Novel boron-nitrogen coordinated polymers as next-generation n-type thermoelectric materials

尽管人们对新的、更环保的能源很感兴趣，但我们并没有有效地利用现有的能源：2019年英国产生的废热大约相当于同年全国电力需求的10%。除了寻找新能源外，回收未使用的能源，特别是占大部分能源损失的废热，对于未来更可持续的世界也至关重要。热电发电机可以捕获废热并将其转化为电能，因此近年来它们在促进可持续性方面的重要性得到了强调。有机热电发电机是由有机聚合物p型和n型热电材料偶联构成的，在可持续性方面比传统的重金属材料更受青睐。虽然建立了许多优良的p型热电材料，但缺乏优良的n型热电材料，滞后了有机热电发电机的发展。这是因为良好的n型材料需要较低的HOMO/LUMO能量和窄带隙，以实现有效的电荷转移和良好的空气稳定性。到目前为止，只有几组化合物符合标准。这个项目将研究一组新的n型有机热电材料：硼氮配位聚合物。B-N配位单元作为一种提高电子亲和的有效方法，已应用于多种电子材料中，但在热电领域几乎尚未得到开发。将B-N配位单元引入有机热电材料中，可以发现更多高性能的n型热电材料。该项目旨在开发结构中含有硼单元的共轭聚合物，这些结构要么是新颖的，要么是尚未研究的n型热电材料。一般来说，鉴定的目标将被合成、表征并制成薄膜。将测量固有热电性能，以确定目标是否显示良好的n型性能。在可能的情况下，开发的材料将与市售的高性能p型热电材料（如PEDOT:PSS）配对，以构建概念验证热电发电机，以展示能量收集能力。实现目标的方法将有以下四条路线，从路线1到路线4，目标的新颖性和技术难度逐渐增加：路线1：已知硼氮基聚合物的热电性能。最初发表的n型B-N配位聚合物已经在热电材料以外的领域开发，但显示出符合良好n型热电材料要求的有希望的性能（例如低洼前沿轨道，窄带隙），将进行试验。路线2：在已知的n型热电聚合物上进行B-N装饰。这条路线将专注于已知的n型热电聚合物的例子，并发现通过将B-N配位单元纳入结构中对n型热电性能的增强程度。路线3：优化已开发目标。n型热电材料常用的优化方法有增加吸电子基团、延长侧链长度等。因此，这条路线将进一步优化从1号和2号路线开发的化合物，以最大限度地提高其性能。在目标合成之前，计算计算（例如DFT）将评估设计，特别是HOMO/LUMO能级。路线4：带有其他配合单元的聚合物。除了B-N配位外，其他类型的配位单元，如B-O，在n型热电材料中可能比B-N做得更好。同样，在合成之前，将在计算机上进行计算，作为概念的证明。

Despite the high interest in new, greener energy sources, we are not using our current energy sources efficiently: the amount of waste heat generated in the UK in 2019 equals approximately 10% of the national electricity demand in the same year. In addition to finding new energy sources, recycling unused energy, especially waste heat which is attributed to the majority of the energy loss, is also vital for a more sustainable world in the future. Thermoelectric generators can capture the waste heat and convert it to electricity, hence their importance in contributing to sustainability has been highlighted in recent years. Organic thermoelectric generators, which are built up with organic polymeric p-type and n-type thermoelectric material couples, are more favoured over conventional heavy-metal materials concerning sustainability. Although many good p-type thermoelectric materials are established, a lack of good n-type materials lags the development of organic thermoelectric generators. This is because good n-type materials require low-lying HOMO/LUMO energies and narrow band gaps for effective charge transfers and decent air stabilities. So far only a few groups of compounds meet the criteria. This project will work on a new group of n-type organic thermoelectric materials: boron-nitrogen coordinated polymers. The B-N coordination unit has been applied in several families of electronic materials as an effective way to boost up the electron affinities but has almost not been exploited in the thermoelectric field. Introducing the B-N coordination unit to organic thermoelectric materials may allow us to discover more high-performance n-type thermoelectric materials.This project aims to develop conjugated polymers bearing boron units within the structures that are either novel or yet to be studied as n-type thermoelectric materials. In general, the identified targets will be synthesised, characterised and made into thin films. Intrinsic thermoelectric properties will be measured to determine if targets display good n-type performance. When possible, the developed materials will be paired up with commercially available, high-performance p-type thermoelectric materials, such as PEDOT:PSS, to build proof-of-concept thermoelectric generators to showcase energy harvesting abilities. Approaches towards the targets will be the following four routes, with target novelties and technical difficulties gradually increasing from Route 1 to Route 4:Route 1: Thermoelectric performance of known boron-nitrogen based polymers. Initially published n-type B-N coordinated polymers that have been exploited in fields other than thermoelectric materials but show promising properties (e.g. low-lying frontier orbitals, narrow band gaps) that fit the requirements for good n-type thermoelectric materials will be trialled.Route 2: B-N decoration on known n-type thermoelectric polymers. This route will focus on known examples of n-type thermoelectric polymers and discover the extent of enhancement on the n-type thermoelectric performance by incorporating B-N coordination units into the structures.Route 3: Optimisation on developed targets. Optimisation methods like adding electron-withdrawing groups and extending the length of sidechains are commonly used on n-type thermoelectric materials. Therefore, this route will further optimise the compounds developed from Route 1 and 2 to maximise their performance. Computational calculations (e.g. DFT) will evaluate the design, particularly the HOMO/LUMO levels, before targets are synthesised.Route 4: Polymers bearing other coordination units. In addition to B-N coordination, other types of coordination units, such as B-O, might do a better job than B-N in n-type thermoelectric materials. Likewise, calculations in silico will be done as a proof of concept before synthesis.