Charging and Charged Species in Quantum Dot Light-Emitting Diodes

Keating, Logan P.; Lee, Hyunho; Rogers, Stanley; Huang, Conan; Shim, Moonsub

doi:10.1021/acs.nanolett.2c03564

Cited by 17 publications

(6 citation statements)

References 64 publications

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“…In the previous works, the delay stages of OLED and QLED were usually explained as the capacitor charging process 19,20 or slower carrier migration process from the electrode to the QD emission layer. 21 The observed EL intensity increase during the delay stage provides further information to analyze the physical mechanism in the delay stage. We studied the influence of carrier concentration on luminescence in the delay stage at different temperatures and voltages.…”

Section: ■ Results and Discussionmentioning

confidence: 94%

“…To our knowledge, this phenomenon is reported for the first time. In the previous works, the delay stages of OLED and QLED were usually explained as the capacitor charging process , or slower carrier migration process from the electrode to the QD emission layer . The observed EL intensity increase during the delay stage provides further information to analyze the physical mechanism in the delay stage.…”

Section: Resultsmentioning

confidence: 99%

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Single-Photon-Camera-Based Time and Spatially Resolved Electroluminescence Spectroscopy for Micro-LED Analysis

Cao,

Bao,

Peng

et al. 2024

ACS Photonics

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To investigate the operational mechanisms of micrometer-sized light-emitting diodes (micro-LEDs), we here demonstrate a transient methodology of time and spatially resolved electroluminescence spectroscopy (TSR-EL) to measure the spatial distribution of light emission from LED devices. By combining a single-photon camera (SPC) with the time-gated sampling method, we derived the time and spatially resolved electroluminescence intensity with increasing time. Benefiting from the high sensitivity of the SPC, this methodology can detect ultralow electroluminescence (EL) at the delay stage from the device operated around the turn-on voltage. Furthermore, we investigated the spatial light distribution of a typical quantum dots light-emitting diode (QLED) under different applied voltages and varied temperatures. It was found that the EL emission of the QLED device became more uniform with increasing temperature and applied voltage. Moreover, the methodology of TSR-EL is versatile to investigate other LEDs such as organic light-emitting diodes (OLEDs), micro-LEDs, etc.

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Section: ■ Results and Discussionmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Single-Photon-Camera-Based Time and Spatially Resolved Electroluminescence Spectroscopy for Micro-LED Analysis

Cao,

Bao,

Peng

et al. 2024

ACS Photonics

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“…Moreover, the charging and contamination of QDs facilitate the degradation by promoting the oxidation of HTL and QD ligands. [180] Up to now, researchers have gradually focused on the stability issue of QLEDs. While significant progress has been made in improving the stability of QLEDs through material and structural design, the underlying mechanisms responsible for degradation are not yet fully understood.…”

Section: Operational Degradationmentioning

confidence: 99%

Color Revolution: Prospects and Challenges of Quantum‐Dot Light‐Emitting Diode Display Technologies

Chen

Yuan

et al. 2023

Small Methods

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Light‐emitting diodes (LEDs) based on colloidal quantum‐dots (QDs) such as CdSe, InP, and ZnSeTe feature a unique advantage of narrow emission linewidth of ≈20 nm, which can produce highly accurate colors, making them a highly promising technology for the realization of displays with Rec. 2020 color gamut. With the rapid development in the past decades, the performances of red and green QLEDs have been remarkably improved, and their efficiency and lifetime can almost meet industrial requirements. However, the industrialization of QLED displays still faces many challenges; for example, (1) the device mechanisms including the charge injection/transport/leakage, exciton quenching, and device degradation are still unclear, which fundamentally limit QLED performance improvement; (2) the blue performances including the efficiency, chromaticity, and stability are relatively low, which are still far from the requirements of practical applications; (3) the color patterning processes including the ink‐jet printing, transfer printing, and photolithography are still immature, which restrict the manufacturing of high resolution full‐color QLED displays. Here, the recent advancements attempting to address the above challenges of QLED displays are specifically reviewed. After a brief overview of QLED development history, device structure/principle, and performances, the main focus is to investigate the recent discoveries on device mechanisms with an emphasis on device degradation. Then recent progress is introduced in blue QLEDs and color patterning. Finally, the opportunities, challenges, solutions, and future research directions of QLED displays are summarized.

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“…As a transient measurement method, time-resolved electroluminescence (TREL) is a nondestructive technique to investigate the operation mechanism of light-emitting diodes including the III–V semiconductor LEDs and the later developed OLEDs and QLEDs. , Basically, a typical TREL spectrum records the evolution of brightness of a LED device under a pulsed voltage, usually including four stages of delay, rise, balance, and decay. Efforts have been made to explain the physical processes related to these stages.…”

mentioning

confidence: 99%

Quantitative Determination of Charge Accumulation and Recombination in Operational Quantum Dots Light Emitting Diodes via Time-Resolved Electroluminescence Spectroscopy

Bao

Chen

Cao

et al. 2023

J. Phys. Chem. Lett.

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In this work, we report the quantitative determination of charge accumulation and recombination in an operated QLED using time-resolved electroluminescence (TREL) spectroscopy. As a supplement technique, time-resolved current (TRC) measurement was introduced and simulated using equivalent circuit model with a series resistance, a parallel resistance, and a capacitance. By modeling the key processes in a typical TREL spectra, the stages of delay, rising, and decay can be correlated to the charge accumulations, charge injection and recombination, and charge release and recombination, respectively. In particular, the rising stage can be described using a modified Langevin recombination model. The electroluminescence recombination rate can be derived by fitting the rising stage curves in the TREL spectra, providing an intrinsic parameter of the emissive materials. In all, this work provides a methodology to quantitatively determine the charge accumulation and recombination of an operational QLED device.

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Charging and Charged Species in Quantum Dot Light-Emitting Diodes

Cited by 17 publications

References 64 publications

Single-Photon-Camera-Based Time and Spatially Resolved Electroluminescence Spectroscopy for Micro-LED Analysis

Single-Photon-Camera-Based Time and Spatially Resolved Electroluminescence Spectroscopy for Micro-LED Analysis

Color Revolution: Prospects and Challenges of Quantum‐Dot Light‐Emitting Diode Display Technologies

Quantitative Determination of Charge Accumulation and Recombination in Operational Quantum Dots Light Emitting Diodes via Time-Resolved Electroluminescence Spectroscopy

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