Séminaire IPCM | Pr. Chihaya Adachi "The past, present and prospects of organic optoelectronics"

The IPCM informs you

Professor Chihaya ADACHI from Kyushu University in Japan will be giving a conference entitled:

"The past, present and prospects of organic optoelectronics".

This is one of a series of conferences that he will give as part of his French conference tour under the CNRS's program of Ambassadors of the Chemical Sciences.

Through the extensive R&D of organic light-emitting diodes (OLEDs) for more than 30 years, plenty of well elaborated novel organic optoelectronic materials and device architectures have been extensively developed, resulting in the unique commercial utilization of OLEDs for cutting-edge smartphones, large-area TVs, and further new future display applications by taking advantage of light-weight and flexibility. From the aspect of materials science, the creation of novel light-emitting materials in OLEDs has been the central issue aimed at high electroluminescence quantum efficiency (EQE). Starting from the development ofconventional fluorescence materials (1st generation) during 1990-2000th, the room-temperature phosphorescence (2000-) (2nd generation) and thermally activated delayed fluorescence (TADF) (2012-) (3rd generation) continuously pioneered the novel possibilities of organic emitters, resulted in not only high-performance OLEDs but also enriched organic photochemistry. Recently, there have been a wide variety of studies on TADF-OLEDs because of the unlimited possibilities of TADF molecular design. Further, hyperfluorescence (HP)-OLEDs have been developed since they can realize the compatibility of high efficiency and narrow spectral width, which is ideal for practical display applications.

Here we report our recent cutting-edge HP-OLEDs demonstrating high OLED performance by optimizing host, TADF, and terminal emitter (TE) molecules1-3). In particular, we focus on the blue-emission, which can show narrow FWHM and high EL quantum yield. Blue HP-OLEDs based on two new TEs are fabricated, resulting in high external quantum efficiency (EQE) of over 20%, high color purity, and high brightness. By analyzing the transient PL characteristics of the HP-OLEDs, we found the presence of efficient FRET between TADF-assistant dopant (TADF-AD) and TE molecules. Further, transient EL analysis confirmed that a smaller EHOMO difference between TADF-AD and TE efficiently helps to decrease hole trapping inside the emitting layer, hence resulting in a lower efficiency rolloff and a longer operational device lifetime. This report provides a designing principle for a TADF and TE in HP-OLEDs with well-matched energy levels, leading to efficient FRET and no significant carrier trapping.

In my talk, we will mention the importance of the charge transfer (CT) phenomenon in designing high performance organic luminescent molecules in OLEDs. Also, CT issues play a crucial role in maximizing the device's operation. Further, we will outlook the prospect of advanced CT technologies.