Exciplex Based Electroluminescence: Over 21% External Quantum

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Exciplex Based Electroluminescence: Over 21% External Quantum Efficiency and Approaching 100 lm/W Power Efficiency Baoyan Liang, JIaxuan Wang, Zong Cheng, Jinbei Wei, and Yue Wang J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b01140 • Publication Date (Web): 13 May 2019 Downloaded from http://pubs.acs.org on May 13, 2019

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The Journal of Physical Chemistry Letters

Exciplex Based Electroluminescence: Over 21% External Quantum Efficiency and Approaching 100 lm/W Power Efficiency Baoyan Liang, Jiaxuan Wang, Zong Cheng, Jinbei Wei,* and Yue Wang* State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, P. R. China Corresponding Author *E-mail: [email protected] (J. W.); *E-mail: [email protected] (Y. W.)

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ABSTRACT. Benzimidazole-triazine based electron acceptor PIM-TRZ with high triplet exited state energy and strong electron-transport ability was newly developed. A series of highly efficient exciplex emitters have been fabricated. The TAPC:PIM-TRZ (TAPC: di-[4-(N,Nditoly-amino)-phenyl]cyclohexane) film shows a high photoluminescence (PL) quantum yields (PLQY, Φf) of 93.4% and the device based on TAPC:PIM-TRZ exhibits a low turn-on voltage of 2.3 V, high maximum efficiency of 71.2 cd A−1 (current efficiency, CE), 97.3 lm W−1 (power efficiency, PE), and 21.7% (external quantum efficiency, EQE), as well as a high EQE of 16.2% at a luminance of 5000 cd m−2. The device displays the highest efficiency among reported organic light-emitting devices with exciplex film as emitting layer. Furthermore, green device is also fabricated with a TAPC:PIM-TRZ cohost using C545T (C545T: (10-(2-Benzothiazolyl)2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-benzopyrano[6,7-8-I,j]quinolizin-11-one)) as dopant, the highest CE, PE and EQE are 68.3 cd A−1, 86.6 lm W−1 and 20.2%, respectively.

TOC GRAPHICS

KEYWORDS exciplex emission; intermolecular charge transfer; TADF; OLEDs; efficiency roll-off


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Organic light-emitting diodes (OLEDs) have drawn tremendous attention from both science and industry owing to their promising applications in full-color displays or next generation lighting sources.1-3 In recent years, a new approach for utilizing all excited states called thermally activated delayed fluorescence (TADF) mechanism was developed and employed to fabricate OLEDs, which is the most promising for practical applications.4 For TADF materials the critical characteristics are the intramolecular charge-transfer excited state and very small singlet-triplet energy splitting (ΔES-T). The ΔES-T is corresponding to the overlapping degree between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).5-7 Usually TADF materials have twisted configurations with large distortion angles between electron donor and acceptor units, leading to a separation between HOMO and LUMO and hence a small ΔES-T.8 TADF-OLEDs with >30% EQE have been reported.9-11 It is well known that at high luminance most of TADF based OLEDs with overlong lifetime of excited states often exhibited efficiency roll-off induced by triplet-triplet annihilation and triplet-polaron quenching.12 Beyond intramolecular charge transfer (ICT) excited state based TADF emitters, the other class of efficient TADF-OLEDs was verified by constructing intermolecular charge-transfer excited states between electron-donor (D) and electron-acceptor (A) molecules.13-14 Recently, Zhang et al. adopted a TADF electron-donor MAC, and the maximum EQE and PE of the exciplex OLED based MAC:PO-T2T were 17.8% and 45.8 lm W-1, respectively.15 Przemyslaw et al. reported an exciplex OLED with a EQE of 20% and a PE of 71 lm W-1, the emitter was TSBPA:PO-T2T.16 Although considerable progress was made of the OLEDs with exciplex materials as emitters, their EQE and PE are obviously lower than that of ICT based TADFOLEDs.17-18 It is worth to note that PE is more important for OLED because it is a crucial factor


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for energy consume actually. On the other hand, the exciplex systems can also act as cohost for fluorescence OLEDs.19-23 Fast fluorescence decay can decrease exciton annihilation and the adjustable molar ratio of D:A can balance the carrier migration, which are beneficial to suppress efficiency roll-off. The lifetime of TADF based OLEDs may be extended by using exciplex cohost.24-25 It is worth to note that some triazine-based electron-transport or acceptor materials have been reported.26-28 Therefore, the development of intermolecular charge transfer exciplex based emitters with not only high EQE but also high PE is an important issue for high performance TADF OLEDs. For achieving high performance exciplex based emitters the design and synthesis of electron acceptor molecules still remains a great challenge.

