High-Efficiency and Stable Colloidal One-Dimensional Core/Shell Nanorod Light-Emitting Diodes

Abstract

Anisotropic nanocrystals such as nanorods (NRs) display unique linearly polarized emission, which is expected to break the external quantum efficiency (EQE) limit of quantum dot-based light-emitting diodes (LEDs). However, the progress in achieving a higher EQE using NRs encounters several challenges, primarily involving a low photoluminescence quantum yield (PLQY) of NRs and imbalanced charge injection in NR-LEDs. In this work, we investigated NR-LEDs based on CdSe/CdZnS/ ZnS rod-in-rod NRs with a high PLQY and higher linear polarization compared to those of dot-in-rod NRs. The balanced charge injection is achieved using ZnMgO nanoparticles as the electron transport layer and poly-TPD {poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine]} as the hole transport layer. Therefore, the NR-LEDs exhibit a maximum EQE of 21.5% and a maximum luminance of >120 000 cd/m 2 owing to the high level of in-plane transitions with a dipole moment of 90%. The NR-LEDs also have greatly inhibited droop in EQE under a high current density as well as outstanding operation lifetime and cycle stability.

Synthesis and Optical Properties of CdSeTe/CdZnS/ZnS Core/Shell Nanorods

“…These results correspond well with previously published reports [ 29 , 31 , 32 ]. The anisotropy value is increased from 0.203 of CdSeTe/CdS NRs to 0.221 of CdSeTe/CdZnS/ZnS NRs, which is due to the more uniform morphology of CdSeTe/CdZnS/ZnS NRs and the radial distribution of Zn in the CdZnS shell [ 33 ]. Note that the amount of Zn-OA must be precisely controlled, since high Zn content in the CdZnS shell will accumulate an excess strain to the CdSeTe core and increase the interface defect density, resulting in a lower PL intensity.…”

“…In recent years, such core–shell structures have been increasingly explored in NRs [ 29 , 30 ]. Recently, Zeng et al reported CdSe/CdZnS/ZnS NRs and CdSe/CdZnS/CdZnS/ZnS NRs with carefully designed multilayer shell structures, achieving the highest EQE of red NR-LEDs to date [ 31 , 32 , 33 ]. However, reports on the tunability of the emission wavelength of NRs are not as comprehensive as those on QDs.…”