Solution-processed thermally activated delayed fluorescence organic light-emitting diodes using a new polymeric emitter containing non-conjugated cyclohexane units

Kim, Hyung Jong; Lee, Chiho; Godumala, Mallesham; Choi, Suna; Park, Seo Yeon; Cho, Min Ju; Park, Sungnam; Choi, Dong Hoon

doi:10.1039/c7py02113e

Cited by 73 publications

(47 citation statements)

References 58 publications

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“…Choi and Park introduced the 1,1‐diphenylcyclohexane ( Cp ) moiety into the backbone of the polymer . The Cp moiety with the sp 3 bridge not only acts as a linker between the conjugated monomeric units, but also adjusts polymer solubility and conjugation length, while 10‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐9,9‐dimethyl‐9,10‐dihydroacridine ( DMAC‐TRZ ) was selected as the TADF monomeric unit.…”

Section: Tadf Polymersmentioning

confidence: 99%

“…Solution‐processed TADF‐OLED devices were fabricated to evaluate the performance of polymeric emitter, based on the structure ITO/PEDOT:PSS (40 nm)/PVK (30 nm)/ P(DMTRZ‐Cp) : mCP blend (40 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm), with varying the polymeric emitter doping ratio from 5 wt% to 30 wt%. The green OLED device with 25 wt% doping ratio of polymeric emitter exhibited the best EL performance, with a low turn‐on voltage of 4.0 V at 1 cd m −2 , a maximum CE of 50.5 cd A −1 , and a maximum EQE of 15.4% …”

Section: Tadf Polymersmentioning

confidence: 99%

See 1 more Smart Citation

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

Wei

Voit

2018

Macromol. Rapid Commun.

124

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%

Section: Tadf Polymersmentioning

confidence: 99%

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

Wei

Voit

2018

Macromol. Rapid Commun.

124

100

View full text Add to dashboard Cite

show abstract

“…To address these problems,w eh ave ag reat interest in another concept, where small molecular TADF units are bonded to each other by an appropriate linker.Bymaking full use of the diversity and richness of the entire library of existing small molecular TADF emitters,inthis case,the gap from small molecules to polymers is anticipated to be removed easily.T hus,s uch a" TADF + Linker" strategy ( Figure 1) is believed to be simple and applicable for various emissive colors.T here have been two limited examples to create nonconjugated TADF polymers according to this route. [26,27] However,i ts potential in conjugated TADF polymers remains unexplored, even though the conjugated backbone possesses am ore favorable charge transport, as well as intense absorption and emission, than the nonconjugated counterpart. [28,29] With methyl-substituted phenylene as the linker,h erein, we report the successful construction of conjugated polymers with highly efficient delayed fluorescence ( Figure 2).…”

Section: Introductionmentioning

confidence: 99%

Bridging Small Molecules to Conjugated Polymers: Efficient Thermally Activated Delayed Fluorescence with a Methyl‐Substituted Phenylene Linker

Rao

Liu

et al. 2019

Angew Chem Int Ed

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Based on a “TADF + Linker” strategy (TADF=thermally activated delayed fluorescence), demonstrated here is the successful construction of conjugated polymers that allow highly efficient delayed fluorescence. Small molecular TADF blocks are linked together using a methyl‐substituted phenylene linker to form polymers. With the growing number of methyl groups on the phenylene, the energy level of the local excited triplet state (3LEb) from the delocalized polymer backbone gradually increases, and finally surpasses the charge‐transfer triplet state (3CT). As a result, the diminished delayed fluorescence can be recovered for the tetramethyl phenylene containing polymer, revealing a record‐high external quantum efficiency (EQE) of 23.5 % (68.8 cd A−1, 60.0 lm W−1) and Commission Internationale de l′Eclairage (CIE) coordinates of (0.25, 0.52). Combined with an orange‐red TADF emitter, a bright white electroluminescence is also obtained with a peak EQE of 20.9 % (61.1 cd A−1, 56.4 lm W−1) and CIE coordinates of (0.36, 0.51).

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“…The device displayed distinct green emission with CIE coordinates of (0.32, 0.58), and achieved an EQE max of 10%. Such nonconjugated linker design was also presented by Choi and co‐workers, who combined the nonconjugated diphenylcyclohexane (Cp) linker with the well‐known TADF emitter of DMAC‐TRZ (Figure c) . The resulted polymer P(DMTRZ‐Cp) not only exhibited pronounced TADF characters that succeeded from DMAC‐TRZ, but also showed greatly improved solubility owing to the cyclohexane units.…”

Section: Tadf Polymersmentioning

confidence: 81%

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

211

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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Solution-processed thermally activated delayed fluorescence organic light-emitting diodes using a new polymeric emitter containing non-conjugated cyclohexane units

Abstract: A new solution-processable polymeric emitter containing non-conjugated cyclohexane units was developed for high-performing TADF-OLEDs.

Cited by 73 publications

References 58 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

Bridging Small Molecules to Conjugated Polymers: Efficient Thermally Activated Delayed Fluorescence with a Methyl‐Substituted Phenylene Linker

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

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