Achieving Balanced Charge Injection of Blue Quantum Dot Light

Subscriber access provided by WEBSTER UNIV

Energy Conversion and Storage; Plasmonics and Optoelectronics

Achieving Balanced Charge Injection of Blue Quantum Dots LightEmitting Diodes through Transport Layer Doping Strategies Fuzhi Wang, Wenda Sun, Pai Liu, Zhibin Wang, Jin Zhang, Jiangliu Wei, Yang Li, Tasawar Hayat, Ahmed Alsaedi, and Zhan'ao Tan J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b00189 • Publication Date (Web): 11 Feb 2019 Downloaded from http://pubs.acs.org on February 11, 2019

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 30 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 Letters

Achieving Balanced Charge Injection of Blue Quantum Dots Light-Emitting Diodes through Transport Layer Doping Strategies Fuzhi Wang1,Wenda Sun1,2, Pai Liu3,4, Zhibin Wang1, Jin Zhang2, Jiangliu Wei4, Yang Li4, Tasawar Hayat5, Ahmed Alsaedi5, Zhan’ao Tan1,2,*

1. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China.

2. Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.

3. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China.

ACS Paragon Plus Environment

1

The Journal of Physical Chemistry Letters 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

Page 2 of 30

4. Poly OptoElectronics TECH. Ltd. Jiangmen 529020, China.

5. NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia.

AUTHOR INFORMATION

Corresponding Author E-mail: [email protected] (Zhan’ao Tan)


2

Page 3 of 30 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

For blue quantum dots (QDs) light-emitting diodes (QLEDs), the imbalance of charges transport and injection severely affects their efficiency and lifetime. A better charge balance can be realized by improving hole injection while suppressing redundant electrons. Introducing dopants into charge transport layers (CTLs) is an effective and simple strategy to modulate charge injection barrier and mobility. In this work, optoelectronic simulation is performed to investigate the change in physical process within the devices upon CTLs doping. The results confirm that the charge distribution in QDs layer is more balanced and the recombination rate is greatly improved. Under the guidance of theoretical simulation, high performance blue QLEDs were achieved by fine-tuning the charge balance through CTLs doping. The luminance and external quantum efficiency have been dramatically increased from 18679 to 34874 cd/m2 and from 4.7% to 10.7%, respectively. The operation lifetime is also improved ~3.5 times due to the more balanced charge injection.

TOC GRAPHICS


3


Page 4 of 30

KEYWORDS: quantum dots light-emitting diodes, doping, electron-transporting layer, hole-transporting layer, charge balance

Colloidal quantum dots (QDs) have attracted extensive attention owing to their unique properties, such as tunable color emission, narrow full width at half maximum (FWHM), high luminescence quantum yield and solution processability.1 These characteristics make it possible to fabricate QDs light-emitting diodes (QLEDs) on a large scale by solution processes, which forecasts their applications in next-generation displays and lightings.2-9 Since the first QLED was reported in 1994, significant improvement has been achieved in the performance of red and green QLEDs due to the great efforts people made on materials chemistry of QDs and device architecture engineering.5, 8, 1012

However, the performance of blue QLEDs is still inferior to that of green and red ones


4

Page 5 of 30 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


in terms of brightness, efficiency, and especially lifetime, which severely limits their commercial applications.5-6, 8-9, 13-21 For QLEDs, the balance between the injection of electrons and holes is the key factor that affects device efficiency and lifetime.22-24 At present, the state-of-the-art QLEDs mostly adopt organic-inorganic hybrid device structure, in which inorganic metal oxides (such as ZnO nanoparticles) are used as electron transport layer (ETL) and organic materials are used as hole transport layer (HTL). However, due to the difference in injection and transportation between holes and electrons, most QLEDs, especially blue ones, face serious charge imbalance problems. It is well known that the electron mobility of ZnO nanoparticles (~2 × 10-3 cm2v-1s-1)25 is higher than that of commonly used organic HTL materials, which will lead to unbalanced carrier transport in QLEDs. From the perspective of energy level alignment, it is difficult for holes to inject into QDs layer due to the large energy offset at the HTL/QDs interface, especially for blue QDs which have deep highest occupied molecular orbital (HOMO). However, at the ETL/QDs interface, electrons can be easily injected into the EML because the conduction band of ZnO nanoparticles matches well with that of the QDs. All the above leads to excess


