Layered copper oxychalcogenides for next generation p-type transparent conductors

愿景：了解一类氧-硫和氧-硒混合化合物（称为层状氧硫族化合物）的结构和组成如何控制其光电特性，并利用这一特性开发具有商业上可行的透明度和导电性的“p型”透明导体。透明导体，顾名思义，就是既透明又具有高导电性的材料。它们是现代电子产品中不可或缺的一类材料，存在于智能手机和平板电脑的屏幕、太阳能电池板和热效率高的玻璃涂层中。2018年，全球透明导体市场规模超过71亿美元。然而，这个市场仅由两种材料主导，氧化铟锡（ITO）和氟掺杂氧化锡（FTO），至关重要的是，这两种材料都是“n型”，其中导电源于带负电粒子-电子的运动。在“p型”材料中，导电是在缺电子层中，被认为是携带形式正电荷的“空穴”的运动。在非透明半导体电子学中，n型和p型材料都被使用，它们的组合可以形成二极管和晶体管，这是现代电子设备的基本组成部分。相比之下，对于透明导体，没有稳定的p型导体具有足够的透明度或导电性来与n型ITO或FTO竞争。这种p型透明导体的发现将在实现新技术方面具有变革性。结合现有的n型透明导体，p型透明涂层的可用性将允许形成透明的p-n结，可用于制造透明晶体管，从而制造透明电子产品。这将开启在车窗、后视镜和汽车挡风玻璃上集成电子设备的可能性——例如，为汽车或下一代智能眼镜提供平视显示器。透明电子产品的其他应用将包括集成在窗户上的光伏电池，用于安全的不可见射频识别，以及更高效、更亮、更轻的led。p型透明导体还可以为现有透明导体的应用提供替代方案，从而降低材料供应风险。我们的建议是研究层状氧硫属化合物，这类材料已经产生了至少八个已知的具有p型导电性的例子，如果不是光学透明度的话。从文献来看，至少有六种不同结构的层状氧硫属化合物是已知的；考虑到所有这些并应用一系列设计规则，我们可以生成950个氧化硫化物和氧化硒化物的目标相空间，以识别透明导电材料。这是一个太大的相空间，通过详尽的合成来研究，所以我们将使用一种选择性的方法来创建一个化合物库，并使用它来了解组成对光电性能的影响。该化合物库的电导率评估将使我们能够改进我们的设计策略并有效地针对高迁移率材料。我们还将与伦敦大学学院的大卫·斯坎伦教授的研究小组合作，利用计算材料建模的优势，更快地评估目标成分的稳定性和特性。到项目结束时，我们将合成和表征20到40种新的层状氧硫属化合物，并从这一组中确定最有希望用于透明p型导体应用的候选材料。我们还将对这类重要的固态材料的结构-性能关系产生新的理解，并利用它来识别和优化至少一种新的p型透明导体，其导电性与商业材料相等。

Vision: To develop an understanding of how the structure and composition of a class of mixed oxygen-sulfur and oxygen-selenium compounds, known as layered oxychalcogenides, controls their optoelectronic properties and use this to develop a 'p-type' transparent conductor with commercially viable transparency and conductivity.Transparent conductors, as the name implies, are materials that are transparent while also having high electrical conductivity. They are an indispensable class of material for modern electronics, being found in the screens of smart phones and tablet computers, in solar cell panels and in coatings for thermally efficient glazing. The global market for transparent conductors in 2018 was in excess of $7.1 billion. However, this market is dominated by just two materials, indium tin oxide (ITO) and fluorine doped tin oxide (FTO), and crucially both of these are 'n-type' where the conduction originates through movement of negatively charged particles - electrons. In 'p-type' materials, the conduction is in electron deficient layers and is considered as movement of 'holes' carrying a formal positive charge. In non-transparent semiconductor electronics both n-type and p-type materials are used, and their combination allows formation of diodes and transistors which are the fundamental building blocks of modern electronic devices.In contrast, for transparent conductors there is no stable p-type conductor with sufficient transparency or conductivity to rival n-type ITO or FTO. The discovery of such a p-type transparent conductor would be transformative in enabling new technology. In combination with existing n-type transparent conductors, the availability of p-type transparent coatings would allow for formation of transparent p-n junctions that could be used to create transparent transistors, and hence transparent electronics. This would open up the possibility of integrated electronics on windows, mirrors and car windscreens - for example, providing a head-up-display for cars or in the next generation of smart glasses. Additional applications of transparent electronics would include integrated photovoltaics on windows, invisible RFIDs for security, and more efficient, brighter and lighter LEDs. A p-type transparent conductor would also reduce materials supply risk by providing alternative options for existing transparent conductor applications. Our proposal is to investigate the layered oxychalcogenides, a materials class that has already produced at least eight known examples with p-type conductivity, if not optical transparency. From the literature, at least six different structure classes of layered oxychalcogenides are known; considering all of these and applying a series of design rules allows us to generate a target phase space of 950 oxysulfides and oxyselenides in which to identify transparent conductive materials. This is too large a phase space to investigate by exhaustive synthesis, so we will instead use a selective approach to create a compound library and use this to gain an understanding of the effect of composition on optoelectronic properties. Assessment of conductivity for this compound library will allow us to improve our design strategy and effectively target high mobility materials. We will also take advantage of computational materials modelling in collaboration with the research group of Prof David Scanlon at UCL, to more rapidly assess the stability and properties of target compositions. By the end of the project we will have synthesized and characterised between 20 and 40 new layered oxychalcogenides and identified from within this set the most promising candidates for transparent p-type conductor applications. We will also generate a new understanding of the structure-property relations in this important class of solid-state material, and use this to identify and optimise at least one new p-type transparent conductor with conductivity equal to commercial materials.