₂Te₃@尼龙热电膜,但由于滤膜衬底耐受温度较低限制了热压温度,导致热电膜致密程度较低、电导率较差,仅获得15.8μW m^-1 K^-2的最大功率因子（352 K）;相比之下,利用丝网印刷制备的Bi₂Te₃@聚酰亚胺热电膜可承受更高的热压温度与压力,热压后热电膜致密程度得到显著改善,其在427 K下获得了37.2μW m^-1 K^-2的最大功率因子。（2）通过优化热电膜制备工艺并调节Bi₂Te₃材料的微结构,进一步提升了Bi₂Te₃@聚酰亚胺热电膜的载流子迁移率和热电性能。首先,利用聚酰亚胺衬底粗糙化,解决了热压后Bi₂Te₃热电膜形状完整度问题。随后,Bi₂Te₃粉末在氩气气氛下经过热处理后,发生聚集长大、界面密度减少,同时Bi₂Te₃粉末中残留的有机物得到有效去除,显著提升了在相同热压温度下热电膜的载流子迁移率,由1.7 cm²V^-1 s^-1提升至27.2 cm² V^-1 s^-1（773 K热处理）及31.6 cm² V^-1 s^-1（823 K热处理）。此外,随热压温度的提升,Bi₂Te₃@聚酰亚胺热电膜的载流子迁移率继续升高,达到41.9 cm² V^-1 s^-1,最终在427 K时获得了1186.3μW m^-1 K^-2的最大功率因子。该热电膜同时表现出良好柔性,在半径为10 mm的圆柱体上弯曲1000次后,其电阻仅增加了约11%。（3）基于功率因子最优的Bi₂Te₃@聚酰亚胺热电膜,分别以银浆和导电铝箔作为连接材料,探索并优化了Bi₂Te₃热电腿的连接工艺。研究表明,固化的银浆与热电腿的结合较弱,界面接触电阻较大且不稳定;相比之下,使用导电胶将Bi₂Te₃热电腿与铝箔紧密结合制备的热电器件具有更好的导电能力和稳定性。最后,通过聚二甲基硅氧烷对器件进行封装,以增强其使用时的稳定性。该器件在30 K的温差下,开路电压和输出功率密度分别达到10.4 mV和2.90 W m^-2,并且该器件在半径为10 mm的圆柱上弯曲500次后,内阻仅增加了8%,展示出良好的柔性。更多还原

【Abstract】 Thermoelectric conversion technology can directly convert body heat or heat in the environment into electricity,with stable performance,continuous energy supply and other advantages,possessing important potential in power generation from waste heat and continuous energy supply for flexible electronic devices.Bismuth telluride（Bi₂Te₃）-based materials have excellent thermoelectric properties in the near-room-temperature region;however,conventional Bi₂Te₃-based bulk materials are difficult to fit to the surface of complexly shaped heat sources due to their intrinsic brittleness and rigidity,resulting in low energy utilization.The development of an efficient,fast and controllable preparation strategy for Bi₂Te₃ flexible thermoelectric films is essential to facilitate the practical application of Bi₂Te₃ flexible thermoelectric devices.In this study,vacuum-assisted filtration and screen printing are used to prepare flexible thermoelectric films by combining Bi₂Te₃ materials with flexible substrates,and the power factor of Bi₂Te₃ films is enhanced by heat treatment and hot-pressing process adjustment.Finally,the thermoelectric films are connected and encapsulated,and flexible thermoelectric devices with relatively high output power density are constructed.The main research content of this study is as follows.（1）Bi₂Te₃ nanotubes were synthesized by hot injection method,and the influence of the injection temperature of reducing agent on the product purity is systematically investigated;based on the synthesized single-phase Bi₂Te₃ powders,Bi₂Te₃@nylon thermoelectric films were obtained by vacuum-assisted filtration.However,the low tolerance temperature of the filtration substrate limits the hot-pressing temperature,which results in a less dense film with poor electrical conductivity.As a result,a low maximum power factor of 15.8μW m^-1 K^-2（352 K）is obtained.In contrast,the Bi₂Te₃@polyimide films prepared by screen printing can withstand higher hot-pressing temperature and pressure,and the thermoelectric films are well densed via hot pressing,leading to a maximum power factor of 37.2μW m^-1 K^-2 at 427 K.（2）The carrier mobility and thermoelectric properties of the Bi₂Te₃@polyimide thermoelectric films are further enhanced by optimizing the thermoelectric film preparation process and tuning the microstructure of the Bi₂Te₃ materials.Firstly,the complete shape of Bi₂Te₃ thermoelectric films after hot pressing is effectively retained by using a rough polyimide substrate.Subsequently,the Bi₂Te₃ powders were heat-treated under argon atmosphere,which resulted in aggregation,growth and the density of interfaces reduction,as well as the effective removal of the residual organic matter in the Bi₂Te₃ powders.All these significantly improve the carrier mobility of the thermoelectric films obtained at the same hot-pressing temperature from 1.7 cm² V^-1 s^-1to 27.2 cm² V^-1 s^-1（heat treatment at 773 K）and 31.6 cm² V^-1 s^-1（heat treatment at823 K）.In addition,with the increase of the hot-pressing temperature,the carrier mobility of the Bi₂Te₃@polyimide thermoelectric film increases further and reaches41.9 cm² V^-1 s^-1,and a maximum power factor of 1186.3μW m^-1 K^-2 is finally obtained at 427 K.The thermoelectric film also exhibits good flexibility,and its electrical resistance only increases by about 11%after bending on a cylinder with a radius of 10 mm for 1000 times.（3）Based on the Bi₂Te₃@polyimide thermoelectric film with the highest power factor,the joining process of Bi₂Te₃ thermoelectric legs was explored and optimized using silver paste and conductive aluminium foil as the joining materials,respectively.It is shown that the bonding between cured silver paste and thermoelectric legs is weak,and the interfacial contact resistance is large and unstable;in contrast,the thermoelectric device prepared by tightly bonding the Bi₂Te₃ thermoelectric legs to aluminium foil using conductive adhesive has better conductive ability and stability.Finally,the thermoelectric device was encapsulated with polydimethylsiloxane to enhance its stability during use.The open-circuit voltage and output power density of the device reach 10.4 mV and 2.90 W m^-2,respectively,at a temperature difference of30 K.Moreover,the internal resistance of the device increases by only 8%after bending on a cylinder with a radius of 10 mm for 500 times,demonstrating good flexibility.更多还原