Quantum dot light-emitting diodes (QLEDs) are promising next-generation display devices due to their stable inorganic components, sharp emission peaks, and simple device structures. Although Cd-based QLEDs exhibit good device performance, Cd-free devices are expected to be developed for reducing negative environmental impact. Cd-free QDs are ready to be oxidized. We therefore propose a procedure for fabrication of QLEDs, in which the interparticle space of the QD layer is gradually filled with an inorganic carrier transport material (ZnS) by the successive ionic layer adsorption and reaction (SILAR) method. Since organic ligands of the QDs are removed and the QDs are embedded in the inorganic matrix in the SILAR process, QDs are protected from the oxidizing environment by the matrix. This room-temperature process would not cause significant damage to the underlayers. The SILAR process was optimized through replacement of the countercation of the anionic precursor (S2-) with a larger one (from Na+ to K+) and doping the matrix with Mg2+ for suppressing nonradiative leak currents. As a result, the external quantum efficiency of the QLED device was improved by a factor of 2.1, and the device lifetime was extended by more than 80 times in comparison with the device fabricated without the SILAR process.

Inorganic ion treatment for Cd‐free colloidal quantum dot (QD) layers improved their carrier injection efficiency, resulting in improved external quantum efficiency (EQE) and electroluminescence (EL) lifetime of the QD light‐emitting diode (QD‐LED). Inorganic ion treated QD layers patterned at 176 ppi by photolithography enabled emission of each primary color.

The ligands of quantum dots (QDs) not only play an important role in dispersion of the QDs in solvents and the protection of the QDs but could also block carrier injection into the QDs. Therefore, ligand engineering is important for improving performances of QD light-emitting diode (QLED) displays. In particular, exchange of an organic ligand with inorganic ones such as halides is expected to enhance efficiency and stability of QLED devices. In this study, an organic ligand on CdSe/ZnS QDs was exchanged with F− ligand in a non-polar solvent, which is suitable for device fabrication. As a result, stability of the QDs was improved, while the processability of QLED devices was maintained. Both external quantum efficiency of electroluminescence and device lifetime were improved, mainly because the thinner ligand layer improved the carrier injection efficiency.

This paper reports the highly efficient and high color purity red, green and blue cadmium‐free quantum dots and light‐emitting diodes (QD‐LED). Especially the red and green cadmium‐free QDs have developed with optimized structure. These new QDs have great potential to be used in next generation QD‐LED display with wide color gamut.

In this study, we evaluated the degradation mechanism in quantum dot light-emitting diodes (QLEDs) to improve the device lifetime. We measured the hole mobility using the delay time of transient electroluminescence for three types of hole transport layer (HTL) materials. In addition, we estimated the degradation of luminance efficiency and hole mobility under constant current drive. As a result, the HTL material with a higher hole mobility yielded longer QLED device lifetimes. Through substitution of the HTL material from poly (9-vinylcarbazole) (PVK) to poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (TFB), the hole mobility and the 95% luminance lifetime from initial luminance improved from 0.5 × 10−5 cm2/V⋅s and 2.90 h at J = 10 mA/cm2 to 1.1 × 10−5 cm2/V⋅s and 179 h, respectively. Moreover, we clarified that the degradation of the luminescent efficiency is correlated with the hole mobility.

When we applied colloidal quantum dots (QDs) for quantum dot light emitting diodes, it was well known that shell thickness played an important role in core protection, confinement of electrons and holes, and charge injection efficiency. However, although the shell thickness dependence of electroluminescence properties was reported, carrier injection efficiency has not been discussed in detail. In this paper, we investigated the effect of shell thickness on the carrier injection efficiency that was evaluated by photoelectrochemical measurements. By comparing the product of internal quantum yield of photoluminescence and the evaluated carrier injection efficiency with external quantum efficiency (EQE) for QDs with various shell thicknesses, we found that the optimal shell thickness for increasing EQE is determined by the balance between protection of QD's surface and carrier injection efficiency.

This paper reports the highly efficient red, green and blue cadmium‐free quantum dots and light‐emitting diodes (QD‐LED). The red and green cadmium‐free QDs with well optimized structure exhibits high color purity. These new QDs have great potential to be used in next generation QD‐LED display with wide color gamut.

We report outstanding electroluminescence properties of high‐efficiency blue cadmium‐free quantum dot light‐emitting diodes (QD‐LED). External quantum efficiency (EQE) of 14.7% was achieved for QD‐LED emitting at 428 nm. Furthermore, we developed high‐efficiency and narrow wavelength emission zinc selenide (ZnSe) nanocrystals emitting at 445 nm and achieved QD‐LED with an EQE of 10.7%. These new QDs have great potential to be used in next‐generation QD‐LED display with wide color gamut.

We report outstanding electroluminescence properties of high efficient blue cadmium‐free quantum dot light emitting diodes (QD‐LED). External quantum efficiency (EQE) of 14.7% was achieved for QD‐LED emitting at 428nm. Furthermore we developed high efficiency and narrow wavelength emission Zinc Selenide (ZnSe) nanocrystals emitting at 445nm and achieved QD‐LED with an EQE of 10.7%. These new QDs have great potential to be used in next generation QD‐LED display with wide colour gamut.