Exciplex-Forming Cohost for High Efficiency and High Stability Phosphorescent Organic Light-Emitting Diodes

Shih, Chun‐Jen; Lee, Chih‐Chien; Chen, Yinghao; Biring, Sajal; Kumar, Gautham; Yeh, Tzu‐Hung; Sen, Somaditya; Liu, Shun‐Wei; Wong, Ken‐Tsung

doi:10.1021/acsami.7b15034

Cited by 68 publications

(54 citation statements)

References 40 publications

(76 reference statements)

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“…The PLQYs of the exciplex-basedf ilms are comparable to those of the Bebq 2 -basedf ilms, and the t PL values are slightly longer,w hich is likelyt ob edue to delayed energy transfer from the exciplex causedb yt he additional intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes before energy transfer ( Figure S4 and Ta ble S2 in the Supporting Information). [15] To confirm the utility of the TCTA:PIM-TRZ exciplex system as the cohost for 1F-Ir/2F-Ir and gain an insight into the influence of host material on device performance, OLEDs with structures of ITO/TAPC (40 nm)/TCTA( 10 nm)/TCTA:PIM-TRZ:x wt % 1F-Ir or 2F-Ir (30 nm)/PIM-TRZ (60 nm)/LiF( 1nm)/Al (100 nm) were then fabricated. Besides workinga st he components of the cohost,T CTAa nd PIM-TRZ also worked as carrier transporting layers.…”

Section: Resultsmentioning

confidence: 99%

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Liang

Zhuang

et al. 2020

Chemistry A European J

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Two new iridium(III) complexes were synthesized by introducing two trifluoromethyl groups into an ancillary ligand to develop pure‐red emitters for organic light‐emitting diodes (OLEDs). The electron‐donating ability of the ancillary ligands is suppressed, owing to the electron‐withdrawing nature of trifluoromethyl groups, which can reduce the HOMO energy levels compared with those of compounds without trifluoromethyl groups. However, the introduction of trifluoromethyl groups into the ancillary ligand has little impact on the LUMO energy levels. Therefore, a well‐tuned, pure‐red, excited‐state energy was achieved by regulating the relative energy level between the HOMO and LUMO. OLEDs with these complexes as emitters showed high external quantum efficiencies (EQEs) of 26 % and realized high EQEs of about 25 % and fairly low driving voltages of 3.3–3.6 V for practical luminance of 1000 cd m−2, as well as excellent Commission Internationale de L'Eclairage (CIE) coordinates of (0.66, 0.33) and (0.67, 0.33); thus, this demonstrates the successful molecular design strategy by modifying the electron‐donating ability of ancillary ligand.

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Section: Resultsmentioning

confidence: 99%

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Liang

Zhuang

et al. 2020

Chemistry A European J

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“…For serving as host, the exciplex system must satisfy certain conditions such as (i) T 1 level of the exciplex has to be lower compared to the individual counterparts for the confinement of the excitation energy within the exciplex state, and (ii) T 1 level of the exciplex has to be higher than that of the dopant for confining the emission solely on the emissive dopants, ( carbazole hole-transporting material, TCTA, and a triazine electron-transporting material, 3P-T2T for a green phosphorescent emitter, Ir(ppy) 2 (acac) to achieve an OLED with high efficiency and very good electroluminescent lifetime. 10 The device fabricated with this system was found to display maximum external quantum efficiency of 29.6%, power efficiency of 147.3 lm/W, and current efficiency of 107 cd/A. For a comparative study, two devices, D1 and D2 were studied and their electroluminescent performances are summarized in Table 2.…”

Section: Resultsmentioning

confidence: 99%

“…In this interface, sufficient charge accumulation occurred owing to large energy-level offsets, and thus, efficient exciplex exciton formation resulted in the EML. 10 The molecular structures used in this study are shown in Figure 3 and the device data summarized in Table 2.…”

Section: Resultsmentioning

confidence: 99%

26‐1: Invited Paper: High Efficiency and High Stability Exciplex‐Based OLEDs

Sarma

Wong

Liu

et al. 2018

Symp Digest of Tech Papers

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Organic materials exhibiting thermally activated delayed fluorescence (TADF) are an outstanding class of functional materials that have witnessed a significant development in recent years. Besides the pure TADF emitters, a new class of efficient TADF-based OLEDs have also been fabricated which encompasses the intermolecular charge transfer between physically blended electron donor and acceptor moieties.In such systems, the electron and hole are positioned on two different molecules, thereby giving small exchange energy and thus, the ΔE ST values are observed to be very small in the range 0-0.05 eV, even smaller than that of pure TADF materials. Consequently, exciplex-based OLEDs have the potential to maximize the contribution from TADF and realize theoretical 100% internal quantum efficiency. As a result, the challenging task of achieving small ΔE ST in organic systems has been resolved. In this paper, we demonstrated the molecular design strategy of using " remote steric effect" on the donor molecules for improving the efficiency of exciplex-based OLEDs and the importance of acceptor structure on the stability of exciplexhosted phosphorescent OLEDs.

