Development of new blue emitting organic molecule based on the hyperfluorescence

The focus today is on high luminance of the microdisplays to meet the requests for AR/VR application. The performance of current OLEDs, in terms of luminance and lifetime, especially for blue, have great difficulty in meeting these high luminance specdifications. Improvements in the efficiency and lifetime of the blue emitter are therefore mandatory.

Fluorescent emissive materials are gradually giving way to phosphorescent emissive materials (PhOLEDs) and thermally activated delayed fluorescence (TADF) materials, which allow a quantum efficiency close to 100%, unlike fluorescent which reaches 25% at maximum. Unfortunately, the current efficiency and / or lifetime as well as the color purity are poor for blue.

In order to provide a solution to this problem, we propose, through this thesis project, to explore a new strategy for obtaining high-performance blue OLEDs with good color purity, based on the concept of hyperfluorescence. This is based on the use of a high energy TADF matrix incorporating a blue fluorescent emitter. The role of the TADF molecule will be to efficiently transfer the singlet and triplet excitons to the final emitter, possessing a high luminescence quantum yield. This approach will significantly reduce the concentration of excited triplet states within the emissive layer and the parasitic reactions linked to the reactivity of these states. The thesis project will be done in collaboration with a CNRS chemistry laboratory and the CEA / LETI LCEM laboratory specializing in organic semiconductors. The work of the student will be to synthesize organic molecules and to characterize their photophysical (absorption and emission) and opto-electronic properties. The most promising molecules will be integrated into OLED devices. Work on defining the OLED stack will thus be required to optimize the electro-optical performance of the OLED.

The photophysical synthesis and characterization part will be carried out in the chemistry laboratory of the CNRS (Institut des Sciences Chimiques de Rennes) over a short period. The heart of the thesis will be oriented towards the integration of molecules in OLEDs devices. This work will be done in the LCEM laboratory of CEA Grenoble where the deposit equipment is located (PVD chamber for organic materials) and the opto-electronic characterization tests bench.

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