5


Page 6 of 30

electrons injected into the EML, which makes the QDs negatively charged, thus leading to the quenching of fluorescence through non-radiative auger recombination process. This is the main reason that restricts the improvement of device efficiency and leads to efficiency roll-off at high operating luminance.23, 26 In addition, the excess electrons may leak into the organic HTL and lead to HTL material degradation. In addition, the heat generated by the process of non-radiative auger recombination and Joule heating further aggravates the degradation of organic materials. The key to improving charge balance in EML is inhibiting redundant electron injection while enhancing hole injection. Introducing additional functional layers (electron blocking layer or double HTLs) and doping CTLs are two effective strategies toward regulate charge transport mobility and charge injection barriers.8,

14, 27-29

Although the incorporation of functional layer can

improve the device performance, it makes the device fabrication via solution process more complicated.7 In contrast, doping CTLs is a simpler and more efficient method. In

this

work,

ZnCdS/ZnS

core/shell

QDs,

poly(9,9-dioctylfluorene-co-N-(4-(3-

methylpropyl))diphenylamine) (TFB) and Al doped ZnO (AZO) nanoparticles were chosen as emitting HTL and ETL materials, respectively. TCTA was chosen as HTL


6

Page 7 of 30 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


dopant to decrease the hole injection barrier30 and the electron mobility of AZO nanoparticles was regulated by the doping metal complexes, zirconium acetylacetonate (ZrAcac) at the cathode side. Optoelectronic simulation is performed to investigate the regulation effect of CTLs doping on the change in physical process within the QLEDs. The simulated results confirm that the charge distribution in EML is more balanced and the recombination rate is greatly improved. Under the guidance of theoretical simulation, high performance blue QLEDs were achieved by fine tuning the charge balance through CTLs doping. Through optimization, the maximum luminance has been dramatically increased from 18679 to 34874cd cd/m2, which is the highest value ever reported for blue QLEDs. The external quantum efficiency (EQE) is increased from 4.7% to 10.7%. Even more striking is that the EQE of the optimized device can be kept above 10% in the luminance range of 5000-22000 cd/m2. At the same time, the stability of the blue QLEDs is improved by CTLs doping due to the improved charge balance.


7


Page 8 of 30

Figure 1 a) energy level diagram QLEDs. b) J-V characteristics of hole-only devices (ITO/PEDOT/HTL/QDs/MoO3/Al) and electron-only devices (ITO/Al/QDs/ETL/Al).

The architecture of the multilayer QLEDs consists of an ITO anode, a PEDOT:PSS hole injection layer (HIL), a HTL, a QDs EML, an ETL and an Al cathode. ZnCdS/ZnS core/shell QDs are selected as blue EML. Figure S2 shows the transmission electron microscopy (TEM) graph of the QDs. This core/shell structure can improve the fluorescence quantum yield and stability of quantum dots. The energy level diagram of the device is depicted as Figure 1a. At the hole injection side, TFB is a widely used HTL


8

Page 9 of 30 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


material for organic light emitting diodes (OLEDs) and QLEDs due to its high hole mobility of ~10-2 cm2v-1s-1. However, it is clear that the large energy offset (1.04 eV) between the HOMO levels of blue QDs (6.44 eV) and TFB (5.4 eV) makes it difficult for hole injection. The HOMO level of TCTA (5.8 eV) is deeper than TFB, therefore stepwise energy levels can be formed at TCTA/QDs interface to facilitate hole injection. Unfortunately, the hole mobility of TCTA is only 3×10-4 cm2v-1s-1

31

and it is difficult for

small organic molecules to form a uniform and continuous film via solution process. In order to take advantage of the excellent hole mobility of TFB and deep HOMO level of TCTA, TCTA is doped into TFB as HTL to guarantee both high mobility and smooth injection of holes. On the other hand, Al doped ZnO nanoparticles are used as ETL. Al doping can effectively alleviate the electron transfer process at the QDs/AZO interface and inhibit blinking in QDs.28 It can be seen from the energy diagram that the electrons can be injected smoothly due to the similar lowest unoccupied molecular orbital (LUMO) levels between the ETL and EML. In order to balance the electron and hole injections, ZrAcac doping is employed to reduce the electron mobility of ETL and thus decelerate the electron injection rate. The electronic energy levels of AZO and ZrAcac are


