Correlation between electronic and optical properties of materials used in printed organic solar cells (Project 7)

在本项目中，我们应用光电子能谱(PES)、反向光电子能谱(IPES)以及椭圆偏振光谱(SE)分别测定了纯非富勒烯受体(NFA)、施主和多嵌段共低聚物层以及施主-受体共混物的电学和光学性质，并根据不同的老化过程进行了测试。PES和IPES分别提供了占据态和未占据态的密度信息，由此可以得到功函数、电离能、电子亲和力等有价值的参数，从而可以得到输运或单粒子带隙。另一方面，椭圆偏振光谱由联合态密度定义，并分别向介电函数提供光学常数，由此可以推导出光学带隙。此外，SE还可以用来确定薄膜厚度、成分和成分梯度、由分子取向引起的光学各向异性、表面和界面粗糙度以及水平和垂直不均匀。该项目有三个研究重点，即a)整齐的NFA、施主和多嵌段共低聚物层，b)施主-受体共混物，以及c)降解/老化过程的影响。对于整齐的层，我们研究了可用的非饱和脂肪酸、供体和在研究单位内合成的含有非饱和脂肪酸的新型多嵌段共低聚物。所获得的参数可作为参考数据，并作为研究股内设备建模的输入。第二个重点在于供体-受体共混物，PES/IPES与SE的结合提供了与纯净层相同的有价值的参数。然而，SE的作用变得更加重要，因为它可以通过有效介质近似(EMA)方法来研究形貌。EMA模型提供了有关供体和受体混合以及相分离的信息。除了常见的EMA方法之外，还提出了检测作为工艺参数函数的旋涂和印花共混物中的相互作用诱导效应的方法。在此基础上，进一步研究了混合层的横向和纵向不均匀性。最后，我们重点研究了混合层的降解/老化过程，主要使用SE及其现场监测能力。

In this project we apply photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) as well as spectroscopic ellipsometry (SE) for the determination of electronic and optical properties, respectively, of neat non-fullerene acceptor (NFA), donor, and multiblock co-oligomers layers and donor-acceptor blends as-prepared and as a function of various ageing processes. PES and IPES deliver information on the densities of occupied states and unoccupied states, respectively, from which valuable parameters such as the work function, the ionization energy, the electron affinity, and thus the transport or single particle bandgap can be derived. Ellipsometry spectra, on the other hand, are defined by the joint density of states and provide the dielectric function respectively the optical constants, from which the optical bandgap can be derived. Moreover, SE can be employed to determine thin film thicknesses, composition and compositional gradients, optical anisotropies induced by molecular orientation, surface and interface roughnesses, as well as horizontal and vertical inhomogeneities. There are three research foci in this project, namely the investigations of a) neat NFA, donor, and multiblock co-oligomers layers, b) donor-acceptor blends, and c) the influence of degradation/ageing processes. Regarding neat layers we study available NFAs, donors, and novel NFA-containing multiblock co-oligomers synthesized within the Research Unit. The parameters obtained serve as reference data and as input for the device modelling within the Research Unit. The second focus lies on donor-acceptor blends and PES/IPES in combination with SE deliver the same valuable parameters as for neat layers. However, the role of SE becomes more important as it can be employed to investigate the morphology by using effective medium approximation (EMA) approaches. EMA modelling delivers information on the intermixing of donors and acceptors and phase separation. Approaches beyond the common EMA approaches are addressed to detect interaction-induced effects in both spin-coated and printed blends as a function of processing parameters. SE is further employed to investigate inhomogeneities of blended layers both lateral and in depth. Finally, we focus on degradation/ageing processes of blended layers using mainly SE and its in situ monitoring capabilities.