Annealing Solution-Processed CuSCN Hole Injection Layer for Blue

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Annealing Solution-Processed CuSCN Hole Injection Layer for Blue Phosphorescent Organic LightEmitting Diodes with Extremely Low Efficiency Roll-Off Ligang Xu, Yifan Li, Lingfeng Chen, Jun Wang, Chao Zheng, Yuanyuan Qi, Runfeng Chen, and Wei Huang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04561 • Publication Date (Web): 07 Nov 2018 Downloaded from http://pubs.acs.org on November 7, 2018

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ACS Sustainable Chemistry & Engineering

Annealing Solution-Processed CuSCN Hole Injection Layer for Blue Phosphorescent Organic Light-Emitting Diodes with Extremely Low Efficiency Roll-Off Ligang Xu,Δ Yifan Li,Δ Lingfeng Chen, Jun Wang, Chao Zheng, Yuanyuan Qi, Runfeng Chen* and Wei Huang

Key Laboratory for Organic Electronics and Information Displays (KLOEID) & Jiangsu Key Laboratory for Biosensors, Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023, China. E-mail address: [email protected]

KEYWORDS: CuSCN film; PhOLEDs; Annealing treatment; Hole injection layer; Efficiency roll-off

ACS Paragon Plus Environment

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ABSTRACT: Phosphorescent organic light-emitting diodes (PhOLEDs) have attracted tremendous attention recently but still suffer serious efficiency roll-off at high luminance, which will significantly limit their practical application in the future. Here, using a spincoated transparent CuSCN film as hole injection layer (HIL), we succeed in achieving high-performance blue PhOLEDs with extremely low efficiency roll-offs based on widely used host and guest materials in a conventional device structure; by thermal and current annealing treatments, the external quantum efficiency (EQE) is up to 12.5% at 8370 cd m-2 and the EQE roll-off can be as low as 2% at 10000 cd m-2 and 7% at 20000 cd m-2, respectively. The inorganic molecular semiconductor feature of CuSCN and the improved hole mobility after the annealing treatment were proved to be the main reasons for the highly stable PhOLEDs. The successful application of solution-processed CuSCN HIL for blue PhOLEDs with low efficiency roll-offs could provide important guidelines for the development of low-cost and highly efficient devices at high luminance.

INTRODUCTION

Phosphorescent organic light-emitting diodes (PhOLEDs) that can harvest both triplet and singlet


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excitons for electroluminescence with theoretically 100% internal quantum efficiency have attracted tremendous attention in recent years, owing to their great potential in the fields of flexible flat-panel displays and large-area lighting

[1-2].

However, PhOLEDs generally suffer significant

efficiency roll-off, i.e. current efficiency (CE) or external quantum efficiency (EQE) drastically drops as the applied voltage or brightness increases, leading to undesired low efficiencies at high luminance [3-5]. This problem, which is intrinsically related to the long-lived triplet excitons due to the serious quenching effects including triplet–triplet annihilation (TTA) or/and triplet–polaron quenching (TPQ) in the emissive layer at high brightness levels, has been a long-lasting obstacle for the commercialization of PhOLEDs [6]. With high-lying singlet and triplet energy levels of both the blue emitters and host molecules, blue PhOLEDs exhibit even more severe efficiency roll-offs, since it is more difficult to support a balanced charge injection/transport and to avoid quenching effects of non-radiative centers or trap/barrier state defects at high energetic states for blue electroluminance (EL) [7,8]. To alleviate the efficiency roll-off of PhOLEDs at high luminance, various strategies on either structure engineering of the devices or molecular design of the materials have been proposed. Holmes et al. reported a graded dopant concentration profile in the emissive layer of the device to construct a broadened recombination zone for the generated excitons, presenting a feasible approach to suppress TTA and TPQ for low efficiency roll-offs [9]. Hao et al. found that in stack emitting layer devices, the triplet exciton diffusion can be accelerated, resulting in reduced rolloff effectively

[10].

