Promoted Hole Transport Capability by Improving Lateral Current Spreading for High-Efficiency Quantum Dot Light-Emitting Diodes

Qianqian Wu; Fan Cao; Haoran Wang; Jianquan Kou; Zi-Hui Zhang; Xuyong Yang

doi:10.1002/advs.202001760

Promoted Hole Transport Capability by Improving Lateral Current Spreading for High-Efficiency Quantum Dot Light-Emitting Diodes

Adv Sci (Weinh). 2020 Nov 1;7(23):2001760. doi: 10.1002/advs.202001760. eCollection 2020 Dec.

Authors

Qianqian Wu¹, Fan Cao¹, Haoran Wang¹, Jianquan Kou², Zi-Hui Zhang², Xuyong Yang¹

Affiliations

¹ Key Laboratory of Advanced Display and System Applications of Ministry of Education Shanghai University 149 Yanchang Road Shanghai 200072 China.
² State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of Technology 5340 Xiping Road, Beichen District Tianjin 300401 China.

Abstract

Carrier imbalance resulting from stronger electron injection from ZnO into quantum-dot (QD) emissive layer than hole injection is one critical issue that constrains the performance of QDs-based light-emitting diodes (QLEDs). This study reports highly efficient inverted QLEDs enabled by periodic insertion of MoO₃ into (4,4'-bis(N-carbazolyl)-1,1'-biphenyl) (CBP) hole transport layer (HTL). The periodic ultrathin MoO₃/CBP-stacked HTL results in improved lateral current spreading for the QLEDs, which significantly relieves the crowding of holes and thus enhances hole transport capability across the CBP in QLEDs. Comprehensive analysis on the photoelectric properties of devices shows that the optimal thickness for MoO₃ interlayer inserted in CBP is only ≈1 nm. The resulting devices with periodic two insertion layers of MoO₃ into CBP exhibit better performance compared with the CBP-only ones, such that the peak current efficiency is 88.7 cd A^-1 corresponding to the external quantum efficiency of 20.6%. Furthermore, the resulting QLEDs show an operational lifetime almost 2.5 times longer compared to CBP-only devices.

Keywords: current spreading; electroluminescence; hole transport capability; light‐emitting diodes; quantum dots.