Compositional and electronic inhomogeneities in printed non-fullerene solar cells andtheir effect on device performance and stability

印刷有机光伏提供了生产廉价、大面积和柔性产品的可能性，但在将其集成到工业应用之前，仍需要解决某些挑战。其中一个挑战与在大面积上形成均匀、均匀薄膜的困难有关。不均匀性的存在将影响印刷器件的功能和性能及其稳定性。在这个项目中，我们将利用空间和能量分辨光发射光谱（PES）研究印刷有机太阳能电池中成分和电子不均匀性的形成。通过使用PES成像或PES制图，可以获得大面积的空间分辨率信息，分辨率分别为1微米和100微米。这些长度尺度与不均匀性的研究高度相关，并使表征大样本（在厘米长度尺度上）成为可能。通过将光谱表征与气团离子束的温和蚀刻相结合，可以实现1-2 nm的垂直分辨率测量，从而实现对有机材料的基本无损伤蚀刻。这两种方法可以结合起来，以跟踪在器件有源层的不同深度的大面积上材料的组成和电子结构的演变。这些方法将使我们能够将成分和电子不均匀性作为横向尺寸和深度的函数进行表征。与研究单位POPULAR的其他合作伙伴一起，我们将揭示这些不均匀性如何影响设备性能，特别是稳定性。后者将在本项目中进行详细研究，以阐明在制造过程中形成的不均匀性如何导致降解，或者，均匀印刷层的老化如何导致不均匀性的形成。

Printed organic photovoltaics offer the possibility to produce inexpensive, large area and flexible products, yet certain challenges still need to be addressed prior to its integration in industrial applications. One of these challenges is related to the difficulty of forming uniform, homogeneous films over large areas. The presence of inhomogeneities will affect the function and performance of the printed devices as well as its stability. In this project, we will investigate the formation of compositional and electronic inhomogeneities in printed organic solar cells by spatially and energetically resolved photoemission spectroscopy (PES). Spatially resolved information across large areas can be obtained by using PES imaging or PES mapping, offering a resolution of 1 and 100 um, respectively. These length scales are highly relevant to the study of inhomogeneities and make it possible to characterise large samples (on a cm length scale). Vertically resolved measurements with a resolution of 1–2 nm are made possible by coupling the spectroscopic characterisation with gentle etching by a gas cluster ion beam, which offers an essentially damage-free etching of organic materials. The two methods can be combined in order to track the evolution of the composition and electronic structure of materials across large areas at various depths of the device active layer. These methods will enable us to characterise both compositional and electronic inhomogeneities as a function of lateral dimensions and depth. Together with other partners of the Research Unit POPULAR we will reveal how these inhomogeneities impact on the device performance, and in particular on the stability. The latter will be examined in detail in this project in order to elucidate how the presence of inhomogeneities formed during fabrication can lead to degradation, and alternatively, how the ageing of homogeneous printed layers can lead to the formation of inhomogeneities.