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Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient full-color PhOLEDs
Journal Pre-proof Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient full-color PhOLEDs Hui-Ting Mao, Wei-Lin Song, Chun-Xiu Zang, Guang-Fu Li, Guo-Gang Shan, Hai-Zhu Sun, Wen-Fa Xie, Zhong-Min Su PII:
S1566-1199(19)30540-3
DOI:
https://doi.org/10.1016/j.orgel.2019.105513
Reference:
ORGELE 105513
To appear in:
Organic Electronics
Received Date: 18 August 2019 Revised Date:
26 September 2019
Accepted Date: 16 October 2019
Please cite this article as: H.-T. Mao, W.-L. Song, C.-X. Zang, G.-F. Li, G.-G. Shan, H.-Z. Sun, W.-F. Xie, Z.-M. Su, Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient full-color PhOLEDs, Organic Electronics (2019), doi: https://doi.org/10.1016/ j.orgel.2019.105513. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient fullcolor PhOLEDs Hui-Ting Mao,a Wei-Lin Song,a Chun-Xiu Zang,b Guang-Fu Li,a Guo-Gang Shan,a,* Hai-Zhu Sun,a Wen-Fa Xie,b,** Zhong-Min Su,a,c***
a
Institute of Functional Material Chemistry and National & Local United Engineering
Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China. b
State Key Laboratory on Integrated Optoelectronics, College of Electronic Science
and Engineering, Jilin University, Changchun, Jilin 130012, P. R. China. c
Jilin Provincial Science and Technology Innovation Center of Optical Materials and
Chemistry, School of Chemistry and Environmental Engineering, Changchun University of Science and Technology Changchun, 130022, P. R. China.
*
Corresponding author. Institute of Functional Material Chemistry and National &
Local United Engineering Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China. E-mail address: [email protected] (G.-G. Shan). **
Corresponding author. State Key Laboratory on Integrated Optoelectronics, College
of Electronic Science and Engineering, Jilin University, Changchun, Jilin 130012, P. R. China. E-mail address: [email protected] (W. Xie).
1
***
Corresponding author. Jilin Provincial Science and Technology Innovation Center
of Optical Materials and Chemistry, School of Chemistry and Environmental Engineering, Changchun University of Science and Technology Changchun, 130022, P. R. China. E-mail address: [email protected] (Z.-M. Su).
2
Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient fullcolor PhOLEDs Hui-Ting Mao,a Wei-Lin Song,a Chun-Xiu Zang,b Guang-Fu Li,a Guo-Gang Shan,a,* Hai-Zhu Sun,a Wen-Fa Xie,b,** Zhong-Min Su,a,c***
a
Institute of Functional Material Chemistry and National & Local United Engineering
Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China. Email: [email protected] (G.-G. Shan); E-mail: [email protected] (Z.-M. Su) b
State Key Laboratory on Integrated Optoelectronics, College of Electronic Science
and Engineering, Jilin University, Changchun, Jilin 130012, P. R. China. E-mail: [email protected] (W. Xie) c
Jilin Provincial Science and Technology Innovation Center of Optical Materials and
Chemistry, School of Chemistry and Environmental Engineering, Changchun University of Science and Technology Changchun, 130022, P. R. China.
1
Abstract Many efforts have been focused on exploring highly efficient host materials that capable of function in phosphorescent organic light-emitting devices (PhOLEDs). However, superior hosts reported to date that are generally suitable to full-color devices are rare and the resultant device performances are far from satisfactory. A class of host compounds DCzPBI, POCzPBI, and DPOPBI, incorporating carbazole and diphenylphosphoryl oxide moieties as electron-donating and -accepting groups, respectively, are synthesized and successfully applied as universal hosts in the fabrication of full-color PhOLEDs. The effect of substituted groups on the photophysical, theoretical calculations, and electrochemical characters for host materials is systematically investigated. We adopt the same device architecture to fabricate the blue, green, yellow, and red PhOLEDs with the combination of the three hosts. As a result, DPOPBI and POCzPBI with good charge carrier transporting properties supported the devices with the impressive efficiencies. The best current efficiency (CE) are 23.2, 48.4, 45.7, 21.5 cd A−1 for blue, green, yellow, and red devices, respectively. Even at the brightnesses of 1000 cd m−2, the efficiency roll-offs are only 2% for green and 0.2% for yellow devices, indicating the promising applications as universal hosts for highly efficient PhOLEDs.
2
Keywords host material; phosphorescent organic light-emitting device; impressive efficiency; good charge carrier transporting property
3
1. Introduction Phosphorescent organic light-emitting diodes (PHOLEDs) are highly attractive owing to the high performances relative to those of conventional singlet fluorescent devices [1,2]. In principle, 100% internal quantum efficiency (IQE) can be achieved by effectively employing singlet and triplet excitons [3-5]. Generally, the triplet phosphors involve longer lifetimes for emission, which result in notorious selfquenching and triplet-triplet annihilation (TTA) [6-8]. Concerning this issue, the phosphorescent guest dyes are ordinarily dispersed in suitable host to suppress the intermolecular interaction-induced quenching, making the fabrication of high performance hosts fitting for guest dopants imperative [9-12]. Several significant conditions for host compounds should be satisfied: i) a larger triplet energy (ET) than the guest to sustain the positive energy transfer to the guest dopant [13-15]; ii) good thermal properties to guarantee device operation and fabrication [16]; iii) excellent charge carrier transport characters for exciton recombination and balanced charge flux in emissive layers (EMLs) [13,17,18]; iv) matched energy levels regarding highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) [19,20], thereby reducing the operation voltage and facilitating charge transporting. With an enhancing demand of device performances, particularly device efficiencies, a large amount of effort in the exploration of hosts is focus on 4
fundamental investigation of the structure property correlations. Some effective strategies, for example, unite integration, structure optimization, and molecular splicing have been successfully explored to obtain multifunctional host materials with a high T1 energy and considerable carrier transporting ability, significantly elevating the device performance. However, up to date, there are only few universal hosts that capable of function in full-color phosphorescent devices. Actually, the lack of universal hosts can be ascribed to a wide variety of molecular structures of guest dopants possessing different emission peaks, subsequently leading to worse intermolecular interactions in dopant-dopant and host-dopant. In this case, some molecules with spiro [21-23], twisted [24,25], unsymmetrical configurations [26-29] are adopted to construct hosts to restraining intermolecular interactions and suppressing TTA effects. Nevertheless, it is shown that the hosts based on these kinds of structures could not supply satisfied hole and electron transport capability and subsequently result in serious efficiency roll-offs.
Insert Scheme 1 Scheme 1. Chemical structures of DCzPBI, POCzPBI, and DPOPBI.
Recently, research focus have tended to the development of multifunctional hosts possessing both electron-donating and -accepting moieties. The combination of these functional moieties as steric hindrance can efficiently reduce intermolecular interaction and achieve balanced charge fluxes at the same time. The electrondonating moieties are mainly carbazole [30-33], triphenylamine [34-36], and diphenylamine [37,38]. The electron-accepting moieties mainly include oxadiazole [2,39], triazole [40], triazine [41], pyridine [42-44], and phosphine oxide [21,45].
5
Among these donating and accepting moieties, the carbazole and diphenylphosphoryl oxide groups exhibit good charge carrier transporting properties. On the other hand, 1,2-diphenyl-H-benzoimidazole (HPBI) have been widely reported as building block due to easy synthesis and chemical modificaton [46-48]. For the purpose of developing outstanding host compounds suitable for highly efficient full-color PhOLEDs and explore the intrinsic structure-property relationships for further molecular design, herein, we designed and synthesized three novel hosts, DCzPBI, POCzPBI,
and
DPOPBI
by
integrating
HPBI
with
carbazole
and
diphenylphosphoryl oxide units (see Scheme 1). By virtue of the steric hindrance, considerable carrier transporting ability and appropriate energy level of these functional moieties, the resulting materials were expected to be the excellent host materials for PhOLEDs. The effect of substituted unites on the thermal, photophysicl, and electrochemical characters of the compounds was systematically studied. Through introducing
the
functional
moieties,
promising
electroluminescence
(EL)
performances of the blue, green, yellow, and red devices with the combination of the host compounds were achieved. Among these compounds, DPOPBI and POCzPBI with good charge carrier transporting properties supported the devices with the impressive efficiencies. The best current efficiency (CE) were 23.2, 48.4, 45.7, 21.5 cd A−1 for blue, green, yellow, and red devices, respectively. In addition, all the devices realized minor efficiency roll-offs with the increase of luminance, especially, the efficiency roll-offs were only 2% for green, 0.2% for yellow devices.
6
Insert Scheme 2 Scheme 2. Synthetic procedures of DCzPBI, POCzPBI, and DPOPBI. i) DMA, 1 h, CH3COOH, 12 h; ii) carbazole, CuI, K2CO3, DMPU, 18-Crown-6, 12 h; iii) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h; iv) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h, carbazole, CsCO3, DMF, 12 h.
2. Results and discussion 2.1. Synthesis and thermal properties Synthetic procedures and chemical structures of the hosts were presented in Scheme 2. The detailed synthetic procedures of a (Scheme S1) (ESI), b, and c were described in supporting information. The molecule configurations of DCzPBI, POCzPBI, and DPOPBI were confirmed by 1H NMR and mass spectra. The rigid chemical structures of hosts compounds endowed them with good thermal and morphological properties by using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The host materials depicted favorable decomposition temperatures (Td) of 451 °C for DCzPBI, 436 °C for POCzPBI, and 434 °C for DPOPBI, indicating that they can be enduring by vacuum deposition and fufilling the demand of the hosts to be adopted in devices [19,49]. Additionally, the glass-transition temperatures (Tg) were estimated to be 120 °C for DCzPBI, 127 °C for POCzPBI, and 135 °C for DPOPBI according to the DSC curves (see Fig. 1). The favorable thermal properties are of importance for the hosts because they can reduce potential phase separation between hosts and guest dopants [24].
7
Insert Fig. 1 Fig. 1. DSC curves for DCzPBI, POCzPBI, and DPOPBI collected at a heating rate of 10 °C min−1.