9


Page 10 of 30

determined from the UV-visble absorption spectra (UV) and ultraviolet photoelectron spectroscopy (UPS), as shown in Figure S1. The modulation effect on charge injection balance through HTL and ETL doping are manifested using the J-V characteristics of single-carrier devices (Figure 1b). The electron-only devices with structure of ITO/Al(30 nm)/QDs(20 nm)/ETL(60 nm)/Al(100 nm) were fabricated to explore the influence of ZrAcac doping on electron transport property. The current density of the device with AZO:ZrAcac hybrid ETL decreases significantly as compared to that of the device with neat AZO ETL. The variation in current density in electron-only devices can reflect the variation in electron current in the working QLEDs. Therefore, it can be concluded that the incorporation of ZrAcac can reduce the electron mobility. The hole-only devices were also fabricated with the structure of ITO/PEDOT(30 nm)/HTL(35 nm)/QDs(20 nm)/MoO3(20 nm)/Al(100 nm). With addition of TCTA into TFB, the current density of the device increases more than one order of magnitude, which proves that the incorporation of TCTA helped to promote the hole injection. By doping HTL and the ETL, the transport of electrons and holes in


10

Page 11 of 30 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 device is more balanced, which forecasts the enhancement in device brightness and efficiency.

Figure 2 Photoelectron simulation of carrier distribution and recombination rate in EML. (a) and (c), neat TFB and AZO are used as HTL and ETL, respectively; (b) and (d), TFB:TCTA and AZO:ZrAcac are used as HTL and ETL, respectively. (0nm represent the interface of HTL/EML)


11


Page 12 of 30

In order to theoretically verify the rationality of our device architecture, optoelectronic simulation was performed to further reveals the change in physical process in the devices with hybrid CTL, as shown in Figure 2. Since there are holes and electron injection barriers, depletion at the injection interface and carrier accumulation at the opposite side in the EML can be observed in Figure 2a and 2b.32, 33 Serious imbalance between holes and electrons concentrations in EML can be observed when neat TFB and AZO are used as CTLs, and the concentration of electrons is significantly higher than that of holes, as shown in Figure 2a. This results in a low recombination rate and uneven recombination region distribution in the EML. Figure 2b and 2d show the charge concentration distribution and recombination rate within EML with hybrid CTLs. The densities of electrons and holes are very close, indicating enhanced charge injection balance. The uniform distribution along the whole depth of recombination region allows more excitons to be formed inside the EML, as a result, the exciton recombination rate is improved by nearly two orders of magnitude, which gives rise to the improvement of


12

Page 13 of 30 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


device brightness. All the simulated results predict an improvement in QLEDs performance.

Figure 3 (a) Cross-sectional SEM image and the performance of QLEDs with different CTLs: (b) current density- luminance-voltage (J-L-V), (c) EQE-L curves and (d) Electroluminescent spectra.


13


Page 14 of 30

Table 1 The parameters of blue QLEDs with different CTLs

Peak HTL

ETL

luminance

Von (V)

(cd/m2)

Peak ηA (cd/A)

Peak EQE (%)

λ

max

(nm)

TFB

AZO

18679

2.6

2.5

4.7

468

TFB:TCTA

AZO:ZrAcac

34874

3.0

5.7

10.7

464

The cross-sectional SEM of the device with TFB:TCTA HTL and AZO:ZrAcac ETL is shown in Figure 3a. The thickness of each functional layer is in good agreement with that acquired by the step profiler. No obvious interface can be observed between the functional layers, thus ensuring the smooth transportation of charges between the layers. Control device is prepared by using neat TFB as HTL. By systematically changing the mass ratio of TFB:TCTA and AZO:ZrAcac, the performances of the devices are analyzed. The mass ratio of TFB:TCTA and AZO:ZrAcac for the optimized device is determined to be 4:6 and 7:8, respectively. The electroluminescence (EL)


