Enabling High Efficiency Organic Light Emitting Diode with a Tri

Subscriber access provided by Binghamton University | Libraries

C: Energy Conversion and Storage; Energy and Charge Transport

Enabling High Efficiency Organic Light Emitting Diode with a Tri-functional Solution-Processable CuSCN Sudam Dhudaku Chavhan, Tsu Hao Ou, Ming-Ruei Jiang, Ching-Wu Wang, and Jwo-Huei Jou J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b05029 • Publication Date (Web): 27 Jul 2018 Downloaded from http://pubs.acs.org on July 28, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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

The Journal of Physical Chemistry

Enabling High Efficiency Organic Light Emitting Diode with a Tri-functional SolutionProcessable CuSCN Sudam D. Chavhan†, Tsu Hao Ou†, Ming-Ruei Jiang†, Ching-Wu Wang‡, Jwo-Huei Jou†* †

Departments of Materials Science and Engineering, National Tsing Hua University, Hsin-Chu, Taiwan, 30013, Republic of China ‡ Institute of Optoelectronic & Electrical Engineering, National Chung Cheng University, Chiayi, Taiwan, 62102, Republic of China

*Corresponding author: [email protected] Tel: +886-(0)3-5742617

1 ACS Paragon Plus Environment

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

Abstract We report on a low temperature solution processed tri-functional inorganic p-type semiconductor, copper (I) thiocyanate (CuSCN), as a hole injection/transporting and electron blocking layer for high efficiency organic light emitting diode (OLED). The electroluminescence (EL) characteristics of the CuSCN and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), (PEDOT:PSS) based devices were studied with structure of 4,4’-Bis(N-carbazolyl)-1,1’-biphenyl as host, bis[2(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium (III) ((ppy)2Ir (acac)) as green emitter, 2,2',2"(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) as electron transporting layer and lithium fluoride/aluminum cathode electrode. The power efficacies for the CuSCN based devices are found to be 51.7 and 40.3 lm/W at 100 and 1,000 cd/m2, respectively, which are 13 % and 60 % higher than the PEDOT:PSS based control parts. These are the highest power efficacies ever reported for this particular device architecture. The superior EL characteristics may be explained by its unique electronic properties. We believe that the high LUMO (-1.8 eV) and deep HOMO (-5.5 eV) of CuSCN assist to confine the electron injected into the emission layer and facilitate the injection of hole, likewise enhancing recombination. Present study will serve to enable highly efficient white OLEDs for general lighting purpose.


Page 2 of 17

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


1. Introduction Solution-processed organic light emitting-diode (OLED) is one of the promising alternatives to the conventional solid-state lighting and display technologies because of their low-cost, flexibility and roll-to-roll fabrication process1-5. Therefore, it is vitally important to pay more attention to enhance the overall performance of the solution processed OLEDs to substitute expensive vacuumbased fabrication technique. So far PEDOT:PSS is widely used as a hole injection /transport layer (HIL/HTL) for solution processed OLEDs. However, its low work function and problematical chemical properties, such as being hygroscopic and corrosiveness, compromising the power efficiency and device lifetime6-9. Moreover, it lacks the ability to block electrons and excitons effectively crossing from an emissive layer (EML). Efforts to use customized organic small molecules as HIL/HTL appears to be immaterialized because the deposited thin layer of small molecule can either be dissolved or physically washed away by the solvents of the subsequent EML deposition10,11. Hence, to get rid of the difficulty, it is crucial to search new class of HIL/HTL materials, which can be stable in ambient atmosphere as well as possesses superior electronic properties that of organic materials. To keep an eye out for new HIL/HTL materials, a prerequisite condition for selecting the HIL/HTL material is to possess excellent electronic properties, which can effectively block the electrons and excitons, besides, it will exhibits chemically compatible with EML and environmentally robust to avoid the degradation at HTL/EML interface. One promising approach is to use inorganic wide band-gap semiconductor materials that are easy to process over large-area substrates because of their excellent optoelectronic properties such as optical transparency and high conduction band value and deep valence band level12.



