Highly Efficient Deep Blue Fluorescent Organic Light-Emitting Diodes Boosted by Thermally Activated Delayed Fluorescence Sensitization

Ahn, Dae Hyun; Jeong, Jae Ho; Song, Jie; Lee, Ju Young; Kwon, Jang Hyuk

doi:10.1021/acsami.7b19030

Cited by 93 publications

(62 citation statements)

References 33 publications

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“…High PLQY is necessary for the fluorescent emitter, and a small dipole moment is beneficial to realize the deep blue color coordinate to prevent redshift of the emission spectrum by high polarity of the emitter. Based on these insights, BPPyA was developed as a blue fluorescent emitter for high EQE in TADF sensitized devices . A Stokes' shift of 28 nm, high PLQY of 98.5%, and little solvatochromic effect from a small dipole moment of 0.2 D were features of the BPPyA emitter.…”

Section: Singlet‐exciton‐harvesting Approaches For Fluorescent Oledsmentioning

confidence: 99%

Recent Progress of Singlet‐Exciton‐Harvesting Fluorescent Organic Light‐Emitting Diodes by Energy Transfer Processes

et al. 2019

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OLEDs and TADF OLEDs are essential. One method to overcome those issues is to harvest singlet excitons by triplet-triplet fusion (TTF) process which converts triplet excitons into singlet excitons. [18][19][20] The TTF approach has been used in the blue fluorescent OLEDs, but the triplet to singlet conversion efficiency is limited, resulting in relatively low EQE compared to the phosphorescent and TADF OLEDs. The other method is to apply singlet-exciton-harvesting technology of fluorescent OLEDs by energy transfer to achieve high EQE and long device lifetime by overcoming the deficiencies of the two technologies. The EQE can be comparable to that of phosphorescent and TADF OLEDs if singlet excitons can be fully harvested, and the device lifetime can be better than that of those devices due to the intrinsic stability of the molecular structures and triplet excitons critical to the device lifetime are excluded in the final light-emission process.Herein, recent progress on the singlet harvesting approach of fluorescent emitters by an energy transfer process from host or sensitizer is discussed. Basic concepts, material requirements, and device architecture for the singlet-exciton-harvesting technology are covered to understand the light-emission process and to develop an ideal emitting layer system for both high EQE and long device lifetime. Additionally, future prospects of singletexciton-harvesting fluorescent OLEDs are proposed. Basic Concept of Singlet-Exciton-Harvesting Fluorescent OLEDsFluorescent emitters can emit light by photoluminescence (PL) or electroluminescence (EL) processes although other processes such as chemiluminescence and mechanoluminescence can induce light emission. [21][22][23][24] In the PL process, fluorescent emitters can exhibit 100% photon conversion efficiency by light excitation if there is no intersystem crossing from the singlet excited state to triplet excited state and no loss during the radiative transition from singlet excited state to ground state. However, an ideal 100% PL efficiency is not realized in the EL process because 75% triplet excitons generated by the electrical carrier injection process are lost by nonradiative pathways. [25][26][27][28][29][30] Only 25% of the singlet excitons contribute to the EL emission process, and the internal quantum efficiency (IQE) of fluorescent OLEDs is limited to 25%. However, the low IQE of fluorescent OLEDs can be improved if triplet exciton The external quantum efficiency (EQE) of organic light-emitting diodes (OLEDs) has been dramatically improved by developing highly efficient organic emitters such as phosphorescent emitters and thermally activated delayed fluorescent (TADF) emitters. However, high-EQE OLED technologies suffer from relatively poor device lifetimes in spite of their high EQEs. In particular, the short lifetimes of blue phosphorescent and TADF OLEDs remain a big hurdle to overcome. Therefore, the high-EQE approach harvesting singlet excitons of fluorescent emitters by energy transfer processes from the host or sensit...

