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

在这个项目中，我们应用光谱学（PES）和逆光谱学（IPES）以及光谱椭偏法（SE）分别测定了纯非富勒烯受体（NFA）、供体和多嵌段共聚物层以及供体-受体共混物的电子和光学性质，并将其作为各种老化过程的函数。PES和IPES分别提供了占据态和未占据态密度的信息，从中可以推导出功函数、电离能、电子亲和等有价值的参数，从而可以推导出输运或单粒子带隙。另一方面，椭偏光谱由态的联合密度定义，并分别提供介电函数和光学常数，由此可以推导出光学带隙。此外，SE还可用于测定薄膜厚度、组成和组成梯度、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性。该项目有三个研究重点，即a)纯NFA，供体和多块共聚物层的研究，b)供体-受体共混物，以及c)降解/老化过程的影响。关于整齐层，我们研究了可用的nfa，供体和在研究单位合成的新型含nfa的多块共低聚物。所获得的参数可作为参考数据，并作为研究单位内设备建模的输入。第二个重点是供体-受体共混物，PES/IPES与SE结合提供与纯层相同的有价值参数。然而，SE的作用变得更加重要，因为它可以通过使用有效介质近似（EMA）方法来研究形貌。EMA模型提供了供体和受体混合和相分离的信息。除了常见的EMA方法之外，还提出了检测自旋涂层和印刷共混物中相互作用诱导效应的方法，作为加工参数的函数。进一步利用SE研究混合层的横向和深度不均匀性。最后，我们主要使用SE及其原位监测能力来关注混合层的降解/老化过程。

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.