Material designs for low efficiency roll-offs focus on developing high-

performance host molecules of PhOLEDs with balanced hole and electron injection and transportation, ranging from bipolar small molecules [11], co-host systems [12], thermally activated delayed fluorescence (TADF) molecules

[13],

exciplex with TADF properties

[14],

etc. To our


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knowledge, the best results of EQE roll-offs for blue PhOLEDs are currently as low as 0.53% at 1000 cd m-2,[15] and 4.3% at 10000 cd m-2 [16]. Here, we found that the hole-injection layer (HIL) also has a significant influence on the efficiency roll-off of PhOLEDs; by replacing the widely used poly(3,4-ethylenedioxythiophene: polystyrenesulphonate) (PEDOT:PSS) with copper(I) thiocyanate (CuSCN), extremely low efficiency roll-offs of blue PhOLEDs were observed. Specifically, the PhOLEDs based on bis(3,5difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium(III)) (FIrpic) with solution processed CuSCN HIL exhibit a luminance over 20000 cd m-2, a maximum CE of 24.1 cd A-1, a power efficiency (PE) up to 6.9 lm W-1 and a maximum EQE of 12.5%; and, the efficiency roll-offs of the devices (>10000 cd m-2) are remarkably lower than that of control devices based on PEDOT:PSS HIL, showing an EQE roll-off of 2% at 10000 cd m-2 and 7% at 20000 cd m-2 after a set of thermal and current annealing treatments. These results illustrate profound implications for the fabrication of stable blue PhOLEDs using inorganic HILs and proper annealing treatment to optimize the organic/inorganic interfaces.

RESULT AND DISCUSSION

CuSCN, which is an inorganic wide-bandgap (> 3.4 eV) molecular semiconductor, exhibits excellent hole-transport (p-type) characteristics with high optical transparency, attractive mechanical properties, low cost and commercial availability

[17].

Therefore, CuSCN has been

increasingly used as an hole-injection layer or hole transport layer of optoelectronic devices, especially in thin-film transistors and organic and organometal halide perovskite solar cells[17,18]. However, there are relatively fewer reports on the applications of CuSCN in PhOLEDs. Perumal


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et al used CuSCN as HIL for solution-processed green PhOLEDs; superior performance than conventional PEDOT:PSS-based device was observed, showing a maximum luminance values over 10000 cd m–2, CE of 51 cd A–1 and PE of 55 lm W–1 [2]. Very recently, Jou et al fabricated green PhOLEDs by employing CuSCN as a hole injection/transporting and electron-blocking layer; the PE of the CuSCN-based devices reaches 51.7 and 40.3 lm/W at 100 and 1000 cd/m2, respectively[19]. Chen et al used both CuSCN and PEDOT:PSS as HIL of yellow-green and green PhOLEDs; EQEs up to 13.9% were achieved[20-21]. Also, Sun et al reported that CuSCN is efficient as a solution-processed HIL for quantum dot-based light-emitting diodes (QLEDs), exhibiting comparable performance to PEDOT:PSS-based QLEDs[22]. CuSCN is largely insoluble in a vast majority of organic solvents but effectively soluble in sulfurbased solvents such as diethyl sulfide (DES); therefore, it can be deposited at low temperature using solution-processing methods on substrate materials

[18].

In this study, DES solution of

CuSCN was spin-coated on indium tin oxide (ITO) substrates to prepare semiconductive CuSCN film with high transmittance (Figure S1). Atomic force microscopy (AFM) surface topography images with a scan area of 5*5 μm2 show that the roughness of ITO surface (Figure 1a) is significantly reduced after the coverage of CuSCN layer with much smaller root mean square (RMS) value (Figure 1b). And, the RMS of CuSCN film is quite close to that of PEDOT:PSS film (Figure 1c), suggesting that the highly transparent, uniform and dense film of CuSCN can be deposited on ITO surface by spin-coating to planarize the ITO surface and reduce the concentration of interfacial defects for high performance optoelectronic devices [17]. In light of the successful solution deposition of uniform CuSCN layer on ITO substrate, we further investigated its performance as HIL for blue PhOLEDs under the following device


