Infrared Spectroscopy in the Ultra-High Vacuum

超高真空红外光谱

• 批准号: RTI-2022-00520
• 负责人: Salzmann, Ingo
• 金额: $ 10.93万
• 依托单位: Concordia University
• 依托单位国家: 加拿大
• 项目类别: Research Tools and Instruments
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=742961
• 关键词: Infrared; Spectroscopy; Ultra; Vacuum

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.

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加工成柔性结构，用于新型显示技术、固态照明、光电子、智能纺织品或印刷电子。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。虽然基本上该领域中的所有成功应用（例如基于有机发光二极管（OLED）的显示技术）都采用掺杂材料，但当今掺杂剂的掺杂效率低，并且工作中的基础工艺尚未完全理解。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，我们已经确定化学相互作用会显著降低电荷转移程度，从而降低掺杂效率。 从我们以前的工作中出现了更有效的分子空穴掺杂剂的设计策略，这需要是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。我们目前正在合成一个基于这一原理的新型掺杂剂库，然而，它们对氧/水高度敏感。虽然由于工业中的有效封装策略，这对于它们的实际应用来说没有问题，但是通过傅里叶变换红外光谱（FTIR）对其进行分析以评估化学完整性并量化其效率需要在原位进行。同样，我们正在探索使用刘易斯酸作为替代掺杂剂掺杂有机半导体的潜在机制，其中最近提出的水辅助过程诱导半导体质子化是基本过程。然而，这与最近的数据不一致，这些数据表明这一过程在能量上是不利的。因此，阐明刘易斯酸掺杂的过程需要在完全无水的环境中工作，该环境仅由超高真空（UHV）实现。 因此，我们要求FTIR光谱仪与我们现有的互连UHV/手套箱系统相结合。该仪器能够在不暴露于氧气/水的情况下原位表征掺杂有我们的新型空穴掺杂剂和刘易斯酸的有机半导体薄膜。薄膜样品通过旋涂在手套箱中建立，转移到UHV系统中，通过掺杂剂的真空升华进行掺杂，并在不破坏真空的情况下通过FTIR原位分析。该光谱仪的掠入射反射的能力，允许调查dielectric薄膜下降到单层区域，同样调查散装掺杂和界面效应。这使得能够推动有机半导体掺杂的极限，并促进对其基本过程的理解，这是未来掺杂策略基于知识的发展的关键。