Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Solution-Processable Highly Conductive Spinel Structure CuCo2O4 Hole Injection Layer

Min Ho Park; Min Gye Kim; Jin Hyun Ma; Jun Hyung Jeong; Hyoun Ji Ha; Wonsik Kim; Soohyung Park; Seong Jun Kang

doi:10.3390/ma16030972

Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Solution-Processable Highly Conductive Spinel Structure CuCo₂O₄ Hole Injection Layer

Materials (Basel). 2023 Jan 20;16(3):972. doi: 10.3390/ma16030972.

Authors

Min Ho Park^{1

2}, Min Gye Kim^{1

2}, Jin Hyun Ma^{1

2}, Jun Hyung Jeong^{1

2}, Hyoun Ji Ha^{1

2}, Wonsik Kim³, Soohyung Park^{3

4}, Seong Jun Kang^{1

2}

Affiliations

¹ Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yongin 17104, Republic of Korea.
² Integrated Education Program for Frontier Materials (BK21 Four), Kyung Hee University, Yongin 17104, Republic of Korea.
³ Advanced Analysis Center, Korea Institute of Science and Technology, 5 Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea.
⁴ Division of Nano & Information Technology, KIST School, University of Science and Technology (UST), Seoul 02792, Republic of Korea.

Abstract

Charge imbalance in quantum-dot light-emitting diodes (QLEDs) causes emission degradation. Therefore, many studies focused on improving hole injection into the QLEDs-emitting layer owing to lower hole conductivity compared to electron conductivity. Herein, CuCo₂O₄ has a relatively higher hole conductivity than other binary oxides and can induce an improved charge balance. As the annealing temperature decreases, the valence band maximum (VBM) of CuCo₂O₄ shifts away from the Fermi energy level (E_F), resulting in an enhanced hole injection through better energy level alignment with hole transport layer. The maximum luminance and current efficiency of the CuCo₂O₄ hole injection layer (HIL) of the QLED were measured as 93,607 cd/m² and 11.14 cd/A, respectively, resulting in a 656% improvement in luminous performance of QLEDs compared to conventional metal oxide HIL-based QLEDs. These results demonstrate that the electrical properties of CuCo₂O₄ can be improved by adjusting the annealing temperature, suggesting that solution-processed spinel can be applied in various optoelectronic devices.

Keywords: CuCo2O4; colloidal quantum dot (QD); hole injection layer; light-emitting diode (LED); spinel.

Abstract

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