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“…Therefore, the driving voltage can be greatly reduced and the exciton recombination zone can also be significantly broaden, thus enhancing the PE and alleviating the efficiency roll‐off. At present, the monochromatic OLEDs based on exciplexes as hosts of phosphors have achieved the higher EQE over 30% 5c,7a,8. However, there is still no good report on the preparation of high efficiency white OLEDs (WOLEDs) with exciplexes as hosts due to the difficulty of matching between exciplex hosts and different phosphor guests 5b,9…”

Section: Summary Of the Key El Parameters For The Fabricated Devices mentioning

confidence: 99%

High‐Performance White Organic Light‐Emitting Diodes with High Efficiency, Low Efficiency Roll‐Off, and Superior Color Stability/Color Rendering Index by Strategic Design of Exciplex Hosts

Ying

Shu

Yao

et al. 2019

Advanced Optical Materials

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TADF) materials have attracted more attention in OLEDs, because they could not only serve as emitters to achieve 100% IQE by harvesting singlet excitons as well as triplet excitons owing to small charge transfer singlet-triplet state splitting (ΔE ST ), but also act as effective hosts for fluorophors and phosphors. [3f,4] As a new class of materials with TADF characteristics, exciplexes formed by mixing electron-donating and electron-accepting molecules similarly exhibits an intrinsically small ΔE ST (≈0-50 meV), since holes and electrons are positioned on donor and acceptor molecules, respectively, thus giving small exchange energy and low driving voltage. [5] This makes exciplexbased OLEDs rapid and vigorous development in recent years. As for an illumination source in lighting applications, the figure-of-merit power efficiency (PE) is the most relevant efficiency value. [6] Supposing that the emission pattern of OLEDs is the Lambertian type, then PE has a positive association with external quantum efficiency (EQE), whereas it is associated negatively with the operational voltage (U). The correlation can be described as PE α EQE/U. To achieve higher PE, the operational voltage should be lowered, and the EQE should be enlarged. This is affected by the device structures as well as the used materials, particularly the properties of hosts in phosphorescent OLEDs. A suitable host for highly efficient phosphorescent OLEDs not only needs higher triplet energy level (T 1 ) than that of phosphorescent dopant (a suitable triplet energy gap (ΔE T ) value should be ≤0.3 eV between the respective host and guest), but also demands as small as possible energy gap (E g ) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. [1c,7] As we know, exciplexes as hosts possess such properties. The holes are injected into the HOMO of electrondonating molecule, while the electrons are injected into the LUMO of electron-accepting molecule, and finally they are barrier-freely injected into the emissive layer (EML). Therefore, the driving voltage can be greatly reduced and the exciton recombination zone can also be significantly broaden, thus enhancing the PE and alleviating the efficiency roll-off. At present, the White organic light-emitting diodes (WOLEDs) are one of the most cogent candidates for environment friendly and healthy solid-state lighting due to many unique merits. Here, a strategic design of exciplex hosts is applied to simultaneously realize the superior color stability, high color rendering index (CRI), high efficiency, and low efficiency roll-off properties of WOLEDs. The resulting WOLEDs emit the forward-viewing maximum power efficiency (PE) of 59.9 lm W −1 , and the PE still remains 45.3 and 31.9 lm W −1 at 1000 and 5000 cd m −2 , respectively, exhibiting extremely low efficiency roll-off. More remarkably, the devices also show high CRI over 80 and extremely stable spectral emission in the luminance ranges from 1000 to 15 000 cd m −2 . The excellent...

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Exciplex-Forming Cohost for High Efficiency and High Stability Phosphorescent Organic Light-Emitting Diodes

Cited by 68 publications

References 40 publications

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

Achieving High‐Performance Pure‐Red Electrophosphorescent Iridium(III) Complexes Based on Optimizing Ancillary Ligands

26‐1: Invited Paper: High Efficiency and High Stability Exciplex‐Based OLEDs

High‐Performance White Organic Light‐Emitting Diodes with High Efficiency, Low Efficiency Roll‐Off, and Superior Color Stability/Color Rendering Index by Strategic Design of Exciplex Hosts

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