Quantum Dot Light-Emitting Diodes (QLEDs) have attracted significant attention as next-generation display technologies due to their high color purity, tunable emission wavelengths, and compatibility with solution-based fabrication. Among various electron transport materials, zinc oxide (ZnO) nanoparticles are widely used as electron transport layers (ETLs) because of their high electron mobility, favorable energy level alignment with quantum dots, and excellent optical transparency. However, pristine ZnO often suffers from excessive electron injection, abundant surface defects, and spontaneous interfacial charge transfer with the quantum dot emissive layer (QD-EML), which lead to charge imbalance, exciton quenching, and device instability. To overcome these limitations, extensive efforts have been devoted to modifying ZnO through various doping strategies. This review briefly summarizes recent advances in doped ZnO ETLs for QLED applications, including metal cation doping, halogen anion passivation, and organic-inorganic hybrid modification. The roles of these dopants in regulating energy band alignment, suppressing defect states, and optimizing carrier transport are discussed. Finally, the remaining challenges and future research directions for doped ZnO ETLs are outlined, providing insights for the development of high-efficiency and long-lifetime QLED devices.
References
[1] Qian, X. Y., Tang, Y. Y., Zhou, W., Shen, Y., Guo, M. L., Li, Y. Q., Tang, J. X. (2021) Strategies to improve luminescence efficiency and stability of blue perovskite light‐emitting devices. Small Science, 1(8), 2000048.
[2] Jiang, Y., Sun, C., Xu, J., Li, S., Cui, M., Fu, X., Liu, Y., Wan, H., Wei, K., Zhou, T., Zhang, W., Yang, Y., Yang, J., Qin, C., Gao, S., Pan, J., Liu, Y., Hoogland, S., Sargent, E. H., Chen, J., Yuan, M. (2022) Synthesis-on-substrate of quantum dot solids. Nature, 612(7941), 679-684.
[3] Lee, T. W. (2025) Over a decade of progress in metal-halide perovskite light-emitting diodes. Advanced Materials (Deerfield Beach, Fla.), 37(25), e2508542.
[4] Lu, X., Deng, Y., He, S., Zhu, X., Zelewski, S. J., Wang, H., Ren, A., Zhou, X., Wu, J., Li, X., Zeng, J., Dai, X., Shen, Q., Chen, D., Penty, R. V., Friend, R. H., Jin, Y. (2025) Accelerated response speed of quantum-dot light-emitting diodes by hole-trap-induced excitation memory. Nature Electronics, 8(4), 331-342.
[5] Choi, M. K., Yang, J., Hyeon, T., Kim, D. H. (2018) Flexible quantum dot light-emitting diodes for next-generation displays. Npj Flexible Electronics, 2(1), 10.
[6] Zhang, Z., Ye, Y., Pu, C., Deng, Y., Dai, X., Chen, X., Chen, D., Zheng, X., Gao, Y., Fang, W., Peng, X., Jin, Y. (2018) High‐performance, solution‐processed, and insulating‐layer‐free light‐emitting diodes based on colloidal quantum dots. Advanced Materials, 30(28), 1801387.
[7] Liu, B., Lan, L., Liu, Y., Tao, H., Li, H., Xu, H., Zou, J., Xu, M., Wang, L., Peng, J., Cao, Y. (2019) Improved performance of quantum dot light-emitting diodes by hybrid electron transport layer comprised of ZnO nanoparticles doped organic small molecule. Organic Electronics, 74, 144-151.
[8] Chung, D. S., Lyu, Q., Cotella, G. F., Chun, P., Aziz, H. (2023) Suppressing degradation in QLEDs via doping ZnO electron transport layer by halides. Advanced Optical Materials, 11(20), 2300686.
[9] Wang, S., Zhu, B., Peng, J., Kang, Z., Chi, X., Yu, R., Zhang, H., Ji, W. (2025) Mechanisms and perspectives of positive ageing effect in Quantum‐Dot Light‐Emitting Diodes. Advanced Physics Research, 4(2), 2400103.
[10] Jing, J., Lin, L., Yang, K., Hu, H., Guo, T., Li, F. (2022) Highly efficient inverted quantum dot light-emitting diodes employing sol-gel derived Li-doped ZnO as electron transport layer. Organic Electronics, 103, 106466.
[11] Mude, N. N., Yang, H. I., Thuy, T. T., Kwon, J. H. (2023) Performance enhancement by sol-gel processed Ni-doped ZnO layer in InP-based Quantum Dot Light-Emitting Diodes. Organic Electronics, 112, 106696.
[12] Wang, T., Xie, L., Su, F., Meng, X., Song, Y., Su, W., Cui, Z. (2023) Sn-doped ZnO for efficient and stable Quantum Dot Light-Emitting Diodes via a microchannel synthesis strategy. Nanoscale, 15(45), 18523-18530.
