Infrared Spectroscopy in the Ultra-High Vacuum

有机半导体，即共轭分子和聚合物，承诺具有成本效益的大面积可加工性，可用于新型显示技术、固态闪电、光伏、智能纺织品或印刷电子产品的灵活结构。然而，与硅等无机半导体相比，我们通过杂质掺杂精确控制复杂结构中电荷分布的能力仍然有限。尽管有机发光二极管(OLED)等显示技术在该领域的成功应用基本上都是使用掺杂材料，但今天的掺杂剂的掺杂效率很低，其潜在的工作过程还不完全清楚。这主要是因为用于有机半导体的掺杂剂本身就是有机分子，我们已经确定了化学相互作用可以显著降低电荷转移的程度，从而降低掺杂效率。根据我们以前的工作，我们提出了更有效的分子空穴掺杂的设计策略，这要求是具有高电子亲和力的大分子，以减少通过空间位阻的相互作用，同时促进有效的电荷转移。我们目前正在基于这一原理合成一系列新型的掺杂剂，但它们对氧/水高度敏感。虽然由于工业上有效的封装策略，这对于它们的实际应用来说是不成问题的，但它们的分析需要通过傅立叶变换红外光谱(FTIR)来评估化学完整性和量化它们的效率，这需要原位完成。同样，我们正在探索有机半导体掺杂的潜在机制，使用Lewis酸作为替代掺杂剂，其中诱导半导体质子化的水辅助过程最近被认为是基本过程。然而，这与最近的数据不符，这些数据表明，这一过程在能量上是不利的。因此，要弄清路易斯酸掺杂的过程，需要在完全无水的环境中工作，这只能通过超高真空(UHV)才能实现。因此，我们要求将FTIR光谱仪与我们现有的互连UHV/手套盒系统相结合。该仪器能够在不接触氧气/水的情况下，对掺入我们的新型空穴掺杂剂和Lewis酸的有机半导体薄膜进行原位表征。薄膜样品通过手套盒中的旋涂建立，通过掺杂剂的真空升华转移到超高真空系统进行掺杂，并在不打破真空的情况下进行原位FTIR分析。该光谱仪的掠入射反射能力使其能够研究直到单层区域的超薄膜，以同样地研究体掺杂和界面效应。这使得能够推动有机半导体兴奋剂的极限，并促进对其基本过程的了解，这是以知识为基础制定未来兴奋剂战略的关键。

Organic semiconductors, that is, conjugated molecules and polymers promise cost-effective large area processability into flexible structures for novel display technology, solid-state lightning, photovoltaics, intelligent textiles or printed electronics. In contrast to inorganic semiconductors such as silicon, however, our ability to precisely control the distribution of charge in complex structures by impurity doping is still limited. While essentially all successful applications in the field such as organic light emitting diode (OLED) based display technology employ doped materials, the doping efficiency of today's dopants is low and the underlying processes at work are not yet fully understood. This is mainly because dopants used for organic semiconductors are organic molecules themselves, where we have identified chemical interaction to significantly lower the degree of charge transfer and, therefore, the doping efficiency. From our previous work emerge design strategies for more efficient molecular hole dopants, which require to be bulky molecules of high electron affinity to reduce interaction through steric hindrance while promoting efficient charge transfer. We are currently synthesizing a library of novel doping agents based on this rationale, which are, however, highly sensitive to oxygen/water. While this is no issue for their practical application due to efficient encapsulation strategies in industry, their analysis via Fourier-transform infrared spectroscopy (FTIR) to assess chemical integrity and to quantify their efficiency requires to be done in-situ. In the same vein, we are exploring the mechanisms underlying the doping of organic semiconductors using Lewis acids as alternative dopants, where a water-assisted process inducing semiconductor protonation has recently been suggested as fundamental process. This is, however, at odds with recent data suggesting this process to be energetically unfavorable. Elucidating the process of Lewis acid doping therefore requires working in an entirely water-free environment which is only enabled by ultrahigh vacuum (UHV). Therefore, we request an FTIR spectrometer to be combined with our available interconnected UHV/glovebox system. This instrument enables in-situ characterization of organic semiconductor thin films doped with our novel hole dopants and Lewis acids without exposure to oxygen/water. Thin film samples are established via spin coating in the glovebox, transferred to the UHV system for doping via vacuum sublimation of the dopants, and analysed by FTIR in-situ without breaking the vacuum. The spectrometer's capabilities for grazing incidence reflectance allow to investigate ultrathin films down to the monolayer region to equally investigate bulk doping and interface effects. This enables pushing the limits of organic semiconductor doping and foster the understanding of its basic processes, which is key for the knowledge-based development of future doping strategies.