Design and synthesis of triazine-based blue and oriented TADF emitters for high-efficiency OLEDs

Abstract

This thesis focuses on the design, synthesis, characterization and OLED fabrication and testing of TADF emitters, with a particular emphasis on trying to achieve high horizontal orientation of their TDM. Chapter 1 explains the basic concepts behind light-matter interaction, photoluminescence, and electroluminescence, focusing on TADF materials and their use in OLEDs. An in-depth explanation of the outcoupling effect will be given, with a discussion of several literature-known strategies to achieve optimal orientation of the emitter in the OLED stack. Chapter 2 focuses on a highly oriented TADF emitter, ICzTRZ. The theoretical and optoelectronic properties and TDM orientation of the material were studied, with its most interesting feature being the nearly completely horizontal orientation of the TDM in the film. OLED performance is then discussed. Chapter 3 describes a study to try and enhance the efficiency of ICzTRZ by adopting a twin-emitter design strategy, with DICzTRZ. Due to its high molecular weight, we hypothesize that DICzTRZ could also maintain horizontal orientation in solution-processed films. Chapter 4 concludes the work on the ICz family, with a study on how the horizontal orientation of ICzTRZ derivates changes when the position and the number of tert-butyl groups on the material are modified. In Chapter 5, the knowledge gathered from the previous study on the ICz series is applied to the known randomly oriented emitter DMAC-TRZ, to try in achieving horizontal orientation of the material and therefore generate an improvement in the device efficiency. Chapter 6 continues the work on DMAC-TRZ by investigating the effect that a heteroaromatic bridge has on the photophysics of the emitter. Chapter 7 summarizes and compares the results from Chapters 2-6. A discussion of the future work and outlooks of these projects is also presented.