Figure 1. Molecular structures of PIM-TRZ, electron donors and dopant used in this study. In this contribution, an electron acceptor PIM-TRZ (Figure 1) composed of 1-phenyl-1Hbenzo[d]imidazole (PIM) and 1,3,5-triazine (TRZ) hybrids was designed and synthesized (see Supporting Information). A series of exciplex emitters were fabricated by using TAPC, TCTA (TCTA: 4,4',4''-Tris(N-carbazolyl)triphenylamine) and Tris-PCz (Tris-PCz : 9,9',9''-Triphenyl9H,9H',9H''-[3,3':6',3'']-tercarbazole) (Figure 1) as electron donors. All exciplex emitters exhibited green emission with low operating voltages (turn on voltage (Von) = 2.3~2.4 V), high efficiencies of 52.0~71.2 cd A-1, 69.4~97.3 lm W-1, the maximum EQEs were 18.6%~21.7%. Particularly the OLEDs with TAPC:PIM-TRZ as emitting layer showed extremely low turn-on


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voltage of 2.3 V with a maximum EQE of 21.7%, which could maintain 16.2% at 5000 cd m-2. The maximum PE was 97.3 lm W-1, which can efficiently decrease energy consume. Furthermore we fabricated green fluorescence emitter with TAPC:PIM-TRZ cohost doping C545T. The maximum EQE were 20.2% for doping 0.6% C545T, the EQE roll-offs were only 0.99% and 8.91% at 100 cd m-2 and 1000cd m-2, respectively. These results are the best for OLEDs with exciplex material as emitters and exciplex based cohost for traditional fluorescence materials up to date.29-31 PIM-TRZ was synthesized via one step Suzuki cross-coupling reaction between 1-phenyl-2(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1H-benzo[d]imidazole (m-BPIM) and commercial available 2-chloro-4,6-diphenyl-1,3,5-triazine with a good yield. The target compound was a white powder after purified by column chromatography and vacuum sublimation. The product was characterized using nuclear magnetic resonance (1H and

13C

NMR), mass spectrometry and elemental analysis. Good thermal stability of PIM-TRZ could be demonstrated by the high decomposition temperatures (Td, corresponding to 5% weight loss) of 422 °C from thermogravimetric analysis (TGA) as well as high glass transition temperatures of 95 °C from differential scanning calorimetry (DSC) (Figure S1).


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Figure 2. (a) Molecular structure of PIM-TRZ from single-crystal X-ray diffraction; (b) and (c) intermolecular interactions; (d) crystal packing mode. The single crystal of PIM-TRZ was prepared by temperature-gradient vacuum sublimation and further confirmed by the X-ray diffraction (XRD) studies. The single crystal structure and packing arrangements are presented in Figure 2. The dihedral angles between the 1,3,5-triazine core and three attached benzene rings are 1.82°, 2.27° and 22.19°, respectively. The dihedral angle between the benzo-imidazole plane and phenyl ring linker is 29.51°. These results indicated that PIM-TRZ molecule adopts a planar-like configuration. In the crystal, PIM-TRZ molecules are packed together through abundant intermolecular C-H…π (2.825 Å) interactions as well as C-H…N (2.946 Å, 3.146 Å) hydrogen bonds between the PIM moieties and phenyl rings in the neighboring molecules (Figure 2b). In addition, two adjacent molecules stack together based on intermolecular π…π interaction with contact distance of 3.316 Å (Figure 2c). The π…π stacking molecular dimmers pack up resulting in the formation of crystal (Figure 2d). Good charge-carrier mobility of PIM-TRZ may benefit from these multiple intermolecular interactions demonstrated in the crystal.32 Density functional theory (DFT) calculations were carried out for PIM-TRZ at B3LYP/631G(d) level in order to gain further insight into the molecular frontier orbital characteristics of PIM-TRZ. As shown in Figure S2a, the fully optimized PIM-TRZ shows a planar configuration, which is in accordance with the single crystal analysis. The highest occupied molecular orbital (HOMO) was calculated to be mainly distributed over the PIM moiety. The PIM unit serves as an electron donating group when attached to 1,3,5-triazine moiety, which possesses a much stronger electron-withdrawing ability. The lowest occupied molecular orbital


