J. Semicond. > 2023, Volume 44 > Issue 9 > 091603, doi: 10.1088/1674-4926/44/9/091603
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REVIEWS

Impedance spectroscopy for quantum dot light-emitting diodes

Xiangwei Qu1, 2 and Xiaowei Sun1, 2,

+ Author Affiliations

 Corresponding author: Xiaowei Sun, sunxw@sustech.edu.cn

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Abstract: Impedance spectroscopy has been increasingly employed in quantum dot light-emitting diodes (QLEDs) to investigate the charge dynamics and device physics. In this review, we introduce the mathematical basics of impedance spectroscopy that applied to QLEDs. In particular, we focus on the Nyquist plot, Mott−Schottky analysis, capacitance-frequency and capacitance-voltage characteristics, and the dC/dV measurement of the QLEDs. These impedance measurements can provide critical information on electrical parameters such as equivalent circuit models, characteristic time constants, charge injection and recombination points, and trap distribution of the QLEDs. However, this paper will also discuss the disadvantages and limitations of these measurements. Fundamentally, this review provides a deeper understanding of the device physics of QLEDs through the application of impedance spectroscopy, offering valuable insights into the analysis of performance loss and degradation mechanisms of QLEDs.

Key words: quantum dot light-emitting diode, impedance spectroscopy, equivalent circuit model, charge dynamics



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Fig. 1.  (Color online) (a) J−V characteristic, (b) C−V characteristic, which reflects (c) the charge dynamics in QLED, (d) Nyquist plot at the selected working voltage, (e) an equivalent circuit model can be built up according to the Nyquist plot, (f) C−f characteristic at the selected working voltage, (g) the trap distribution can be calculated if the capacitance rise is induced by carrier trapping.

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Fig. 2.  (Color online) Nyquist plot and its equivalent circuit model of a blue QLED.

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Fig. 3.  (Color online) Equivalent circuit model of QLEDs based on (a) device structure, (b) the function of each circuit element. Modified with permission from (a) Ref. [45] Copyright 2022 Springer Nature, (b) Ref. [47] Copyright 2022 American Chemical Society.

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Fig. 4.  (Color online) (a) Equivalent circuit model of QLED based on CPE circuit element, (b) Nyquist plot of QLED with two semicircles and its equivalent circuit model. Modified with permission from (a) Ref. [54] Copyright 2020 American Chemical Society, (b) Ref. [55] Copyright 2022 Springer Nature.

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Fig. 5.  (Color online) Capacitance−frequency characteristics of (a) blue QLED at 1.7 V and 2.3 V, (b) purple QLED within the voltage range from 0 to 10 V. Modified with permission from (a) Ref. [41] Copyright 2022 AIP Publishing, (b) Ref. [60] Copyright 2019 AIP Publishing.

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Fig. 6.  (Color online) Capacitance−frequency characteristic of the QLED. Modified with permission from Ref. [60] Copyright 2019 AIP Publishing.

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Fig. 7.  Energy level of a p−i−n heterojunction. Modified with permission from Ref. [37] Copyright 1992 AIP Publishing.

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Fig. 8.  (Color online) Capacitance−frequency characteristics of OPV with two-step capacitance rise. Modified with permission from Ref. [64] Copyright 2016 American Physical Society.

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Fig. 9.  (Color online) Capacitance−voltage characteristic of a blue QLED.

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Fig. 10.  (Color online) (a) Capacitance−voltage characteristics of (a) pristine device and UV-ozone treated device, (b) pristine device and CF4-treated device. Modified with permission from (a) Ref. [75] Copyright 2019 RSC Pub, (b) Ref. [45] Copyright 2022 Springer Nature.

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Fig. 11.  (Color online) (a) Capacitance−voltage characteristics of (a) the inverted QLED, (b) normal QLED with ZnO and TPBi ETLs. Modified with permission from (a) Ref. [53] Copyright 2022 Elsevier Ltd and (b) Ref. [20] Copyright 2021 Wiley-VCH Verlag GmbH & Co. KGaA.

