Highly luminescent blue-emitting In1−xGaxP@ZnS quantum dots and their applications in QLEDs with inverted structure†
In order to resolve the issues of uncontrollably high reactivity of tris(trimethylsilyl)phosphine, a widely used P precursor, and the very low solubility of metal halide precursors in noncoordinating solvents with ligands in the synthesis of environmentally benign group III–V quantum dots (QDs), we created bis(trimethylsilyl)phosphine (HP(TMS)2), a novel P precursor with controllable reactivity and new metal complex precursors (indium-trioctylphosphine (In-TOP), Ga-TOP, and Zn-TOP) soluble in octadecene—a noncoordinating solvent with dodecanethiol (C12SH). Another challenging issue with group III–V QDs is to generate highly luminescent photostable blue-emitting nanocrystals. We present a strategy toward synthesizing pure group III–V In1−xGaxP blue-emitting alloy cores in a noncoordinating solvent. Gallium was introduced in the core to effectively adjust the exciton energy and to reduce the lattice mismatch with the zinc sulfide shell, which contributed toward the removal of surface defects and photostability enhancement; consequently, the photoluminescence quantum yield (PLQY) and high color purity of QDs with narrow full width at half maximum (FWHM) were enhanced. The blue-emitting QDs, i.e., In1−xGaxP@ZnS, with outstanding quality (PLQY: 65%; FWHM: 46 nm) were successfully synthesized with our new P and metal complex precursors. Furthermore, we applied these QDs to fabricate blue-emitting QD light-emitting devices (QLEDs) yielding external quantum efficiency of 0.20%, which is the best among group III–V-based blue-emitting QLEDs that have been reported until now.