14

Page 15 of 30 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


performances of control and optimum devices are shown in Figure 3b-d and the parameters are summarized in Table 1. It can be seen that, the control QLED with neat TFB and AZO exhibits a poor performance. The maximum brightness is 18679 cd/m2, with a peak current efficiency of 2.5 cd/A and a maximum EQE of 4.7%. The EL peak of the control device is located at 468nm, which shows a redshift of 4 nm in comparison with the photoluminescence (PL) peak of the QDs. Upon CTLs doping, significant change in current density and luminance can be observed, as shown in Figure 3b. The current density is remarkably decreased, while the luminance is raised significantly, which leads to enhancement in efficiency. The change in current density comes from two aspects, electron current and hole current. As mentioned above, the deep HOMO level of TCTA can effectively reduce the hole injection barrier, but at the same time, its low hole mobility will decrease the hole mobility of hybrid HTL. Therefore, in order to achieve the best device performance, it is important to find the optimum balance point between hole mobility degradation and injection efficiency improvement. From the variation in current density acquired from the hole-only devices, the hole current increases more than one order of magnitude upon doping TCTA in TFB, which confirms


15


Page 16 of 30

that the incorporation of TCTA helped to promote the hole injection. Therefore, it can be inferred that the drop in device current density comes from the sharp decrease in electron current. This can be attributed to the lowered electron transport ability of AZO upon introduction of ZrAcac. The reduction of redundant electrons injected effectively improves the charge balance in EML, thereby avoiding the Auger non-radiative recombination caused by the negatively charged QDs and leading to enhancement in efficiency. When the mass ratio of AZO:ZrAcac is 7:8, the peak luminance of the QLEDs reaches 34874 cd/m2, and the efficiency reaches the highest values with current efficiency of 5.7 cd/A and EQE of 10.7%, respectively. Further increasing the ZrAcac concentration deteriorates the device’s performance. This is because that too high concentration of ZrAcac causes over-decrease in electron mobility, which in turn deteriorates the balance between electrons and holes. The EL spectra have peaks located at 464nm with full width at half maximum (FWHM) of 25 nm, which is the same as the PL peak of the QDs, and confirms that the recombination position is located in the QDs films.


16

Page 17 of 30 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


Figure 4 (a) Stability curves (luminance versus time) for the blue QLEDs operated at a current density of 50 mA/cm2, and (b) the evolution of EL spectra with operating time.

Currently known QLED degradation occurs mainly through the following ways: electrode corrosion, material degradation, charge accumulation/leakage and Joule heating.22-23 In addition to the intrinsic stability of each functional material itself, charge balancing is one of the key factors affecting device lifetime. The unbalanced charges lead to charging of QDs, nonradiative Auger recombination and leakage currents into the HTLs, all of which deteriorate the operating life of the QLEDs.22, 34, 35 Benefiting from the more balanced charge injection, enhancement in operation lifetime for the QLEDs


17


Page 18 of 30

was achieved. For this lifetime test, both the control and the optimum QLEDs were operated at a constant current density of 50 mA/cm2 in a N2-filled glove box. The curves of luminance versus time are shown in Figure 4a. The initial luminance of the control and the optimum QLEDs was 1196 and 1284 cd/m2, respectively. The luminance decreases with operation time. It can be seen that the QLEDs shows much higher operating lifetime upon CTLs doping. The half lifetime, T50 for the device with TFB:TCTA-AZO:ZrAcac CTLs is 2.02 h, which is almost 3.5 times of that for the QLED with neat TFB-AZO CTLs (0.57 h). This can be ascribed to the more balanced charge injection in the QDs emitting layer. The EL spectra of both the control and the optimum devices show good stability during device operation. After operating under a current density of 50 mA/cm2 for 3 hours, a slight red shift of only 1-2 nm is observed for the EL spectra peak of the both devices, as shown in Figure 4b. Although our device lifetime is still lower than that of red and green ones reported, it is the highest value among the high-performance blue QLEDs reported in literatures, as seen in Table S1. These results prove that doping CTLs is an effective and simple strategy to regulate charge balance in QLEDs.


18

Page 19 of 30 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


In conclusion, high-performance blue QLEDs have been fabricated under the guidance of optoelectronic simulation results performed on blue QLEDs. By finely tuning the charge transport property and charge injection barrier, charge balance is achieved in the QDs EML. The hybrid HTL composed of TCTA and TFB possess the advantages of both high hole mobility and lowered hole injection barrier. The use of hybrid HTL can effectively promote hole injection efficiency. On the cathode side, the electron transport in ETL is effectively reduced by doping ZrAcac into AZO, thus suppressing the excessive electron current. The use of hybrid HTL and ETL results in that more balanced electrons and holes can be injected into the EML. The more balanced charges lead to decrease in QDs charging, nonradiative Auger recombination and leakage currents into the HTLs, all of which greatly improve the operating life of the blue QLEDs. The usage of hybrid CTLs is a simple and effective way to optimize the performance of blue QLEDs.

