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世界能源需求增加，寻找可再生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，也有足够的能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，并使人们能够获得它。拟议的项目“太阳能转换亚稳氮化物的晶格动力学和电荷传输”通过实现对一类新材料亚稳氮化物的基本理解来应对这一挑战，这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，该项目解决了它们的动态稳定和电荷传输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基础物理学的新见解。亚稳材料呈现出一个相对未开发的相空间，提供了新的设计机会，以及令人兴奋的基础研究的理想平台。具有代表性的氮化铜钽CuTaN 2将首先进行研究，因为它显示出在太阳能电池中应用的巨大潜力。除了其极其有效的光吸收外，它在高达250°C的实验中是稳定的，这对于所提出的研究和真实的设备实现是理想的。从所获得的知识晶格动力学和电荷输运CuTaN 2，这些基本机制和材料的亚稳性之间的关系将被导出。这些概念将被推广到更广泛的亚稳氮化物，特别是那些不含稀有元素的亚稳氮化物。特别有前途的是（Sn 1-xTix）3 N4和CaxZn 2-xN 2，它们最近首次合成。它们表现出理想的光电性能，同时由地球丰富的元素组成。通过对CuTaN 2所建立的方法，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。总的来说，具体的研究目标是：（i）提供关于CuTaN 2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谐效应，（iii）研究电荷载流子输运以及它如何受到动态核运动的影响，以及（iv）应用所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。所提出的方法将为新一代环境友好的、丰富的和廉价的光吸收半导体材料铺平道路，并因此为寻找更好和更有效的用于收集太阳光的解决方案铺平道路。

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.