Understanding the electronic structure landscape in wide band gap metal halide perovskites

为了减轻气候变化的最严重影响，全球迫切需要清洁，安全和高效的能源生产。通过光伏发电的太阳能发电有潜力为不断增长的人口生产所需的电力，这种发电技术价格便宜，碳排放量比传统发电技术低得多。近年来，金属卤化物钙钛矿（MHP）已经作为一种令人兴奋的新光伏技术而出现，无论是其自身还是与串联光伏中令人兴奋的太阳能技术相结合。后者，其中两个或更多个太阳能电池被耦合以克服热力学限制，将产生功率转换效率> 30%的光致发光。由于光电转换的实现取决于其成本，并且这与其功率转换效率直接相关，串联光伏器件为降低光伏实现成本提供了相当大的潜力。（> 1.7 eV）对于钙钛矿串联光致发光材料是必不可少的，然而，与它们的窄带隙对应物相比，它们经历了较少的研究，导致它们的性能被限制在远低于理论极限人们对这些材料的电子结构缺乏了解，这些材料直接转化为光伏器件中的显著电压损耗。这导致了在器件设计中对电荷传输层的定性选择，并且不能微调这些界面处的能级对准。理解这些系统的困难在很大程度上是由于这些系统的化学复杂性。性能最高的宽带隙MHP是混合阳离子、混合卤化物系统，它们的复杂性使得研究它们的电子结构具有难以置信的挑战性。为了克服这些挑战，该项目将建立宽带隙MHP的电子结构的整体概述，使用实验模型系统和从头算材料建模来创建理论模型，可用于理解设备相关系统的实验测量。MHP的单晶将被用作模型系统，并使用光电子和电子物理光谱来研究它们的电子结构。高分辨率的原子力显微镜技术将适用于非破坏性图像的晶体结构，并提供有关表面上存在的结构缺陷的信息。这些测量将有助于模型的开发，这将为MHP的基本电子结构提供新的见解。这些模型将被应用到光伏器件架构，以确定电压损失的起源和克服这些损失的一系列定量的建议将产生。了解MHP材料的电子结构对于确保基于这些令人兴奋的新半导体的技术成功商业化至关重要。这项研究不仅将促进基于这些材料的光电子学的持续发展，而且将有助于我们对这类新的半导体材料的基本理解。

To mitigate the worst impacts of climate change there is an immediate global need for clean, secure, and efficient energy generation. Solar energy generation through photovoltaics has the potential to produce the electricity required for a growing population which is cheap and produces significantly lower carbon emissions than conventional power generation technologies. Metal halide perovskites (MHPs) have emerged in recent years as an exciting new photovoltaic technology both on their own and in combination with exciting solar technologies in tandem photovoltaics. The latter, wherein two or more solar cells are coupled to overcome thermodynamic limits, will produce photovoltaics with power conversion efficiencies > 30 %. As the implementation of photovoltaics hinges on their cost and this is directly related to their power conversion efficiencies, tandem photovoltaics offer considerable potential for lowering the cost of photovoltaic implementation.Wide band gap MHPs (> 1.7 eV) are essential for perovskite tandem photovoltaics however they have undergone less investigation than their narrow band gap counterparts resulting in their performance being constrained far below the theoretical limit. There is a lack of understanding of the electronic structure of these materials which translates directly into significant voltage losses in photovoltaic devices. This has led to qualitative selection of charge transport layers in device design and an inability to fine tune the energy level alignment at these interfaces. The difficulty in understanding these systems is due, in large part, to the chemical complexity of these systems. The highest performing wide band gap MHPs are mixed cation, mixed halide systems and their complexity makes studying their electronic structure incredibly challenging. To overcome these challenges this project will build a holistic overview of the electronic structure of wide band gap MHPs, using experimental model systems and ab-initio materials modelling to create theoretical models which can be used to understand experimental measurements of device relevant systems. Single crystals of MHPs will be used as model systems and studied using photoelectron and photophysical spectroscopies to probe their electronic structure. High resolution atomic force microscopy techniques will be adapted to non-destructively image the structure of the crystals and provide information on the structural defects present on the surfaces. Together these measurements will facilitate the development of models which will provide new insights into the fundamental electronic structure of MHPs. These models will be applied to photovoltaic device architectures to determine the origin of voltage losses and a quantitative series of recommendations for overcoming these losses will be produced. Understanding the electronic structure of MHP materials is critical in ensuring the successful commercialisation of technologies based on these exciting new semiconductors. This research will not only facilitate the continued development of photovoltaics based on these materials but will contribute to our fundamental understanding of this new class of semiconductor materials.