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configuration: ITO/CuSCN (30 nm)/TAPC (20 nm)/mCP:10 wt% FIrpic (20 nm)/TmPyPB (35 nm)/LiF(1 nm)/Al (100 nm) (Figure 2a) with an emitting area of 3*3 mm2 (Figure S2). In the devices, 1,3,5-tri[(3-pyridyl)-phen-3-yl] benzene (TmPyPB) and di-[4-(N,N-ditolyl- amino)phenyl]cyclohexan (TAPC) act as the electron and hole transport materials, respectively; LiF serves as the electron-injecting materials. The emission layer (EML) is comprised by a guest-host blend with 10 wt% of the guest molecule of FIrpic for phosphorescent emission in a widely used host material of 1,3-bis(carbazol-9-yl) benzene (mCP). It should be emphasized that this device structure is identical to the widely used blue PhOLEDs [23], except for a simple replacement of the widely used HIL material of PEDOT:PSS with CuSCN. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of CuSCN is -5.5 and -1.5 eV respectively

[24],

which are favorable for

optoelectronic devices using conventional organic semiconductors. From the energy level diagram of the devices (Figure 2b-c), the gradually decreased HOMO from that of the anode to EML supports the efficient hole injection and transport to EML for EL, while the deep HOMO of TmPyPB is helpful to confine the excitons on EML by preventing hole leakage to the cathode [25]. Both the triplet energy of mCP (2.93 eV) and its frontier orbital alignment is suitable to host FIrpic for efficient blue phosphorescence, which has been documented in many literatures

[26]

and

confirmed by typical EL spectrum of FIrpic-based PhOLEDs peaked at 468 and 490 nm (Figure 3a). The pristine PhOLED based on CuSCN HIL without post-annealing treatments (Device A) shows a turn-on voltage (Von) of 5.6 V, a maximum luminance of 26424 cd m-2 (Figure 3b) and maximum efficiencies of CE (CEmax) up to 17.6 cd A-1, PE (PEmax) of 5.6 lm W-1, and EQE (EQEmax) of 9.2% (Figure 3c). The thermal annealing of the devices leads to improved device performance with


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increased efficiencies and decreased Von and efficiency roll-offs (Table S1). The optimal thermal annealing conditions were found to be at 70oC for 10 min (Device B), showing much improved (~37%) device efficiencies with EQEmax up to 12.5%. Interestingly, both devices exhibit increasing efficiencies at strengthening luminance and reach the highest efficiencies when the brightness is up to 13400 and 8370 cd m-2 for Device A and Device B, respectively (Figure 3c). Therefore, extremely low EQE roll-offs of 2.0% and 7.0% at 10000 and 20000 cd m-2 were observed for Device B. Such low efficiency roll-offs are among the best reports of blue PhOLEDs (Table S2). It should be also noted that using CuSCN as HIL in perovskite solar cells, stabilized efficiencies exceeding 20% were achieved and the devices retain >95% of their initial efficiency after aging at a maximum power point for 1000 hours under full solar intensity at 60°C

[18].

These results are

also in line with the excellent performance of the CuSCN-based HIL in green PhOLEDs

[2]

and

QLEDs [22]. From Figure 3b, the curves of current density have an obvious bulge in the voltage range of 5~7 V, demonstrating the presence of negative differential resistance phenomenon in these devices. Since the negative differential resistance has the negative impacts on emission stability and device performance, CuSCN HIL-based PhOLEDs were further treated by current annealing under different voltage scanning ranges [27]. Indeed, there is no negative differential resistance any more in the Devices C-E after the current annealing treatment, according to their J-V-L curves (Figure 4a). Interestingly, their Vons are also reduced and the higher the scanning voltage during the current annealing, the lower Von is resulted (Figure 4b). More importantly, the efficiency roll-off can be improved by current annealing too; the EQE roll-off at 20000 cd m-2 is reduced to 6.4%, 2.7% and 5.6% after current annealing by scanning to 8, 9, and 10 V, respectively (Table 1). Scan times and scan speed of the current annealing also have significant influence on the device performance. By