2.2. Photophysical properties The absorption and photoluminescence (PL) spectra of DCzPBI, POCzPBI, and DPOPBI in CH2Cl2 were presented in Fig. 2. The pertinent photophysical and electrochemical parameters were listed in Table 1. The strong absorption peaks (at about 290 nm) for DCzPBI and POCzPBI could be attributed to the carbazolecentered π-π* transition. To better comprehend the feature of the excited states of the compounds, the simulated absorption spectra were calculated and presented in supporting information (see Fig. S1-S3), which were consistent with the experiment data. The calculated orbital excitation analyses and oscillator strength (f) of the three compounds were given in Table S1-S3. In the case of DCzPBI (Fig. S1 and Table S1), the HOMO, HOMO-4 involved in the main excitations predominantly located on 1, 2-diphenyl-H-benzoimidazole and one of the carbazole moieties, while HOMO-1 resided on one of the carbazole unites with there being a small distribution from adjacent benzene ring. For the LUMO, it resided on 1, 2-diphenyl-H-benzoimidazole with a part contribution from carbazole groups. On the basis of the calculated results,
8
the absorption band (band 1) between 230 and 250 nm originated mainly from the excitation of HOMO → LUMO+8, HOMO-5 → LUMO+2, and HOMO-1 → LUMO+7. Correspondingly, they were predominantly ascribed to the carbazolecentered π-π* transition. Furthermore, the band 2 and band 3 in low-energy region at around 290 and 350 nm resulted from the excitation of HOMO-4 → LUMO, HOMO1 → LUMO+3, and HOMO → LUMO. Thus, these absorption bands were mostly assigned to the π-π* transition from one of the carbazoles to the 1, 2-diphenyl-Hbenzoimidazole moiety, which were in agreement with the experimental section mentioned above. The corresponding assignments, including POCzPBI and DPOPBI, could be also obtained from the TD-DFT results (Fig. S2, S3 and Table S2, S3).
Insert Fig. 2 Fig. 2. Electronic absorption and the emission spectra of DCzPBI, POCzPBI, and DPOPBI in dichloromethane solution (10−5 mol L−1). Inset: phosphorescence (PH) spectra in dichloromethane (10−6 mol L−1) at low temperature (77 K).
The emission wavelengths of the hosts were 399 nm (DCzPBI), 406 nm (POCzPBI), and 373 nm (DPOPBI), respectively. Inset of Fig. 2 depicted the phosphorescence spectra of the hosts in frozen dichloromethane measured at low
9
temperature (77 K), exhibiting structured spectra profiles. Furthermore, regarding the highest-energy vibronic sub-band of this spectra as the transition energy of T1 → S0, the ET were 2.60 eV for DCzPBI, 2.59 eV for POCzPBI, and 2.62 eV for DPOPBI, respectively. In virtue of the higher triplet energy levels, they can be considered as the suitable host compounds for blue to red phosphors [26,50].
Insert Table 1 Table 1 Thermal, photophysical, and electrochemical properties of the three compounds.
2.3. Theoretical calculations In order to obtain more insight into the feature of excited states of DCzPBI, POCzPBI, and DPOPBI, the structure optimization and frontier molecular orbitals of them were gained with the Gaussian 09 package [51] at the B3LYP level [52,53]. The optimized molecular configurations and electron density distributions for DCzPBI, POCzPBI, and DPOPBI were presented in Fig. 3. Taking DPOPBI for instance, the HOMO was mainly localized on the phenylbenzimidazole moiety. While the LUMO was mostly resided on the 1, 2-diphenyl-H-benzoimidazole, with there being a small distribution from diphenylphosphoryl oxide fragment. For DCzPBI and POCzPBI,
10
similar HOMOs and LUMOs regarding the orbital features were gained, the HOMOs contributed mainly from the phenylbenzimidazole and carbazole moieties, while the LUMOs contributed mainly from the 1, 2-diphenyl-H-benzoimidazole and therefore they exhibited similar HOMO and LUMO energies.
Insert Fig. 3 Fig. 3. Contours and energy levels of frontier molecular orbitals of DCzPBI, POCzPBI, and DPOPBI.
2.4. Electrochemical properties We also studied the electrochemical properties of DCzPBI, POCzPBI, and DPOPBI in dilute CH2Cl2 by using cyclic voltammetry (CV) (Fig. S4). All of the compounds showed irreversible oxidation peaks in dichloromethane. The HOMO values obtained from the onset oxidation potentials were 5.38, 5.37, 6.05 eV for DCzPBI, POCzPBI, and DPOPBI, respectively. The LUMO energy levels were measured to be 2.06, 2.08, 2.53 eV for DCzPBI, POCzPBI, and DPOPBI, respectively, depending on HOMO values and optical energy levels [8]. The data were in consistent with DFT calculations presented in previous section. Consequently, the compounds as host materials can facilitate charge injection (hole and electron) to
11
realize balanced charge carrier transporting.
2.5. Electroluminescence properties It was generally known that the device performances were relevant to the carrier injecting and transporting characters [54,55]. The electron affinities (EA) and ionization potentials (IP) were primary factors affecting the abilities of charge injection [47,56]. In order to study the influences of the carbazole and diphenylphosphoryl oxide moieties of the compounds on the charge injecting and transporting characters, some important parameters such as IP, EA, and the reorganization energy (λ) were obtained according to the theoretical calculations. A schematic diagram of the calculated parameters was showed in Fig. S5. Moreover, the values of calculated hole (HEP) and electron extraction potential (EEP) were also shown in Table 2. Compared to DCzPBI, POCzPBI and DPOPBI exhibited significant
increase
in
EA,
demonstrating
that
the
incorporation
of
diphenylphosphoryl oxide unites endowed the compounds with improved electron transport ability. To confirm this issue, the hole- and electron-only devices by employing the compounds were constructed to further discuss their hole and electron transporting features. The single-carrier transport devices had the configurations of ITO/MoO3 (5 nm)/TAPC (40 nm)/Host (20 nm)/TAPC (40 nm)/MoO3 (5 nm)/Ag (120 nm) and ITO/LiF (2 nm)/TmPyPB (40 nm)/Host (20 nm)/TmPyPB (40 nm)/LiF (2 nm)/Ag:Mg (1:15 120 nm) (Fig. 4). Obviously, all the three host materials had the lower hole current density. However, in contrast to DCzPBI, DPOPBI and POCzPBI exhibited enhanced electron current density and showed more balanced transport property, which was in good accordance with the results obtained from theoretical
12
calculations (see Table 2). Therefore, it was speculated that DPOPBI and POCzPBIhosted devices may be more superior in widening the exciton recombination zone of the emitting layer to reduce the concentration quenching and thus alleviate efficiency roll-offs [57,58].
Insert Table 2 Table 2 Summary of the important parameters affecting the abilities of charge injecting and transporting, including IP, HEP, EA, EEP, λhole and λelectron. The units in eV.
Insert Fig. 4 Fig. 4. J−V characteristics of the single-carrier devices for DCzPBI, POCzPBI, and DPOPBI.
The
excellent
thermal
stabilities,
photophysical
properties,
matched
HOMO/LUMO levels, and excellent carrier transport characters, encouraged us to fabricate full-color phosphorescent devices incorporating DCzPBI, POCzPBI, and DPOPBI as universal hosts. Firstly, we fabricated the blue OLEDs B1-B3 employing FIrpic as the guest possessing the structure of ITO/MoO3 (3 nm)/TAPC (35 nm)/TCTA (5 nm)/host:10 wt% FIrpic (20 nm)/TmPyPB (40 nm)/LiF (0.5 nm)/Ag:Mg (1:15, 120 nm). Here, TAPC and TmPyPB were employed as the
13
transporting emitting layers. MoO3 and LiF acted as the injecting emitting layers. TCTA used as a buffer layer to promote hole injection and block electron drifting out of hosts. The energy level diagrams and chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs were shown in Fig. 5. The current density-voltage-luminance (J−V−L) properties and efficiency-brightness curves of DCzPBI, POCzPBI, and DPOPBI-hosted devices were described in Fig. 6a, b and the electroluminescence (EL) results were listed in Table 3. Device B3 using DPOPBI as host realized the best EL efficiencies with a peak CE value of 23.2 cd A−1, a peak PE value of 24.4 lm W−1, and a peak EQE value of 11.5%. The highest efficiencies of the device B3 based on DPOPBI may be ascribed to the highest ET and favorable carrier transporting features. In addition, we also constructed green, yellow, and red PhOLEDs employing the identical device configuration but different phosphors, for instance, Ir(ppy)3, PO-01, (MDQ)2Ir(acac), respectively, to verify their potential as universal emitters host. The corresponding dopant concentration was optimized as 10 wt% for green, 7 wt% for yellow, 5 wt% for red phosphorescent devices [57,59,60].
Insert Fig. 5 Fig. 5. a) Energy level diagrams of the PhOLEDs hosted by DCzPBI, POCzPBI, and
14
DPOPBI. b) The chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs, including FIrpic, Ir(ppy)3, PO-01, (MDQ)2Ir(acac).
Devices G1-G3 using Ir(ppy)3 as phosphors emitted bright green light, corresponding the CIE coordinates of (0.31, 0.61), (0.31, 0.61), and (0.31, 0.61). As depicted in Fig. 6c, d, low turn-on voltages of 2.2, 2.5, 2.5 V were achieved for DCzPBI-hosted G1, POCzPBI-hosted G2, and DPOPBI-hosted G3, respectively. Additionally, for display and indoor lighting, they exhibited low driving voltages at 100 cd m−2 and 1000 cd m−2 at the same time. They were as low as 3.1/4.0, 2.9/3.5, 3.1/3.7 V for G1, G2, and G3, respectively. The maximum brightness (Lmax) reached to >100000 cd m−2. The green devices displayed the promising efficiencies of 48.4 cd A−1, 50.6 lm W−1, and 13.8% for G2 and 47.4 cd A−1, 42.6 lm W−1, and 13.7% for G3. Inspiringly, G2 and G3 exhibited minor efficiency roll-off of only 3% and 2% for EQE at 1000 cd m−2. Except for possessing the effective carrier transport feature in PhOLEDs, we ascribed the favorable performance to the efficient exciton confinement in the emitting layer as well. As illustrated in Fig. 6c inset, the absence of the emission stemming from adjacent emitting layers implied that TCTA and TmPyPB could be served as important block layers to confine the excitons within the emitting region [61,62].
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Insert Fig. 6 Fig. 6. a) J−V−L characteristics of B1-B3. Inset: the EL spectra. b) Efficienciesluminance curves of devices B1-B3. c) J−V−L curves of G1-G3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices G1-G3.
Then, the yellow emitter PO-01 and red emitter (MDQ)2Ir(acac) were utilized to further discuss the universality of host materials without changing the device configuration. The related device performances were given in Fig. 7. The favorable efficiencies of 39.6 cd A−1, 41.5 lm W−1, and 12.7% for O2 and 45.7 cd A−1, 35.6 lm W−1, and 15.0% for O3 were achieved by the yellow devices. It is noteworthy that the PhOLEDs exhibited negligible efficiency roll-offs with the increase of brightness. Even at 1000 cd m−2, the CE maintained as high as 38.2 and 45.6 cd A−1, coupled with minor efficiency roll-offs of only 3%, and 0.2%, respectively, verifying DPOPBI that can be acted as the most effective yellow host. Its red device also exhibited the promising efficiencies of 21.5 cd A−1, 19.3 lm W−1, and 13.5% and small CE roll-off of 13% at 1000 cd m−2. These data demonstrated that the DPOPBI- and POCzPBIhosted devices exhibited the much better OLEDs efficiency than those of DCzPBIhosted devices, which were predominantly ascribed to the moderately bipolar
16
character of DPOPBI and POCzPBI, leading to balanced carrier transporting abilities and widened recombination zone. Conventional devices are almost hole-predominant devices, Ir3+ complexes usually exhibit intense trapping capability, the appropriate electron-predominant transporting in host materials can promote balanced charge transport [63,64]. Thus, it is believed that manipulating the carrier transporting characters of the phosphorescent hosts is significant for accurately satisfying the basic requirement of the OLEDs.
