Understanding the Origin of Degradation of InP‐Quantum Dot Light‐Emitting Diodes

Shin, Dong Hyun; Lampande, Raju; Kim, Su Jeong; Jung, Young Hun; Kwon, Jang Hyuk

doi:10.1002/aelm.202200256

Cited by 17 publications

(21 citation statements)

References 23 publications

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“…Under constant electron stress to EOD with Zn 0.85 Mg 0.15 O ETL, shows an operating voltage drop, but with the combination of exciton–electron stress, QD degradation is more serious, and therefore, it shows an increase in operating voltage. A similar tendency was observed by our group in a previously reported study …”

Section: Resultssupporting

confidence: 92%

“…However, EODs with the Zn 0.85 Mg 0.15 O ETL showed a decrease in operating voltage from 5.8 to 3.0 V over 30 h. Such a decrease in the operating voltage is because of a change in the intrinsic physical properties of Zn 0.85 Mg 0.15 O under electrical stress. Generally, when thin Zn 0.85 Mg 0.15 O films are stressed or in storage, the oxygen vacancies and hydroxyl bond content may change due to the intrinsic physical properties of Zn 0.85 Mg 0.15 O. , These data show that Zn 0.85 Mg 0.15 O is unstable to electron stress, which limits the QLED device lifetime when Zn 0.85 Mg 0.15 O is used. Under constant electron stress to EOD with Zn 0.85 Mg 0.15 O ETL, shows an operating voltage drop, but with the combination of exciton–electron stress, QD degradation is more serious, and therefore, it shows an increase in operating voltage.…”

Section: Resultsmentioning

confidence: 99%

“…Later, our group analyzed the causes of degradation in our InP QLEDs; the ZnMgO ETL exhibited an unstable behavior under electrical stress. The unstable behavior of the ZnMgO ETL was found to be due to oxygen vacancies and hydroxyl bonds, which caused changes in the intrinsic physical properties of the ETL over time. , For the progress of long-lifetime and high-efficiency InP QLED based devices, stable low-mobility ETLs are necessary.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Stable ZnS Electron Transport Layer for High-Performance Inverted Cadmium-Free Quantum Dot Light-Emitting Diodes

Mude

Khan

Thuy

et al. 2022

ACS Appl. Mater. Interfaces

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We report high-efficiency and long-lifetime inverted green cadmium-free (InP-based) quantum dot light-emitting diodes (QLEDs) using a stable ZnO/ZnS cascaded electron transport layer (ETL). We have successfully developed a strategy to spin-coat stable ZnS ETLs with a relatively higher conduction band minimum (CBM) and lower electron mobility than that of ZnO, which leads to balanced carrier injection and an improved device lifetime. Analysis shows that by using the ZnO/ZnS cascaded ETL, electron injection is reduced, resulting in an improved charge balance in the QD layer and suppressed exciton quenching, which preserves the emission properties of QDs. Optimized devices with ZnO/ZnS cascaded ETLs show a maximum external quantum efficiency of 10.8% and a maximum current efficiency of 37.5 cd/A; these efficiency values are an almost 2.2-fold improvement compared to those of reference devices without ZnS. The QLED devices also showed a remarkably long lifetime (LT 70 ) of 265 h at an initial luminance of 1000 cd/m 2 . The predicted half-lifetime (LT 50 ) at 100 cd/m 2 is 60,255 h, which, to our knowledge, is currently the longest lifetime yet reported for InP-based green QLEDs.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stable ZnS Electron Transport Layer for High-Performance Inverted Cadmium-Free Quantum Dot Light-Emitting Diodes

Mude

Khan

Thuy

et al. 2022

ACS Appl. Mater. Interfaces

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“…As reported, InP-based QDs are more vulnerable to exciton and electron−exciton stress than Cd-based QDs or organic emitters because of the more populated surface defects after the operation, which could induce the nonradiative Auger recombination process (Figure 11f). 193 Although the operational lifespan of Cd-free QD-LEDs has achieved rapid improvement 44,50 based QDs, the surface/crystalline defects required further control to obtain improved stability.…”

Section: Degradation Mechanismsmentioning

confidence: 99%

Review: Quantum Dot Light-Emitting Diodes

Jang

2023

Chem. Rev.