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changing the scan speed from 200 to 600 mV s-1, the CE performance of the blue PhOLEDs varies in a range of ± 2 cd A-1; more cycles of the scan can effectively reduce Von, but efficiencies are slightly decreased (Table S3), probably due to the less balanced charge injection and transport of the over-annealed devices. Control devices using traditional PEDOT:PSS HIL (Device F) or without HIL (Device G) under the identical device configuration of CuSCN HIL-based blue PhOLEDs were further fabricated to understand the extremely low efficiency roll-off and high efficiencies at high brightness (Figures 4c-d). In line with the literature reports, Devices F and G exhibit high efficiencies at low luminance but show severe EQE roll-off about 50% at 20000 cd m-2. Consequently, at a high luminance of 10000 cd m-2, their EQEs are only 7.1% and 6.6%, which are rather lower than that of Devices B and C with EQEs up to 12.3% and 10.0%, respectively. Current annealing of the PEDOT:PSSbased PhOLEDs (Device H) leads to slightly decreased device efficiencies, but heavy efficiency roll-off was still observed (Table 1). This heavy roll-off of the PEDOT:PSS-based blue PhOLEDs could be related to its several intrinsic limitations, including that the acidity of PEDOT:PSS can damage ITO anodes and EML materials, its work function is rather low to act effectively as an electron-blocking layer, and it has relatively low thermal stability [22]. The HIL-free device would easily lose the charge injection and transport balance during the device operation for low efficiencies, especially at high driving voltages and current densities [28]. To reveal the significant effects of thermal and current annealing treatments of CuSCN HIL on performance improvement of blue PhOLEDs, hole-only devices of CuSCN and CuSCN-TAPC films were fabricated to figure out hole transporting ability variations in the classical single carrier device structure of ITO/CuSCN (30 nm) or CuSCN (30 nm)-TAPC (50 nm) /MoO3


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(10 nm)/Al (Figure S3). The hole mobility can be measured by fitting the J-V curves of the hole-only devices according to the space-charge-limited current (SCLC) modeling equation (1):

9 V2 J   0 r  3 8 d

(1)

In this equation, ε0 is the dielectric permittivity of free space (ε0=1), εr is the relative permittivity of the sample (εr=3 for the conventional semiconductors), µ is the mobility, and d is the thickness of sample measured by Dektak-XT of Bruker. According to Equation (1), the pristine CuSCN film without annealing has a hole mobility of 7.00×10-3 cm2V-1s-1, while CuSCN-TAPC exhibits a lower value of 1.37×10-4 cm2V-1s-1 mainly owing to the presence of the organic-inorganic interface since TAPC was reported to have a high hole mobility of ~10-2 cm2V-1s-1 [29. Both thermal annealing and current annealing of the CuSCN film exhibit limited effects on its hole mobility (Figure 5). In contrast, the thermal annealing of CuSCN-TAPC film at 70oC for 10 min increases the mobility to 1.47×10-4 cm2V-1s-1, while current annealing at a scanning bias of ITO from 0 to 8 V (400 mV s-1) leads to much improved mobility of 3.52×10-4 cm2V-1s-1. And, the combined thermal and current annealing gives the highest hole mobility of the solution-processed CuSCN-TAPC film up to 4.59×10-4 cm2V-1s-1 (Figure 5). These results indicate that both thermal annealing and current annealing can significantly improve the hole injection and transport of the CuSCN-TAPC film with higher hole mobilities of over 3 folds compared to the pristine film, possibly by optimizing the organic-inorganic interface between TAPC and CuSCN layers; this should be an important reason for the higher device performance of the blue PhOLEDs after the annealing treatments.


