Understanding the evolution of structure, ion migration and defect properties during (de)mixing of lead-halide perovskites (DE-MIX)

卤化铅钙钛矿目前被认为是下一代太阳能电池最有前途的半导体材料之一。由于它们结合不同卤化物的混合物的结构灵活性，混合钙钛矿组合物的带隙能量是容易适应的，使得可以生产高效的串联太阳能电池。然而，当暴露于光时，混合卤化物钙钛矿表现出其离子的严重分层行为，这导致钙钛矿和相应太阳能电池的光电和器件性能的劣化，目前阻碍了它们的成功商业化。因此，该项目旨在全面了解卤化物钙钛矿混合过程中发生的复杂结构动力学，以提高其相稳定性，同时保持其优异的光电性能。为此，我们将生产具有明确形态以及本体和表面缺陷性质的物理MAPbI 3-MAPbBr 3混合物，例如，使用添加剂，并系统地将它们暴露于温度和/或光照以引发和驱动混合和随后的分层过程。这些过程将使用强大的和互补的表征方法，即，XRD、NMR和PL光谱的组合。多模态原位测量和相应的分析将使我们能够详细了解相关参数的时间演变，例如化学计量比，缺陷密度，激发态性质和中间相的形成。我们将评估形貌，不同类型的缺陷（在表面和本体中）和具有增加的热力学稳定性的可能的中间组合物对离子扩散长度和路径起作用。这将使发展的离子迁移的动力学和热力学规律，从而（去）混合过程中的混合卤化物钙钛矿的清晰的理解。这样，决定混合（去）化过程的可逆性和不可逆性的相关材料性质将变得清晰。因此，该项目将有助于对混合卤化物钙钛矿的形态、缺陷性质和添加剂对离子迁移和相稳定性的影响有一个基本的了解。

Lead halide perovskites are currently considered one of the most promising semiconductor materials for the next generation of solar cells. Due to their structural flexibility to incorporate mixtures of different halides, the band gap energy of mixed perovskite compositions is easily adaptable so that highly efficient tandem solar cells can be produced. However, when exposed to light, mixed halide perovskites exhibit a severe demixing behavior of their ions, which leads to deterioration of the optoelectronic and device performance of the perovskite and corresponding solar cells, currently hindering their successful commercialization. This project thus aims to comprehensively understand the complex structural dynamics that occur during the (de)mixing of halide perovskites, to improve their phase stability, while preserving their excellent optoelectronic properties. To this end, we will produce, physical MAPbI3 – MAPbBr3 mixtures with well-defined morphological, as well as bulk and surface defect properties, e.g., using additives, and systematically expose them to temperature and/or illumination to initiate and drive mixing and subsequent demixing processes. These processes will be investigated in-situ using powerful and complementary characterization methods, i.e., a combination of XRD, NMR and PL spectroscopy. The multi-modal in-situ measurements and corresponding analysis will allow us to extract detailed insights about the time evolution of relevant parameters such as stoichiometry, defect densities, excited state properties and formation of intermediate phases.We will evaluate which role the morphology, different types of defects (at the surface and in the bulk) and possible intermediate compositions with increased thermodynamic stability play for ion diffusion lengths and pathways. This will enable the development of a clear understanding of the kinetic and thermodynamic laws of ion migration and thus (de)mixing processes in mixed halide perovskites. With that, relevant material properties determining reversibility and irreversibility of (de)mixing processes will become clear. Thus, this proposed project significantly will contribute to developing a fundamental understanding about the impact of morphology, defect properties and additives on ion migration and phase stability of mixed halide perovskites.