ASSOCIATED CONTENT


19


Page 20 of 30

Supporting Information. The following files are available free of charge. Experimental Methods (PDF) UV-visble absorption spectra and ultraviolet photoelectron spectroscopy (UPS) of the charge transport layers (PDF)

Comparison of operation lifetime for single junction blue QLEDs

AUTHOR INFORMATION

Corresponding Author *[email protected] (Zhan’ao Tan)

Author Contributions Fuzhi Wang, Wenda Sun and Pai Liu contributed equally to this work.

The authors declare no competing financial interests.

ACKNOWLEDGMENT


20

Page 21 of 30 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


This work was supported by the National Natural Science Foundation of China (51573042, 51873007, 21835006, 51602102), the Fundamental Research Funds for the Central Universities in China (2018MS032, 2016MS50, 2017MS027, 2018ZD07, 2017XS084,

2016YQ06),

Jiangmen Innovative & Entepreneurial Research Team Program

and

Guangdong

Provincial Science and Technology (2016B090906001).


21


Page 22 of 30

REFERENCES (1) Dai, X.; Deng, Y.; Peng, X.; Jin, Y. Quantum-Dot Light-Emitting Diodes for LargeArea Displays: Towards the Dawn of Commercialization. Adv. Mater. 2017, 29, 201256.

(2) Ji, W.; Liu, S.; Zhang, H.; Wang, R.; Xie, W.; Zhang, H. Ultrasonic Spray Processed, Highly Efficient All-Inorganic Quantum Dot Light Emitting Diodes. ACS

Photonics 2017, 4, 1271−1278.

(3) Zhang, M.; Hu, B.; Meng, L.; Bian, R.; Wang, S.; Wang, Y.; Liu, H.; Jiang, L. Ultrasmooth Quantum Dot Micropatterns by a Facile Controllable Liquid-Transfer Approach: Low-Cost Fabrication of High-Performance QLED. J. Am. Chem. Soc. 2018,

140, 8690-8695.

(4) Kim, T.-H.; Cho, K.-S.; Lee, E. K.; Lee, S. J.; Chae, J.; Kim, J. W.; Kim, D. H.; Kwon, J.-Y.; Amaratunga, G.; Lee, S. Y.; Choi, B. L.; Kuk, Y.; Kim, J. M.; Kim, K. Fullcolour quantum dot displays fabricated by transfer printing. Nat. Photonics 2011, 5, 176182.


22

Page 23 of 30 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


(5) Zhang, H.; Chen, S.; Sun, X. W. Efficient Red/Green/Blue Tandem Quantum-Dot Light-Emitting Diodes with External Quantum Efficiency Exceeding 21%. ACS Nano 2018, 12, 697-704.

(6) Liu, Y.; Jiang, C.; Song, C.; Wang, J.; Mu, L.; He, Z.; Zhong, Z.; Cun, Y.; Mai, C.; Wang, J.; Peng, J.; Cao, Y. Highly Efficient All-Solution Processed Inverted Quantum Dots Based Light Emitting Diodes. ACS Nano 2018, 12, 1564-1570.

(7) Zhang, Z.; Ye, Y.; Pu, C.; Deng, Y.; Dai, X.; Chen, X.; Chen, D.; Zheng, X.; Gao, Y.; Fang, W.; Peng, X.; Jin, Y. High-Performance, Solution-Processed, and InsulatingLayer-Free Light-Emitting Diodes Based on Colloidal Quantum Dots. Adv. Mater. 2018,

30, e1801387.

(8) Dai, X.; Zhang, Z.; Jin, Y.; Niu, Y.; Cao, H.; Liang, X.; Chen, L.; Wang, J.; Peng, X. Solution-processed, high-performance light-emitting diodes based on quantum dots.

Nature 2014, 515, 96-99.