Recently, much research has been devoted to utilize metal oxide HTMs such as nickel oxide (NiO)13-15, vanadium oxide (V2O5)16-18, molybdenum oxide (MoO3)16,19, and tungsten oxide (WO3) for solution processed OLEDs20, 21. However, the employment of these materials requires the additional extra step of thermal decomposition to remove unwarranted hydroxide species steamed from the precursor solution in order to act as an HIL/HTL efficiently. As such wide bandgap metal oxides materials harbor high resistivity that limits their singular role as an HIL rather than multifunctional HIL/HTL layer and requires an additional layer of HTL for high power efficiency and hence the device fabrication process becomes time-consuming and expensive one21. To overcome the problems associated with metal oxide materials, we have opted to use CuSCN inorganic p-type semiconductor material because of its excellent transparent properties across the visible range of the electromagnetic spectrum. Besides, it is very stable in ambient atmosphere, easily deposited by the solution process, earthly abundant and thereof low cost, which makes it very attractive material to utilize it in optoelectronic device applications. CuSCN has been widely used in dye sensitize, organic-inorganic hybrid perovskite and polymer solar cell as an HTL due to its excellent optoelectronic properties22. Perumal et al successfully demonstrated the role of CuSCN as an HTL into OLED devices23. Ding et al fabricated quantum dot based light emitting diode by employing CuSCN as an HIL24. However, the power efficiency of these devices is low at high luminance. In the present study, we have fabricated high-efficiency green OLEDs by employing CuSCN as HIL/HTL and compared it with PEDOT:PSS based control parts. It is revealed that the CuSCN based device shows 51.7 and 40.3 lm/w power efficacies at 100 and 1000 cd/m 2, respectively, which are 13% and 60% higher than the PEDOT:PSS based counterparts. These are the highest power efficacies ever reported for this particular device architecture. 4 ACS Paragon Plus Environment

Page 4 of 17

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


2. Experimental details 2.1 Materials and thin film characterization The host material 4,4'-bis(carbazol-9-yl)biphenyl (CBP), guest material Bis [2-(2-pyridinly-N) phenyl-C] (acetylacetone)iridium (III), (Ir(ppy)2(acac)) and electron transport material 2,2',2"(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)

(TPBi)

were

purchased

from

Luminescence Technology Corporation Ltd., Taiwan. Hole injection/transport materials poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate), (PEDOT:PSS) was obtained from Heraeus, copper thiocyanate (CuSCN) was brought from sigma Aldrich. Absorption and transmittance spectra of quartz/PEDOT:PSS and quartz/CuSCN thin films were measured by UV-Vis spectrophotometer 2.2 Device fabrication and characterization Indium tin oxide (ITO) coated 3 x 3 cm2 glass substrates were cleaned with acetone and isopropyl alcohol via water bath sonication for 30 min. UV-Ozone treatment was carried out for 15 min to remove the residue of organic moieties. PEDOT:PSS as a hole injection/transport layer was deposited on cleaned ITO substrate via spin coating at 4000 rpm for 20 s and dried at 120 oC for 20 min. The as-prepared CuSCN solution was utilized to deposit CuSCN layer via spin coating at 3000 rpm for 60 sec. The EML solution consists of CBP and Ir(ppy)2(acac) was prepared by dissolving the molecules in tetrahydrofuran at 40 oC and subjected to sonication for 90 min. Prior to the EML deposition, the solution was filtered by 0.45 m PET filter and spin-coated at 2500 rpm for 20 s in nitrogen filled glove box. The deposition of TPBi, LiF and Al was carried out under high vacuum thermal evaporator. The characterization of the final device was done in an ambient atmosphere without encapsulation. The current-voltage-luminance characterization was done by the computer interfaced Keithley 2400 electrometer and Minolta CS-100A luminance–meter. 5 ACS Paragon Plus Environment


Page 6 of 17

Emission spectra were recorded by PR-655 spectroradiometer. The emission area of OLED device was 0.09 cm2, calculated from the overlapping of ITO and Al electrodes. 3. Results and discussion Figure 1 (a) shows molecular structures of organic materials and CuSCN compound. The studied device architecture along with the energy band diagram consists of PEDOT:PSS and CuSCN as hole transporting materials are shown in Figure 1 (b-d). Energy-levels diagrams reveal that PEDOT:PSS comprised device will have poor electron blocking properties to CuSCN counterpart because of its relatively low LUMO level.