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CONCLUSIONS

In summary, we found that by replacing the widely used PEDOT:PSS with CuSCN as HIL for blue PhOLEDs, high device performance, especially high efficiencies at high luminance with extremely low efficiency roll-offs can be realized after proper thermal and current annealing treatments. The solution-processed CuSCN film exhibit good morphology with low surface roughness, and the FIrpic-based blue PhOLEDs using CuSCN HIL show a maximum luminance over 20000 cd m-2, a maximum CE of 24.1 cd A-1, a PE up to 6.9 lm W-1 and a maximum EQE of 12.5%. Impressively, the EQE roll-off of 2% at 10000 cd m-2 and 7% at 20000 cd m-2 have been achieved in the blue PhOLEDs based on CuSCN HIL, which are among the best results of PhOLEDs at high luminance. In light of the good hole mobility, high optical transparency and low temperature solution processing of the CuSCN film for highly stable blue PhOLEDs, this green, cheap and commercially available molecular semiconductor of CuSCN could be a promising alternative to traditional inorganic/organic HIL materials.


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Figure 1. AFM topography images of (a) ITO, (b) ITO/CuSCN, and (c) ITO/PEDOT:PSS surfaces.


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Figure 2. (a) Schematic device structure of blue PhOLEDs using CuSCN HIL and (b) the energy level diagram and (c) molecular structures of the related materials.


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Figure 3. Device performance of CuSCN HIL-based blue PhOLEDs before (Device A) and after the thermal annealing treatment (Device B) showing (a) the normalized EL spectra with digital photograph of Device B driving at 7 V, (b) current density-voltage-luminance (J-V-L) characteristics and (c) efficiencies-luminance curves.


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Figure 4. (a, c) J-V-L characteristics and (b, d) efficiencies-luminance curves of current annealed blue PhOLEDs (Devices C, D, and E) and control devices using PEDOT:PSS as HIL (Device F) or without HIL (Device G).


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Figure 5. Current-voltage (J-V) characteristics of the hole-only devices of CuSCN and CuSCNTAPC films with thermal (TA) and/or current (CA) annealing treatments.


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Table 1. Device performance of blue PhOLEDs using different HILs under different annealing conditionsa

Device

HIL

A B C D E

CuSCN CuSCN CuSCN CuSCN CuSCN

F

PEDOT:PS S None PEDOT:PS S

G H

aThermal

Von [V]

Lmax [cd m-2]

CEmax [cd A1]

PEmax [lm w-1]

EQEmax [%]

/ TA CA (8 V) CA (9 V) CA (10 V) TA

5.6 5.3 4.3 3.7 3.6

26,424 26,427 26,426 26,435 26,434

17.6 24.1 20.4 16.9 15.9

5.6 6.9 6.5 5.2 5.2

3.2

29,015

21.5

TA CA (8 V)

4.1 3.4

23,615 23,458

16.7 20.8

Annealing

Roll-off @10000 cd m-2

@20000 cd m-2

9.2 12.5 10.6 8.8 8.3

1.9% 2.0% 5.8% 6.1% 1.0%

10.2% 7.0% 6.4% 2.7% 5.6%

16.7

11.2

37%

49%

6.8 17.0

8.7 10.8

24% 35%

50% 57%

annealing (TA) at 70oC for 10 min; current annealing (CA) driving at varied voltages


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ASSOCIATED CONTENT

Supporting Information.