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(LUMO) is mainly located at TRZ moiety and the adjacent phenyl ring. The electrochemical properties were also examined by cyclic voltammetry (CV) analysis (Figure S2b). The HOMO level was -5.90 eV, the LUMO energy level was calculated to be -2.90 eV, which was assigned to the reduction of triazine moiety.33 It is noteworthy that the LUMO energy level of PIM-TRZ is quite similar to that of the common cathode LiF/Al (-2.9 eV), which is advantageous for the electron injection from cathode to electron-transport layer thus resulting in low driving voltage and high efficiency.

Figure 3. (a) Room temperature UV-vis absorption (solvent: dichloromethane) and PL (solvent: toluene) spectra of PIM-TRZ in dilute solution (10-5 M) and neat thin film as well as corresponding phosphorescence (Phos) spectrum recorded in toluene dilute solution (10-5 M) at


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77 K. (b) UV-vis absorption and PL spectra of TAPC, PIM-TRZ, TAPC:PIM-TRZ deposited films. (c) PL decay cruves of the TAPC:PIM-TRZ blend film measured at room temperature. (d) Time-resolved PL decay curves of TAPC:PIM-TRZ (1:3) thin film at different temperatures. Ultraviolet-visible (UV-vis) absorption and photoluminescence spectra of PIM-TRZ are shown in Figure 3a. The absorption maxima at 270~280 nm was attributed to π–π* transitions.19,34 The triplet energy ET of PIM-TRZ was 2.64 eV estimated from the phosphorescence spectrum. The high ET can effectively prevent the energy of the exciton from being transferred to the donors or acceptors, which is important for high fluorescence quantum yields. Normalized absorption and emission spectra of TAPC, PIM-TRZ and TAPC:PIM-TRZ blend films are presented in Figure 3b. The mixed film absorption spectrum shows features that are very similar to the absorption profiles of the constituting molecules suggesting that no new ground-state transition existed in the blend film. The PL spectrum of the blend film is shown along with the fluorescence spectra of constituting molecules films for comparison. The PL maximum of the mixed film is located at 521 nm, which is obviously bathochromic shift compared to the emission from the composed molecules films caused by exciplex formation between TAPC and PIM-TRZ.13-14 The current density-voltage (J-V) characteristics (Figure S3) of single carrier (electron-only) devices of PIM-TRZ and TmPyPz (2,4,6-Tri(m-pyridin-3ylphenyl)-1,3,5-triazine) suggested that PIM-TRZ is a better electron transporting material. Significantly, the TAPC:PIM-TRZ blend film exhibits high PL quantum yields (PLQYs) of 93.4%, which is the most outstanding result among the exciplexs.16,19,35-37 The transient PL decay curve for exciplex emission under ambient conditions is presented in Figure 3c, which could be divided into prompt and delayed components. For TAPC:PIM-TRZ film, a fast decay component with life time of 92 ns is generated from conventional fluorescence-based exciplex