Insert Fig. 7 Fig. 7. a) J−V−L curves of O1-O3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices O1-O3. c) J−V−L curves of R1-R3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices R1-R3.
Insert Table 3 Table 3 EL data of the phosphorescent devices hosted by DCzPBI, POCzPBI, and DPOPBI.
3. Conclusions In summary, we have synthesized novel HPBI-based hosts, DCzPBI, POCzPBI,
17
and DPOPBI, comprising carbazole and diphenylphosphoryl oxide moieties. Among them, DPOPBI and POCzPBI can be considered as the most effective universal hosts for high performance PhOLEDs, in view of the outstanding thermal properties, matched energy levels, and balanced carrier transporting. The blue, green, yellow, and red PhOLEDs with CE of 23.2, 48.4, 45.7, 21.5 cd A−1 have been achieved by using DPOPBI and POCzPBI as the hosts. In addition, all the devices showed low driving voltages and minor efficiency roll-offs with the increase of brightness, which may be ascribed to reduced intermolecular interaction in dopant-dopant and host-dopant and balanced charge transporting feature. The excellent device performances obtained with simple device configuration implied that these carbazole and diphenylphosphoryl oxide based hosts had great potential for the applications in full-color highperformance phosphorescent devices.
Acknowledgments The authors gratefully acknowledge the financial support form National Natural Science Foundation of China (21303012 and 61474054), the Fundamental Research Funds for the Central Universities (2412019FZ012 and 2412019QD007), and China Postdoctoral Science Foundation funded project (2019M551184).
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References [1] M.A. Baldo, D.F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M.E. Thompson, S.R. Forrest, Nature 395 (1998) 151. [2] Y.T. Tao, Q.A. Wang, C.L. Yang, C. Zhong, J.G. Qin, D.G. Ma, Adv. Funct. Mater. 20 (2010) 2923. [3] S.C. Lo, R.E. Harding, C.P. Shipley, S.G. Stevenson, P.L. Burn, I.D. Samuel, J. Am. Chem. Soc. 131 (2009) 16681. [4] Y. Sun, X. Yang, Z. Feng, B. Liu, D. Zhong, J. Zhang, G. Zhou, Z. Wu, ACS Appl. Mater. Interfaces 11 (2019) 26152. [5] C. Fan, C. Yang, Chem. Soc. Rev. 43 (2014) 6439. [6] A. Haldi, A. Kimyonok, B. Domercq, L.E. Hayden, S.C. Jones, S.R. Marder, M. Weck, B. Kippelen, Adv. Funct. Mater. 18 (2008) 3056. [7] J. Ding, B. Wang, Z. Yue, B. Yao, Z. Xie, Y. Cheng, L. Wang, X. Jing, F. Wang, Angew. Chem., Int. Ed. 48 (2009) 6664. [8] T.S. Qin, J.Q. Ding, L.X. Wang, M. Baumgarten, G. Zhou, K. Mullen, J. Am. Chem. Soc. 131 (2009) 14329. [9] G.Z. Lu, Q. Zhu, L. Liu, Z.G. Wu, Y.X. Zheng, L. Zhou, J.L. Zuo, H. Zhang, ACS Appl. Mater. Interfaces 11 (2019) 20192. [10] T. Ito, H. Sasabe, Y. Nagai, Y. Watanabe, N. Onuma, J. Kido, Chem. Eur. J. 25 (2019) 7308. [11] H. Shin, Y.H. Ha, H.G. Kim, R. Kim, S.K. Kwon, Y.H. Kim, J.J. Kim, Adv. Mater. 31 (2019) 1808102. [12] J. Lin, Y. Wang, P. Gnanasekaran, Y.-C. Chiang, C.-C. Yang, C.-H. Chang, S.-H. Liu, G.-H. Lee, P.-T. Chou, Y. Chi, S.-W. Liu, Adv. Funct. Mater. 27 (2017) 1702856.
19
[13] F.-M. Hsu, C.-H. Chien, C.-F. Shu, C.-H. Lai, C.-C. Hsieh, K.-W. Wang, P.-T. Chou, Adv. Funct. Mater. 19 (2009) 2834. [14] M. Sudhakar, P.I. Djurovich, T.E. Hogen-Esch, M.E. Thompson, J. Am. Chem. Soc. 125 (2003) 7796. [15] H. Inomata, K. Goushi, T. Masuko, T. Konno, T. Imai, H. Sasabe, J.J. Brown, C. Adachi, Chem. Mater. 16 (2004) 1285. [16] S. Tokito, K. Noda, H. Fujikawa, Y. Taga, M. Kimura, K. Shimada, Y. Sawaki, Appl. Phys. Lett. 77 (2000) 160. [17] C.T. Chen, Y. Wei, J.S. Lin, M.V. Moturu, W.S. Chao, Y.T. Tao, C.H. Chien, J. Am. Chem. Soc. 128 (2006) 10992. [18] F.K. Kong, M.C. Tang, Y.C. Wong, M.Y. Chan, V.W. Yam, J. Am. Chem. Soc. 138 (2016) 6281. [19] I.S. Park, H. Seo, H. Tachibana, J.U. Kim, J. Zhang, S.M. Son, T. Yasuda, ACS Appl. Mater. Interfaces 9 (2017) 2693. [20] S. Gong, Y. Chen, C. Yang, C. Zhong, J. Qin, D. Ma, Adv. Mater. 22 (2010) 5370. [21] J. Zhao, G.H. Xie, C.R. Yin, L.H. Xie, C.M. Han, R.F. Chen, H. Xu, M.D. Yi, Z.P. Deng, S.F. Chen, Y. Zhao, S.Y. Liu, W. Huang, Chem. Mater. 23 (2011) 5331. [22] W.C. Chen, Y. Yuan, Z.L. Zhu, S.F. Ni, Z.Q. Jiang, L.S. Liao, F.L. Wong, C.S. Lee, Chem. Commun. 54 (2018) 4541. [23] S. Thiery, D. Tondelier, C. Declairieux, B. Geffroy, O. Jeannin, R. Métivier, J. Rault-Berthelot, C. Poriel, J. Phys. Chem. C 119 (2015) 5790. [24] Y. Zhao, C. Wu, P. Qiu, X. Li, Q. Wang, J. Chen, D. Ma, ACS Appl. Mater. Interfaces 8 (2016) 2635.
20
[25] J. Li, D. Ding, Y. Tao, Y. Wei, R. Chen, L. Xie, W. Huang, H. Xu, Adv. Mater. 28 (2016) 3122. [26] L.S. Cui, J.U. Kim, H. Nomura, H. Nakanotani, C. Adachi, Angew. Chem., Int. Ed. 55 (2016) 6864. [27] D. Zhang, M. Cai, Z. Bin, Y. Zhang, D. Zhang, L. Duan, Chem. Sci. 7 (2016) 3355. [28] J. Zhang, D. Ding, Y. Wei, H. Xu, Chem. Sci. 7 (2016) 2870. [29] E. Mondal, W.-Y. Hung, H.-C. Dai, K.-T. Wong, Adv. Funct. Mater. 23 (2013) 3096. [30] D. Zhang, X. Song, M. Cai, H. Kaji, L. Duan, Adv. Mater. 30 (2018) 1705406. [31] S.M. Kim, J.H. Yun, S.H. Han, J.Y. Lee, J. Mater. Chem. C 5 (2017) 9072. [32] Z. Zhao, G. Yu, Q. Chang, X. Liu, Y. Liu, L. Wang, Z. Liu, Z. Bian, W. Liu, C. Huang, J. Mater. Chem. C 5 (2017) 7344. [33] H.H. Chou, C.H. Cheng, Adv. Mater. 22 (2010) 2468. [34] Y.T. Tao, Q. Wang, L. Ao, C. Zhong, J.G. Qin, C.L. Yang, D.G. Ma, J. Mater. Chem. 20 (2010) 1759. [35] X. Lv, W. Zhang, D. Ding, C. Han, Z. Huang, S. Xiang, Q. Zhang, H. Xu, L. Wang, Adv. Opt. Mater. 6 (2018) 1800165. [36] C.J. Shih, C.C. Lee, T.H. Yeh, S. Biring, K.K. Kesavan, N.R.A. Amin, M.H. Chen, W.C. Tang, S.W. Liu, K.T. Wong, ACS Appl. Mater. Interfaces 10 (2018) 24090. [37] S.L. Gong, Y.H. Chen, J.J. Luo, C.L. Yang, C. Zhong, J.G. Qin, D.G. Ma, Adv. Funct. Mater. 21 (2011) 1168. [38] J. Jin, Y. Tao, H. Jiang, R. Chen, G. Xie, Q. Xue, C. Tao, L. Jin, C. Zheng, W. Huang, Adv. Sci. 5 (2018) 1800292.
21
[39] Y.T. Tao, Q. Wang, C.L. Yang, C. Zhong, K. Zhang, J.G. Qin, D.G. Ma, Adv. Funct. Mater. 20 (2010) 304. [40] Y. Tao, Q. Wang, L. Ao, C. Zhong, C. Yang, J. Qin, D. Ma, J. Phys. Chem. C 114 (2009) 601. [41] L.S. Cui, S.B. Ruan, F. Bencheikh, R. Nagata, L. Zhang, K. Inada, H. Nakanotani, L.S. Liao, C. Adachi, Nat. Commun. 8 (2017) 2250. [42] S. Liu, X. Zhang, C. Ou, S. Wang, X. Yang, X. Zhou, B. Mi, D. Cao, Z. Gao, ACS Appl. Mater. Interfaces 9 (2017) 26242. [43] S.-h. Ye, L. Li, M. Zhang, Z. Zhou, M.-h. Quan, L.-F. Guo, Y. Wang, M. Yang, W.-y. Lai, W. Huang, J. Mater. Chem. C 5 (2017) 11937. [44] S. Hu, J. Zeng, X. Zhu, J. Guo, S. Chen, Z. Zhao, B.Z. Tang, ACS Appl. Mater. Interfaces 11 (2019) 27134. [45] Q. Liang, C. Han, C. Duan, H. Xu, Adv. Opt. Mater. (2018) 1800020. [46] H.T. Mao, C.X. Zang, G.G. Shan, H.Z. Sun, W.F. Xie, Z.M. Su, Inorg. Chem. 56 (2017) 9979. [47] G.G. Shan, H.B. Li, H.Z. Sun, H.T. Cao, D.X. Zhu, Z.M. Su, Dalton Trans. 42 (2013) 11056. [48] H.T. Cao, H.Z. Sun, Y.M. Yin, X.M. Wen, G.G. Shan, Z.M. Su, R.L. Zhong, W.F. Xie, P. Li, D.X. Zhu, J. Mater. Chem. C 2 (2014) 2150. [49] S.-C. Dong, L. Zhang, J. Liang, L.-S. Cui, Q. Li, Z.-Q. Jiang, L.-S. Liao, J. Phys. Chem. C 118 (2014) 2375. [50] W. Li, J. Li, D. Liu, D. Li, F. Wang, ACS Appl. Mater. Interfaces 8 (2016) 21497. [51] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M.
