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提供所需的电力，这种电力价格低廉，而且比传统发电技术产生的碳排放量要低得多。近年来，金属卤化物钙钛矿（MHPs）作为一种令人兴奋的新型光伏技术出现，无论是单独使用还是与令人兴奋的串联光伏太阳能技术相结合。后者，其中两个或更多的太阳能电池被耦合以克服热力学限制，将产生具有功率转换效率bbb30 %的光伏电池。由于光伏发电的实施取决于其成本，这直接关系到其功率转换效率，串联光伏发电为降低光伏发电的实施成本提供了相当大的潜力。宽带隙mps （> 1.7 eV）对于钙钛矿串联光伏至关重要，但与窄带隙相比，它们的研究较少，导致其性能远远低于理论极限。人们对这些材料的电子结构缺乏了解，这直接导致了光伏器件中显著的电压损失。这导致了器件设计中电荷传输层的定性选择，以及无法微调这些界面的能级排列。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极具挑战性。为了克服这些挑战，本项目将建立宽带隙mps电子结构的整体概述，使用实验模型系统和ab-initio材料建模来创建可用于理解设备相关系统实验测量的理论模型。mps的单晶将被用作模型系统，并使用光电子和光物理光谱来探测它们的电子结构。高分辨率原子力显微镜技术将适用于对晶体结构进行非破坏性成像，并提供有关表面结构缺陷的信息。总之，这些测量将促进模型的发展，为MHPs的基本电子结构提供新的见解。这些模型将应用于光伏设备架构，以确定电压损失的来源，并将产生一系列克服这些损失的定量建议。了解MHP材料的电子结构对于确保基于这些令人兴奋的新型半导体技术的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伏发电的持续发展，而且将有助于我们对这种新型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.