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emission and a delay decay with lifetime of 5.12 μs is ascribed to the delayed exciplex emission based on reverse intersystem crossing (RISC) process from nonradiative triplet excited states to the radiative singlet excited states.38 The ratio of Φd/Φp was 14.0, which is crucial for high efficiency and small roll-off.39 Figure 3d shows the temperatures dependent transient PL decay curves of TAPC:PIM-TRZ blend film under vacuum condition, the lifetime and proportion of delayed fluorescence were 9.00 μs, 75.3% at 100 K, 8.02 μs, 78.4% at 200 K, 5.02 μs, 86.3% at 300K suggesting a typical TADF feature. Unfortunately we didn’t obtain the phosphorescence spectrum of TAPC:PIM-TRZ blend film because the delay time was not long enough for spectrum recording. The other aromatic amine compounds TCTA and Tris-PCz were also chosen as electron donors, the PLQY of blend films were 90.9% and 65.4%, respectively. The triplet energy of Tris-PCz (2.67 eV) is lower than that of TCTA (2.80 eV), and much lower than that of TAPC (2.90 eV) (Figures S4). The phosphorescence spectra of PIM-TRZ in toluene (10-5 M) and Tris-PCz:PIM-TRZ blend film was compared in Figure S5. The typical exciplex based phosphorescent spectra should be completely structural-less. The phosphorescence spectrum of Tris-PCz:PIM-TRZ blend film displays slight structure feature, which is similar to that of PIM-TRZ in frozen toluene matrix. In frozen toluene matrix and blend film the concentrations and surround environments of PIMTRZ molecules are different. Therefore the phosphorescent spectra of PIM-TRZ in the two systems should be not very identical. The ET1 of Tris-PCz:PIM-TRZ exciplex was 2.71 eV which was higher than that of PIM-TRZ, so the triplet energy transfer process from exciplex to PIM-TRZ may exist in Tris-PCz:PIM-TRZ film resulting a lower PLQY. It is well known that the process of intermolecular charge transfer based excilpex emission in solid thin film is very complex and the theory to explain its detail mechanism is remain undeveloped. So far, we can’t


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provide complete explanation for the photophysical properties of exciplex systems in this study. The steady and transient PL spectra (Figures S6-8) of TCTA:PIM-TRZ and Tris-PCz:PIMTRZ blend films displayed TADF feature. The fluorescence and phosphorescence spectra of TCTA:PIM-TRZ and Tris-PCz:PIM-TRZ blend films exhibit nearly full overlap feature indicating a quite small ΔES-T (Figure S9).40-41

Figure 4. (a) Electroluminescence (EL) spectra, (b) Current density–Voltage–Brightness (J–V– L) plots, (c) EQE–Brightness plots, and (d) CE–Brightness–PE plots of exciplex OLEDs based


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on TAPC:PIM-TRZ, TCTA:PIM-TRZ, Tris-PCz:PIM-TRZ. (e) EL spectra of TAPC:PIMTRZ and TAPC:PIM-TRZ cohost doping 0.6% C545T. (f) EQE–Brightness–PE plots of TAPC:PIM-TRZ cohost doping 0.6% C545T. To verify the potential applications in OLEDs ， PIM-TRZ based blend films were used as emission material layer (EML) to fabricate devices. Firstly we explored the optimal weight radio between the electro-donor TAPC and the electro-acceptor PIM-TRZ with the configuration of [ITO/TAPC (40 nm)/TAPC:PIM-TRZ (1:3) (35 nm)/PIM-TRZ (60 nm)/LiF (1 nm)/Al (100 nm)]. The optimal radio between TAPC and PIM-TRZ was 1:3 (weight:weight) (Figure S10). ITO (indium tin oxide) and LiF/Al were the anode and the cathode, respectively. The pure PIMTRZ and TAPC were used as electron and hole transporting layer, respectively, so there is no carrier transporting energy barrier from hole transporting layer (HTL) or electron transporting layer (ETL) to EML, which will reduce driving voltage and conduce to high PE. The device exhibited low turn-on voltage (estimated at the brightness of 1 cd m−2) of 2.3 V, which benefits from the small energy barrier between the LUMO energy level of PIM-TRZ and that of LiF/Al. The device exhibited voltage-independent EL emissions with a peak at 526 nm and a CIE coordinate of (0.35, 0.58). The maximum luminance (L), CE, PE, and EQE of the device were 35410 cd m-2, 71.2 cd A−1, 97.3 lm W−1 and 21.7%, respectively that is the best performance of exciplex OLED up to date.37 An extra exciton-blocking layer TCTA or Tris-PCz was introduced avoiding the formation of exciplex between TAPC and the electron acceptor when TCTA and Tris-PCz act as electron donors. The optimized structure was [ITO/TAPC (35 nm)/TCTA or Tris-PCz (10 nm)/TCTA:PIM-TRZ (1:2) or Tris-PCz:PIM-TRZ (1:2) (30 nm)/PIM-TRZ (60 nm)/LiF (1 nm)/Al (100 nm)]. The driving voltage was higher owing to the carrier transport barrier between HTL (TAPC) and exciton-blocking layer (TCTA or Tris-PCz). A lower Φf of


