Influence of shells on the charge tunnelling behaviour in quantum-dot light-emitting diodes

Abstract Due to the advances on quantum dot (QD) synthesis and device design, quantum-dot light-emitting diodes (QLEDs) have gained much progress in luminance, efficiency, and operational stability. However, fabricating high-performance QLEDs remains to be empirical, lacking full understanding on the electroluminescent mechanism of QDs. The formation and recombination of excitons are one of the most crucial charge-carrier dynamics, determining device design and performance. As a fingerprint, ideality factor of diodes is used here to evaluate the transportation and recombination of charge carriers in QLEDs. The ideality factor of the current for QLEDs deviates significantly from 2, indicating that tunneling behavior dominates the charge injection and transportation processes in the low driving region. The ideality factor of the luminance strongly depends on the core-shell structure of the QDs. For QLEDs with I-QDs that have an alloying shell, the luminance ideality factor falls between 1 and 2, suggesting the coexistence of both trap-assisted recombination and Langevin bimolecular radiative recombination processes. In contrast, for II-QDs with a sharp core-shell structure, the luminance ideality factor is approximately 2, indicating that trap-assisted recombination prevails in the device.