A Novel Sterically Bulky Hole Transporter to Remarkably Improve the Lifetime of Thermally Activated Delayed Fluorescent OLEDs at High Brightness

Abstract

For the practical application of organic light emitting devices (OLEDs) based on thermally activated delayed fluorescence (TADF) for large area TV and solid state lighting, low power consumption as well as the operation lifetime at high brightness over 1000 cd m must be improved. Here, we have developed a novel hexaphenylbenzene-based sterically bulky hole-transport layer named 4DBTHPB with deep ionization potential of 5.8 eV and high triplet energy of 2.7 eV. By using 4DBTHPB, we can realize a highly efficient and stable TADF OLED exhibiting external quantum efficiency of 21.6 % and power efficiency of 54.3 lm W and operation lifetime at 50 % (LT ) of approximately 10 000 h at an initial luminance of 1000 cd m . These performances are comparable to those of the state-of-the-art green phosphorescent OLEDs reported in the scientific literatures.

Marching Toward Highly Efficient, Pure‐Blue, and Stable Thermally Activated Delayed Fluorescent Organic Light‐Emitting Diodes

“…For instance, the half‐lifetime of the green TADF‐OLED based on 4CzIPN emitter reached ≈10 000 h at the initial luminance of 1000 cd m −2 and further improvement could be obtained by employing numerous strategies in the areas of molecular design and device engineering. [73b,88] The prevailing view is that the unsatisfactory stability of blue PH‐OLEDs is associated with an energy‐driven Auger‐like process, where an electrically generated triplet exciton with high energy on the phosphorescent dopant encounters a polaron within the emitting layer . Subsequently, bimolecular interaction and collisions occur, yielding a high‐energy polaron (up to an ultrahigh energy level greater than 7.0 eV) after absorbing the energy released from the deactivation of the high‐energy exciton.…”

“…The use of host materials that eliminate easily destroyed chemical bonds and offer good charge carrier transport properties, as well as good thermal and electrochemical stability, would be ideal in view of the present state of research in this area. Moreover, the use of stable hole and electron transport/blocking materials with high T g , appropriate T 1 energy levels for exciton confinement and high mobility for low power consumption would be favorable as we strive to develop stable blue TADF‐OLEDs with low driving voltages and suppressed efficiency roll‐off behaviors at practical high luminance values . Finally, strategies that employ TADF materials as the host material appear very promising as people work to enhance device operational lifetimes, given that the triplet exciton lifetime can be significantly shortened by introducing a rapid FRET process, which in turn reduces the ISC and RISC cycles in the excited state and lowers the possibility of bimolecular annihilation processes for the generation of high‐energy “hot” excitons.…”

Effect of Carrier Balance on Device Degradation of Organic Light‐Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitters

“…[4,5] To date, there have been a number of important reports on degradation mechanisms and strategies to enhance the device lifetimes of OLEDs have also been proposed. [4,5] To date, there have been a number of important reports on degradation mechanisms and strategies to enhance the device lifetimes of OLEDs have also been proposed.…”

Molecular Design and Device Design to Improve Stabilities of Organic Light-Emitting Diodes

“…In 2017, another amine derivative based on dibenzothiophene was synthesized as a high-tripletenergy HTM for efficient and stable OLEDs using a TADF emitter [21]. The chemical structure of the synthesized HTM, named 4DBTHPB, is shown in Fig.…”

“…However, in recent years, the stability of OLEDs has begun to be intensively discussed from two viewpoints: operational stability and air-stability. Since high operational stability is essential for almost all OLEDs used for practical applications, there have been many reports on materials suitable for achieving operationally stable OLEDs [12][13][14][15][16][17][18][19][20][21][22][23]. Some OLEDs employing flexible substrates or simple encapsulation structures have been applied for optoelectronic sensors and biophotonics in recent years [24][25][26].…”