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TCTA:PIM-TRZ and Tris-PCz:PIM-TRZ blend films results in a lower efficiency. In order to check the performance of TAPC:PIM-TRZ blend film as host, C545T (Figure 1) was employed as dopant emitter to fabricate OLEDs. The UV-vis absorption spectrum of C545T in toluene (105

M) is shown in Figure S11 along with the fluorescence spectra of TAPC:PIM-TRZ deposited

film suggesting the possibility of the complete energy transfer from TAPC:PIM-TRZ to C545T. The

optimized

structure

is

[ITO/TAPC

(50

nm)/TCTA

(10

nm)/TAPC:PIM-TRZ

(1:3):0.6wt%C545T (30 nm)/PIM-TRZ (60 nm)/LiF (1nm)/Al (100 nm)]. The luminescence, CE, PE, and EQE of the device were 42560 cd m-2, 68.3 cd A−1, 86.4 lm W−1 and 20.2%, respectively. The roll-offs of EQE are only 0.99% and 8.91% at 100 cd m-2 and 1000 cd m-2, respectively. The results are the best for OLED using C545T as dopant emitter.16,31 The key eletroluminescnece performance parameters were listed in Table 1.

Table 1. Electroluminescent parameters of the devices Emitter G1 TAPC:PIM-TRZ G2 TCTA:PIM-TRZ G3 Tris-Cz:PIM-TRZ G4 cohost:0.6% C545T [a]

Von [V][a]

Lmax [cd m−2][b]

CE [cd A−1][c]

PE [lm W−1][c]

EQE [%][c]

CIE (x, y)[d]

2.3

35410

71.2,69.7,64.8

97.3,81.1,53.9

21.7,21.3,19.8

0.35,0.58

2.4

18230

58.6,58.3,55.9

69.4,65.7,46.2

19.1,19.0,17.8

0.31,0.56

2.4

15630

52.0,50.5,43.2

71.0,59.4,39.9

18.6,17.8,15.6

0.26,0.51

2.4

42560

68.3,67.6,62.0

86.4,72.4,51.1

20.2,20.0,18.4

0.29,0.62

turn-on votage at 1.0 cd m-2. [b] maximum luminance. [c] in the order of maximum, then the

values recorded at 100 and 1000 cd m–2. [d] recorded at 100 cd m-2. In conclusion, a unique electron acceptor material based on benzimidazole and triazine units was developed. PIM-TRZ showed remarkable thermal stability and electron transporting property, the LUMO energy of PIM-TRZ matches well with that of LiF/Al. Moreover the exciplex blend films showed high Φf composed of PIM-TRZ. Highly efficient exciplex-based OLEDs with simple structures were fabricated by mixing it with suitable electron-donors and


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displayed extremely low turn-on voltages and low efficiency roll-offs. In particular, the OLED with TAPC:PIM-TRZ as an emitting layer showed the best EL performance with extremely low driving voltage of 2.7 V at 100 cd m-2 and maximum EQE and PE are up to 21.7% and 97.3 lm W-1, which is best result among the exciplex-OLEDs. More importantly, the exciplex system was used as cohost for green OLED by doping 0.6wt% C545T. The device showed extraordinary EQE of 18.4% at 1000 cd m-2 with a roll-off of 8.91%. Supporting Information. The Supporting Information is available free of charge Additional details of the detailed experimental information, synthesis, graphs, crystallographic information of single crystals and calculations geometric coordinate (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; *E-mail: [email protected]; Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (21772064) and National Basic Research Program of China (2015CB655003). REFERENCES


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(1)

Page 14 of 18

Tang, C. W.; VanSlyke, S. A. Organic Electroluminescent Diodes. Appl. Phys. Lett. 1987, 51, 913-915.

(2)

Zhang, Y.; Miao, Y.; Song, X.; Gao, Y.; Zhang, Z.; Ye, K.; Wang, Y. Single-Moleculebased White-Light Emissive Organic Solids with Molecular-Packing-Dependent Thermally Activated Delayed Fluorescence. J. Phys. Chem. Lett. 2017, 8, 4808-4813.

(3)

Li, Z.; Li, C.; Xu, Y.; Xie, N.; Jiao, X.; Wang, Y. Nonsymmetrical Connection of Two Identical Building Blocks: Constructing Donor-Acceptor Molecules as Deep Blue Emitting Materials for Efficient Organic Emitting Diodes. J. Phys. Chem. Lett. 2019, 10, 842-847.