The Supporting Information is available free of charge on the ACS Publications website at DOI:xxxxx/x0xx00000x

Materials and measurements; Device fabrication and characterization; Transmittance spectra of quartz substrate and CuSCN film coated on quartz surface; Photograph of the pattern structure of blue PhOLEDs; Schematic device structures of the hole-only devices of CuSCN and CuSCN-TAPC films; A brief summary of the recently reported highperformance FIrpic-based PhOLEDs on current efficiency, external quantum efficiency, and EQE roll-off at high brightness. Device performance of the blue PhOLEDs under various thermal and current annealing conditions. AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]


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Author Contributions

Δ

X.L. and L.Y equally contributed as first authors.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

This study was supported in part by the National Natural Science Foundation of China (21674049, 21772095, 61604079 and 61704089), Science Fund for Distinguished Young Scholars of Jiangsu Province of China (BK20150041), 1311 Talents Program of Nanjing University of Posts and Telecommunications (Dingshan) and the Six Talent Plan of Jiangsu

Province

(2016XCL050),

the

Initiative

Postdocs

Supporting

Program

(BX201600076), China Postdoctoral Science Foundation (2017M611879), Scientific Starting Fund from Nanjing University of Posts and Telecommunications (NUPTSF) (NY215015), The Natural Science Fund for Colleges and Universities in Jiangsu Province


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(17KJD15006), and Jiangsu Planned Projects for Postdoctoral Research Funds (1701045A，1601066C).

REFERENCES

(1) Guo, J. J.; Li, X. L.; Nie, H.; Luo, W. W.; Gan, S. F.; Hu, S. M.; Hu, R. R.; Qin, A. J.; Zhao, Z. J.; Su, S. J.; Tang, B. Achieving High-Performance Nondoped OLEDs with Extremely Small Efficiency Roll-Off by Combining Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence. Adv. Funct. Mater. 2017, 27 (13), 1606458. (2) Perumal, A.; Faber, H.; Yaacobi-Gross, N.; Pattanasattayavong, P.; Burgess, C.; Jha, S.; McLachlan, M. A.; Stavrinou, P. N.; Anthopoulos, T. D.; Bradley, D. D. C. High-Efficiency, Solution-Processed, Multilayer Phosphorescent Organic Light-Emitting Diodes with a Copper Thiocyanate Hole-Injection/Hole-Transport Layer. Adv. Mater. 2015, 27 (1), 93-100. (3) Zhang, Q.; Tsang, D.; Kuwabara, H.; Hatae, Y.; Li, B.; Takahashi, T.; Lee, S. Y.; Yasuda, T.; Adachi, C. Nearly 100% Internal Quantum Efficiency in Undoped Electroluminescent Devices Employing Pure Organic Emitters. Adv. Mater. 2015, 27 (12), 2096-2100. (4) Zhang, T. M.; Shi, C. S.; Zhao, C. Y.; Wu, Z. B.; Chen, J. S.; Xie, Z. Y.; Ma, D. G. Extremely Low Roll-Off and High Efficiency Achieved by Strategic Exciton Management in Organic LightEmitting Diodes with Simple Ultrathin Emitting Layer Structure. ACS Appl. Mater. Interfaces 2018, 10 (9), 8148-8154. (5) Tao, Y.; Xu, L. J.; Zhang, Z.; Chen, R. F.; Li, H. H.; Xu, H.; Zheng, C.; Huang, W. Achieving Optimal Self-Adaptivity for Dynamic Tuning of Organic Semiconductors through Resonance Engineering. J. Am. Chem. Soc. 2016, 138 (30), 9655-9662.


