Handbook of Aggregation-Induced Emission, Volume 3. Группа авторов

Handbook of Aggregation-Induced Emission, Volume 3 - Группа авторов


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Based on these both advantages, the traditional fluorescent AIE emitters have covered wide range of spectrum from blue to green and red, and even the white OLEDs based on these emitters have been fabricated, although EQE limitation of 5% for traditional AIE emitters‐based OLEDs due to the theoretical out‐coupling efficiency of 20%. Among these monochromatic OLED, the blue and green AIE‐active emitters share the larger part, while the red counterparts take up the smaller portion. In this section, we will demonstrate the conventional AIE‐active emitters‐based OLEDs in detail, according to different colors [27].

      1.2.1 Blue Aggregation‐induced Emissive Emitters

      One major method to prepare AIE emitters is to integrate the AIE groups into some previous ACQ emitters, such as carbazole, fluorene, and anthracene to change these emitters’ aggregated behaviors. Among various AIE moieties, tetraphenylethene (TPE) moiety is the most popular building block to construct AIE emitters, due to its simple structure and facile modification. Due to the sky‐blue emitting behaviors of TPE moiety, the blue and green emitters took the majority of AIE‐active emitters.

Schematic illustration of molecular structures of TPE-based conventional blue AIE-active emitters.

      In some other works, TPE served as single fluorescent moieties to construct more complicated AIE emitters. Li et al. merged two TPE units together through linking at different positions to obtain four BTPE (Figure 1.2) derivatives with deep‐blue emission. Nondoped sky‐blue OLED devices with a configuration of ITO/MoO3 (10 nm)/NPB (60 nm)/EML (15 nm)/TPBi (35 nm)/LiF (1 nm)/Al (100 nm) were fabricated, with maximum luminance, CE, and PE of 3266 cd/m2, 2.8 cd/A, and 2.0 lm/W, respectively [50]. They further decorated the benzene core with different number of TPE moiety peripheries to obtain three AIE emitters PhTPE, Ph2TPE, and Ph3TP (Figure 1.2), based on which nondoped blue OLEDs were fabricated with the structure of ITO/MoO3 (10 nm)/NPB (80 nm)/EML (20 or 30 nm)/TPBi (30 nm)/LiF (1 nm)/Al, with emission ranging from 457 to 488 nm, and maximum CE, luminance, and PE of 5.0 cd/A, 3966 cd/m2, and 3.87 lm/W, respectively [51].

      On the other hand, as an important factor, balanced factor of carriers’ transport (electrons and holes) can also decide the overall electroluminescent performance. However, owing to the electron‐rich nature of most organic materials, they exhibit high hole transport but relatively low electron mobility, and finally lead to unbalanced electron‐hole recombination. In this regard, bipolar materials with donor−acceptor (D−A) structures can favor both holes and electrons injection and transport to result in balanced factor of carriers’ transport (electrons and holes), which finally enhance the efficiency of the OLEDs. Additionally, the dipolar luminogens tend to align horizontally in solid state, which can also result in high out‐coupling efficiency over 20%. In previous research, most dipolar emitters were served as host or dopant, because the strong D−A interaction usually showed lower PL efficiency at solid state [52, 53]. For example, Xie et al. designed and prepared two novel AIE materials of TPEPBN and TPE‐2PBN (Figure 1.2) with the property of liquid crystal due to 4‐cynobiphenyl moiety serving as the mesogenic unit, and the PLQYs can be obtained 71 and 83% in solid state, respectively. Due to liquid crystals of electron‐accepting moiety of CN, these both compounds showed high hole mobility. Based on these two AIE emitters, both nondoped and doped OLED devices were fabricated and the better OLED device were obtained for nondoped ones based on the emitter of TPE‐PBN (Figure 1.2), with maximum EQE of 4.1%, which is one of the highest values reported for blue fluorescent OLEDs base on AIE emitters [54].


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