Preferential alignment of anisotropic transition dipole moments in organic and perovskite thin films

Applications for thin film optoelectronics are commercially established and widely used in different technologies. Especially organic and hybrid organic-inorganic semiconducting materials are the state-of-the-art technology for smartphone and television displays. Despite the first discovery of organic semiconductors as lighting technology more than 22 years ago, new processes within the complex thin films regularly arise. Due to its importance for light emitting applications, this thesis focuses on the excitonic emission of photons from amorphous and hybrid thin films, such as organic semiconducting guest-host systems. The author describes selected topics of organic thin films and their application to light emitting devices. Further, special focus is set to the anisotropic properties of amorphous thin films and their quantification. From a methodical perspective, several approaches can be taken to quantify amorphous thin films. While experimental efforts include precise measurements of the thin film radiation pattern as well as polarization and transient phenomena, none of those experiments can contribute to an understanding of the system without computational input. The results of this thesis focus on selected topics regarding the anisotropy in amorphous and hybrid thin films. In particular, the author describes the molecular preferential alignment in organic fluorescent and phosphorescent thin films. The aforementioned organic films are subject to great disorder. Hence, it is even more surprising that many organic systems exhibit some anisotropy despite their naturally amorphous structure. While some effects are more straightforward to access, such as dipolar interaction or preferred orientation of rod-like molecules, a different chapter will set the topic to organometallic Ir-complexes. These molecules exhibit numerous different anisotropic effects despite their bulky structure. Hence, the unintuitive behavior of this class of materials requires extensive investigations to understand their amorphous properties. Finally, the most remarkable effect observed throughout this thesis is discussed. The preferential alignment of the emissive transition dipole within cubic nanocrystals is unexpected due to the symmetric structure of the emissive species. However, theoretical approaches confirm the observed properties. Further, the research was extended to quantum confined nanocrystals. Within the experiments, the author was able to conclude a significant effect on the emissive transitions within the thin films. Additionally, the findings were used to unravel the performance limit of perovskite light emitting diodes, revealing a vast potential for their application in display and lighting technologies