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Research Article | Open Access

Quantum rod light emitting diodes: Suppressing leakage current and improving external quantum efficiency

Kumar Mallem1,§Maksym F. Prodanov1,§Zebing Liao1Chengbin Kang1Jianxin Song1Debjyoti Bhadra1Roja Ramani Gavara1Abhishek K. Srivastava1,2 ( )
State Key Laboratory on Advanced Displays and Optoelectronics Technologies and Centre for Display Research, Department of Electronics and Computer Engineering, The Hong Kong University of Science and Technology, Hong Kong 999077, China
Institute for Advanced Study (IAS) Center for Quantum Technologies, The Hong Kong University of Science and Technology, Hong Kong 999077, China

§ Kumar Mallem and Maksym F. Prodanov contributed equally to this work.

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Graphical Abstract

The spin-coated quantum rods (QRs) exhibit voids and gaps in the film, which lead to leakage current in the devices due to ZnMgO penetration. When paraffin is mixed into the QRs, it fills these voids and gaps, effectively blocking the ZnMgO penetration. Consequently, the paraffin-doped devices demonstrate a twofold improvement in external quantum efficiency (EQE), current efficiency (CE), and luminance compared to the reference device without paraffin.

Abstract

Semiconductor quantum rods (QRs) have unique advantages over spherical quantum dots (QDs), such as linearly polarized emission and higher light out-coupling efficiency, which can potentially improve the external quantum efficiency (EQE) of light-emitting diodes (LEDs). However, the EQE of QR LEDs is trailing far behind the QD LEDs, primarily due to the low quantum yield of QRs in the thin films and voids that show up in the film due to the low packing density of the rod-shaped nanoparticles. This study synthesized CdSe/CdS QRs with various aspect ratios and investigated QR LED performance issues. The study found that the main factors impeding the performance of QR LEDs were electron leakage current and exciton quenching, with QR length significantly impacting these factors. To address these issues, without compromising on the QRs shape, we blended an insulator (i.e., paraffin in this case) into the QRs film, which fills the voids/gaps (causing the leakage current) in the QRs film and minimizes infiltration of the charge transporting material in the emitting material, i.e., ZnMgO nanoparticles. As a result, the leakage current in QR LEDs was suppressed over 10 times by blocking direct contact between the electron-transporting material (ETL) and hole-transporting material (HTL). It improved the photoluminescence quantum yield (PLQY) of the QRs film. This approach suppresses exciton quenching, guides both carriers to the QRs and pushes the electron–hole (e–h) recombination zone to the QRs emitting layer. In comparison to the reference QR LEDs, the QR LEDs with paraffin show ~ two-fold improvement in EQE, whereas current efficiency and luminance of the QR LEDs increased from 5.6 to 14 cd·A−1 and 17,500 to 42,300 cd·m−2, respectively. The efficiency roll-off was also curtailed by 73% at relatively higher current densities. Overall, the use of paraffin in the QR LED fabrication process shows promising improvement in the performance of QR LEDs and overcoming some of the challenges that have impeded their performance compared to QD LEDs.

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Nano Research
Article number: 94907071
Cite this article:
Mallem K, Prodanov MF, Liao Z, et al. Quantum rod light emitting diodes: Suppressing leakage current and improving external quantum efficiency. Nano Research, 2025, 18(1): 94907071. https://doi.org/10.26599/NR.2025.94907071
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Received: 13 August 2024
Revised: 29 September 2024
Accepted: 11 October 2024
Published: 25 December 2024
© The Author(s) 2025. Published by Tsinghua University Press.

This is an open access article under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0, https://creativecommons.org/licenses/by/4.0/).

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