(a)

PEDOT:PSS Ir(ppy)2 (acac)

TPBi

CuSCN

CBP

(b)

(d)

(c)

Figure 1. Schematic diagrams of (a) molecular structures of the organic materials and CuSCN compound, (b) green OLED device architecture; energy-levels of the studied green OLED devices containing, c) PEDOT:PSS as hole injection layer, and (d) CuSCN as an electron blocking, hole-injection and –transporting layer. 6 ACS Paragon Plus Environment

Page 7 of 17

Absorption and transmittance of the PEDOT:PSS and CuSCN thin films deposited on quartz substrates were carried out using UV-Vis spectrophotometer and it is shown in Figure 2. The absorption spectra reveal that CuSCN thin film absorbs strongly near ultraviolet region and it is weaker in the visible region. Conversely, PEDOT:PSS film absorb less light in the UV region and it increases in the visible spectrum. The absorption of light in the visible region is attributed to internal optical transitions involved in intragap polaron levels of the PEDOT:PSS23. Transmittance of CuSCN thin films is higher in the visible region as compare to PEDTO:PSS film as shown in Figure 2.

Quartz/PEDOT:PSS Quartz/CuSCN

0.3

80 60

0.2

40 0.1 0.0

20 300

400 500 600 700 Wavelength (nm)

800

Transmittance (%)

100

Absorption (a.u)

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


0

Figure 2. UV-Vis absorption spectra of solution processed PEDOT:PSS and CuSCN thin films on quartz substrate. Tapping mode atomic force microscopy (AFM) employed to study the surface morphology of ITO, ITO/PEDOT:PSS, and ITO/CuSCN thin films, and it is shown in Figure 3 (a-c). Surface morphology of bare ITO reveals the crystalline grain of ITO with surface roughness around 3.8 nm. PEDOT:PSS film exhibited 1.1 nm surface roughness indicating the very smooth layer deposition. The decreased surface roughness indicates that uniform deposition of PEDOT:PSS fill voids present in bare ITO substrates. The surface roughness of CuSCN film is found to 2.3 nm. 7 ACS Paragon Plus Environment


Page 8 of 17

Morphology of CuSCN covered ITO substrate looks like bare ITO substrates except with some dark and light contrast. CuSCN layer thickness was optimized by changing spin coating speed from 3000 rpm to 4000 rpm and it corresponds to 15 and 9 nm respectively (Figure S1). The effect of CuSCN layer thickness on green OLED device performance is shown in supporting information. The best green OLED performance is obtained by employing 15 nm thick layer of CuSCN.

Figure 3. Surface morphologies of a) pristine ITO, solution-processed films of (b) PEDOT:PSS and (c) CuSCN coated on ITO.

Table 1. Comparison of the green OLED device employing the tri-functional CuSCN against that of PEDOT:PSS from the perspectives of operation voltage (OV), power efficacy (PE), current efficacy (CE), external quantum efficiency (EQE), CIE coordinates, and maximum luminance HTL

Ir(ppy)2 (acac) con.(wt%)

OV (V)

PE lm/W)

CE (cd/A)

EQE (%) (%)

CIE (x,y)

Max. luminance (cd/m2)

@ 100/1,000/10,000 cd/m2 PEDOT:

12.5

4.4/5.3/9.0 31.8/15.9/1.7 44.8/26.7/4.8

11.8/7.0/1.3

(0.33, 0.63)/(0.33, 0.63)/(0.33, 0.63)

10,390

PSS

15.0

4.1/5.0/6.7

45.6/25.1/9.1 59.8/40.1/19..5

15.6/10.5/5.1 (0.33, 0.63)/(0.33, 0.63)/(0.33, 0.63)

18,200

17.5

3.6/4.3/-

20.5/13.4/-

23.2/18.3/-

6.0/4.7/-

(0.32, 0.64)/(0.32, 0.64)/-

7,072

12.5

3.2/4.1/-

46.7/30.0/-

47.4/38.7/-

12.3/10.0/-

(0.33, 0.63)/(0.33, 0.63)/-

7,569

15.0

3.5/4.2/6.4 51.7/40.3/13.4 56.8/53.7/26.9 14.7/13.9/7.0 (0.33, 0.63)/(0.33, 0.63)/(0.34, 0.63)