(4)

Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly Efficient Organic Light-Emitting Diodes from Delayed Fluorescence. Nature 2012, 492, 234-238.

(5)

Tao, Y.; Yuan, K.; Chen, T.; Xu, P.; Li, H.; Chen, R.; Zheng, C.; Zhang, L.; Huang, W. Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of Organoelectronics. Adv. Mater. 2014, 26, 7931-7958.

(6)

Wong, M. Y.; Zysman-Colman, E. Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes. Adv. Mater.2017, 29， 1605444.

(7)

Yang, Z.; Mao, Z.; Xie, Z.; Zhang, Y.; Liu, S.; Zhao, J.; Xu, J.; Chi, Z.; Aldred, M. P. Recent Advances in Organic Thermally Activated Delayed Fluorescence Materials. Chem. Soc. Rev. 2017, 46, 915-1016.

(8)

Zhang, Q.; Kuwabara, H.; Potscavage, W. J., Jr.; Huang, S.; Hatae, Y.; Shibata, T.; Adachi, C. Anthraquinone-Based Intramolecular Charge-Transfer Compounds: Computational Molecular Design, Thermally Activated Delayed Fluorescence, and Highly Efficient Red Electroluminescence. J. Am. Chem. Soc. 2014, 136, 18070-18081.

(9)

Lin, T. A.; Chatterjee, T.; Tsai, W. L.; Lee, W. K.; Wu, M. J.; Jiao, M.; Pan, K. C.; Yi, C. L.; Chung, C. L.; Wong, K. T.; Wu, C. C. Sky-Blue Organic Light Emitting Diode with


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Page 15 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


37% External Quantum Efficiency Using Thermally Activated Delayed Fluorescence from Spiroacridine-Triazine Hybrid. Adv. Mater. 2016, 28, 6976-6983. (10) Rajamalli, P.; Senthilkumar, N.; Huang, P. Y.; Ren-Wu, C. C.; Lin, H. W.; Cheng, C. H. New Molecular Design Concurrently Providing Superior Pure Blue, Thermally Activated Delayed Fluorescence and Optical Out-Coupling Efficiencies. J. Am. Chem. Soc .2017, 139, 10948-10951. (11) Lee, D. R.; Kim, B. S.; Lee, C. W.; Im, Y.; Yook, K. S.; Hwang, S. H.; Lee, J. Y. Above 30% External Quantum Efficiency in Green Delayed Fluorescent Organic Light-Emitting Diodes. ACS Appl. Mater. Interfaces 2015, 7, 9625-9629. (12) Cao, X.; Zhang, D.; Zhang, S.; Tao, Y.; Huang, W. CN-Containing Donor–AcceptorType Small-Molecule Materials for Thermally Activated Delayed Fluorescence OLEDs. J. Mater. Chem. C 2017, 5 , 7699-7714. (13) Goushi, K.; Yoshida, K.; Sato, K.; Adachi, C. Organic Light-Emitting Diodes Employing Efficient Reverse Intersystem Crossing for Triplet-to-Singlet State Conversion. Nat.Photonics 2012, 6, 253-258. (14) Goushi, K.; Adachi, C. Efficient Organic Light-Emitting Diodes Through up-Conversion from Triplet to Singlet Excited States of Exciplexes. Appl. Phys. Lett. 2012, 101, 023306. (15) Liu, W.; Chen, J.-X.; Zheng, C.-J.; Wang, K.; Chen, D.-Y.; Li, F.; Dong, Y.-P.; Lee, C.S.; Ou, X.-M.; Zhang, X.-H. Novel Strategy to Develop Exciplex Emitters for HighPerformance OLEDs by Employing Thermally Activated Delayed Fluorescence Materials. Adv. Funct. Mater. 2016, 26, 2002-2008. (16) Chapran, M.; Pander, P.; Vasylieva, M.; Wiosna-Salyga, G.; Ulanski, J.; Dias, F. B.; Data, P. Realizing 20% External Quantum Efficiency in Electroluminescence with Efficient Thermally Activated Delayed Fluorescence from an Exciplex. ACS Appl. Mater. Interfaces. 2019, 11, 13460−13471


