The Role of Reverse Intersystem Crossing Using a TADF‐Type Acceptor Molecule on the Device Stability of Exciplex‐Based Organic Light‐Emitting Diodes

Abstract

Exciplex system exhibiting thermally activated delayed fluorescence (TADF) holds a considerable potential to improve organic light‐emitting diode (OLED) performances. However, the operational lifetime of current exciplex‐based devices, unfortunately, falls far behind the requirement for commercialization. Herein, rationally choosing a TADF‐type electron acceptor molecule is reported as a new strategy to enhance OLEDs' operating lifetime. A comprehensive study of the exciplex system containing 9,9′,9′′‐triphenyl‐9H,9′H,9′′H‐3,3′:6′,3′′‐tercarbazole (Tris‐PCz) and triazine (TRZ) derivatives clarifies the relationship between unwanted carrier recombination on acceptor molecules, TADF property of acceptors, and the device degradation event. By employing a proposed “exciton recycling” strategy, a threefold increased operational lifetime can be achieved while still maintaining high‐performance OLED properties. In particular, a stable blue OLED that employs this strategy is successfully demonstrated. This research provides an important step for exciplex‐based devices toward the significant improvement of operational stability.

Efficient and Stable Deep‐Blue Fluorescent Organic Light‐Emitting Diodes Employing a Sensitizer with Fast Triplet Upconversion

“…[ 20 ] Works with unimolecular TADF material or bimolecular exciplex‐forming host to sensitizer MR‐TADF emitters have been reported, combining the advantages of both kind materials. [ 16,21 ] Yet, the device performances are still far away from satisfactory. Our work greatly boosts both the device efficiency and stability, testifying the crucial importance of proper TADF sensitizer and the effectiveness of the molecule design strategy here.…”

Rigid Oxygen‐Bridged Boron‐Based Blue Thermally Activated Delayed Fluorescence Emitter for Organic Light‐Emitting Diode: Approach towards Satisfying High Efficiency and Long Lifetime Together

“…To overcome these limitations, fewer studies have been reported on the long operational lifetime of blue TADF‐OLEDs. [ 18–22 ] S. G. Ihn et al reported indolocarbazole and pyrimidine‐based TADF emitter, 5,8‐bis(4‐(2,6‐diphenylpyrimidin‐4‐yl)phenyl)‐5,8‐dihydroindolo[2,3‐c]carbazole (BDpyInCz) with a long‐delayed exciton lifetime of 32 µs. [ 18 ] However, their device exhibited a low external quantum efficiency (EQE) (12%) and device lifetime (LT 80 ) of only 8 h at the initial luminance of 500 cd m −2 with deep‐blue color coordinates of (0.16, 0.20).…”

Recent Advancement in Boron-Based Efficient and Pure Blue Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

“…The maximum EQE and brightness of 8.9% and 830 cd/m 2 and 19% and 1,260 cd/m 2 for the devices with and without ν-DABNA were observed. Further, the LT 50 lifetime of both devices showed almost similar values (∼350 h) and indicates the promising way of making stable devices (Nguyen et al, 2020). Recently, Oda et al (2019) reported two multiple resonance-based TADF materials, ADBNA-Me-Mes and ADBNA-Me-Tip; these materials possess one nitrogen atom in the center of the core and two boron atoms in the outer of the core unit.…”

“…This is the highest efficiency of multiple resonancebased TADF materials reported so far. Recently, Nguyen et al (2020) evaluated the performances of exciplex host-based TADF devices, and they compared the device performances with and without ν-DABNA as 1 wt% emitting dopant. The maximum EQE and brightness of 8.9% and 830 cd/m 2 and 19% and 1,260 cd/m 2 for the devices with and without ν-DABNA were observed.…”