22
Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.01, Gaussian, Inc., Wallingford CT, (2009). [52] A.D. Becke, J. Chem. Phys. 98 (1993) 5648. [53] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785. [54] G.M. Li, D.X. Zhu, T. Peng, Y. Liu, Y. Wang, M.R. Bryce, Adv. Funct. Mater. 24 (2014) 7420. [55] Y. Feng, P. Li, X. Zhuang, K. Ye, T. Peng, Y. Liu, Y. Wang, Chem. Commun. 51 (2015) 12544. [56] S.-F. Huang, H.-Z. Sun, G.-G. Shan, Y. Wu, M. Zhang, Z.-M. Su, New J. Chem. 40 (2016) 4635. [57] C. Zang, X. Peng, H. Wang, Z. Yu, L. Zhang, W. Xie, H. Zhao, Org. Electron. 50 (2017) 106. [58] J.Q. Ding, J.H. Lu, Y.X. Cheng, Z.Y. Xie, L.X. Wang, X.B. Jing, F.S. Wang, Adv. Funct. Mater. 18 (2008) 2754. [59] J. Yu, C.X. Zang, Z.W. Yu, H. Wang, S.H. Liu, L.T. Zhang, W.F. Xie, H.Y. Zhao, Org. Electron. 38 (2016) 301. 23
[60] Y. Tao, Q. Wang, C. Yang, Q. Wang, Z. Zhang, T. Zou, J. Qin, D. Ma, Angew. Chem., Int. Ed. 47 (2008) 8104. [61] D. Luo, X.-L. Li, Y. Zhao, Y. Gao, B. Liu, ACS Photonics 4 (2017) 1566. [62] B. Liu, H. Tao, L. Wang, D. Gao, W. Liu, J. Zou, M. Xu, H. Ning, J. Peng, Y. Cao, Nano Energy 26 (2016) 26. [63] C. Han, Z. Zhang, H. Xu, J. Li, G. Xie, R. Chen, Y. Zhao, W. Huang, Angew. Chem., Int. Ed. 51 (2012) 10104. [64] Y. Tao, C. Yang, J. Qin, Chem. Soc. Rev. 40 (2011) 2943.
24
Table Captions
Table 1 Thermal, photophysical, and electrochemical properties of the three compounds.
Table 2 Summary of the important parameters affecting the abilities of charge injecting and transporting, including IP, HEP, EA, EEP, λhole and λelectron. The units in eV.
Table 3 EL data of the phosphorescent devices hosted by DCzPBI, POCzPBI, and DPOPBI.
Table 1 Thermal, photophysical, and electrochemical properties of the three compounds. λabsa
λPLa
HOMOb
LUMOc
Egd
ETe
Tdf
Tgg
(nm)
(nm)
(eV)
(eV)
(V)
(eV)
(°C)
(°C)
DCzPBI
237, 293, 326
399
−5.38
−2.06
3.32
2.60
451
120
POCzPBI
230, 293, 330
406
−5.37
−2.08
3.29
2.59
436
127
DPOPBI
228, 305
373
−6.05
−2.53
3.52
2.62
434
135
host
a
Obtained in a CH2Cl2 at 298 K.
b
Estimated by electrochemical measurements.
c
ELUMO = EHOMO + Eg. d Optical band gap. e Collected in frozen dichloromethane at 77 K. f Decomposition temperature (corresponding to 5% weight loss). g Glass-transition temperature.
Table 2 Summary of the important parameters affecting the abilities of charge injecting and transporting, including IP, HEP, EA, EEP, λhole and λelectron. The units in eV. compound
IP
HEP
EA
EEP
λhole
λelectron
DCzPBI
6.43
6.32
0.52
0.22
0.11
0.30
POCzPBI
7.25
6.76
0.86
0.35
0.49
0.50
DPOPBI
6.49
6.25
0.66
0.25
0.25
0.40
Table 3 EL data of the phosphorescent devices hosted by DCzPBI, POCzPBI, and DPOPBI. device
host
guest
Vturn-ona
Lmaxb
CEc
PEd
EQEe
Efficiency roll-offsf
[V]
[cd m−2]
[cd A−1]
[lm W−1]
[%]
[%] CE
PE
EQE
B1
DCzPBI
FIrpic
2.8/4.2/6.3
2170
9.5/2.8
10.8/1.4
4.9/1.4
70
87
71
B2
POCzPBI
FIrpic
2.9/4.0/5.3
11030
12.1/8.5
12.7/4.9
5.9/4.1
30
61
30
B3
DPOPBI
FIrpic
2.7/3.7/4.8
18457
23.2/14.2
24.4/9.2
11.5/7.1
39
62
38
G1
DCzPBI
Ir(ppy)3
2.2/3.1/4.0
58530
45.8/36.2
47.8/27.2
13.2/10.5
21
43
20
G2
POCzPBI
Ir(ppy)3
2.5/2.9/3.5
101115
48.4/46.8
50.6/41.1
13.8/13.4
3
19
3
G3
DPOPBI
Ir(ppy)3
2.5/3.1/3.7
91224
47.4/46.4
42.6/39.4
13.7/13.4
2
7
2
O1
DCzPBI
PO-01
2.5/3.1/3.7
84338
36.8/24.7
25.7/20.8
11.6/7.9
33
19
32
O2
POCzPBI
PO-01
2.5/2.8/3.5
75806
39.6/38.2
41.5/34.0
12.7/12.1
3
18
5
O3
DPOPBI
PO-01
2.8/3.5/4.4
71106
45.7/45.6
35.6/32.6
15.0/14.9
0.2
8.4
0.7
R1
DCzPBI
Ir(MDQ)2 3.1/4.7/6.5
8891
9.2/4.8
8.2/2.3
6.2/3.1
48
72
50
R2
POCzPBI Ir(MDQ)2 3.0/4.1/5.3
41877
15.4/12.7
13.8/7.5
10.4/8.2
17
46
21
R3
DPOPBI
Ir(MDQ)2 3.0/3.9/5.0
58249
21.5/18.7
19.3/11.8
13.5/11.3
13
39
16
a
Turn-on voltage at 1 cd m−2.
b
Maximum brightness.
c
Order of CE values: peak
values, then values at 1000 cd m−2. d Order of PE values: peak values, then values at 1000 cd m−2.
e
Order of EQE values: peak values, then values at 1000 cd m−2.
Efficiency roll-offs at 1000 cd m−2.
f
Figure Captions
Scheme 1. Chemical structures of DCzPBI, POCzPBI, and DPOPBI. Scheme 2. Synthetic procedures of DCzPBI, POCzPBI, and DPOPBI. i) DMA, 1 h, CH3COOH, 12 h; ii) carbazole, CuI, K2CO3, DMPU, 18-Crown-6, 12 h; iii) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h; iv) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h, carbazole, CsCO3, DMF, 12 h. Fig. 1. DSC curves for DCzPBI, POCzPBI, and DPOPBI collected at a heating rate of 10 °C min−1. Fig. 2. Electronic absorption and the emission spectra of DCzPBI, POCzPBI, and DPOPBI in dichloromethane solution (10−5 mol L−1). Inset: phosphorescence (PH) spectra in dichloromethane at low temperature (77 K). Fig. 3. Contours and energy levels of frontier molecular orbitals of DCzPBI, POCzPBI, and DPOPBI. Fig. 4. J−V characteristics of the single-carrier devices for DCzPBI, POCzPBI, and DPOPBI. Fig. 5. a) Energy level diagrams of the PhOLEDs hosted by DCzPBI, POCzPBI, and DPOPBI. b) The chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs, including FIrpic, Ir(ppy)3, PO-01, (MDQ)2Ir(acac). Fig. 6. a) J−V−L characteristics of B1-B3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices B1-B3. c) J−V−L curves of G1-G3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices G1-G3.
Fig. 7. a) J−V−L curves of O1-O3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices O1-O3. c) J−V−L curves of R1-R3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices R1-R3.
Scheme 1. Chemical structures of DCzPBI, POCzPBI, and DPOPBI.
Scheme 2. Synthetic procedures of DCzPBI, POCzPBI, and DPOPBI. i) DMA, 1 h, CH3COOH, 12 h; ii) carbazole, CuI, K2CO3, DMPU, 18-Crown-6, 12 h; iii) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h; iv) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h, carbazole, CsCO3, DMF, 12 h.
Fig. 1. DSC curves for DCzPBI, POCzPBI, and DPOPBI collected at a heating rate of 10 °C min−1.
Fig. 2. Electronic absorption and the emission spectra of DCzPBI, POCzPBI, and DPOPBI in dichloromethane solution (10−5 mol L−1). Inset: phosphorescence (PH) spectra in dichloromethane at low temperature (77 K).
Fig. 3. Contours and energy levels of frontier molecular orbitals of DCzPBI, POCzPBI, and DPOPBI.
Fig. 4. J−V characteristics of the single-carrier devices for DCzPBI, POCzPBI, and DPOPBI.
Fig. 5. a) Energy level diagrams of the PhOLEDs hosted by DCzPBI, POCzPBI, and DPOPBI. b) The chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs, including FIrpic, Ir(ppy)3, PO-01, (MDQ)2Ir(acac).
Fig. 6. a) J−V−L characteristics of B1-B3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices B1-B3. c) J−V−L curves of G1-G3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices G1-G3.
Fig. 7. a) J−V−L curves of O1-O3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices O1-O3. c) J−V−L curves of R1-R3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices R1-R3.
Highlights The hosts consisting carbazole and diphenylphosphoryl oxide were designed. The relationship between the structures and EL performances were studied. They can be applied as universal hosts in highly efficient full-color PhOLEDs. DPOPBI and POCzPBI exhibited good charge carrier transporting properties. Yellow device showed extremely low efficiency roll-off of only 0.2%.