23


Page 24 of 30

(9) Shen, H.; Cao, W.; Shewmon, N. T.; Yang, C.; Li, L. S.; Xue, J. High-efficiency, low turn-on voltage blue-violet quantum-dot-based light-emitting diodes. Nano Lett. 2015, 15, 1211-6.

(10) Colvin, V. L.; Schlamp, M. C.; Alivisatos, A. P. Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer. Nature 1994, 370, 354357.

(11) Ghosh, B.; Yamada, H.; Chinnathambi, S.; Ozbilgin, I. N. G.; Shirahata, N. Inverted Device Architecture for Enhanced Performance of Flexible Silicon Quantum Dot Light-Emitting Diode. J. Phys. Chem. Lett. 2018, 9, 5400-5407.

(12) Cao, W.; Xiang, C.; Yang, Y.; Chen, Q.; Chen, L.; Yan, X.; Qian, L. Highly stable QLEDs with improved hole injection via quantum dot structure tailoring. Nat. Commun. 2018, 9, 2608.

(13) Lee, K.-H.; Lee, J.-H.; Song, W.-S.; Ko, H.; Lee, C.; Lee, J.-H.; Yang, H. Highly Efficient, Color-Pure,Color-Stable Blue Quantum Dot Light-Emitting Devices. ACS Nano 2013, 7, 7295-7302.


24

Page 25 of 30 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


(14) Lin, Q.; Wang, L.; Li, Z.; Shen, H.; Guo, L.; Kuang, Y.; Wang, H.; Li, L. S. Nonblinking Quantum-Dot-Based Blue Light-Emitting Diodes with High Efficiency and a Balanced Charge-Injection Process. ACS Photonics 2018, 5, 939-946.

(15) Cheng, T.; Wang, Z.; Jin, S.; Wang, F.; Bai, Y.; Feng, H.; You, B.; Li, Y.; Hayat, T.; Tan, Z. a. Pure Blue and Highly Luminescent Quantum-Dot Light-Emitting Diodes with Enhanced Electron Injection and Exciton Confinement via Partially Oxidized Aluminum Cathode. Adv. Opt. Mater. 2017, 5, 1700035.

(16) Wang, F.; Jin, S.; Sun, W.; Lin, J.; You, B.; Li, Y.; Zhang, B.; Hayat, T.; Alsaedi, A.; Tan, Z. a. Enhancing the Performance of Blue Quantum Dots Light-Emitting Diodes through Interface Engineering with Deoxyribonucleic Acid. Adv. Opt. Mater. 2018, 6, 1800578.

(17) Kwak, J.; Bae, W. K.; Lee, D.; Park, I.; Lim, J.; Park, M.; Cho, H.; Woo, H.; Yoon, D. Y.; Char, K.; Lee, S.; Lee, C. Bright and efficient full-color colloidal quantum dot lightemitting diodes using an inverted device structure. Nano Lett. 2012, 12, 2362-6.


25


Page 26 of 30

(18) Pan, J.; Wei, C.; Wang, L.; Zhuang, J.; Huang, Q.; Su, W.; Cui, Z.; Nathan, A.; Lei, W.; Chen, J. Boosting the efficiency of inverted quantum dot light-emitting diodes by balancing charge densities and suppressing exciton quenching through band alignment.

Nanoscale 2018, 10, 592–602.

(19) Yang, Y.; Zheng, Y.; Cao, W.; Titov, A.; Hyvonen, J.; MandersJesse, R.; Xue, J.; Holloway, P. H.; Qian, L. High-efficiency light-emitting devices based on quantum dots with tailored nanostructures. Nat. Photonics 2015, 9, 259-266.

(20) Acharya, K. P.; Titov, A.; Hyvonen, J.; Wang, C.; Tokarz, J.; Holloway, P. H. High efficiency quantum dot light emitting diodes from positive aging. Nanoscale 2017, 9, 14451-14457.

(21) Wang, O.; Wang, L.; Li, Z.; Xu, Q.; Lin, Q.; Wang, H.; Du, Z.; Shen, H.; Li, L. S. High-efficiency, deep blue ZnCdS/CdxZn1−xS/ZnS quantum-dot-light-emitting devices with an EQE exceeding 18%. Nanoscale 2018, 10, 5650-5657.


26

Page 27 of 30 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


(22) Moon, H.; Lee, C.; Lee, W.; Kim, J.; Chae, H. Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light-Emitting Diodes for Display Applications.

