Efficient green light-emitting diodes based on alloy quantum dots with an organic/inorganic hybrid surface passivation

Abstract

As we know, the ligands on the surface of core/shell structured quantum dots (QDs) play an important role. They not only bind with metal ions to passivate surface defects but also have a great influence on colloidal stability. All-organic or all-inorganic ligands afford QDs with some disadvantages such as low conductivity, poor dispersibility and undesirable stability. By combining with the advantages of organic and inorganic ligands, herein, we achieve an organic/inorganic hybrid surface passivation through exchanging partial oleic acid ligands with chlorine ions (Cl−), affording QD with a core/shell structure of CdZnSe/ZnSe/ZnS/OACl. It exhibits an excellent nanostructure with a mean size of around 11.6 nm. According to X-ray photoelectron spectroscopy (XPS) spectra, around 30% oleid acid ligands are removed by Cl−, resulting in the hybrid surface passivation. The CdZnSe/ZnSe/ZnS/OACl QD exhibit an efficient green emission at the wavelength of around 535 nm with a quantum yield of over 90%. The QD light-emitting diode (QLED) based on CdZnSe/ZnSe/ZnS/OACl exhibits a peak EQE of 15.6% and a brightness of over 1.1 × 105 cd m−2 at 6 V, corresponding to an efficient green emitting device. Therefore, we believe that the hybrid surface passivation could provid a reliable avenue to efficient QD materials.