19


Page 20 of 24

(6) Guo, K. P.; Wang, H. D.; Wang, Z. X.; Si, C. F.; Peng, C. Y.; Chen, G.; Zhang, J. H.; Wang, G. F.; Wei, B. Stable green phosphorescence organic light-emitting diodes with low efficiency roll-off using a novel bipolar thermally activated delayed fluorescence material as host. Chem. Sci. 2017, 8 (2), 1259-1268. (7) Jeltsch, K. F.; Lupa, G.; Weitz, R. T., Materials depth distribution and degradation of a FIrpic based solution-processed blue OLED. Org. Electron. 2015, 26, 365-370. (8) Schmidbauer, S.; Hohenleutner, A.; Koenig, B., Chemical Degradation in Organic LightEmitting Devices: Mechanisms and Implications for the Design of New Materials. Adv. Mater. 2013, 25 (15), 2114-2129. (9) Erickson, N. C.; Holmes, R. J., Engineering Efficiency Roll-Off in Organic Light-Emitting Devices. Adv. Funct. Mater. 2014, 24 (38), 6074-6080. (10) Yuan, S. Q.; Hao, Y. Y.; Miao, Y. Q.; Sun, Q. J.; Li, Z. F.; Cui, Y. X.; Wang, H.; Shi, F.; Xu, B. S., Reduced efficiency roll-off in phosphorescent OLEDs with a stack emitting layer facilitating triplet exciton diffusion. RSC Adv., 2015, 5 (108), 89031-89036. (11) Wong, M. Y.; Zysman-Colman, E. Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes. Adv. Mater. 2017, 29 (22), 1605444. (12) Yao, B.; Lin, X. D.; Zhang, B. H.; Wang, H. L.; Liu, X. J.; Xie, Z. Y. Power-efficient and solution-processed red phosphorescent organic light-emitting diodes by choosing combinations of small molecular materials to form a well-dispersed exciplex co-host. J. Mater. Chem. C 2018, 6 (16), 4409-4417. (13) Hirata, S.; Sakai, Y.; Masui, K.; Tanaka, H.; Lee, S. Y.; Nomura, H.; Nakamura, N.; Yasumatsu, M.; Nakanotani, H.; Zhang, Q. S.; Shizu, K.; Miyazaki, H.; Adachi, C. Highly efficient blue electroluminescence based on thermally activated delayed fluorescence. Nature Mater. 2015,


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14 (3), 330-336. (14) Wang, Z.; Wang, H.; Zhu, J.; Wu, P.; Shen, B.; Dou, D.; Wei, B. Manipulation of Thermally Activated Delayed Fluorescence of Blue Exciplex Emission: Fully Utilizing Exciton Energy for Highly Efficient Organic Light Emitting Diodes with Low Roll-Off. ACS Appl. Mater. Interfaces 2017, 9 (25), 21346-21354. (15) Bian, C.; Wang, Q.; Liu, X. Y.; Fan, J.; Liao, L. S. Orthogonally substituted aryl derivatives as bipolar hosts for blue phosphorescent organic light-emitting diodes. Org. Electron. 2017, 46, 105-114. (16) Zuo, L.; Han, G.; Sheng, R.; Xue, K.; Duan, Y.; Chen, P.; Zhao, Y. Dramatic efficiency improvement in single-layer orange phosphorescent organic light-emitting devices with suppressed efficiency roll-off. RSC Adv. 2016, 6 (60), 55017-55021. (17) Wijeyasinghe, N.; Regoutz, A.; Eisner, F.; Du, T.; Tsetseris, L.; Lin, Y. H.; Faber, H.; Pattanasattayavong, P.; Li, J. H.; Yan, F.; McLachlan, M. A.; Payne, D. J.; Heeney, M.; Anthopoulos, T. D. Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers Processed from Aqueous Precursor Solutions and Their Application in Thin-Film Transistors and Highly Efficient Organic and Organometal Halide Perovskite Solar Cells. Adv. Funct. Mater.2017, 27 (35), 1701818. (18) Arora, N.; Dar, M. I.; Hinderhofer, A.; Pellet, N.; Schreiber, F.; Zakeeruddin, S. M.; Gratzel, M. Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20%. Science 2017, 358 (6364), 768-771. (19) Chavhan, S. D.; Ou, T. H.; Jiang, M.-R.; Wang, C.-W.; Jou, J.-H. Enabling High-Efficiency Organic Light-Emitting Diode with Trifunctional Solution-Processable Copper(I) Thiocyanate. J. Phys. Chem. C 2018, 122 (33), 18836-18840.


