Design Strategy for Solution‐Processable Thermally Activated Delayed Fluorescence Emitters and Their Applications in Organic Light‐Emitting Diodes

Abstract

Organic light-emitting diodes (OLEDs) with fascinating features, such as high image quality, large viewing angle, thin, and lightweight, and their compatibility with rollable, wearable, and stretchable technology, have gradually entered into our daily life as the most promising next-generation displays. As to the advancements of OLED technology, there is ongoing demand on developing highly efficient emitting materials with color variability, which plays a crucial role in governing optoelectronic properties of OLEDs. Following the first generation of traditional fluorescent emitters and the second generation of heavy-metal phosphorescent emitters, [1] thermally activated delayed fluorescence (TADF) materials have emerged in the past few years and have been regarded as the most promising third generation emitters. [2] Aside from their triplet exciton Solution-processable thermally activated delayed fluorescence (TADF) emitters have received tremendous attentions in recent years due to their intrinsic merits of theoretical 100% exciton harvesting capability and excellent compatibility to low-cost and easily scalable solution processes. Herein, a comprehensive review of solution-processable TADF emitters is presented, including small molecules, dendrimers, and polymers. Their molecular design, optoelectronic properties, and device performances are summarized, and specific emphasis is placed on the structure-property relationships of these emitters. This review not only offers a guideline for designing highly efficient TADF emitters compatible with solution-processed organic lightemitting diodes, but also paves further directions for the development of solution-processable TADF emitters.

Fused tetracyclic tris[1,2,4]triazolo[1,3,5]triazine as a novel rigid electron acceptor for efficient thermally activated delayed fluorescence emitters

“…14,15 The solution processability and lm forming ability encourage these materials to be used in solution processed OLEDs, which is economically feasible for low cost and large-area displays. [16][17][18][19][20][21][22][23][24][25][26] Therefore, it is highly fascinating to develop molecular design to increase the luminescence efficiency and stability of solution-processed OLEDs, specically on star-shaped TADF emitters. Generally, planar star-shaped molecule has an inherent problem of aggregation-caused quenching (ACQ) due to its planar intermolecular p-p stacking which is a glaring problem in decreasing the luminescence efficiency in solid state.…”

“…Heptazine was the latest included in the nitrogen heterocyclic family having seven sp 2 hybridized nitrogen atoms in the fused ring, used as an acceptor in orange-red TADF emitter with high EQE max of 17.5%. 26 Tris [1,2,4]triazolo [1,3,5]triazine (TTT) is another heterocycle based on fused triazole and triazine moiety with nine sp 2 hybridized nitrogen atoms and a C 3 symmetry [5][6][7][30][31][32][33][35][36][37][38][39][40] which can provide an striking and remarkable alternative. It can be considered as a strong acceptor unit for the construction of donor acceptor (D 3 -A) TADF structure because of its rigid large electron decient plane.…”

5H-Benzo[d]Benzo[4,5]Imidazo[2,1-b][1,3]Thiazine as a Novel Electron-Acceptor Cored High Triplet Energy Bipolar Host Material for Efficient Solution-Processable Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes

“…In recent years, various TADF materials processed through vacuum deposition have been developed, and the majority of them have already been employed to achieve high external quantum efficiency (EQE) of over 25.0% (up to 38.0%) (Uoyama et al, 2012;Ahn et al, 2019;Kondo et al, 2019). In spite of the high performances of vacuum processed devices, the OLEDs fabricated through the solution process have many unique advantages, including an easy fabrication process, mass production of large-scale products, easy control of dopant concentration and low-cost manufacturing (Shao et al, 2017;Huang et al, 2018;Zou et al, 2018;Tsai et al, 2019).…”

Highlights on Gold TADF Complexes

“…Emitting materials for organic light-emitting diodes (OLEDs) have been a significant focus of academic and industrial research in recent years [1][2][3][4][5][6]. In this respect, thermally activated delayed fluorescence (TADF) represents a promising concept for harvesting both singlet and triplet excitons ( Figure 1) [7][8][9][10][11][12]. As displayed in Figure 1, TADF ensures that both singlet and triplet excitons can be used for the generation of light due to intersystem crossing and small energy separation between singlet and triplet states, ∆E ST .…”