Cadmium-Free InP/ZnSeS/ZnS Heterostructure-Based Quantum Dot Light-Emitting Diodes with a ZnMgO Electron Transport Layer and a Brightness of Over 10 000 cd m?2

The heating up method to synthesize thick-shelled cadmium-free InP/ZnSeS/ZnS QDs was studied. High performance Cd-free QLEDs are demonstrated by using thick-shelled InP/ZnSeS/ZnS QDs and ZnMgO commercial electron transport layer in an inverted structure. After the formation of the InP/Zn core, we inject the sulfur source to form the ZnS shell that protects the InP/Zn core. To increase the thickness of the ZnS shell, we should consider the problem of lattice mismatch. Given the higher lattice mismatch between the InP core and ZnS shell, the thick shell of ZnS will cause the lattice to collapse and decrease the stability of QDs. Thus, we inject the selenium-TOP precursor to the InP/ZnS solution to form a ZnSe buffer layer. Finally, we can increase the thickness of the ZnS shell. We optimize the thickness of the ZnS layer to improve the quality of the InP/ZnSeS/ZnS QDs. The average particle size of the InP/ZnSeS QDs was estimated to be 3.3 ? 0.4 nm using a high-resolution transmission electron microscope (HR-TEM). The thickness of the overgrown ZnS shell was =2.1 nm. The thick ZnS shell enabled the InP QDs to maintain their high fluorescent stability and lifetime against environmental changes on the surface of QDs. The optimized InP/ZnSeS/ZnS inverted device showed a redshift compared with the original PL spectra, which had an emission wavelength of 525 nm.