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Page 22 of 24

(20) Xu, L. J.; Wang, J. Y.; Zhu, X. F.; Zeng, X. C.; Chen, Z. N. Phosphorescent Cationic Au4Ag2 Alkynyl Cluster Complexes for Efficient Solution-Processed Organic Light-Emitting Diodes. Adv. Funct. Mater. 2015, 25 (20), 3033-3042. (21) Xu, L.-J.; Zhang, X.; Wang, J.-Y.; Chen, Z.-N. High-efficiency solution-processed OLEDs based on cationic Ag6Cu heteroheptanuclear cluster complexes with aromatic acetylides. J. Mater. Chem. C 2016, 4 (9), 1787-1794. (22) Ding, T.; Wang, N.; Wang, C.; Wu, X. H.; Liu, W. B.; Zhang, Q. C.; Fan, W. J.; Sun, X. W. Solution-processed inorganic copper(I) thiocyanate as a hole injection layer for high-performance quantum dot-based light-emitting diodes. RSC Advances 2017, 7 (42), 26322-26327. (23) Tao, Y.; Guo, X.; Hao, L.; Chen, R. F.; Li, H. H.; Chen, Y. H.; Zhang, X. W.; Lai, W. Y.; Huang, W. A Solution-Processed Resonance Host for Highly Efficient Electrophosphorescent Devices with Extremely Low Efficiency Roll-off. Adv. Mater. 2015, 27 (43), 6939-6944. (24) Pattanasattayavong, P.; Promarak, V.; Anthopoulos, T. D. Electronic Properties of Copper(I) Thiocyanate (CuSCN). Adv. Electron. Mater. 2017, 3 (3), 1600378. (25) Kim, J. W.; Yoo, S. I.; Kang, J. S.; Yoon, G. J.; Lee, S. E.; Kim, Y. K.; Kim, W. Y. Quenching in single emissive white phosphorescent organic light-emitting devices. Org. Electron. 2016, 38, 230-237. (26) Sarada, G.; Cho, W.; Maheshwaran, A.; Sree, V. G.; Park, H. Y.; Gal, Y. S.; Song, M.; Jin, S. H. Deep-Blue Phosphorescent Ir(III) Complexes with Light-Harvesting Functional Moieties for Efficient Blue and White PhOLEDs in Solution-Process. Adv. Funct. Mater. 2017, 27 (27), 1701002. (27) Zhang, Q.; Chen, S. F.; Zhang, S.; Shang, W. J.; Liu, L. H.; Wang, M. H.; Yu, H. T.; Deng, L. L.; Qi, G. Q.; Wang, L. Y.; Han, S. Y.; Hu, B.; Kang, Q.; Liu, Y. J.; Yi, M. D.; Ma, Y. W.;


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Yang, W. J.; Feng, J.; Liu, X. G.; Sun, H. B.; Huang, W. Negative differential resistance and hysteresis in graphene-based organic light-emitting devices. J. Mater. Chem. C 2018, 6 (8), 19261932. (28) Zheng, Q.; You, F.; Xu, J.; Xiong, J.; Xue, X.; Cai, P.; Zhang, X.; Wang, H.; Wei, B.; Wang, L. Solution-processed aqueous composite hole injection layer of PEDOT:PSS+MoOx for efficient ultraviolet organic light-emitting diode. Org. Electron. 2017, 46, 7-13. 29) Borsenberger, P. M.; Pautmeier, L.; Richert, R.; Bassler, H. Hole transport in 1,1-bis(di-4tolylaminophenyl)cyclohexane. J. Chem. Phys. 1991, 94 (12), 8276-8281.


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TOC Figure

Synopsis Solution-processed CuSCN hole injection layer for blue phosphorescent organic light-emitting diodes show extremely low efficiency roll-offs with thermal and current annealing.


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Annealing Solution-Processed CuSCN Hole Injection Layer for Blue

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