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Section: Singlet‐exciton‐harvesting Approaches For Fluorescent Oledsmentioning

confidence: 99%

Recent Progress of Singlet‐Exciton‐Harvesting Fluorescent Organic Light‐Emitting Diodes by Energy Transfer Processes

et al. 2019

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“…The fluorophores are also chosen to exhibit high radiative decay rates and narrow emission spectra; fast FRET processes contribute to shorten the overall exciton lifetimes in the device, which improves operational stability. [9][10][11][12][13][14][15][16][17][18][19] Interestingly, two-component "hyperfluorescence" layers where the TADF molecules also play the role of the host have been developed to achieve OLEDs with EQE >11%. [20][21][22][23][24] To maximize forward exciton energy transfer from the TADF molecules to the fluorescent emitters and minimize reverse energy transfer, the S 1 state of the TADF material should have a higher energy than that of the conventional fluorescent emitter (i.e., ΔE S1 > 0, as shown in Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

Abroshan

Zhang

et al. 2020

Adv Funct Materials

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Hyperfluorescence is emerging as a powerful strategy to develop optoelectronic devices with high-color purity and enhanced stability. It requires appropriate integration of a sensitizer displaying efficient thermally activated delayed fluorescence (TADF) and an emitter displaying strong, narrowband fluorescence. Here, through a joint computational and experimental approach, an unprecedented, end-to-end systems level description of the electronic and optical processes that take place in a hyperfluorescent emissive layer composed of a TADF sensitizer, 2,5-bis(2,6-di(9H-carbazol-9-yl) phenyl)-1,3,4-oxadiazole (4CzDPO), and a fluorescent emitter, 2,5,8,11-tetratert-butylperylene (TBPe) is provided. The photophysical properties measurement of the emissive layer is combined with the computational determination of the electronic properties, film morphology, and excitation transfer phenomena. The Förster resonance energy transfer rates from 4CzDPO to TBPe are on the order of 10 11 s −1 , considerably higher than the radiative and nonradiative recombination rates for 4CzDPO. These features ensure nearly complete energy transfer to TBPe, leading to a five-fold increase in the photoluminescence quantum yields in the 4CzDPO:TBPe system in comparison to neat films of 4CzDPO. This approach highlights the factors that can provide efficient energy transfer from TADF molecules to fluorescent emitters, suppress energy transfer among TADF molecules, and avoid the need for a host material within the emissive layer.

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“…Examples for hyper-fluorescence systems from the literature are ACRSA/TBPe (blue) and ACRXTN/TTPA (green) [8], 4CzIPN-Me/TBRb (yellow) [9], and DMAC-DMT/BPPyA (blue) [10]. Table 1 shows emission and absorption properties for a selection of these material combinations, along with three systems using CYNORA TADF emitters.…”

Section: -3 / T Baumannmentioning

confidence: 99%

33‐3: TADF Emitter Selection for Deep‐Blue Hyper‐Fluorescent OLEDs

Baumann

Budzynski

Kasparek

2019

Symp Digest of Tech Papers

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Blue fluorescent OLEDs are still the bottleneck for the power consumption in today´s OLED panels. In recent years, the TADF technology has shown fast progress towards high-efficiency deepblue emitter systems. The TADF technology can be used in a selfemitting or in a co-emitting (or hyper) approach. To make the coemitting system work efficiently, the combination of TADF and fluorescent emitter has to be chosen carefully. In this paper, we will discuss how to match TADF and fluorescent emitter combinations for the co-emitting approach. We will also show results for highly efficient deep-blue hyper-fluorescent devices.

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Highly Efficient Deep Blue Fluorescent Organic Light-Emitting Diodes Boosted by Thermally Activated Delayed Fluorescence Sensitization

Cited by 93 publications

References 33 publications

Recent Progress of Singlet‐Exciton‐Harvesting Fluorescent Organic Light‐Emitting Diodes by Energy Transfer Processes

Recent Progress of Singlet‐Exciton‐Harvesting Fluorescent Organic Light‐Emitting Diodes by Energy Transfer Processes

Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

33‐3: TADF Emitter Selection for Deep‐Blue Hyper‐Fluorescent OLEDs

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