[13] Alexandrov, A., Zvaigzne, M., Lypenko, D., Nabiev, I., Samokhvalov, P. (2020) Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for Quantum Dot Light-Emitting Diodes. Scientific Reports, 10(1), 7496.
[14] Deng, Y., Peng, F., Lu, Y., Zhu, X., Jin, W., Qiu, J., Dong, J., Hao, Y., Di, D., Gao, Y., Sun, T., Zhang, M., Liu, F., Wang, L., Ying, L., Huang, F., Jin, Y. (2022) Solution-processed green and blue quantum-dot light-emitting diodes with eliminated charge leakage. Nature Photonics, 16(7), 505-511.
[15] Yang, D., Zhao, B., Yang, T., Lai, R., Lan, D., Friend, R. H., Di, D. (2022) Toward stable and efficient perovskite light‐emitting diodes. Advanced Functional Materials, 32(9), 2109495.
[16] Shen, H., Gao, Q., Zhang, Y., Lin, Y., Lin, Q., Li, Z., Chen, L., Zeng, Z., Li, X., Jia, Y., Wang, S., Du, Z., Li, L., Zhang, Z. (2019) Visible quantum dot light-emitting diodes with simultaneous high brightness and efficiency. Nature Photonics, 13(3), 192-197.
[17] Fan, J., Han, C., Yang, G., Song, B., Xu, R., Xiang, C., Zhang, T., Qian, L. (2024) Recent progress of Quantum Dots Light‐Emitting Diodes: materials, device structures, and display applications. Advanced Materials, 36(37), 2312948.
[18] Alsharafi, R., Zhu, Y., Li, F., Xu, Z., Hu, H., Guo, T. (2019) Boosting the performance of quantum dot light-emitting diodes with Mg and PVP Co-doped ZnO as electron transport layer. Organic Electronics, 75, 105411.
[19] Sun, Y., Jiang, Y., Peng, H., Wei, J., Zhang, S., Chen, S. (2017) Efficient quantum dot light-emitting diodes with a Zn 0.85 Mg 0.15 O interfacial modification layer. Nanoscale, 9(26), 8962-8969.
[20] Qi, D., Xie, L., Yang, M., Meng, X., Yi, Y. Q. Q., Hao, Y., Su, W., Xu, L., Gai, Y., Cui, Z. (2022) Finely Controlled Synthesis of Zn1-x Mg x O Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs. ACS Applied Electronic Materials, 4(4), 1875-1881.
[21] Cao, S., Zheng, J., Zhao, J., Yang, Z., Li, C., Guan, X., Yang, W., Shang, M., Wu, T. (2017) Enhancing the performance of quantum dot light-emitting diodes using room-temperature-processed Ga-doped ZnO nanoparticles as the electron transport layer. ACS Applied Materials & Interfaces, 9(18), 15605-15614.
[22] Sun, Y., Wang, W., Zhang, H., Su, Q., Wei, J., Liu, P., Chen, S., Zhang, S. (2018) High-performance quantum dot light-emitting diodes based on Al-doped ZnO nanoparticles electron transport layer. ACS Applied Materials & Interfaces, 10(22), 18902-18909.
[23] Wu, Z., Liu, P., Zhang, W., Wang, K., Sun, X. W. (2020) Development of InP quantum dot-based light-emitting diodes. ACS Energy Letters, 5(4), 1095-1106.
[24] Pan, J., Chen, J., Huang, Q., Khan, Q., Liu, X., Tao, Z., Zhang, Z., Lei, W., Nathan, A. (2016) Size tunable ZnO nanoparticles to enhance electron injection in solution processed QLEDs. ACS Photonics, 3(2), 215-222.
[25] Franco, M. A., Conti, P. P., Andre, R. S., Correa, D. S. (2022) A review on chemiresistive ZnO gas sensors. Sensors and Actuators Reports, 4, 100100.
[26] Thi, T. T., Mude, N. N., Ansari, R., Pode, R., Kwon, J. H. (2024) Optimization the potential of solution process fluorine passivated zinc oxide electron transport layer for stable InP-quantum dot light emitting diodes. Organic Electronics, 132, 107098.
[27] Boles, M. A., Ling, D., Hyeon, T., Talapin, D. V. (2016) The surface science of nanocrystals. Nature Materials, 15(2), 141-153.
[28] Shin, H. S., Kim, D. H., Lee, D., Kim, J. (2025) Resistive switching behavior of sol-gel-processed ZnMgO/ZnO bilayer in optoelectronic devices. Nanomaterials, 15(17), 1353.