15,180

17.5

3.1/3.7/-

8,582

CuSCN

21.4/19.6/-

20.9/22.8/-

5.4/5.9/-


(0.33, 0.63)/(0.33, 0.63)/-

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


Table 1 shows the comparison of electroluminescent characteristics like power efficiency (p), current efficiency (c) and external quantum efficiency (EQE) at 100, 1000 and 10,000 cd/m 2 of three dopant concentrations of the green emitter with CBP host OLED devices made up of PEDOT: PSS and tri-functional CuSCN. The best performance was noticed for CuSCN based OLED devices at 15 wt % dopant concentration, revealing p of 40.3 lm/W, c of 53.7 cd/A and EQE of 14.7 % at 1000 cd/m2. By comparing the results of PEDOT:PSS counterpart at 1000 cd/m2, the increments in p, c and EQE were found to be 60.5, 33.9 and 32.4 %, respectively. With the increase in emitter dopant concentration from 15 to 17.5 wt %, the power efficacy of the device decreased by 46.8 %. The deleterious effect of high dopant concentration on the electroluminescent characteristic of the device is imputed to low exciton generation originate from the adverse morphology of emissive layer caused by self-aggregation of emitter material after spin coating25.

Figure 4. Comparison of the green OLED device employing the tri-functional CuSCN against that of PEDOT:PSS from the perspectives on the resulting (a) current density, (b) luminance, (c) power efficacy, (d) current efficiency, and (e) external quantum efficiency.



Figure 4 a shows the current density versus voltage (J-V) plot 15 wt % dopant concentration green OLED device based on PEDOT:PSS and CuSCN HIL/HTL. J-V curve was obtained by connecting the positive terminal to the ITO electrode and negative to the Al electrode. It is noticed that by an increase in positive bias voltage, the forward bias current of the device increases significantly, however, the reverse bias current remains low, which indicate that device is excellently working as a rectifying diode. PEDOT:PSS based device shows high forward bias current as compared to CuSCN counterpart at a high bias voltage. Figure 4b shows the plot of luminance versus applied bias voltage of PEDOT:PSS and CuSCN devices. It reveals that the operating voltage of CuSCN based device is lower than PEDOT:PSS counterparts by ~ 0.5 V. The low operating voltage for CuSCN is attributed to its high work function (5.5 eV) as compared to PEDOT:PSS (5.0 eV) device that reduce the hole injection energy barrier between CuSCN and EML interface by 0.5 eV, as depicted in Figure 1 (c & d). In case of PEDOT:PSS, the hole injection energy barrier height at HIL/HTL and EML interface is around 1.0 eV that is beyond the permissible limit of ohmic contact, hence require an extra energy to effectively inject the holes into EML, resulting into the high operative voltage and the experimental results corroborate the hypothesis. The power efficacy is shown in Figure 4c exhibit that CuSCN HIL/HTL enhance the power efficacy by 13, 60 and 47 % at 100, 1000 and 10,000 cd/m2, as compared to PEDOT:PSS counterpart, respectively. The superior performance of CuSCN based device at high luminance is attributed to its high conduction band value, which is located at 1.8 eV. The energy barrier height between the conduction band of CuSCN and lowest unoccupied molecular orbital (LUMO) of EML is close to 1.1 eV. In contrast, LUMO of PEDOT:PSS is 0.4 eV lower than LUMO of CBP EML. This explains that CuSCN is capable to effectively block the electrons than the PEDOT:PSS. More importantly, the high conduction band of CuSCN confines the excitons tightly within the


Page 10 of 17

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


EML at the high operating voltage and eventually help to give high power efficacy at high luminance. In both types of devices, the power efficacy roll-off is slow at low luminance; however, it accelerated from 1000 cd/m2 and significantly declined beyond 10,000 cd/m 2. The current efficiency and EQE plots follow the similar trend at high luminance, as shown in Figure 4 (d and e). The high current efficiency and EQE demonstrated by PEDOT:PSS, as compared to CuSCN counterpart at 100 cd/m2, is attributed to its high charge carrier mobility due to oxidative doping, whereas CuSCN is intrinsic wide band gap material and possesses low charge carrier mobility.

Figure 5. Comparison of the green OLED device employing the tri-functional CuSCN against that of PEDOT:PSS from the perspectives of electroluminescence (EL) spectra at 1,000 nits.

Figure 5 shows normalized electroluminescent spectra of the devices containing 15 wt% green Ir (ppy)2 (acac) dye in the CBP host corresponds to the PEDOT:PSS and CuSCN HIL/HTLs devices. The peaks of the emission spectra exhibit the emission from both devices are in the green region. The slightly spectral difference observed between 540 to 560 nm regions is attributed to different optical properties of both HIL/HTLs rather than their light absorption property.



