Design of encapsulated hosts and guests for highly efficient blue and green thermally activated delayed fluorescence OLEDs based on a solution-process

Ban, Xinxin; Zhu, Aiyun; Zhang, Tianlin; Tong, Zhiwei; Jiang, Wei; Sun, Yueming

doi:10.1039/c7cc06967g

Cited by 32 publications

(16 citation statements)

References 33 publications

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“…The peripheral carbazole dendrons can suppress both the molecular aggregation and triplet‐polaron quenching (TPQ) effect. Based on these dendritic emitters, solution‐processed blue and green TADF OLED devices with the structure ITO/PEDOT:PSS (40 nm)/(Cz‐3CzCN:Cz‐CzCN or Cz‐3CzBN:Cz‐4CzBN) (60 nm)/TPBi (40 nm)/Cs 2 CO 3 (2 nm)/Al and with maximum EQEs of 23.5% and 23.8%, respectively, have been prepared, some of the highest values reported so far for any solution‐processed OLED devices …”

Section: Tadf Polymersmentioning

confidence: 99%

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

Wei

Voit

2018

Macromol. Rapid Commun.

122

100

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several organic layers like hole injection layer, hole-and electron transport layer, and most importantly, the emissive layers (EML), inserted between the electrodes (Figure 1). Under external voltage, opposite charge carriers of holes and electrons are injected from anode and cathode and finally recombined to produce photons within the EML. [10][11][12] Emitters can largely determine not only the performance but also the processing methods of devices, and therefore they are the key material among all the components of the OLEDs. During the past three decades, the emitter materials have seen a rapid progress, from traditional fluorescent, phosphorescent, and triplet-triplet annihilation (TTA) materials into the era of thermally activated delayed fluorescent (TADF) materials, and from small molecules to polymers. [13] According to spin statistics, singlet and triplet excitons are formed within the EML at the ratio of 1:3, when OLED devices are working under electrical excitation; however, the organic emitters have different capabilities to utilize the exciton to induce photons which results in different efficiencies of OLED devices. The electricity-photon conversion efficiency of OLED can be evaluated by the quantum efficiency (QE), referring to the numeral ratio of photons to the injected electronhole pairs. [14,15] QE can be further subdivided into internal quantum efficiency (IQE) and external quantum efficiency (EQE). The IQE, defined as photon generation within the EML, is directly determined by the emitters, [16] while EQE refers to the numerical ratio of total photons emitting out of the device to the charge pairs injected. Since the photons are generated within and emitted out from the EML, the chemical structure of the emitter and the resulting properties can deeply influence the device efficiency. The traditional fluorescent emitters can only take advantages of singlet excitons for luminescence, with maximal IQE of roughly 25%. Given that out-coupling efficiency is normally 20%, the maximal EQE is only 5%, far below expectation. Phosphorescent OLEDs have the capability to reach 100% IQE, because phosphorescent emitters usually contain heavy atoms like iridium or platinum to harvest both, singlet and triplet excitons for phosphorescence through significant spin-orbit coupling, but the heavy metals usually bring about serious issues of comparable high costs and low long-term stability in OLEDs. [17] TTA fluorescent emitters can only reach a maximum IQE of 62.5% through conversion of two triplet excitons into one singlet exciton, and show mainly blue emission. [18] TADF materials, however, can harvest triplet Organic Light-Emitting Diodes Thermally activated delayed fluorescent (TADF) polymers are promising emitting materials to realize highly efficient, large-scale, and low-cost organic light-emitting diodes (OLEDs) since they exhibit various advantages such as heavy-metal-free structures, 100% theoretical internal quantum efficiency, and ease of large-area fabrication through solution process. At present,...

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Section: Tadf Polymersmentioning

confidence: 99%

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

Wei

Voit

2018

Macromol. Rapid Commun.

122

100

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“…An efficient and simple D-A approach to achieve white light from organic solids with a polymorph dependent TADF property has been developed by Ban et al ( 2017 ). A purely organic molecule of 3-(diphenylamino)-9H-xanthen-9-one (3-DPH-XO) has been reported, which was found to display bright white light emission with the CIE value (0.27, 0.35) in its solid state, facilitated by spontaneous formation of polymorphs with distinguished intermolecular non-covalent interaction features that determined the different emission colors, and which was further demonstrated by single crystal studies of the compound (shown in Figure 17 ).…”

Section: Recent Progress On Multi-functional Tadf Emittersmentioning

confidence: 99%

“…Moreover, an ever-increasing demand to use them as a solution-processed non-doped fabrication technique gives them an extra edge over other existing methods for solid-state lighting. However, the major issues of efficiency improvement affected by emission quenching in non-doped thin-film state is mainly due to singlet-triplet annihilation (STA), long lifetime triplet-polaron, and triplet-triplet annihilation (TTA) (Ban et al, 2017 ). Yet, quenching the effect of TADF emitters can be fixed by co-existing with an impressive solid state emission property, called aggregation induced emission (AIE), a condensed state emission behavior that can arrest the rotation or vibration in a highly twisted molecular configuration likewise TADF molecular structure.…”

Section: Introductionmentioning

confidence: 99%

Recent Developments on Multi-Functional Metal-Free Mechanochromic Luminescence and Thermally Activated Delayed Fluorescence Organic Materials

et al. 2020

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Metal-free organic compounds with highly ordered π-conjugated twisted skeletons are capable of generating brilliant multi-colored light. Additionally, the co-existence of numerous other multi-functional properties have endowed them with the potential to be a promising class of materials for several electronic and photonic applications and next-generation advanced luminescent material-based devices. This review highlights the recent developments made in this fascinating class of multi-property encompassing materials, involving a highly twisted donor-acceptor based single molecular platform with synchronized photophysical behavior such as thermally activated delayed fluorescence (TADF), mechanoresponsive (MR), room-temperature phosphorescence (RTP), and aggregation induced emission (AIE) with associated unique and inherently manifested structure-property relationship investigations. Furthermore, a brief summary of the optoelectronic behavior of TADF materials are also presented by correlating their performances in the organic light-emitting diodes (OLEDs) and corresponding EL devices. In addition to mechanochromic luminescence (MCL) with TADF behavior, new types of emitters are also being developed, with tunable color changes such as blue-green, yellow-orange, yellow-red, etc., with some emitters crossing the entire visible span to produce white OLEDs. These developments have enriched the library of fascinating organic materials in addition to providing new directions of multifunctional material design for solutions processed OLED and several other advanced devices.

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“…Due to the independent energy and charge transfer channels of nonconjugated molecular configuration in this type of TADF dendrimers, the dendrimer‐based EL devices were also investigated by using Cz‐3CzCN as the host and Cz‐4CzCN being guest, aiming at suppressing of the triplet‐polaron quenching (TPQ) effect of both the host and guest materials without sacrificing their TADF feature . The transient PL spectrum of Cz‐3CzCN:Cz‐4CzCN exhibited more delayed component than the parent 3CzCN:4CzCN, indicating that the dendritic structure could suppress triplet–triplet annihilation (TTA) process.…”

Section: Tadf Dendrimersmentioning

confidence: 99%

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

Zou

Gong

Xie

et al. 2018

Advanced Optical Materials

206

115

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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.

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Design of encapsulated hosts and guests for highly efficient blue and green thermally activated delayed fluorescence OLEDs based on a solution-process

Cited by 32 publications

References 33 publications

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

Recent Developments on Multi-Functional Metal-Free Mechanochromic Luminescence and Thermally Activated Delayed Fluorescence Organic Materials

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

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