S1566-1199(19)30540-3
DOI:
https://doi.org/10.1016/j.orgel.2019.105513
Reference:
ORGELE 105513
To appear in:
Organic Electronics
Received Date: 18 August 2019 Revised Date:
26 September 2019
Accepted Date: 16 October 2019
Please cite this article as: H.-T. Mao, W.-L. Song, C.-X. Zang, G.-F. Li, G.-G. Shan, H.-Z. Sun, W.-F. Xie, Z.-M. Su, Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient full-color PhOLEDs, Organic Electronics (2019), doi: https://doi.org/10.1016/ j.orgel.2019.105513. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient fullcolor PhOLEDs Hui-Ting Mao,a Wei-Lin Song,a Chun-Xiu Zang,b Guang-Fu Li,a Guo-Gang Shan,a,* Hai-Zhu Sun,a Wen-Fa Xie,b,** Zhong-Min Su,a,c***
a
Institute of Functional Material Chemistry and National & Local United Engineering
Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China. b
State Key Laboratory on Integrated Optoelectronics, College of Electronic Science
and Engineering, Jilin University, Changchun, Jilin 130012, P. R. China. c
Jilin Provincial Science and Technology Innovation Center of Optical Materials and
Chemistry, School of Chemistry and Environmental Engineering, Changchun University of Science and Technology Changchun, 130022, P. R. China.
*
Corresponding author. Institute of Functional Material Chemistry and National &
Local United Engineering Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China. E-mail address: [email protected] (G.-G. Shan). **
Corresponding author. State Key Laboratory on Integrated Optoelectronics, College
of Electronic Science and Engineering, Jilin University, Changchun, Jilin 130012, P. R. China. E-mail address: [email protected] (W. Xie).
1
***
Corresponding author. Jilin Provincial Science and Technology Innovation Center
of Optical Materials and Chemistry, School of Chemistry and Environmental Engineering, Changchun University of Science and Technology Changchun, 130022, P. R. China. E-mail address: [email protected] (Z.-M. Su).
2
Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient fullcolor PhOLEDs Hui-Ting Mao,a Wei-Lin Song,a Chun-Xiu Zang,b Guang-Fu Li,a Guo-Gang Shan,a,* Hai-Zhu Sun,a Wen-Fa Xie,b,** Zhong-Min Su,a,c***
a
Institute of Functional Material Chemistry and National & Local United Engineering
Lab for Power Battery, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China. Email: [email protected] (G.-G. Shan); E-mail: [email protected] (Z.-M. Su) b
State Key Laboratory on Integrated Optoelectronics, College of Electronic Science
and Engineering, Jilin University, Changchun, Jilin 130012, P. R. China. E-mail: [email protected] (W. Xie) c
Jilin Provincial Science and Technology Innovation Center of Optical Materials and
Chemistry, School of Chemistry and Environmental Engineering, Changchun University of Science and Technology Changchun, 130022, P. R. China.
1
Abstract Many efforts have been focused on exploring highly efficient host materials that capable of function in phosphorescent organic light-emitting devices (PhOLEDs). However, superior hosts reported to date that are generally suitable to full-color devices are rare and the resultant device performances are far from satisfactory. A class of host compounds DCzPBI, POCzPBI, and DPOPBI, incorporating carbazole and diphenylphosphoryl oxide moieties as electron-donating and -accepting groups, respectively, are synthesized and successfully applied as universal hosts in the fabrication of full-color PhOLEDs. The effect of substituted groups on the photophysical, theoretical calculations, and electrochemical characters for host materials is systematically investigated. We adopt the same device architecture to fabricate the blue, green, yellow, and red PhOLEDs with the combination of the three hosts. As a result, DPOPBI and POCzPBI with good charge carrier transporting properties supported the devices with the impressive efficiencies. The best current efficiency (CE) are 23.2, 48.4, 45.7, 21.5 cd A−1 for blue, green, yellow, and red devices, respectively. Even at the brightnesses of 1000 cd m−2, the efficiency roll-offs are only 2% for green and 0.2% for yellow devices, indicating the promising applications as universal hosts for highly efficient PhOLEDs.
2
Keywords host material; phosphorescent organic light-emitting device; impressive efficiency; good charge carrier transporting property
3
1. Introduction Phosphorescent organic light-emitting diodes (PHOLEDs) are highly attractive owing to the high performances relative to those of conventional singlet fluorescent devices [1,2]. In principle, 100% internal quantum efficiency (IQE) can be achieved by effectively employing singlet and triplet excitons [3-5]. Generally, the triplet phosphors involve longer lifetimes for emission, which result in notorious selfquenching and triplet-triplet annihilation (TTA) [6-8]. Concerning this issue, the phosphorescent guest dyes are ordinarily dispersed in suitable host to suppress the intermolecular interaction-induced quenching, making the fabrication of high performance hosts fitting for guest dopants imperative [9-12]. Several significant conditions for host compounds should be satisfied: i) a larger triplet energy (ET) than the guest to sustain the positive energy transfer to the guest dopant [13-15]; ii) good thermal properties to guarantee device operation and fabrication [16]; iii) excellent charge carrier transport characters for exciton recombination and balanced charge flux in emissive layers (EMLs) [13,17,18]; iv) matched energy levels regarding highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) [19,20], thereby reducing the operation voltage and facilitating charge transporting. With an enhancing demand of device performances, particularly device efficiencies, a large amount of effort in the exploration of hosts is focus on 4
fundamental investigation of the structure property correlations. Some effective strategies, for example, unite integration, structure optimization, and molecular splicing have been successfully explored to obtain multifunctional host materials with a high T1 energy and considerable carrier transporting ability, significantly elevating the device performance. However, up to date, there are only few universal hosts that capable of function in full-color phosphorescent devices. Actually, the lack of universal hosts can be ascribed to a wide variety of molecular structures of guest dopants possessing different emission peaks, subsequently leading to worse intermolecular interactions in dopant-dopant and host-dopant. In this case, some molecules with spiro [21-23], twisted [24,25], unsymmetrical configurations [26-29] are adopted to construct hosts to restraining intermolecular interactions and suppressing TTA effects. Nevertheless, it is shown that the hosts based on these kinds of structures could not supply satisfied hole and electron transport capability and subsequently result in serious efficiency roll-offs.
Insert Scheme 1 Scheme 1. Chemical structures of DCzPBI, POCzPBI, and DPOPBI.
Recently, research focus have tended to the development of multifunctional hosts possessing both electron-donating and -accepting moieties. The combination of these functional moieties as steric hindrance can efficiently reduce intermolecular interaction and achieve balanced charge fluxes at the same time. The electrondonating moieties are mainly carbazole [30-33], triphenylamine [34-36], and diphenylamine [37,38]. The electron-accepting moieties mainly include oxadiazole [2,39], triazole [40], triazine [41], pyridine [42-44], and phosphine oxide [21,45].
5
Among these donating and accepting moieties, the carbazole and diphenylphosphoryl oxide groups exhibit good charge carrier transporting properties. On the other hand, 1,2-diphenyl-H-benzoimidazole (HPBI) have been widely reported as building block due to easy synthesis and chemical modificaton [46-48]. For the purpose of developing outstanding host compounds suitable for highly efficient full-color PhOLEDs and explore the intrinsic structure-property relationships for further molecular design, herein, we designed and synthesized three novel hosts, DCzPBI, POCzPBI,
and
DPOPBI
by
integrating
HPBI
with
carbazole
and
diphenylphosphoryl oxide units (see Scheme 1). By virtue of the steric hindrance, considerable carrier transporting ability and appropriate energy level of these functional moieties, the resulting materials were expected to be the excellent host materials for PhOLEDs. The effect of substituted unites on the thermal, photophysicl, and electrochemical characters of the compounds was systematically studied. Through introducing
the
functional
moieties,
promising
electroluminescence
(EL)
performances of the blue, green, yellow, and red devices with the combination of the host compounds were achieved. Among these compounds, DPOPBI and POCzPBI with good charge carrier transporting properties supported the devices with the impressive efficiencies. The best current efficiency (CE) were 23.2, 48.4, 45.7, 21.5 cd A−1 for blue, green, yellow, and red devices, respectively. In addition, all the devices realized minor efficiency roll-offs with the increase of luminance, especially, the efficiency roll-offs were only 2% for green, 0.2% for yellow devices.
6
Insert Scheme 2 Scheme 2. Synthetic procedures of DCzPBI, POCzPBI, and DPOPBI. i) DMA, 1 h, CH3COOH, 12 h; ii) carbazole, CuI, K2CO3, DMPU, 18-Crown-6, 12 h; iii) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h; iv) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h, carbazole, CsCO3, DMF, 12 h.
2. Results and discussion 2.1. Synthesis and thermal properties Synthetic procedures and chemical structures of the hosts were presented in Scheme 2. The detailed synthetic procedures of a (Scheme S1) (ESI), b, and c were described in supporting information. The molecule configurations of DCzPBI, POCzPBI, and DPOPBI were confirmed by 1H NMR and mass spectra. The rigid chemical structures of hosts compounds endowed them with good thermal and morphological properties by using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The host materials depicted favorable decomposition temperatures (Td) of 451 °C for DCzPBI, 436 °C for POCzPBI, and 434 °C for DPOPBI, indicating that they can be enduring by vacuum deposition and fufilling the demand of the hosts to be adopted in devices [19,49]. Additionally, the glass-transition temperatures (Tg) were estimated to be 120 °C for DCzPBI, 127 °C for POCzPBI, and 135 °C for DPOPBI according to the DSC curves (see Fig. 1). The favorable thermal properties are of importance for the hosts because they can reduce potential phase separation between hosts and guest dopants [24].
7
Insert Fig. 1 Fig. 1. DSC curves for DCzPBI, POCzPBI, and DPOPBI collected at a heating rate of 10 °C min−1.
