Surface-Ligand-Modified CdSe/CdS Nanorods for High-Performance Light-Emitting Diodes

Colloidal nanocrystals (NCs) play an important role in the field of optoelectronic devices such as photovoltaic cells, photodetectors, and light-emitting diodes (LEDs). The properties of NC films are strongly affected by ligands attached to them, which constitute a barrier for charge transport between adjacent NCs. Therefore, the method of surface modification by ligand exchange has been used to improve the electrical conductivity of NC films. However, surface modification to NCs in LEDs can also affect emission characteristics. Among NCs, nanorods have unique properties, such as suppression of nonradiative Auger recombination and linearly polarized light emission. In this work, CdSe/CdS nanorods (NRs) were prepared by the hot injection method. To increase the charge transport into CdSe/CdS NRs, we adopted ligand modification to CdSe/CdS NRs. Using this technique, we could shorten the injection barrier length between CdSe/CdS NRs and adjacent layers. It leads to a more balanced charge injection of electron/hole and a greatly increased current efficiency of CdSe/CdS NR-LEDs. In the NR-LEDs, the ligand exchange boosted the electroluminance, reaching a sixfold increase from 848 cd/m2 of native surfactants to 5600 cd/m2 of the exchanged n-octanoic acid ligands at 12 V. The improvement of CdSe/CdS NR-LED performance is closely correlated to the efficient control of charge balance via ligand modification strategy, which is expected to be indispensable to the future NR-LED-based optoelectronic system.