[29] Liao, Y. H., Chang, Y. H., Lin, T. H., Lee, K. M., Wu, M. C. (2024) Recent advances in metal oxide electron transport layers for enhancing the performance of perovskite solar cells. Materials, 17(11), 2722.
[30] He, S., Tang, X., Deng, Y., Yin, N., Jin, W., Lu, X., Chen, D., Wang, C., Sun, T., Chen, Q., Jin, Y. (2023) Anomalous efficiency elevation of quantum-dot light-emitting diodes induced by operational degradation. Nature Communications, 14(1), 7785.
[31] Salim, K. M., Hassanabadi, E., Masi, S., Gualdron-Reyes, A. F., Franckevicius, M., Devizis, A., Gulbinas, V., Fakharuddin, A., Mora-Sero, I. (2020) Optimizing performance and operational stability of CsPbI3 quantum-dot-based light-emitting diodes by interface engineering. ACS Applied Electronic Materials, 2(8), 2525-2534.
[32] Dai, X., Zhang, Z., Jin, Y., Niu, Y., Cao, H., Liang, X., Chen, L., Wang, J., Peng, X. (2014) Solution-processed, high-performance light-emitting diodes based on quantum dots. Nature, 515(7525), 96-99.
[33] Wang, S., Liu, S., Wang, T., Bai, J., Peng, J., Zhang, H., Xie, W., Ji, W. (2025) Operando ZnO recrystallization for efficient quantum-dot light-emitting diodes. Light: Science & Applications, 14(1), 196.
[34] Song, Y. M., Wang, M. W., Liu, H., Bao, H., Ding, T., Jiang, J., Gao, P., Wu, L. J., Lin, X. F., Zhong, H. Z., Ng, K. W., Wang, S. P. (2025) Hole Injection Barrier‐Driven Positive Aging Mechanism in Inverted QLEDs. Advanced Optical Materials, 13(22), 2500986.
[35] Liu, S., Cheng, H. (2024) Manufacturing process optimization in the process industry. International Journal of Information Technology and Web Engineering (IJITWE), 19(1), 1-20.
[36] Ning, M., Zhao, K., Zhao, L., Cao, S., Zhao, J., Gao, Y., Yuan, X. (2024) Passivating defects in ZnO electron transport layer for enhancing performance of red InP-based quantum dot light-emitting diodes. Materials Research Bulletin, 170, 112589.
[37] Choi, H., Shin, D., Bae, W. K., Lee, H. (2025) Enhanced Stability of Cd‐Free Quantum Dot Light‐Emitting Diodes via Yttrium Acetate‐Modified ZnMgO: Suppressing Mg Migration. Advanced Optical Materials, 13(22), 2500988.
[38] Chung, D. S., Davidson-Hall, T., Cotella, G., Lyu, Q., Chun, P., Aziz, H. (2022) Significant lifetime enhancement in QLEDs by reducing interfacial charge accumulation via fluorine incorporation in the ZnO electron transport layer. Nano-Micro Letters, 14(1), 212.
[39] Kim, J. (2024) Recent progresses and challenges in colloidal quantum dot light-emitting diodes: a focus on electron transport layers with metal oxide nanoparticles and organic semiconductors. Nanoscale Horizons, 9(12), 2167-2197.
[40] Kim, H. M., Cho, S., Kim, J., Shin, H., Jang, J. (2018) Li and Mg Co-doped zinc oxide electron transporting layer for highly efficient quantum dot light-emitting diodes. ACS Applied Materials & Interfaces, 10(28), 24028-24036.
[41] Kim, H. H., Kumi, D. O., Kim, K., Park, D., Yi, Y., Cho, S. H., Park, C., Ntwaeaborwa, O. M., Choi, W. K. (2019) Optimization of the electron transport in quantum dot light-emitting diodes by codoping ZnO with gallium (Ga) and magnesium (Mg). RSC Advances, 9(55), 32066-32071.
[42] Lee, Y., Jeong, B. G., Roh, H., Roh, J., Han, J., Lee, D. C., Bae, W. K., Kim, J. Y., Lee, C. (2018) 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. Advanced Quantum Technologies, 1(1), 1700006.
[43] Mokarian Zanjani, S., Tintori, F., Sadeghi, S., Linkov, P., Dayneko, S., Shahalizad, A., Pahlevaninezhad, H., Pahlevani, M. (2022) Tailored ZnO functional nanomaterials for solution‐processed Quantum‐Dot Light‐Emitting Diodes. Advanced Photonics Research, 3(12), 2200159.
Share and Cite
Yang, S., Liu, Z., Guo, R., Shi, H., Pan, H. (2025) Advancements in Doped ZnO as an Efficient Electron Transport Layer for QLEDs. Scientific Research Bulletin, 2(6), 77-90. https://doi.org/10.71052/srb2024/VECS4744