2.2. Photophysical properties The absorption and photoluminescence (PL) spectra of DCzPBI, POCzPBI, and DPOPBI in CH2Cl2 were presented in Fig. 2. The pertinent photophysical and electrochemical parameters were listed in Table 1. The strong absorption peaks (at about 290 nm) for DCzPBI and POCzPBI could be attributed to the carbazolecentered π-π* transition. To better comprehend the feature of the excited states of the compounds, the simulated absorption spectra were calculated and presented in supporting information (see Fig. S1-S3), which were consistent with the experiment data. The calculated orbital excitation analyses and oscillator strength (f) of the three compounds were given in Table S1-S3. In the case of DCzPBI (Fig. S1 and Table S1), the HOMO, HOMO-4 involved in the main excitations predominantly located on 1, 2-diphenyl-H-benzoimidazole and one of the carbazole moieties, while HOMO-1 resided on one of the carbazole unites with there being a small distribution from adjacent benzene ring. For the LUMO, it resided on 1, 2-diphenyl-H-benzoimidazole with a part contribution from carbazole groups. On the basis of the calculated results,
8
the absorption band (band 1) between 230 and 250 nm originated mainly from the excitation of HOMO → LUMO+8, HOMO-5 → LUMO+2, and HOMO-1 → LUMO+7. Correspondingly, they were predominantly ascribed to the carbazolecentered π-π* transition. Furthermore, the band 2 and band 3 in low-energy region at around 290 and 350 nm resulted from the excitation of HOMO-4 → LUMO, HOMO1 → LUMO+3, and HOMO → LUMO. Thus, these absorption bands were mostly assigned to the π-π* transition from one of the carbazoles to the 1, 2-diphenyl-Hbenzoimidazole moiety, which were in agreement with the experimental section mentioned above. The corresponding assignments, including POCzPBI and DPOPBI, could be also obtained from the TD-DFT results (Fig. S2, S3 and Table S2, S3).
Insert Fig. 2 Fig. 2. Electronic absorption and the emission spectra of DCzPBI, POCzPBI, and DPOPBI in dichloromethane solution (10−5 mol L−1). Inset: phosphorescence (PH) spectra in dichloromethane (10−6 mol L−1) at low temperature (77 K).
The emission wavelengths of the hosts were 399 nm (DCzPBI), 406 nm (POCzPBI), and 373 nm (DPOPBI), respectively. Inset of Fig. 2 depicted the phosphorescence spectra of the hosts in frozen dichloromethane measured at low
9
temperature (77 K), exhibiting structured spectra profiles. Furthermore, regarding the highest-energy vibronic sub-band of this spectra as the transition energy of T1 → S0, the ET were 2.60 eV for DCzPBI, 2.59 eV for POCzPBI, and 2.62 eV for DPOPBI, respectively. In virtue of the higher triplet energy levels, they can be considered as the suitable host compounds for blue to red phosphors [26,50].
Insert Table 1 Table 1 Thermal, photophysical, and electrochemical properties of the three compounds.
2.3. Theoretical calculations In order to obtain more insight into the feature of excited states of DCzPBI, POCzPBI, and DPOPBI, the structure optimization and frontier molecular orbitals of them were gained with the Gaussian 09 package [51] at the B3LYP level [52,53]. The optimized molecular configurations and electron density distributions for DCzPBI, POCzPBI, and DPOPBI were presented in Fig. 3. Taking DPOPBI for instance, the HOMO was mainly localized on the phenylbenzimidazole moiety. While the LUMO was mostly resided on the 1, 2-diphenyl-H-benzoimidazole, with there being a small distribution from diphenylphosphoryl oxide fragment. For DCzPBI and POCzPBI,
10
similar HOMOs and LUMOs regarding the orbital features were gained, the HOMOs contributed mainly from the phenylbenzimidazole and carbazole moieties, while the LUMOs contributed mainly from the 1, 2-diphenyl-H-benzoimidazole and therefore they exhibited similar HOMO and LUMO energies.
Insert Fig. 3 Fig. 3. Contours and energy levels of frontier molecular orbitals of DCzPBI, POCzPBI, and DPOPBI.
2.4. Electrochemical properties We also studied the electrochemical properties of DCzPBI, POCzPBI, and DPOPBI in dilute CH2Cl2 by using cyclic voltammetry (CV) (Fig. S4). All of the compounds showed irreversible oxidation peaks in dichloromethane. The HOMO values obtained from the onset oxidation potentials were 5.38, 5.37, 6.05 eV for DCzPBI, POCzPBI, and DPOPBI, respectively. The LUMO energy levels were measured to be 2.06, 2.08, 2.53 eV for DCzPBI, POCzPBI, and DPOPBI, respectively, depending on HOMO values and optical energy levels [8]. The data were in consistent with DFT calculations presented in previous section. Consequently, the compounds as host materials can facilitate charge injection (hole and electron) to
11
realize balanced charge carrier transporting.
2.5. Electroluminescence properties It was generally known that the device performances were relevant to the carrier injecting and transporting characters [54,55]. The electron affinities (EA) and ionization potentials (IP) were primary factors affecting the abilities of charge injection [47,56]. In order to study the influences of the carbazole and diphenylphosphoryl oxide moieties of the compounds on the charge injecting and transporting characters, some important parameters such as IP, EA, and the reorganization energy (λ) were obtained according to the theoretical calculations. A schematic diagram of the calculated parameters was showed in Fig. S5. Moreover, the values of calculated hole (HEP) and electron extraction potential (EEP) were also shown in Table 2. Compared to DCzPBI, POCzPBI and DPOPBI exhibited significant
increase
in
EA,
demonstrating
that
the
incorporation
of
diphenylphosphoryl oxide unites endowed the compounds with improved electron transport ability. To confirm this issue, the hole- and electron-only devices by employing the compounds were constructed to further discuss their hole and electron transporting features. The single-carrier transport devices had the configurations of ITO/MoO3 (5 nm)/TAPC (40 nm)/Host (20 nm)/TAPC (40 nm)/MoO3 (5 nm)/Ag (120 nm) and ITO/LiF (2 nm)/TmPyPB (40 nm)/Host (20 nm)/TmPyPB (40 nm)/LiF (2 nm)/Ag:Mg (1:15 120 nm) (Fig. 4). Obviously, all the three host materials had the lower hole current density. However, in contrast to DCzPBI, DPOPBI and POCzPBI exhibited enhanced electron current density and showed more balanced transport property, which was in good accordance with the results obtained from theoretical
12
calculations (see Table 2). Therefore, it was speculated that DPOPBI and POCzPBIhosted devices may be more superior in widening the exciton recombination zone of the emitting layer to reduce the concentration quenching and thus alleviate efficiency roll-offs [57,58].
Insert Table 2 Table 2 Summary of the important parameters affecting the abilities of charge injecting and transporting, including IP, HEP, EA, EEP, λhole and λelectron. The units in eV.
Insert Fig. 4 Fig. 4. J−V characteristics of the single-carrier devices for DCzPBI, POCzPBI, and DPOPBI.
The
excellent
thermal
stabilities,
photophysical
properties,
matched
HOMO/LUMO levels, and excellent carrier transport characters, encouraged us to fabricate full-color phosphorescent devices incorporating DCzPBI, POCzPBI, and DPOPBI as universal hosts. Firstly, we fabricated the blue OLEDs B1-B3 employing FIrpic as the guest possessing the structure of ITO/MoO3 (3 nm)/TAPC (35 nm)/TCTA (5 nm)/host:10 wt% FIrpic (20 nm)/TmPyPB (40 nm)/LiF (0.5 nm)/Ag:Mg (1:15, 120 nm). Here, TAPC and TmPyPB were employed as the
13
transporting emitting layers. MoO3 and LiF acted as the injecting emitting layers. TCTA used as a buffer layer to promote hole injection and block electron drifting out of hosts. The energy level diagrams and chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs were shown in Fig. 5. The current density-voltage-luminance (J−V−L) properties and efficiency-brightness curves of DCzPBI, POCzPBI, and DPOPBI-hosted devices were described in Fig. 6a, b and the electroluminescence (EL) results were listed in Table 3. Device B3 using DPOPBI as host realized the best EL efficiencies with a peak CE value of 23.2 cd A−1, a peak PE value of 24.4 lm W−1, and a peak EQE value of 11.5%. The highest efficiencies of the device B3 based on DPOPBI may be ascribed to the highest ET and favorable carrier transporting features. In addition, we also constructed green, yellow, and red PhOLEDs employing the identical device configuration but different phosphors, for instance, Ir(ppy)3, PO-01, (MDQ)2Ir(acac), respectively, to verify their potential as universal emitters host. The corresponding dopant concentration was optimized as 10 wt% for green, 7 wt% for yellow, 5 wt% for red phosphorescent devices [57,59,60].
Insert Fig. 5 Fig. 5. a) Energy level diagrams of the PhOLEDs hosted by DCzPBI, POCzPBI, and
14
DPOPBI. b) The chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs, including FIrpic, Ir(ppy)3, PO-01, (MDQ)2Ir(acac).
Devices G1-G3 using Ir(ppy)3 as phosphors emitted bright green light, corresponding the CIE coordinates of (0.31, 0.61), (0.31, 0.61), and (0.31, 0.61). As depicted in Fig. 6c, d, low turn-on voltages of 2.2, 2.5, 2.5 V were achieved for DCzPBI-hosted G1, POCzPBI-hosted G2, and DPOPBI-hosted G3, respectively. Additionally, for display and indoor lighting, they exhibited low driving voltages at 100 cd m−2 and 1000 cd m−2 at the same time. They were as low as 3.1/4.0, 2.9/3.5, 3.1/3.7 V for G1, G2, and G3, respectively. The maximum brightness (Lmax) reached to >100000 cd m−2. The green devices displayed the promising efficiencies of 48.4 cd A−1, 50.6 lm W−1, and 13.8% for G2 and 47.4 cd A−1, 42.6 lm W−1, and 13.7% for G3. Inspiringly, G2 and G3 exhibited minor efficiency roll-off of only 3% and 2% for EQE at 1000 cd m−2. Except for possessing the effective carrier transport feature in PhOLEDs, we ascribed the favorable performance to the efficient exciton confinement in the emitting layer as well. As illustrated in Fig. 6c inset, the absence of the emission stemming from adjacent emitting layers implied that TCTA and TmPyPB could be served as important block layers to confine the excitons within the emitting region [61,62].
15
Insert Fig. 6 Fig. 6. a) J−V−L characteristics of B1-B3. Inset: the EL spectra. b) Efficienciesluminance curves of devices B1-B3. c) J−V−L curves of G1-G3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices G1-G3.
Then, the yellow emitter PO-01 and red emitter (MDQ)2Ir(acac) were utilized to further discuss the universality of host materials without changing the device configuration. The related device performances were given in Fig. 7. The favorable efficiencies of 39.6 cd A−1, 41.5 lm W−1, and 12.7% for O2 and 45.7 cd A−1, 35.6 lm W−1, and 15.0% for O3 were achieved by the yellow devices. It is noteworthy that the PhOLEDs exhibited negligible efficiency roll-offs with the increase of brightness. Even at 1000 cd m−2, the CE maintained as high as 38.2 and 45.6 cd A−1, coupled with minor efficiency roll-offs of only 3%, and 0.2%, respectively, verifying DPOPBI that can be acted as the most effective yellow host. Its red device also exhibited the promising efficiencies of 21.5 cd A−1, 19.3 lm W−1, and 13.5% and small CE roll-off of 13% at 1000 cd m−2. These data demonstrated that the DPOPBI- and POCzPBIhosted devices exhibited the much better OLEDs efficiency than those of DCzPBIhosted devices, which were predominantly ascribed to the moderately bipolar
16
character of DPOPBI and POCzPBI, leading to balanced carrier transporting abilities and widened recombination zone. Conventional devices are almost hole-predominant devices, Ir3+ complexes usually exhibit intense trapping capability, the appropriate electron-predominant transporting in host materials can promote balanced charge transport [63,64]. Thus, it is believed that manipulating the carrier transporting characters of the phosphorescent hosts is significant for accurately satisfying the basic requirement of the OLEDs.
