Highly-efficient low-voltage organic light-emitting diode by controlling hole transporting with doped dual hole-transport layer and the impedance spectroscopy analysis

Zhang, Xiaowen; Mo, Bingjie; You, Fengjiao; Liu, Liming; Wang, Honghang; Wei, Bin

doi:10.1016/j.synthmet.2015.04.001

Cited by 17 publications

(6 citation statements)

References 22 publications

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“…The high impedance values for the YZO devices drastically decrease as the phase changes to 0°. As indicated by previously reported studies, phases of −90° and 0° correspond to insulating and conducting states, respectively . At approximately 2.3–2.5 V, corresponding to the turn‐on voltages of the devices, both the impedance and phase of each YZO device begin to change, indicating a conversion from an insulating state to conducting state.…”

Section: Resultssupporting

confidence: 64%

Enhanced Lifetime and Efficiency of Red Quantum Dot Light‐Emitting Diodes with Y‐Doped ZnO Sol–Gel Electron‐Transport Layers by Reducing Excess Electron Injection

et al. 2018

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Charge balance between electrons and holes, which are injected into the quantum dot (QD) emission layer (EML), is critical for realizing stable and efficient QD light‐emitting diodes (QLEDs). ZnO has been widely used as an electron‐transport layer (ETL) because of its superior performance compared to other metal oxides. However, nearly barrier‐free electron injection into the QD EML leads to spontaneous charge transfer and excess electron injection, resulting in reduced device performance. Here, to adjust electron–hole balance and thereby improve the lifetime and efficiency of QLEDs, we introduce an yttrium (Y)‐doped ZnO (YZO) ETL into QLEDs. The sol–gel processed YZO film, with a mobility that could be simply tuned by varying the Y concentration, provides enhanced charge‐transport balance by suppressing excess electron flow to the QD EML. Furthermore, YZO helps suppress QD charging and smooth the surface morphology. Applying the YZO ETL into the inverted‐structure QLED enables us to achieve color‐saturated red emission, an improved external quantum efficiency of up to 8.6%, and an eight times longer lifetime compared to the device with undoped ZnO. This result provides a simple method for enhancing the performance of QLEDs by easily controlling metal doping concentration in the sol–gel processed ZnO ETL.

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Section: Resultssupporting

confidence: 64%

Enhanced Lifetime and Efficiency of Red Quantum Dot Light‐Emitting Diodes with Y‐Doped ZnO Sol–Gel Electron‐Transport Layers by Reducing Excess Electron Injection

et al. 2018

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“…The impedance–voltage ( Z – V ) correlation is a powerful tool to study the device operational mechanism, , the dispersion, mobility of charge-transporting material, , and the charge injection behavior in the device. , Figure depicts the magnitude of impedance and the phase shifting of all devices corresponding to an external voltage with a frequency of 500 and 1000 Hz. The impedance of the device starts with a higher value at low bias and decreases sharply with the voltage across the turn-on voltage.…”

Section: Resultsmentioning

confidence: 99%

Versatile Exciplex-Forming Co-Host for Improving Efficiency and Lifetime of Fluorescent and Phosphorescent Organic Light-Emitting Diodes

Shih

Lee

Yeh

et al. 2018

ACS Appl. Mater. Interfaces

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We report a new efficient exciplex-forming system consisting of a biscarbazole donor and a triazine-based acceptor. The new exciplex was characterized with a high photoluminescence quantum yield up to 68% and effective thermally activated delayed fluorescence behavior. The BCzPh:3P-T2T (2:1, 30 nm) blend was examined not only as an emitting layer (device D1) but also a reliable co-host of fluorescent and phosphorescent emitters for giving highly efficient exciplex-based organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 15.5 and 29.7% for devices doped with 1 wt % C545T (device D2) and 8 wt % Ir(ppy)(acac) (device D4), respectively. More strikingly, a strongly enhanced lifetime ( T = 16 927 min.) of the C545T-doped device was obtained. The transient electroluminescence measurement as well as capacitance-voltage and impedance-voltage correlations were utilized to explore the factors governing the high efficiency and stability. The obtained results clearly show that the energy transfer and charge transport is highly efficient; they also show the photoelectric semiconducting characteristics of exciplex-based OLEDs, which are significantly different from those of unipolar host-based reference devices D3 (Alq: 1 wt % C545T) and D5 (CBP: 8 wt % Ir(ppy)(acac)). Our works have established a systematic protocol to shed light on the mechanisms behind exciplex-based devices. The combined results also confirm the bright prospect of the exciplex-forming system as the co-host for highly efficient and stable OLEDs.

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“…It can be seen that the voltage of C p increases in the sequence of Cell H 2 (2.5 V) < Cell H e (3.1 V) < Cell H 1 (3.2 V) < Cell H 3 (4.0 V) < Cell H 0 (6.6 V). The voltage of C p corresponding to starting of hole–electron recombination . It is obvious that the hole–electron recombination deteriorates carrier storage ability, which results in capacitance dropping.…”

Section: Resultsmentioning

confidence: 99%

Aqueous Solution‐Processed Vanadium Oxide for Efficient Hole Injection Interfacial Layer in Organic Light‐Emitting Diode

Zhang

et al. 2018

Physica Status Solidi (a)

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Solution‐processing techniques have effectively promoted low‐cost and large‐scale manufacturing of organic light‐emitting diodes (OLEDs). An ecofriendly process is demonstrated here to obtain aqueous solution‐processed vanadium oxide (s‐VOx) for effective hole injection interfacial layer (HIL) by using commercial V2O5 powders. Atomic force microscopy and X‐ray photoelectron spectroscopy measurements show that s‐VOx exhibits superior film morphology and non‐stoichiometry with slight oxygen deficiency which account for exceptional electronic properties in tailoring hole injection. With tris(8‐hydroxy‐quinolinato)aluminum as emitter, s‐VOx‐based OLED gives a maximum luminous efficiency of 6.4 cd A−1 and power efficiency of 4.1 lm W−1, which are comparable to those (6.1 cd A−1 and 3.6 lm W−1) of vacuum thermally deposited VOx‐based counterpart. The current versus voltage characteristics and impedance spectroscopy of hole‐only devices elucidate that s‐VOx possesses robust hole injection capacity and thereby promotes the OLED performance. Our results pave an alternative approach for broadening VOx application with solution process and accelerating OLED development.

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Highly-efficient low-voltage organic light-emitting diode by controlling hole transporting with doped dual hole-transport layer and the impedance spectroscopy analysis

Cited by 17 publications

References 22 publications

Enhanced Lifetime and Efficiency of Red Quantum Dot Light‐Emitting Diodes with Y‐Doped ZnO Sol–Gel Electron‐Transport Layers by Reducing Excess Electron Injection

Enhanced Lifetime and Efficiency of Red Quantum Dot Light‐Emitting Diodes with Y‐Doped ZnO Sol–Gel Electron‐Transport Layers by Reducing Excess Electron Injection

Versatile Exciplex-Forming Co-Host for Improving Efficiency and Lifetime of Fluorescent and Phosphorescent Organic Light-Emitting Diodes

Aqueous Solution‐Processed Vanadium Oxide for Efficient Hole Injection Interfacial Layer in Organic Light‐Emitting Diode

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