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(17) Sun, J. W.; Lee, J. H.; Moon, C. K.; Kim, K. H.; Shin, H.; Kim, J. J. A fluorescent Organic Light-Emitting Diode with 30% External Quantum Efficiency. Adv. Mater. 2014, 26, 5684-8. (18) Seino, Y.; Inomata, S.; Sasabe, H.; Pu, Y. J.; Kido, J. High-Performance Green OLEDs Using Thermally Activated Delayed Fluorescence with a Power Efficiency of over 100 lm W-1. Adv. Mater. 2016, 28, 2638-2643. (19) Hung, W. Y.; Chiang, P. Y.; Lin, S. W.; Tang, W. C.; Chen, Y. T.; Liu, S. H.; Chou, P. T.; Hung, Y. T.; Wong, K. T. Balance the Carrier Mobility To Achieve High Performance Exciplex OLED Using a Triazine-Based Acceptor. ACS Appl. Mater. Interfaces 2016, 8, 4811-4818. (20) Chen, D.; Liu, K.; Gan, L.; Liu, M.; Gao, K.; Xie, G.; Ma, Y.; Cao, Y.; Su, S. J. Modulation of Exciton Generation in Organic Active Planar pn Heterojunction: Toward Low Driving Voltage and High-Efficiency OLEDs Employing Conventional and Thermally Activated Delayed Fluorescent Emitters. Adv. Mater. 2016, 28, 6758-6765. (21) Kim, H. G.; Kim, K. H.; Kim, J. J. Highly Efficient, Conventional, Fluorescent Organic Light-Emitting Diodes with Extended Lifetime. Adv. Mater. 2017, 29, 1702159. (22) Zhang, D.; Song, X.; Cai, M.; Duan, L. Blocking Energy-Loss Pathways for Ideal Fluorescent Organic Light-Emitting Diodes with Thermally Activated Delayed Fluorescent Sensitizers. Adv. Mater. 2018, 30 , 1705250. (23) Huang, M.; Jiang, B.; Xie, G.; Yang, C. Highly Efficient Solution-Processed Deep-Red Organic Light-Emitting Diodes Based on an Exciplex Host Composed of a Hole Transporter and a Bipolar Host. J. Phys. Chem. Lett. 2017, 8, 4967-4973. (24) Jeon, S. K.; Lee, H. L.; Yook, K. S.; Lee, J. Y. Recent Progress of the Lifetime of Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescent Material. Adv. Mater. 2019, 1803524. (25) Tsang, D. P.; Matsushima, T.; Adachi, C. Operational Stability Enhancement in Organic Light-Emitting Diodes with Ultrathin Liq Interlayers. Sci Rep 2016, 6, 22463.


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Page 17 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(26) Fink, R.; Frenz, C.; Thelakkat, M.; Schmidt, H. W. Synthesis and Characterization of Aromatic Poly(1,3,5-triazine-ether)s for Electroluminescent Devices. Macromolecules, 1997, 30, 8177-8181. (27) Cui, L. S.; Ruan, S. B.; Bencheikh, F.; Nagata, R.; Zhang, L.; Inada, K.; Nakanotani, H.; Liao, L. S.; Adachi, C. Long-Lived efficient Delayed Fluorescence Organic LightEmitting Diodes Using n-Yype Hosts. Nat. Commun. 2017, 8, 2250. (28) Jin, G.; Liu, J.-Z.; Zou, J.-H.; Huang, X.-L.; He, M.-J.; Peng, L.; Chen, L.-L.; Zhu, X.-H.; Peng, J.; Cao, Y. Appending Triphenyltriazine to 1,10-Phenanthroline: a Robust Electron-Transport Material for Stable Organic Light-Emitting Diodes. Science Bulletin 2018, 63, 446-451. (29) Liu, X. K.; Chen, Z.; Qing, J.; Zhang, W. J.; Wu, B.; Tam, H. L.; Zhu, F.; Zhang, X. H.; Lee, C. S. Remanagement of Singlet and Triplet Excitons in Single-Emissive-Layer Hybrid White Organic Light-Emitting Devices Using Thermally Activated Delayed Fluorescent Blue Exciplex. Adv. Mater. 2015, 27, 7079-7085. (30) Shih, C. J.; Lee, C. C.; Yeh, T. H.; Biring, S.; Kesavan, K. K.; Amin, N. R. A.; Chen, M. H.; Tang, W. C.; Liu, S. W.; Wong, K. T. Versatile Exciplex-Forming Co-Host for Improving Efficiency and Lifetime of Fluorescent and Phosphorescent Organic LightEmitting Diodes. ACS Appl. Mater. Interfaces 2018, 10, 24090-24098. (31) Chen, L.; Zhang, S.; Li, H.; Chen, R.; Jin, L.; Yuan, K.; Li, H.; Lu, P.; Yang, B.; Huang, W. Breaking the Efficiency Limit of Fluorescent OLEDs by Hybridized Local and Charge-Transfer Host Materials. J. Phys. Chem. Lett. 2018, 9, 5240-5245. (32) Yokoyama, D.; Sasabe, H.; Furukawa, Y.; Adachi, C.; Kido, J. Molecular Stacking Induced by Intermolecular C-H···N Hydrogen Bonds Leading to High Carrier Mobility in Vacuum-Deposited Organic Films. Adv. Funct. Mate. 2011, 21, 1375-1382. (33) Su, S. J.; Sasabe, H.; Pu, Y. J.; Nakayama, K.; Kido, J. Tuning Energy Levels of Electron-Transport Materials by Nitrogen Orientation for Electrophosphorescent Devices with an 'Ideal' Operating Voltage. Adv. Mater. 2010, 22, 3311-3316.