Insert Fig. 7 Fig. 7. a) J−V−L curves of O1-O3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices O1-O3. c) J−V−L curves of R1-R3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices R1-R3.
Insert Table 3 Table 3 EL data of the phosphorescent devices hosted by DCzPBI, POCzPBI, and DPOPBI.
3. Conclusions In summary, we have synthesized novel HPBI-based hosts, DCzPBI, POCzPBI,
17
and DPOPBI, comprising carbazole and diphenylphosphoryl oxide moieties. Among them, DPOPBI and POCzPBI can be considered as the most effective universal hosts for high performance PhOLEDs, in view of the outstanding thermal properties, matched energy levels, and balanced carrier transporting. The blue, green, yellow, and red PhOLEDs with CE of 23.2, 48.4, 45.7, 21.5 cd A−1 have been achieved by using DPOPBI and POCzPBI as the hosts. In addition, all the devices showed low driving voltages and minor efficiency roll-offs with the increase of brightness, which may be ascribed to reduced intermolecular interaction in dopant-dopant and host-dopant and balanced charge transporting feature. The excellent device performances obtained with simple device configuration implied that these carbazole and diphenylphosphoryl oxide based hosts had great potential for the applications in full-color highperformance phosphorescent devices.
Acknowledgments The authors gratefully acknowledge the financial support form National Natural Science Foundation of China (21303012 and 61474054), the Fundamental Research Funds for the Central Universities (2412019FZ012 and 2412019QD007), and China Postdoctoral Science Foundation funded project (2019M551184).
18
References [1] M.A. Baldo, D.F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M.E. Thompson, S.R. Forrest, Nature 395 (1998) 151. [2] Y.T. Tao, Q.A. Wang, C.L. Yang, C. Zhong, J.G. Qin, D.G. Ma, Adv. Funct. Mater. 20 (2010) 2923. [3] S.C. Lo, R.E. Harding, C.P. Shipley, S.G. Stevenson, P.L. Burn, I.D. Samuel, J. Am. Chem. Soc. 131 (2009) 16681. [4] Y. Sun, X. Yang, Z. Feng, B. Liu, D. Zhong, J. Zhang, G. Zhou, Z. Wu, ACS Appl. Mater. Interfaces 11 (2019) 26152. [5] C. Fan, C. Yang, Chem. Soc. Rev. 43 (2014) 6439. [6] A. Haldi, A. Kimyonok, B. Domercq, L.E. Hayden, S.C. Jones, S.R. Marder, M. Weck, B. Kippelen, Adv. Funct. Mater. 18 (2008) 3056. [7] J. Ding, B. Wang, Z. Yue, B. Yao, Z. Xie, Y. Cheng, L. Wang, X. Jing, F. Wang, Angew. Chem., Int. Ed. 48 (2009) 6664. [8] T.S. Qin, J.Q. Ding, L.X. Wang, M. Baumgarten, G. Zhou, K. Mullen, J. Am. Chem. Soc. 131 (2009) 14329. [9] G.Z. Lu, Q. Zhu, L. Liu, Z.G. Wu, Y.X. Zheng, L. Zhou, J.L. Zuo, H. Zhang, ACS Appl. Mater. Interfaces 11 (2019) 20192. [10] T. Ito, H. Sasabe, Y. Nagai, Y. Watanabe, N. Onuma, J. Kido, Chem. Eur. J. 25 (2019) 7308. [11] H. Shin, Y.H. Ha, H.G. Kim, R. Kim, S.K. Kwon, Y.H. Kim, J.J. Kim, Adv. Mater. 31 (2019) 1808102. [12] J. Lin, Y. Wang, P. Gnanasekaran, Y.-C. Chiang, C.-C. Yang, C.-H. Chang, S.-H. Liu, G.-H. Lee, P.-T. Chou, Y. Chi, S.-W. Liu, Adv. Funct. Mater. 27 (2017) 1702856.
19
[13] F.-M. Hsu, C.-H. Chien, C.-F. Shu, C.-H. Lai, C.-C. Hsieh, K.-W. Wang, P.-T. Chou, Adv. Funct. Mater. 19 (2009) 2834. [14] M. Sudhakar, P.I. Djurovich, T.E. Hogen-Esch, M.E. Thompson, J. Am. Chem. Soc. 125 (2003) 7796. [15] H. Inomata, K. Goushi, T. Masuko, T. Konno, T. Imai, H. Sasabe, J.J. Brown, C. Adachi, Chem. Mater. 16 (2004) 1285. [16] S. Tokito, K. Noda, H. Fujikawa, Y. Taga, M. Kimura, K. Shimada, Y. Sawaki, Appl. Phys. Lett. 77 (2000) 160. [17] C.T. Chen, Y. Wei, J.S. Lin, M.V. Moturu, W.S. Chao, Y.T. Tao, C.H. Chien, J. Am. Chem. Soc. 128 (2006) 10992. [18] F.K. Kong, M.C. Tang, Y.C. Wong, M.Y. Chan, V.W. Yam, J. Am. Chem. Soc. 138 (2016) 6281. [19] I.S. Park, H. Seo, H. Tachibana, J.U. Kim, J. Zhang, S.M. Son, T. Yasuda, ACS Appl. Mater. Interfaces 9 (2017) 2693. [20] S. Gong, Y. Chen, C. Yang, C. Zhong, J. Qin, D. Ma, Adv. Mater. 22 (2010) 5370. [21] J. Zhao, G.H. Xie, C.R. Yin, L.H. Xie, C.M. Han, R.F. Chen, H. Xu, M.D. Yi, Z.P. Deng, S.F. Chen, Y. Zhao, S.Y. Liu, W. Huang, Chem. Mater. 23 (2011) 5331. [22] W.C. Chen, Y. Yuan, Z.L. Zhu, S.F. Ni, Z.Q. Jiang, L.S. Liao, F.L. Wong, C.S. Lee, Chem. Commun. 54 (2018) 4541. [23] S. Thiery, D. Tondelier, C. Declairieux, B. Geffroy, O. Jeannin, R. Métivier, J. Rault-Berthelot, C. Poriel, J. Phys. Chem. C 119 (2015) 5790. [24] Y. Zhao, C. Wu, P. Qiu, X. Li, Q. Wang, J. Chen, D. Ma, ACS Appl. Mater. Interfaces 8 (2016) 2635.
20
[25] J. Li, D. Ding, Y. Tao, Y. Wei, R. Chen, L. Xie, W. Huang, H. Xu, Adv. Mater. 28 (2016) 3122. [26] L.S. Cui, J.U. Kim, H. Nomura, H. Nakanotani, C. Adachi, Angew. Chem., Int. Ed. 55 (2016) 6864. [27] D. Zhang, M. Cai, Z. Bin, Y. Zhang, D. Zhang, L. Duan, Chem. Sci. 7 (2016) 3355. [28] J. Zhang, D. Ding, Y. Wei, H. Xu, Chem. Sci. 7 (2016) 2870. [29] E. Mondal, W.-Y. Hung, H.-C. Dai, K.-T. Wong, Adv. Funct. Mater. 23 (2013) 3096. [30] D. Zhang, X. Song, M. Cai, H. Kaji, L. Duan, Adv. Mater. 30 (2018) 1705406. [31] S.M. Kim, J.H. Yun, S.H. Han, J.Y. Lee, J. Mater. Chem. C 5 (2017) 9072. [32] Z. Zhao, G. Yu, Q. Chang, X. Liu, Y. Liu, L. Wang, Z. Liu, Z. Bian, W. Liu, C. Huang, J. Mater. Chem. C 5 (2017) 7344. [33] H.H. Chou, C.H. Cheng, Adv. Mater. 22 (2010) 2468. [34] Y.T. Tao, Q. Wang, L. Ao, C. Zhong, J.G. Qin, C.L. Yang, D.G. Ma, J. Mater. Chem. 20 (2010) 1759. [35] X. Lv, W. Zhang, D. Ding, C. Han, Z. Huang, S. Xiang, Q. Zhang, H. Xu, L. Wang, Adv. Opt. Mater. 6 (2018) 1800165. [36] C.J. Shih, C.C. Lee, T.H. Yeh, S. Biring, K.K. Kesavan, N.R.A. Amin, M.H. Chen, W.C. Tang, S.W. Liu, K.T. Wong, ACS Appl. Mater. Interfaces 10 (2018) 24090. [37] S.L. Gong, Y.H. Chen, J.J. Luo, C.L. Yang, C. Zhong, J.G. Qin, D.G. Ma, Adv. Funct. Mater. 21 (2011) 1168. [38] J. Jin, Y. Tao, H. Jiang, R. Chen, G. Xie, Q. Xue, C. Tao, L. Jin, C. Zheng, W. Huang, Adv. Sci. 5 (2018) 1800292.
21
[39] Y.T. Tao, Q. Wang, C.L. Yang, C. Zhong, K. Zhang, J.G. Qin, D.G. Ma, Adv. Funct. Mater. 20 (2010) 304. [40] Y. Tao, Q. Wang, L. Ao, C. Zhong, C. Yang, J. Qin, D. Ma, J. Phys. Chem. C 114 (2009) 601. [41] L.S. Cui, S.B. Ruan, F. Bencheikh, R. Nagata, L. Zhang, K. Inada, H. Nakanotani, L.S. Liao, C. Adachi, Nat. Commun. 8 (2017) 2250. [42] S. Liu, X. Zhang, C. Ou, S. Wang, X. Yang, X. Zhou, B. Mi, D. Cao, Z. Gao, ACS Appl. Mater. Interfaces 9 (2017) 26242. [43] S.-h. Ye, L. Li, M. Zhang, Z. Zhou, M.-h. Quan, L.-F. Guo, Y. Wang, M. Yang, W.-y. Lai, W. Huang, J. Mater. Chem. C 5 (2017) 11937. [44] S. Hu, J. Zeng, X. Zhu, J. Guo, S. Chen, Z. Zhao, B.Z. Tang, ACS Appl. Mater. Interfaces 11 (2019) 27134. [45] Q. Liang, C. Han, C. Duan, H. Xu, Adv. Opt. Mater. (2018) 1800020. [46] H.T. Mao, C.X. Zang, G.G. Shan, H.Z. Sun, W.F. Xie, Z.M. Su, Inorg. Chem. 56 (2017) 9979. [47] G.G. Shan, H.B. Li, H.Z. Sun, H.T. Cao, D.X. Zhu, Z.M. Su, Dalton Trans. 42 (2013) 11056. [48] H.T. Cao, H.Z. Sun, Y.M. Yin, X.M. Wen, G.G. Shan, Z.M. Su, R.L. Zhong, W.F. Xie, P. Li, D.X. Zhu, J. Mater. Chem. C 2 (2014) 2150. [49] S.-C. Dong, L. Zhang, J. Liang, L.-S. Cui, Q. Li, Z.-Q. Jiang, L.-S. Liao, J. Phys. Chem. C 118 (2014) 2375. [50] W. Li, J. Li, D. Liu, D. Li, F. Wang, ACS Appl. Mater. Interfaces 8 (2016) 21497. [51] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M.
