High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiO<i><sub>x</sub></i> Hole‐Injection Layers with a High and Stable Work Function

Lin, Jian; Dai, Xingliang; Liang, Xiaohui; Chen, Desui; Zheng, Xuerong; Li, Yifei; Deng, Yunzhou; Du, Hui; Ye, Yuxun; Chen, Dong; Lin, Chen; Ma, Luying; Bao, Qinye; Zhang, Haibing; Wang, Linjun; Peng, Xiaogang; Jin, Yizheng

doi:10.1002/adfm.201907265

Cited by 63 publications

(61 citation statements)

References 57 publications

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“…Further experiments, described later and detailed in the Supporting Information (Section S10), support this conclusion. Modification of the work function of the NiO x /perovskite interface, using aminobenzoic acid (“Amino”) or bromobenzoic acid (“Bromo”), [ 40–43 ] yields limited improvement in selectivity, and this improvement is independent of the direction the work function shifts (Figure S8, left, Supporting Information), supporting the hypothesis of an interfacial effect at the perovskite/NiO x junction. However, inserting thin polymeric HTLs between NiO x and the perovskite absorber—which can alleviate this interfacial effect—leads to a substantial improvement in selectivity, with a corresponding increase in V oc of more than 200 mV, resulting in our highest reported V oc of 1143 mV (Figure S8, right, Supporting Information).…”

Section: Resultsmentioning

confidence: 72%

Investigation of the Selectivity of Carrier Transport Layers in Wide‐Bandgap Perovskite Solar Cells

et al. 2021

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Excellent contact passivation and selectivity are prerequisites to realize the full potential of high‐material‐quality perovskite solar cells, first to maximize the internal voltage (or quasi‐Fermi‐level separation) iV within the absorber, then to translate this high internal voltage into a high external voltage V. Experimental quantification of contact passivation and selectivity is, thus, key to improving device performance. Here, open‐circuit measurements of iVoc and Voc, combined with surface photovoltage measurements, are used to systematically quantify the passivation—using iVoc as a metric—and the selectivity—defined as Soc = Voc/iVoc—of a range of common carrier transport layers to wide‐bandgap (1.67 eV) perovskite absorbers. The resulting solar cells suffer from large voltage deficits, particularly when NiOx is used as the hole transport layer, even though it provides better passivation than its polymer‐based counterparts (PTAA and PTAA/PFN). This indicates a poor selectivity of NiOx (Soc < 0.81 for NiOx‐based devices), whereas devices using polymer‐based hole transport layers exhibit high selectivity (Soc = 0.94–0.95). In agreement with recent reports, this low selectivity is attributed to the formation of an interlayer of non‐perovskite material with high resistance to holes at the perovskite/NiOx interface. These measurements also imply that the selectivity of the C60‐based electron transport layers is relatively good.

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Section: Resultsmentioning

confidence: 72%

Investigation of the Selectivity of Carrier Transport Layers in Wide‐Bandgap Perovskite Solar Cells

et al. 2021

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“…In contrast, our QLEDs using monolayer regular QD show much lower brightness at both the100% and 105% bandgap voltages, which are 10 and 27 cd m -2 (Figure 3a), respectively. In previously reported high performance QLEDs, brightness of 10 -600 cd m -2 can be obtained at the bandgap voltages (Extended Data Table 2) [4][5][6][7][8][9][10][11] , and to achieve a brightness of 3000 cd m -2 these devices need to be operated at more than 125% bandgap voltage. Due to the decreased driving voltage, the power conversion efficiencies of QLEDs using large QDs have also been remarkably improved.…”

Section: Figure 1|mentioning

confidence: 99%

“…It is the PCE that determines how energy efficient the QLEDs are, and high PCEs simultaneously require high EQEs and large irradiative recombination currents at low bias voltages 13 . Current state of art QLEDs ubiquitously adopt multiple QD layers, they are featured with high peak EQEs but small recombination currents around the bandgap voltages [4][5][6][7][8][9][10][11][12] . To achieve a brightness ranging from 1,000 to 3,000 cd m -2 -one that required for flat panel and outdoor displays 14,15 , bias voltages that noticeably higher than the bandgap voltage need to be applied.…”

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confidence: 99%

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23% power conversion efficiency light-emitting diodes using monolayer quantum dots

