Nature of Proton and Light induced Defects in Lead Halide Perovskites

随着钙钛矿基混合太阳能电池和钙钛矿/硅串联太阳能电池的效率越来越接近传统硅太阳能电池，其稳定性成为最重要的问题。尽管杂化钙钛矿基器件的稳定性研究取得了进展，但辐射诱导缺陷态的研究仍然不足。然而，在运行中，任何太阳能电池都暴露在电磁波谱的紫外/可见和近红外部分。特别是光谱的高能部分明显地形成了作为非辐射复合中心的陷阱态。同样的现象使得需要紫外线、电子或x射线辐射的光谱方法不可靠。本项目提案旨在对辐射引起的局部缺陷有一个基本的了解。因此，缺陷将以一种受控的方式产生，利用光和高能质子辐照。高能质子是缺陷生成实验的理想选择，因为它们能够通过离解有机阳离子中的键和取代无机晶格中的单个原子核来产生缺陷。由光和质子辐照产生的缺陷将被表征，目的是确定它们的电子、结构和光学性质及其对电荷输运的影响。为此，将采用电子顺磁共振（EPR）、振动光谱和表面光电压光谱的独特组合。为了确定缺陷状态的性质，我们将不遵循成分工程的概念，这是广泛用于高效太阳能电池。相反，分析将从一种最简单的混合钙钛矿开始：CH3NH3PbI3。然后卤化物阴离子，以及有机阳离子，会一个接一个地交换。此外，铅、碳、氮和氢同位素将被纳入钙钛矿，以明确地识别局部缺陷和缺陷复合物的显微结构。通过这种方法，我们将建立对辐射诱导缺陷态的形成和性质的良好理解。这是为开发稳定的杂化钙钛矿奠定基础的重要一步。

As record efficiencies of hybrid perovskite-based single and perovskite/silicon tandem solar cells approach those of conventional silicon solar cells, their stability becomes the most important issue. Although research on the stabilization of hybrid perovskite-based devices progresses, radiation-induced defect states remain under-investigated. Under operation, however, any solar cell is exposed to the UV/VIS and NIR part of the electromagnetic spectrum. Especially the high energetic part of the spectrum evidently forms trap states that act as non-radiative recombination centers. The same phenomena render spectroscopic methods that require UV, electron, or X-Ray radiation unreliable.This project proposal aims at a fundamental understanding of radiation-induced localized defects. Hence, defects will be generated in a controlled way employing light as well as high energetic proton irradiation. High energetic protons are an ideal choice for defect generation experiments, since they are capable of creating defects by dissociation of bonds in the organic cations and by displacing individual nuclei of the inorganic lattice. Defects generated by light and proton irradiation will be characterized with the aim to identify their electronic, structural, and optical properties and their impact on charge transport. For this purpose, a unique combination of electron paramagnetic resonance (EPR), vibrational spectroscopies, and surface photovoltage spectroscopy will be employed. To identify the nature of the defect states, we will not follow the concept of compositional engineering, which is widely used for high-efficiency solar cells. Instead, analysis will begin with one of the simplest hybrid perovskites: CH3NH3PbI3. Then the halide anions, as well as the organic cations, will be interchanged one by one. Additionally, lead, carbon, nitrogen and hydrogen isotopes will be incorporated into the perovskites to unambiguously identify the microscopy structure of localized defects and defect complexes. With this approach we will establish a sound understanding of the formation and the nature of radiation-induced defect states. This is an important step that will lay the foundation for developing stable hybrid perovskites.