22
Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.01, Gaussian, Inc., Wallingford CT, (2009). [52] A.D. Becke, J. Chem. Phys. 98 (1993) 5648. [53] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785. [54] G.M. Li, D.X. Zhu, T. Peng, Y. Liu, Y. Wang, M.R. Bryce, Adv. Funct. Mater. 24 (2014) 7420. [55] Y. Feng, P. Li, X. Zhuang, K. Ye, T. Peng, Y. Liu, Y. Wang, Chem. Commun. 51 (2015) 12544. [56] S.-F. Huang, H.-Z. Sun, G.-G. Shan, Y. Wu, M. Zhang, Z.-M. Su, New J. Chem. 40 (2016) 4635. [57] C. Zang, X. Peng, H. Wang, Z. Yu, L. Zhang, W. Xie, H. Zhao, Org. Electron. 50 (2017) 106. [58] J.Q. Ding, J.H. Lu, Y.X. Cheng, Z.Y. Xie, L.X. Wang, X.B. Jing, F.S. Wang, Adv. Funct. Mater. 18 (2008) 2754. [59] J. Yu, C.X. Zang, Z.W. Yu, H. Wang, S.H. Liu, L.T. Zhang, W.F. Xie, H.Y. Zhao, Org. Electron. 38 (2016) 301. 23
[60] Y. Tao, Q. Wang, C. Yang, Q. Wang, Z. Zhang, T. Zou, J. Qin, D. Ma, Angew. Chem., Int. Ed. 47 (2008) 8104. [61] D. Luo, X.-L. Li, Y. Zhao, Y. Gao, B. Liu, ACS Photonics 4 (2017) 1566. [62] B. Liu, H. Tao, L. Wang, D. Gao, W. Liu, J. Zou, M. Xu, H. Ning, J. Peng, Y. Cao, Nano Energy 26 (2016) 26. [63] C. Han, Z. Zhang, H. Xu, J. Li, G. Xie, R. Chen, Y. Zhao, W. Huang, Angew. Chem., Int. Ed. 51 (2012) 10104. [64] Y. Tao, C. Yang, J. Qin, Chem. Soc. Rev. 40 (2011) 2943.
24
Table Captions
Table 1 Thermal, photophysical, and electrochemical properties of the three compounds.
Table 2 Summary of the important parameters affecting the abilities of charge injecting and transporting, including IP, HEP, EA, EEP, λhole and λelectron. The units in eV.
Table 3 EL data of the phosphorescent devices hosted by DCzPBI, POCzPBI, and DPOPBI.
Table 1 Thermal, photophysical, and electrochemical properties of the three compounds. λabsa
λPLa
HOMOb
LUMOc
Egd
ETe
Tdf
Tgg
(nm)
(nm)
(eV)
(eV)
(V)
(eV)
(°C)
(°C)
DCzPBI
237, 293, 326
399
−5.38
−2.06
3.32
2.60
451
120
POCzPBI
230, 293, 330
406
−5.37
−2.08
3.29
2.59
436
127
DPOPBI
228, 305
373
−6.05
−2.53
3.52
2.62
434
135
host
a
Obtained in a CH2Cl2 at 298 K.
b
Estimated by electrochemical measurements.
c
ELUMO = EHOMO + Eg. d Optical band gap. e Collected in frozen dichloromethane at 77 K. f Decomposition temperature (corresponding to 5% weight loss). g Glass-transition temperature.
Table 2 Summary of the important parameters affecting the abilities of charge injecting and transporting, including IP, HEP, EA, EEP, λhole and λelectron. The units in eV. compound
IP
HEP
EA
EEP
λhole
λelectron
DCzPBI
6.43
6.32
0.52
0.22
0.11
0.30
POCzPBI
7.25
6.76
0.86
0.35
0.49
0.50
DPOPBI
6.49
6.25
0.66
0.25
0.25
0.40
Table 3 EL data of the phosphorescent devices hosted by DCzPBI, POCzPBI, and DPOPBI. device
host
guest
Vturn-ona
Lmaxb
CEc
PEd
EQEe
Efficiency roll-offsf
[V]
[cd m−2]
[cd A−1]
[lm W−1]
[%]
[%] CE
PE
EQE
B1
DCzPBI
FIrpic
2.8/4.2/6.3
2170
9.5/2.8
10.8/1.4
4.9/1.4
70
87
71
B2
POCzPBI
FIrpic
2.9/4.0/5.3
11030
12.1/8.5
12.7/4.9
5.9/4.1
30
61
30
B3
DPOPBI
FIrpic
2.7/3.7/4.8
18457
23.2/14.2
24.4/9.2
11.5/7.1
39
62
38
G1
DCzPBI
Ir(ppy)3
2.2/3.1/4.0
58530
45.8/36.2
47.8/27.2
13.2/10.5
21
43
20
G2
POCzPBI
Ir(ppy)3
2.5/2.9/3.5
101115
48.4/46.8
50.6/41.1
13.8/13.4
3
19
3
G3
DPOPBI
Ir(ppy)3
2.5/3.1/3.7
91224
47.4/46.4
42.6/39.4
13.7/13.4
2
7
2
O1
DCzPBI
PO-01
2.5/3.1/3.7
84338
36.8/24.7
25.7/20.8
11.6/7.9
33
19
32
O2
POCzPBI
PO-01
2.5/2.8/3.5
75806
39.6/38.2
41.5/34.0
12.7/12.1
3
18
5
O3
DPOPBI
PO-01
2.8/3.5/4.4
71106
45.7/45.6
35.6/32.6
15.0/14.9
0.2
8.4
0.7
R1
DCzPBI
Ir(MDQ)2 3.1/4.7/6.5
8891
9.2/4.8
8.2/2.3
6.2/3.1
48
72
50
R2
POCzPBI Ir(MDQ)2 3.0/4.1/5.3
41877
15.4/12.7
13.8/7.5
10.4/8.2
17
46
21
R3
DPOPBI
Ir(MDQ)2 3.0/3.9/5.0
58249
21.5/18.7
19.3/11.8
13.5/11.3
13
39
16
a
Turn-on voltage at 1 cd m−2.
b
Maximum brightness.
c
Order of CE values: peak
values, then values at 1000 cd m−2. d Order of PE values: peak values, then values at 1000 cd m−2.
e
Order of EQE values: peak values, then values at 1000 cd m−2.
Efficiency roll-offs at 1000 cd m−2.
f
Figure Captions
Scheme 1. Chemical structures of DCzPBI, POCzPBI, and DPOPBI. Scheme 2. Synthetic procedures of DCzPBI, POCzPBI, and DPOPBI. i) DMA, 1 h, CH3COOH, 12 h; ii) carbazole, CuI, K2CO3, DMPU, 18-Crown-6, 12 h; iii) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h; iv) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h, carbazole, CsCO3, DMF, 12 h. Fig. 1. DSC curves for DCzPBI, POCzPBI, and DPOPBI collected at a heating rate of 10 °C min−1. Fig. 2. Electronic absorption and the emission spectra of DCzPBI, POCzPBI, and DPOPBI in dichloromethane solution (10−5 mol L−1). Inset: phosphorescence (PH) spectra in dichloromethane at low temperature (77 K). Fig. 3. Contours and energy levels of frontier molecular orbitals of DCzPBI, POCzPBI, and DPOPBI. Fig. 4. J−V characteristics of the single-carrier devices for DCzPBI, POCzPBI, and DPOPBI. Fig. 5. a) Energy level diagrams of the PhOLEDs hosted by DCzPBI, POCzPBI, and DPOPBI. b) The chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs, including FIrpic, Ir(ppy)3, PO-01, (MDQ)2Ir(acac). Fig. 6. a) J−V−L characteristics of B1-B3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices B1-B3. c) J−V−L curves of G1-G3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices G1-G3.
Fig. 7. a) J−V−L curves of O1-O3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices O1-O3. c) J−V−L curves of R1-R3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices R1-R3.
Scheme 1. Chemical structures of DCzPBI, POCzPBI, and DPOPBI.
Scheme 2. Synthetic procedures of DCzPBI, POCzPBI, and DPOPBI. i) DMA, 1 h, CH3COOH, 12 h; ii) carbazole, CuI, K2CO3, DMPU, 18-Crown-6, 12 h; iii) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h; iv) Ph2PH, DMF, NaOAc, Pd(OAc)2, 24 h, carbazole, CsCO3, DMF, 12 h.
Fig. 1. DSC curves for DCzPBI, POCzPBI, and DPOPBI collected at a heating rate of 10 °C min−1.
Fig. 2. Electronic absorption and the emission spectra of DCzPBI, POCzPBI, and DPOPBI in dichloromethane solution (10−5 mol L−1). Inset: phosphorescence (PH) spectra in dichloromethane at low temperature (77 K).
Fig. 3. Contours and energy levels of frontier molecular orbitals of DCzPBI, POCzPBI, and DPOPBI.
Fig. 4. J−V characteristics of the single-carrier devices for DCzPBI, POCzPBI, and DPOPBI.
Fig. 5. a) Energy level diagrams of the PhOLEDs hosted by DCzPBI, POCzPBI, and DPOPBI. b) The chemical configurations of the phosphorescent emitters adopted in the corresponding OLEDs, including FIrpic, Ir(ppy)3, PO-01, (MDQ)2Ir(acac).
Fig. 6. a) J−V−L characteristics of B1-B3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices B1-B3. c) J−V−L curves of G1-G3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices G1-G3.
Fig. 7. a) J−V−L curves of O1-O3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices O1-O3. c) J−V−L curves of R1-R3. Inset: the EL spectra. b) Efficiencies-luminance curves of devices R1-R3.
Highlights The hosts consisting carbazole and diphenylphosphoryl oxide were designed. The relationship between the structures and EL performances were studied. They can be applied as universal hosts in highly efficient full-color PhOLEDs. DPOPBI and POCzPBI exhibited good charge carrier transporting properties. Yellow device showed extremely low efficiency roll-off of only 0.2%.