TADF emitter design

Thermally activated delayed fluorescence (or E-type fluorescence) has gained huge interest recently in the use of OLED devices. OLEDs offer huge potential in display technology offering potentially very efficient, lightweight and flexible devices. Electrical excitation of normal OLED devices results in the formation of 25% singlet states and 75% triplet states. Under normal circumstances only singlet states are emissive as triplet states undergo non radiative decay limiting internal quantum efficiency to 25%. Furthermore as a result of something known as the outcoupling effect only 20% of this actually leaves the device hence external quantum efficiency is limited to 5%. This is a huge problem if OLEDs are to compete with conventional display devices, One way to combat this problem is to make the normally forbidden triplet states emissive. This can be achieved using heavy metal complexes such as iridium and platinum. This offers 100% maximum EQE, which could not be achieved with fluorescent emitter. However, these are rare metals and are expensive, so their use on a large commercial scale is limited. Recently reported by Adachi et al., a new third generation of OLEDs was identified known as thermally activated delayed fluorescence (TADF). This method involves the conversion of non-emissive triplet states to emissive singlet states via a process known as reverse intersystsem crossing. By doing this IQE has a maximum of 100% without the use of heavy metal complexes, hence the importance of TADF emitters for the future of OLED applications.

The project will involve the synthesis and modelling of new TADF emitters. Modelling software will be used with our partners at the university of Mons, and promising structures will be synthesised and their physical properties will be tested in St Andrews. From these compounds those with the best properties will be made into devices and hopefully this will help towards the ultimate goal of improved OLED devices for use on a commercial scale.

A series of initial targets has been proposed following computational studies by the university of Mons, which will be synthesised prior to the visit to Mons. These initial targets make use of TADF molecules, which contain Lewis acids, (e.g. Boron, Zinc, aluminium).

The PhD hopes to gain a better understanding into the design and synthesis of future TADF materials and produce new classes of materials based on the modelling undertaken as part of the project.


Training:
-How to undertake computation methods for TADF design
-How to use various analytical instrumentation such as fluorimeters and electrochemistry equipment to study TADF compounds
-How to prepare OLED devices, this will include spin coating of devices
- How to improve organic synthesis techniques