Molecular doping of organic semiconductors and beyond: resolving fundamental processes and increasing doping efficiency

通过引入杂质来掺杂无机半导体（如晶体硅）是所有晶体管技术的基础，它使当今电子设备的功能成为可能。在过去的几十年里，有机半导体作为无机物的迷人替代品出现，有望在柔性衬底上大面积加工，并且具有巨大的多功能性，因为它们的光电特性，特别是它们的带隙，可以通过它们的化学结构来调节。掺杂的概念直到最近才通过使用分子掺杂剂适用于有机物，其中所有基于有机发光二极管（oled）的新型显示技术今天都使用掺杂共轭材料。然而，尽管在应用上取得了巨大的成功，但人们对有机半导体掺杂的基本过程仍然知之甚少，材料设计也主要是经验主义的。在之前的工作中，我们确定了半导体和掺杂剂之间的化学相互作用是其低掺杂效率的关键因素，因为电荷转移配合物倾向于形成并取代掺杂剂的作用，而不是离子对，然而，强度显着降低。******在目前的多学科研究计划中，我们的目标是，首先，利用这种新的理解，通过修改分子间偶联机制来恢复掺杂剂的强度。我们将采用能够与多种掺杂相互作用的半导体，这将使有效的受体能级在能量上更容易获得。另外，由于电荷转移复合物的形成是由于耦合，我们将通过采用多种立体屏蔽功能芯来抑制耦合。其次，由于我们发现复合物的形成只发生在分子半导体中，而共轭聚合物在掺杂后确实会形成离子对，我们的目标是推导出一幅对两者都有效的统一图景，由此自然产生它们不同的掺杂行为。为此，我们将增加从低聚到聚合物的重复单元的数量，从而评估相互作用局部性的作用，并观察表面上不协调的掺杂现象之间的转变。第三，我们的目标是通过使用路易斯酸作为p掺杂剂，通过化学选择性来增强分子掺杂，其中电荷转移仅限于能够充当路易斯碱的物质。最后，我们将超越传统的掺杂，获得对埋藏层中电荷密度的空间控制。而不是掺杂外加剂，量身定制的能级排列将呈现层p /n掺杂通过与衬底的能级钉住。******总的来说，拟议的计划将建立有机半导体中掺杂的完整图景。它将使基于知识的化学设计能够精确地控制电荷密度，就像我们今天习惯上对无机半导体所做的那样，最终实现类似的功能。

Doping inorganic semiconductors such as crystalline silicon by introducing impurities is the basis of all transistor technology, which enables the functionality of today's electronic devices. In the past decades, organic semiconductors emerged as fascinating alternative to inorganics promising large-area processability on flexible-substrates and enormous versatility, as their opto-electronic properties, their bandgap in particular, can be tuned by their chemical structure. The concept of doping has only recently been adapted for organics by employing molecular dopants, where all novel display technology based on organic light emitting diodes (OLEDs) today uses doped conjugated materials. Despite enormous success in applications, however, the fundamental processes of doping are still poorly understood for organic semiconductors and material design remains largely empirical. In previous work, we identified the chemical interaction between semiconductor and dopant as key factor for their low doping efficiency, as, rather than ion pairs, charge transfer complexes tend to form and take over the role of the dopants, however, of significantly reduced strength.******In the present multidisciplinary research program, we aim to, first, exploit this novel understanding for regaining dopant strength by modifying the mechanism of intermolecular coupling. We will employ semiconductors capable of interacting with more than one dopant, which will make effective acceptor levels energetically more accessible. Alternatively, as charge-transfer complex formation is due to the coupling, we will inhibit the coupling by employing species of sterically shielded functional cores. Second, as we found that complex formation only occurs for molecular semiconductors, while conjugated polymers indeed form ion pairs upon doping, we aim to derive a unifying picture valid for both, from which their different doping behavior emerges naturally. To this end, we will increase the number of repeat units from the oligo- to the polymer limit, thereby assess the role of interaction locality, and observe the transition between the seemingly incongruous doping phenomenologies. Third, we aim to augment molecular doping by chemical selectivity through using Lewis acids as p-dopants, where charge transfer is restricted to species capable of acting as Lewis base. Finally, we will go beyond traditional doping to gain spatial control over the charge density in buried layers. Instead of dopant admixture, tailored energy-level alignment will render layers p-/n-doped via energy level pinning with the substrate. ******Overall, the proposed program will establish a complete picture of doping in organic semiconductors. It will enable knowledge-based chemical design for controlling charge density just as precisely as we customarily do today with inorganic semiconductors, for ultimately approaching similar functionality.