4. Conclusions We have successfully demonstrated the tri-functional role of CuSCN as an excellent HIL/HTL for highly efficient solution processed green OLEDs. The high power efficacy of the green OLED devices with CuSCN relative to PEDOT:PSS HIL/HTL counterparts is mainly attributed to its high conduction band level and deep valence band position. These excellent optoelectronic properties play an important role to reduce the operation voltage of the device as well as effective blocking of the electrons and efficient injection of holes at the HIL/HTL and EML interface. The present results will be helpful to fabricate high efficacy white OLED for general lighting purpose. Supporting Information Thickness depth profiles of CuSCN thin films prepared at 3000 and 4000 rpm by using spin coating are shown in figure S1. CuSCN thickness dependent green OLED performance is tabulated in Table (S2). Acknowledgements The authors would like to acknowledge the support from Ministry of Science and Technology and Ministry of Economic Affairs, Taiwan. This work was financially supported in part by Grants 1062811-M-007 -065 – and 104-EC-17-A-07-S3-012.


Page 12 of 17

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


References [1] Han, T.-H.; Choi, M.-R.; Jeon, C.-W.; Kim, Y.-H.; Kwon, S.-K.; Lee, T.-W. UltrahighEfficiency Solution-Processed Simplified Small-Molecule Organic Light-Emitting Diodes Using Universal Host Materials. Sci. Adv. 2016, 2, e1601428

[2] Aizawa, N.; Pu, Y.-J.; Watanabe, M.; Chiba, T.; Ideta, K.; Toyota, N.; Igarashi, M.; Suzuri, Y.; Sasabe H.; Kido J. Solution-Processed Multilayer Small-Molecule Light-Emitting Devices with High-Efficiency White-Light Emission. Nat. Commun. 2014, 5, 5756.

[3] Kim, H. J.; Lee, C.; Godumala, M.; Choi, S.; Park, S. Y.; Cho, M. J.; Park S.; Choi D. H. Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes Using a New Polymeric Emitter Containing Non-Conjugated Cyclohexane Units. Polym. Chem. 2018, 9, 1318-1326.

[4] Zhang, M.; Höfle, S.; Czolk, J.; Mertens A.; Colsmann A. All-Solution Processed Transparent Organic Light Emitting Diodes. Nanoscale 2015, 7, 20009-2094.

[5] Zeng, X.-C.; Wang, J.-Y.; Xu, L.-J.; Wen H.-M.; Chen Z.-N. Solution-Processed OLEDs Based on Phosphorescent PtAu2 Complexes with Phenothiazine-Functionalized Acetylides. J. Mater. Chem. C 2016, 4, 6096-6013.

[6] Jong, M. P. D.; Ijzendoorn, L. J. V.; Voigt, M. J. A. D. Stability of the Interface Between Indium-Tin-Oxide and Poly(3,4- Ethylenedioxythiophene)/Poly(Styrenesulfonate) in Polymer Light-Emitting Diodes. Appl. Phys. Lett. 2000, 77, 2255-2257.

[7] Girtan, M.; Rusu, M. Role of ITO and PEDOT:PSS in Stability/Degradation of Polymer: Fullerene Bulk Heterojunctions Solar Cells. Sol. Energy Mater. Sol. Cells 2010, 94, 446-450.

[8] Vitoratos, E.; Sakkopoulos, S.; Dalas, E.; Paliatsas, N.; Karageorgopoulos, D.; Petraki, F.; Kennou, S.; Choulis S.A. Thermal Degradation Mechanisms of PEDOT:PSS. Org., Electron. 2009, 10, 61-66. 13 ACS Paragon Plus Environment


[9] Manders, J. R.; Tsang, S.-W.; Hartel, M. J.; Lai, T.-H.; Chen, S.; Amb, C. M.; Reynolds, J. R.; So, F. Solution-Processed Nickel Oxide Hole Transport Layers in High Efficiency Polymer Photovoltaic Cells. Adv. Funct. Mater. 2013, 23, 2993-3001.

[10] So, F.; Krummacher, B.; Mathai, M. K.; Poplavskyy, D.; Choulis, S. A. Recent Progress in Solution Processable Organic Light Emitting Devices. J. Appl. Phys. 2007, 102, 091101.