133

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Quantum dot light-emitting diodes (QD-LEDs) are one of the most promising self-emissive displays in terms of light-emitting efficiency, wavelength tunability, and cost. Future applications using QD-LEDs can cover a range from a wide color gamut and large panel displays to augmented/virtual reality displays, wearable/flexible displays, automotive displays, and transparent displays, which demand extreme performance in terms of contrast ratio, viewing angle, response time, and power consumption. The efficiency and lifetime have been improved by tailoring the QD structures and optimizing the charge balance in charge transport layers, resulting in theoretical efficiency for unit devices. Currently, longevity and inkjet-printing fabrication of QD-LEDs are being tested for future commercialization. In this Review, we summarize significant progress in the development of QD-LEDs and describe their potential compared to other displays. Furthermore, the critical elements to determine the performance of QD-LEDs, such as emitters, hole/electron transport layers, and device structures, are discussed comprehensively, and the degradation mechanisms of the devices and the issues of the inkjet-printing process were also investigated.

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“…The over injected electrons could accumulate at the interface of hole transport layer (HTL)/QD, which charge the QDs and thereby trigger the nonradiative Auger recombination. [12,13] In addition, the excess electrons could overflow into the HTL, leading to the degradation of HTL and the generation of Joule heat. [3,14] 2) Exciton quenching.…”

mentioning

confidence: 99%

Efficient InP Green Quantum‐Dot Light‐Emitting Diodes Based on Organic Electron Transport Layer

Gao

Zhang

Pan

et al. 2022

Advanced Optical Materials

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for blue QLEDs [11] have been reported. The above InP QLEDs are based on a hybrid organic/QDs/inorganic architecture using inorganic ZnO nanoparticles as electron transport layer (ETL) materials. With ZnO ETL, electron injection is very efficient due to the high electron mobility of ZnO and the low electron injection barrier at the interface of QD/ZnO. [7,8] However, the ZnO ETL also induces several issues as discussed below. 1) Charge imbalance. With ZnO ETL, electron injection is more efficient than holes. The over injected electrons could accumulate at the interface of hole transport layer (HTL)/QD, which charge the QDs and thereby trigger the nonradiative Auger recombination. [12,13] In addition, the excess electrons could overflow into the HTL, leading to the degradation of HTL and the generation of Joule heat. [3,14] 2) Exciton quenching. Due to the matched conduction band minimums (CBM) of ZnO and QDs, electron transfer between QDs and ZnO could occur spontaneously, which could turn the QDs into the dark state. [15,16] In addition, the ZnO NPs contain many hydroxyl groups and oxygen vacancies, which serve as the trap states that quench the excitons. [17,18] 3) Positive aging. The ZnO ETL could slowly react with the epoxy resin and the Al metal electrode, and as a result, the defects of ZnO are gradually passivated, leading to a gradually increased device efficiency. [19][20][21] Such a positive aging phenomenon could persist for several days, making it difficult to predict the degradation behavior of devices. [15] 4) Agglomeration. The ZnO NPs are easily aggregated in the solution, [19] making it difficult for storage, processing, and handling.In view of the above problems, various solutions have been proposed; for instance, introducing an insulating layer between QDs and ETL, modificating the surface of ZnO NPs and doping ZnO NPs with metals. In 2013, Char and co-workers inserted an interfacial dipole layer (poly-[(9,9-bis(30-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9-ioctylfluorene)], PFN) between ZnO NPs and InP QDs, which reduces the electron injection barrier and promotes the charge balance of the inverted devices. [20] In 2017, Liu and co-workers utilized Mg-doped ZnO NPs as the ETL materials to improve electron injection of the inverted InP QLEDs. [21] Yang and co-workers reported a series of methods to modify ZnO NPs; for example, doping ZnO NPs with In [22] or Al; [23] recently, they implemented acrylate-functionalized ZnMgO NPs to suppress the emission quenching at QD/ZMO interface. [24] Although these methods are effective in improving the device performances, it is quite hard to completely passivate the defects of ZnO and suppress the interfacial ZnMgO thin film is commonly used as an electron transport layer (ETL) in quantum-dot light-emitting diodes (QLEDs); however, it often induces the problems of interface exciton quenching and electron over-injection in the devices. Herein, an organic molecule 2,4,6-tris(3-(diphenylphosphoryl) phenyl)-1,3,5-triazine (PO-T2T) is investigated as...

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Understanding the Origin of Degradation of InP‐Quantum Dot Light‐Emitting Diodes

Cited by 17 publications

References 23 publications

Stable ZnS Electron Transport Layer for High-Performance Inverted Cadmium-Free Quantum Dot Light-Emitting Diodes

Stable ZnS Electron Transport Layer for High-Performance Inverted Cadmium-Free Quantum Dot Light-Emitting Diodes

Review: Quantum Dot Light-Emitting Diodes

Efficient InP Green Quantum‐Dot Light‐Emitting Diodes Based on Organic Electron Transport Layer

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