Lattice Dynamics and Charge Transport in Metastable Ternary Nitrides for Solar Energy Conversion

鉴于全球气温急剧上升和全球能源需求不断增加，寻找可再生能源和清洁能源变得比以往任何时候都更加紧迫。其中，太阳能是最重要的；即使在地球上最寒冷的地区，也有足够的资源来满足社会的能源需求。问题在于如何收集这些丰富的太阳能并使其为人们所利用。拟议的项目“用于太阳能转换的亚稳态氮化物中的晶格动力学和电荷输运”通过实现对一类新材料的基本理解来解决这一挑战，亚稳态氮化物将对下一代太阳能设备产生重大影响。通过计算和实验方法，本项目研究了它们的动态稳定和电荷输运机制以及它们之间的相互作用。这不仅对光伏应用至关重要，而且还将导致对亚稳态材料的潜在物理学的新见解。亚稳态材料提供了一个相对未开发的相空间，为令人兴奋的基础研究提供了新的设计机会和理想的平台。具有代表性的氮化铜钽CuTaN2将首先被研究，因为它在太阳能电池中显示出巨大的应用前景。除了其极其高效的光吸收外，它在高达250°C的实验中稳定，这对于提出的研究和实际设备的实现是理想的。通过对CuTaN2中晶格动力学和电荷输运的了解，我们将推导出这些基本机制与材料亚稳态之间的关系。然后，这些概念将被推广到更广泛的亚稳态氮化物，特别是那些不含稀有元素的亚稳态氮化物。特别有前途的是（Sn1-xTix）3N4和CaxZn2-xN2，它们是最近首次合成的。它们表现出理想的光电特性，同时由地球上丰富的元素组成。利用为CuTaN2建立的方法，我们将研究它们的基本性质，这将使我们能够在不同的氮化物材料之间进行比较，并评估潜在机制的普遍性。综上所述，具体的研究目标是：(i)提供关于CuTaN2的结构、电子和光学性质的详细理论和实验说明，（ii）全面研究其晶格动力学和非调和效应，（iii）研究电荷载流子输运及其如何受到动态核运动的影响，以及（iv）应用已建立的协议并评估我们的模型与其他亚稳氮化物材料的相关性。总而言之，所提出的方法将为新一代环境友好、丰富、廉价的光吸收半导体材料铺平道路，从而为寻找更好、更有效的太阳能收集解决方案铺平道路。

In view of dramatically rising global temperatures and increasing energy demand worldwide, it becomes more urgent than ever to find renewable and clean energy sources. Out of those, solar power is paramount; even in the coldest regions on Earth, there is more than enough to meet society’s energy needs. The problem lies in harvesting this abundant solar energy and making it accessible to the people. The proposed project “Lattice Dynamics and Charge Transport in Metastable Nitrides for Solar Energy Conversion” tackles this challenge by achieving fundamental understanding of a new class of materials, metastable nitrides, that will have a large impact on next-generation solar energy devices. By means of computational and experimental methods, this project addresses their mechanisms of dynamical stabilisation and charge transport as well as their mutual interplay. This is not only crucial for photovoltaic applications but will also lead to new insights into the underlying physics of metastable materials. Metastable materials present a relatively unexplored phase space that provides new design opportunities as well as an ideal platform for exciting fundamental research.The representative copper tantalum nitride CuTaN2 will be first investigated as it shows large promises for applications in solar cells. Apart from its extremely efficient light absorption, it is experimentally stable up to 250°C, which is ideal for the proposed study and real device implementation. From the gained knowledge of lattice dynamics and charge transport in CuTaN2, relationships between those fundamental mechanisms and the metastability of the material will be derived. These concepts will then be generalised to a much broader pool of metastable nitrides, specifically those that do not contain rare elements. Particularly promising are (Sn1-xTix)3N4 and CaxZn2-xN2, which were recently synthesised for the first time. They exhibit desirable optoelectronic properties while being composed of Earth-abundant elements. With the methodology established for CuTaN2, we will investigate their basic properties, which will allow us to draw comparisons between the different nitride materials and to assess the universality of the underlying mechanisms.Taken together, the specific research objectives are: (i) to provide a detailed theoretical and experimental account on the structural, electronic, and optical properties of CuTaN2, (ii) to comprehensively investigate its lattice dynamics and anharmonic effects, (iii) to study charge carrier transport and how it is influenced by dynamical nuclear motions, and (iv) to apply the established protocol and to assess the relevance of our models to other metastable nitride materials.All in all, the proposed approach will pave the path towards a new generation of environmentally benign, abundant, and inexpensive light-absorbing semiconductor materials and, thus, towards finding better and more efficient solutions for harvesting solar light.