Adv. Mater. 2019, e1804294.

(23) Chang, J. H.; Park, P.; Jung, H.; Jeong, B. G.; Hahm, D.; Nagamine, G.; Ko, J.; Cho, J.; Padilha, L. A.; Lee, D. C.; Lee, C.; Char, K.; Bae, W. K. Unraveling the Origin of Operational Instability of Quantum Dot Based Light-Emitting Diodes. ACS Nano 2018,

12, 10231-10239.

(24) Chang, S.; Zhang, X.; Wang, Z.; Han, D.; Tang, J.; Bai, Z.; Zhong, H. AlcoholSoluble Quantum Dots: Enhanced Solution Processability and Charge Injection for Electroluminescence Devices. Ieee. J. Sel. Top. Quant 2017, 23, 1900708.

(25) Qian, L.; Zheng, Y.; Xue, J.; Holloway, P. H. Stable and efficient quantum-dot light-emitting diodes based on solution-processed multilayer structures. Nat. Photonics 2011, 5, 543-548.


27


Page 28 of 30

(26) Bae, W. K.; Park, Y. S.; Lim, J.; Lee, D.; Padilha, L. A.; McDaniel, H.; Robel, I.; Lee, C.; Pietryga, J. M.; Klimov, V. I. Controlling the influence of Auger recombination on the performance of quantum-dot light-emitting diodes. Nat. Commun. 2013, 4, 2661.

(27) Wang, L.; Chen, T.; Lin, Q.; Shen, H.; Wang, A.; Wang, H.; Li, C.; Li, L. S. Highperformance azure blue quantum dot light-emitting diodes via doping PVK in emitting layer. Org. Electron. 2016, 37, 280-286.

(28) Sun, Y.; Wang, W.; Zhang, H.; Su, Q.; Wei, J.; Liu, P.; Chen, S.; Zhang, S. HighPerformance

Quantum

Dot

Light-Emitting

Diodes

Based

on

Al-Doped

ZnO

Nanoparticles Electron Transport Layer. ACS Appl. Mater. Interfaces 2018, 10, 1890218909.

(29) Conaghan, P. J.; Menke, S. M.; Romanov, A. S.; Jones, S. T. E.; Pearson, A. J.; Evans, E. W.; Bochmann, M.; Greenham, N. C.; Credgington, D. Efficient VacuumProcessed Light-Emitting Diodes Based on Carbene-Metal-Amides. Adv. Mater. 2018,

30, e1802285.


28

Page 29 of 30 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


(30) Reineke, S.; Lindner, F.; Schwartz, G.; Seidler, N.; Walzer, K.; Lüssem, B.; Leo, K. White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency. Nature 2009,

1212, 234-8.

(31) Kang, J. W.; Lee, S. H.; Park, H. D.; Jeong, W. I.; Yoo, K. M.; Park, Y. S.; Kim, J. J. Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes. Appl. Phys. Lett. 2007, 90, 151.

(32) Li, X.; Zhao, Y.-B.; Fan, F.; Levina, L.; Liu, M.; Quintero-Bermudez, R.; Gong, X.; Quan, L. N.; Fan, J.; Yang, Z.; Hoogland, S.; Voznyy, O.; Lu, Z.-H.; Sargent, E. H. Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination. Nat.

Photonics 2018, 12, 159-164.

(33) Pinot, C.; Cloarec, H. n.; Doyeux, H.; Haas, G.; Maindron, T.; Prat, C.; Vaufrey, D.; Bonnassieux, Y. Electrical simulations of doped multilayer organic light-emitting diodes (OLEDs) under temperature stress for high current densities. J. Soc. Inf. Display 2008, 16, 457-464.


29


Page 30 of 30

(34) Lim, J.; Park, Y. S.; Wu, K.; Yun, H. J.; Klimov, V. I. Droop-Free Colloidal Quantum Dot Light-Emitting Diodes. Nano Lett. 2018, 18, 6645-6653.

(35) Achermann, M.; Bartko, A. P.; Hollingsworth, J. A.; Klimov, V. I. The effect of Auger heating on intraband carrier relaxation in semiconductor quantum rods. Nat.

Phys. 2006, 2, 557-561.


30

Achieving Balanced Charge Injection of Blue Quantum Dot Light

Recommend Documents