Fan¹,

Gao²,

Liu³

et al. 2021

Preprint

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Ever since the first proposal of using colloidal quantum dots (QDs) as the active emitting layer of light-emitting diode (LED), a monolayer of QD is considered as a better option than the multilayer ones. Owing to the slow charge transport rate among different QD layers, quantum dot light-emitting diodes (QLEDs) adopting multilayer QDs need to be driven at higher than the bandgap bias voltage to achieve practically useful brightness, resulting in increased power consumptions and heat generations, and reduced device lifetimes. Unfortunately, QLEDs using monolayer QDs always suffer from unwanted recombination in hole transport layers (HTLs) and low external quantum efficiencies (EQEs) as a result of electron overflow from QDs into HTLs. Herein, we tackle this dilemma by packing QDs with large size into monolayers, which enables us to mitigate the unwanted electron overflow and retain high EQE. More importantly, it further allows us to boost the irradiative recombination current at bandgap voltage. By virtue of simultaneously obtained high EQE and irradiative recombination rate, we can achieve brightness of 1,100 cd m-2 and 3,000 cd m-2 at 100% and 105% bandgap voltages with record high power conversion efficiencies (PCEs) of 23% and 22%, respectively. Since heat generation has been depressed and devices can be operated at reduced bias voltage, they show unprecedented T95 operation lifetimes (the time for the luminance to decrease to 95% of the initial value) of more than 4,000 h with an initial brightness of 3,000 cd m-2, and equivalent T95 lifetimes of more than 20,000 h at 1,000 cd m-2.

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“…Quantum‐dot light‐emitting diodes (QLEDs) have drawn considerable research interest because of their narrow emission linewidths, high electroluminescence efficiencies and low‐cost solution‐based fabrication process [1–4] . State‐of‐the‐art QLEDs generally adopt a multilayer structure of anode/hole‐injection layer (HIL)/hole‐transporting layer (HTL)/QDs/electron‐transporting layer (ETL)/metal cathode [3–21] . In this structure, solution‐processed transition metal oxides, including NiO x , VO x , WO x and MoO x , have been investigated as HILs for QLEDs [11,20,22–28] .…”

Section: Figurementioning

confidence: 99%

Synthesis of Cu‐Modified Nickel Oxide Nanocrystals and Their Applications as Hole‐Injection layers for Quantum‐Dot Light‐Emitting Diodes

Wang

et al. 2021

Chemistry A European J

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Solution‐processed NiOx thin films have been applied as hole‐injection layers (HILs) in quantum‐dot light‐emitting diodes (QLEDs). The commonly used NiOx HILs are prepared by the precursor‐based route, which requires high annealing temperatures of over 275 °C to in situ convert the precursors into oxide films. Such high processing temperatures of NiOx HILs hinder their applications in flexible devices. Herein, we report a low‐temperature approach based on Cu‐modified NiOx (NiOx‐Cu) nanocrystals to prepare HILs. A simple post‐synthetic surface‐modification step, which anchors the copper agents onto the surfaces of oxide nanocrystals, is developed to improve the electrical conductivity of the low‐temperature‐processed (135 °C) oxide‐nanocrystal thin films. In consequence, QLEDs based on the NiOx‐Cu HILs exhibit an external quantum efficiency of 17.5 % and a T95 operational lifetime of ∼2,800 h at an initial brightness of 1,000 cd m−2, meeting the commercialization requirements for display applications. The results shed light on the potential of using NiOx‐Cu HILs for realizing high‐performance flexible QLEDs.

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High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiO_x Hole‐Injection Layers with a High and Stable Work Function

Cited by 63 publications

References 57 publications

Investigation of the Selectivity of Carrier Transport Layers in Wide‐Bandgap Perovskite Solar Cells

Investigation of the Selectivity of Carrier Transport Layers in Wide‐Bandgap Perovskite Solar Cells

23% power conversion efficiency light-emitting diodes using monolayer quantum dots

Synthesis of Cu‐Modified Nickel Oxide Nanocrystals and Their Applications as Hole‐Injection layers for Quantum‐Dot Light‐Emitting Diodes

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High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiOx Hole‐Injection Layers with a High and Stable Work Function

Cited by 63 publications

References 57 publications

Investigation of the Selectivity of Carrier Transport Layers in Wide‐Bandgap Perovskite Solar Cells

Investigation of the Selectivity of Carrier Transport Layers in Wide‐Bandgap Perovskite Solar Cells

23% power conversion efficiency light-emitting diodes using monolayer quantum dots

Synthesis of Cu‐Modified Nickel Oxide Nanocrystals and Their Applications as Hole‐Injection layers for Quantum‐Dot Light‐Emitting Diodes

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High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiO_x Hole‐Injection Layers with a High and Stable Work Function