[11] Cai, M.; Xiao, T.; Hellerich, E.; Chen, Y.; Shinar, R.; Shinar, J. High-Efficiency SolutionProcessed Small Molecule Electrophosphorescent Organic Light-Emitting Diodes. Adv. Mater. 2011, 23, 3590-3596.

[12] Yu, X.; Marks, T.J.; Facchetti A. Metal Oxides for Optoelectronic Applications. Nat. Mater. 2016, 15, 383-396.

[13] Liu, S.; Liu, R.; Chen, Y.; Ho, S.; Kim, J. H.; So, F. Nickel Oxide Hole Injection/Transport Layers for Efficient Solution-Processed Organic Light-Emitting Diodes. Chem. Mater. 2014, 26, 4528-4534.

[14] Li, Y.-H.; Lu, X.; Wang, R.; Ma, Y.-Y.; Duhm S.; Fung M.-K. Cu-Doped Nickel Oxide Prepared Using a Low-Temperature Combustion Method as a Hole-Injection Layer for HighPerformance OLEDs. J. Mater. Chem. C 2017, 5, 11751-11757.

[15] Kim, J.; Park, H. J.; Grigoropoulos, C. P.; Lee D.; Jang J. Solution-Processed Nickel Oxide Nanoparticles with NiOOH for Hole Injection Layers of High-Efficiency Organic Light-Emitting Diodes. Nanoscale 2016, 8, 17608-17615.

[16] Li, X.; Xie, F.; Zhang, S.; Hou, J.; Choy, W. CH. MoOx and V2Ox as Hole and Electron Transport Layers Through Functionalized Intercalation in Normal and Inverted Organic Optoelectronic Devices. Light Sci. Applicat. 2015, 4, E273.


Page 14 of 17

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


[17] Chiu T.-L.; Chuang Y.-T.; Spectral Observations of Hole Injection with Transition Metal Oxides for an Efficient Organic Light-Emitting Diode. J. Phys. D: Appl. Phys. 2015, 48, 075101.

[18] Kim, J.; Kanwat, A.; Kim, H.-M.; Jang J. Solution Processed Polymer Light Emitting Diode with Vanadium-Oxide Doped PEDOT:PSS. Phys. Status Solidi A 2015, 212, 640-645.

[19] Zhang, H.; Fu, Q.; Zeng W.; Ma D. High-Efficiency Fluorescent Organic Light-Emitting Diodes with MoO3 and PEDOT:PSS Composition Film as a Hole Injection Layer. J.Mater.Chem. C 2014, 2, 9620-9624.

[20] Chang, C.-C.; Hsieh, M.-T.; Chen J.-F.; Hwang S.-W.; Chen C. H. Highly Power Efficient Organic Light-Emitting Diodes with a p-Doping Layer. Appl. Phys. Lett. 2006, 89, 253504.

[21] Youn, J. H.; Baek, S. J.; Kim, H. P.; Nam, D. H.; Lee, Y.; Lee J. G.; Jang J. Improving The Lifetime of a Polymer Light-Emitting Diode by Introducing Solution Processed Tungsten-Oxide. J.Mater.Chem.C 2013, 1, 3250-3254.

[22] Wijeyasinghe N.; Anthopoulos T. D. Copper(I) Thiocyanate (CuSCN) as a Hole Transport Material for Large-Area Opto/Electronics. Semicond. Sci. Technol. 2015, 30, 104002.

[23] 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, 93-100.

[24] Ding, T.; Wang, N.; Wang, C.; Wu, X.; Liu, W.; Zhang, Q.; Fana W.; Sun, X. W. SolutionProcessed Inorganic Copper(I) Thiocyanate as a Hole Injection Layer for High-Performance Quantum Dot-Based Light-Emitting Diodes. RSC Adv. 2017, 7, 26322-26327.



[25] Sahoo, S.; Dubey, D. K.; Singh, M.; Joseph, V.; Thomas, K. R. J.; Jou, J.-H. Highly Efficient Deep-Blue Organic Light Emitting Diode with a Carbazole Based Fluorescent Emitter. Jap. J. Appl. Phys. 2018, 57, 04FL08.


Page 16 of 17

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


TOC Graphic


Enabling High Efficiency Organic Light Emitting Diode with a Tri

Recommend Documents