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Fig. 12.  (Color online) (a) Capacitance−voltage characteristics of (a) pristine QLED and MoO3-modified QLED, (b) blue QLED at different degradation periods. Modified with permission from (a) Ref. [87] Copyright 2022 AIP Publishing, (b) Ref. [21] Copyright 2019 Springer Nature.

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Fig. 13.  (Color online) Capacitance−voltage and dC/dV−V characteristics of a red QLED. Modified with permission from Ref. [86] Copyright 2022 IOP Publishing.

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Fig. 14.  (Color online) 1/C2−V characteristics of the HOD (a) and EOD (b). Modified with permission from Ref. [6] Copyright 2020 Springer Nature.

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Table 1.   The applications and limitations of the impedance measurement.

Application Limitation
Nyquist plot Charging time constant, equivalent circuit model. Many equivalent circuit models correspond to one Nyquist plot, so the physical meaning of each circuit element should be clear.
C−f characteristic The characteristic time constant for charge accumulation and recombination; trap distribution. The capacitance rise is only contributed to the carrier trapping for the defect spectroscopy.
C−V characteristic Charge injection point, charge injection and recombination rate. The frequency is required to satisfy the charge response to the alternating signal.
dC/dV−V characteristic The characteristic voltage at maximum EQE, Supplementary information to C−V characteristics
Mott−Schottky analysis (1/C2−V characteristic) Doping density, built-in voltage Depletion approximation must be satisfied in a device.
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    Received: 21 May 2023 Revised: 27 June 2023 Online: Accepted Manuscript: 23 August 2023Corrected proof: 23 August 2023Uncorrected proof: 24 August 2023Published: 10 September 2023

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      Article Navigation >  Journal of Semiconductors  > 2023  >  44(9): 091603
      Xiangwei Qu, Xiaowei Sun. Impedance spectroscopy for quantum dot light-emitting diodes[J]. Journal of Semiconductors, 2023, 44(9): 091603. doi: 10.1088/1674-4926/44/9/091603 X W Qu, X W Sun. Impedance spectroscopy for quantum dot light-emitting diodes[J]. J. Semicond, 2023, 44(9): 091603. doi: 10.1088/1674-4926/44/9/091603Export: BibTex EndNote
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      Xiangwei Qu, Xiaowei Sun. Impedance spectroscopy for quantum dot light-emitting diodes[J]. Journal of Semiconductors, 2023, 44(9): 091603. doi: 10.1088/1674-4926/44/9/091603

      X W Qu, X W Sun. Impedance spectroscopy for quantum dot light-emitting diodes[J]. J. Semicond, 2023, 44(9): 091603. doi: 10.1088/1674-4926/44/9/091603
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      Impedance spectroscopy for quantum dot light-emitting diodes

      doi: 10.1088/1674-4926/44/9/091603
      • 1.

        Institute of Nanoscience and Applications, and Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Shenzhen 518055, China

      • 2.

        Key Laboratory of Energy Conversion and Storage Technologies (Southern University of Science and Technology), Ministry of Education, and Shenzhen Key Laboratory for Advanced Quantum Dot Displays and Lighting, Southern University of Science and Technology, Shenzhen 518055, China

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      • Author Bio:

        Xiangwei Qu got his doctoral degree from Southern University of Science and Technology (SUSTech), Shenzhen, China, in 2023, he is currently a postdoctoral researcher in SUSTech, his research focuses on device physics of quantum dot light-emitting diodes

        Xiaowei Sun is a Chair Professor and the Executive Dean of the Institute of Nanoscience and Applications in the Southern University of Science and Technology, Shenzhen, China. He is an academician of the Asia-Pacific Academy of Materials, and the fellow of several other academic societies including Optica (formerly OSA), SPIE, and the Institute of Physics (UK). His main research presently is on high-quality displays based on nanocrystals and naked-eye 3D displays

      • Corresponding author: sunxw@sustech.edu.cn
      • Received Date: 2023-05-21
      • Revised Date: 2023-06-27
        • Available Online: 2023-08-23

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