Design rules for the development of sublimable Iridium emitter complexes with horizontal dipole orientation and improved light outcoupling in OLEDs

与此同时，有机发光二极管(OLED)是一种成熟的显示技术，已在智能手机或电视屏幕上得到商业应用。独特的卖点是它们的高图像质量和低能耗，这源于这些显示器是发射的，因此不需要任何背光。为此，具有强烈的自旋-轨道耦合的磷光发射器提供了决定性的优势，因为它们实现了几乎100%的内部量子效率，因为从三重态到基态的磷光是允许的光学跃迁。然而，获得的外部量子效率受到光输出耦合的限制，在传统的OLED结构中，光输出耦合只占大约20%-25%，因为产生的大部分光子被捕获在OLED内部。改善光输出耦合的一个强大工具是使用发射体分子，该发射体分子具有在薄膜生长期间水平对准的固有倾向，使得它们的光学跃迁偶极子优先向衬底辐射，即在观察者的观察方向上。然而，由于它们的三个配体围绕中心Ir原子具有八面体配位，因此它们的形状各向异性相对较低，因此实现与磷光Ir发射体络合物的高度对准仍然具有挑战性。因此，材料设计的进一步发展需要详细了解这类OLED发射体的结构与性能之间的关系。这个转移项目的主要目的是改进现有的预测和分析蒸发式客户-宿主系统中有Ir滴头的滴头取向的方法，以便建立和验证设计规则。此外，我们计划研究发射体和宿主分子之间的分子间相互作用，以及不同配体之间的分子内能量转移过程，这将允许更好地控制所产生的发射体取向。总体而言，我们计划为工业伙伴(默克公司)开发有针对性的材料设计工具，并为学术伙伴(奥格斯堡大学)创造科学知识。

Organic light-emitting diodes (OLEDs) are meanwhile an established display technology which is commercially used in smartphones or TV screens. Unique selling points are their high image quality and low energy consumption, which originate from the fact that these displays are emissive and, thus, do not require any backlight. To this end, phosphorescent emitters with their strong spin-orbit coupling provide decisive advantages, as they enable almost 100% internal quantum efficiency because phosphorescence from the triplet state to the ground state is an allowed optical transition. Nevertheless, the achieved external quantum efficiency is limited by light outcoupling, which amounts to only about 20-25% in conventional OLED structures since the majority of the produced photons is trapped inside an OLED. A powerful tool to improve light outcoupling is the use of emitter molecules having an inherent tendency to align horizontally during film growth such that their optical transition dipoles radiate preferentially toward the substrate, i.e. in the viewing direction of an observer. However, it remains challenging to achieve high degrees of alignment with phosphorescent Iridium emitter complexes, since their three ligands have an octahedral coordination around the central Iridium atom so that their shape anisotropy is relatively low. Thus, further progress of materials design requires detailed understanding of structure-property relations in this class of OLED emitters. The main goal of this transfer project is to improve existing methods for predicting and analyzing emitter orientation in evaporated guest-host systems with Iridium emitters, such that design rules can be established and verified. Further, we plan to study both intermolecular interactions between emitter and host molecules, as well as intramolecular energy transfer processes among the different ligands, which will allow better control of the resulting emitter orientation. Overall, we plan to develop tools for targeted materials design for the industrial partner (Merck) as well as to create scientific knowledge for the academic partner (University of Augsburg).