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Page 18 of 18

(34) Liu, X. K.; Chen, Z.; Qing, J.; Zhang, W. J.; Wu, B.; Tam, H. L.; Zhu, F.; Zhang, X. H.; Lee, C. S. Remanagement of Singlet and Triplet Excitons in Single-Emissive-Layer Hybrid White Organic Light-Emitting Devices Using Thermally Activated Delayed Fluorescent Blue Exciplex. Adv. Mater. 2015, 27, 7079-85. (35) Liu, X. K.; Chen, Z.; Zheng, C. J.; Liu, C. L.; Lee, C. S.; Li, F.; Ou, X. M.; Zhang, X. H. Prediction and Design of Efficient Exciplex Emitters for High-Efficiency, Thermally Activated Delayed-Fluorescence Organic Light-Emitting Diodes. Adv. Mater. 2015, 27, 2378-83. (36) Colella, M.; Danos, A.; Monkman, A. P. Less Is More: Dilution Enhances Optical and Electrical Performance of a TADF Exciplex. J. Phys. Chem. Lett. 2019, 10 , 793-798. (37) Mamada, M.; Tian, G.; Nakanotani, H.; Su, J.; Adachi, C. The Importance of ExcitedState Energy Alignment for Efficient Exciplex Systems Based on a Study of Phenylpyridinato Boron Derivatives. Angew. Chem. Int. Ed. Engl. 2018, 57, 12380-12384. (38) Li, C.; Duan, R.; Liang, B.; Han, G.; Wang, S.; Ye, K.; Liu, Y.; Yi, Y.; Wang, Y. DeepRed to Near-Infrared Thermally Activated Delayed Fluorescence in Organic Solid Films and Electroluminescent Devices. Angew. Chem. Int. Ed. Engl. 2017, 56, 11525-11529. (39) Li, J.; Nomura, H.; Miyazaki, H.; Adachi, C. Highly Efficient Exciplex Organic LightEmitting Diodes Incorporating a Heptazine Derivative as an Electron Acceptor. Chem. Commun. 2014, 50, 6174-6176. (40) Sommer, G. A.; Mataranga-Popa, L. N.; Czerwieniec, R.; Hofbeck, T.; Homeier, H. H. H.; Muller, T. J. J.; Yersin, H. Design of Conformationally Distorted Donor-Acceptor Dyads Showing Efficient Thermally Activated Delayed Fluorescence. J. Phys. Chem. Lett. 2018, 9, 3692-3697. (41) Wu, K.; Wang, Z.; Zhan, L.; Zhong, C.; Gong, S.; Xie, G.; Yang, C. Realizing Highly Efficient Solution-Processed Homojunction-Like Sky-Blue OLEDs by Using Thermally Activated Delayed Fluorescent Emitters Featuring an Aggregation-Induced Emission Property. J. Phys. Chem. Lett. 2018, 9, 1547-1553.


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Exciplex Based Electroluminescence: Over 21% External Quantum

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