Solid-state µ-MAS and thin-film NMR spectroscopy on hybrid organic/inorganic perovskite photovoltaic materials

有机/无机混合卤化铅钙钛矿材料(APbX3)在过去的十年里引起了人们的极大兴趣，因为它们可能成为传统硅太阳能电池的替代材料，目前具有高达23%的优异的功率转换效率。由于结构灵活，可以获得包括混合阳离子和/或混合卤化物体系在内的宽频带化学成分。此外，除了化学成分外，还可以采用一系列不同的合成策略和处理方法来处理所生成的钙钛矿材料，例如，影响钙钛矿材料的形貌、粒度和晶体缺陷。这些不同水平的结构变化往往会对所得到的薄膜钙钛矿的光电性能产生连锁影响，钙钛矿是用于太阳能电池应用的材料几何形状。与巨大的参数空间相比，系统的研究很少，而且基本上缺乏对太阳能电池的现场工作条件，即光照时的研究。然而，为了指导未来的合成策略和高效率的卤化铅钙钛矿的最佳化学成分，在原子分辨率下进行全面的研究对于推导结构-性质关系是必不可少的。因此，该研究计划致力于填补这一差距，为一套混合的有机/无机混合卤化铅钙钛矿薄膜几何形状。为此，我们选择了核磁共振结晶学方法，因为它除了提供长程有序外，还提供了关于原子水平上的局部环境的补充信息，因此代表了系统结构研究的最佳方法。基于微线圈设计的新型薄膜MAS核磁共振探头的开发和实施将允许直接测量薄膜几何形状。此外，光源将安装在体相和薄膜MAS核磁共振探针中，以便能够在光照下就地监测多种钙钛矿成分和形貌的结构行为。我们期待着一套高性能的光伏钙钛矿材料的关键问题--点缺陷、阳离子或卤化物的有序/无序，以及光照射下的结构响应对光电性能的影响--得到解答。对大块样品和薄膜几何形状的结果进行比较，将有助于深入了解合成条件和结晶条件的影响。总体而言，在实际器件工作条件下对高性能钙钛矿材料的结构洞察最终将指向重要的结构-性能关系，以指导未来钙钛矿材料在太阳能电池器件中的应用。

Hybrid organic/inorganic lead halide perovskites (APbX3) have attracted great interest in the last decade due to their possible application as an alternative to conventional silicon solar cells, with excellent power conversion efficiencies of currently up to 23 %. Due to the flexible structure a wide bandwidth of chemical compositions including mixed cation and/or mixed halide systems are accessible. Furthermore, a series of different synthesis strategies and treatment of the resulting perovskites are possible, that besides chemical compositions impact on e.g. the morphology, particle size and crystallographic defects of the perovskite materials. These structural changes at varying levels often cause interlinked effects on the optoelectronic properties of the resulting thin film perovskites, the materials geometry that is used in solar cell applications. Systematic studies are rare compared to the enormous parameter space, and are essentially missing for in situ working conditions of solar cells, i.e. upon illumination. However, comprehensive studies at atomic resolution are essential to derive structure-property relations in order to guide future synthesis strategies and optimal chemical compositions for high efficiencies of lead halide perovskites. The research proposal, therefore, is dedicated to the closure of this gap for a suit of mixed hybrid organic/inorganic lead halide perovskites in thin film geometries. For this purpose we choose the NMR crystallographic approach as it provides complementary information about the local environment at atomic level in addition to long-range order, and thus represents the optimal methodology for systematic structural studies. The development and implementation of a novel thin film MAS NMR probehead based on microcoil designs will allow for direct measurements of thin film geometries. Furthermore, light sources will be installed in both, bulk and thin film MAS NMR probes, in order to allow for monitoring the structural behaviour of multiple perovskite compositions and morphologies in situ upon illumination. We expect that the key issues, how point defects, cation or halide order/disorder, as well as the structural response upon light irradiation impact on the optoelectronic properties will be answered for a suit of high-performance photovoltaic perovskite materials. The comparison of the results for both bulk samples and thin film geometries will provide insights in the influence of syntheses and thus crystallization conditions.Overall, the achieved structural insights about high-performance perovskite materials under actual device working conditions will eventually point to important structure-property relations to guide future tailoring of perovskite materials with respect to their application in solar cell devices.