Study of TADF (Thermal Activated Delayed Fluorescence) emissive materials to increase the performance of OLED stacks
Published : 4 January 2017
In the field of micro-displays, achieving high luminance has become essential today in order to meet the needs, the projection and the display systems integrated in helmets or glasses. The performances of the current organic light-emitting diodes (OLEDs), in terms of luminance and lifetime, do not make them possible to meet high luminance requirements. Improving the performances of OLEDs and in particular emissive materials is therefore essential. Recently, a new generation of emissive materials, TADF (Thermal Activated Delayed Fluorescence) can achieve the resquested performances. Delayed fluorescence is a concept for increasing the luminescence efficiency of OLED devices. This involves using the passage through the triplet state followed by the return to the singlet state at the origin of the emission of light. Thanks to this concept, it is theoretically possible to achieve a quantum efficiency of 100%. Currently, in our standard OLED devices, the emitting materials used are phosphorescent (PhOLED) based on heavy metals such as iridium or platinum. They are interesting from the emissive point of view but have disadvantages in terms of cost and availability. The objective of this thesis will be to increase the performance of OLED by integrating these TADF materials into our stacks which use a dopded transport materials and are in Top emission configuration. To do this, the PhD student will have to define, in terms of adjustment of the energy levels and thickness of the different materials, the complete OLED stack based on TADF. In addition, he will be responsible for the elaboration of the OLEDs samples, using an evaporation deposition machine, and the electro-optical characterization of these on existing measuring benches. After defining the optimal stacking, a study on the understanding of the phenomena of “Roll Off” and degradation of materials under voltage will have to be carried out.
This work will be in collaboration with one or several partners who manufacture these TADF materials. In this context, the doctoral student will have to manage a collaboration with the partners in the form of regular exchange in order to enter to a loop of continuous improvement of TADF materials.