Nanostructured Bismuth Telluride Thin Films - Advancing the Capability of Thermoelectric Materials

热电(TE)材料可用于将热能转换为电能。它们的特性基于以下两种现象之一：塞贝克效应(用于发电)和帕尔蒂埃效应(用于电子制冷或加热)。当n型掺杂材料通过温差串联和热并联将n型掺杂材料电连接到p型掺杂材料时，形成TE器件，使得电流在两者之间流动。TE发电机具有许多非常有利的特点，因为它们提供固态操作，没有可能磨损的机械部件，几乎不需要维护，寿命长，产生零排放，与热机相比紧凑。尽管如此，由于现有材料的热电效率较低，目前它们仅用于小众应用。固态TE设备为高效、可持续地从内燃机和能源密集型工业过程(如炼油厂和玻璃炉)产生的低品位废热中收集电力提供了一条很有前途的途径。对于低温余热和自然热源，还没有竞争的技术，因此存在巨大的机会。然而，要使TE在这些领域的应用切实可行，需要克服关键障碍，特别是要提高热电效率并减少制造功能TE设备所需的材料体积。纳米结构TE材料可以导致效率的显著提高(由于量子限制效应和晶格热导率的降低)。因此，一个重要的目标是开发低成本的方法来制备纳米结构热电材料。碲化铋Bi2Te3是一种窄禁带半导体，其合金具有已知块体材料中最好的室温热电性能，因此通常用于商业TE器件。已经证明，热电材料的纳米结构可以显著提高效率。目前一个关键的电流限制是在纳米尺度上实现对材料生长、形貌和取向的精确空间控制。在STFC资助的一个项目下，我们开发了一种新型的单源化学气相沉积(CVD)试剂和方法，大大提高了在微图案化表面沉积具有非常高区域选择性的高质量Bi2Te3TEM薄膜的能力。这项应用专注于实现关键里程碑，以建立这种沉积方法的商业潜力，目标是将热电优值系数(ZT)提高到约2，这意味着从工业工厂收集能量将是可以实现的。

Thermoelectric (TE) materials can be used to convert thermal energy into electricity. Their properties are based on one of two phenomena, the Seebeck effect (for power generation) and the Peltier effect (for electronic cooling or heating). A TE device is formed when an n-type doped material is connected electrically in series and thermally in parallel across a temperature differential to a p-type doped material, so that current flows between the two. TE generators have a number of very favourable features as they offer solid-state operation, have no mechanical parts that can wear out, require little maintenance, have long lifetimes, produce zero emissions and are compact compared with heat engines. Despite this, currently they are used only in niche applications because of the low thermoelectric efficiency of the existing materials. Solid state TE devices offer a promising route to efficient and sustainable electrical power harvesting from low grade waste heat produced in internal combustion engines, and in energy-intensive industrial processes, for example refineries and glass furnaces. For low temperature waste heat and natural heat sources, there is no competing technology, thus a huge opportunity exists. However, key barriers need to be overcome in order to make the application of TEs in these areas practicable, particularly to increase the thermoelectric efficiency and reduce the material volume required to create functional TE devices. Nanostructuring TE materials can lead to very significant increases in efficiency (due to both quantum confinement effects and reductions in lattice thermal conductivity). An important target, therefore, is the development of low-cost methods by which nanostructured thermoelectric materials can be produced.Bismuth telluride, Bi2Te3, is a narrow band gap semiconductor whose alloys are commonly used in commercial TE devices as they have among the best room temperature thermoelectric properties of known bulk materials. It has been demonstrated that nanostructuring of thermoelectric materials can lead to significant increases in efficiency. A key current limitation at present is in achieving precise spatial control of material growth, morphology and orientation on the nanoscale. Under a project funded by STFC we have developed a novel single source chemical vapour deposition (CVD) reagent and method that significantly enhances the ability to deposit high quality thin films of Bi2Te3 TEMs with very high area selectivity onto micropatterned surfaces. This application is focussed on achieving key milestones to establish the commercial potential of this deposition method, with the target of increasing the thermoelectric figure of merit (ZT) to ca. 2, which would mean energy harvesting from industrial plants would be achievable.