Effectual Interface and Defect Engineering for Auger Recombination Suppression in Bright InP/ZnSeS/ZnS Quantum Dots

The main issue in developing a quantum dot light-emitting diode (QLED) display lies in successfully replacing heavy metals with environmentally benign materials while maintaining high-quality device performance. Nonradiative Auger recombination is one of the major limiting factors of QLED performance and should ideally be suppressed. This study scrutinizes the effects of the shell structure and composition on photoluminescence (PL) properties of InP/ZnSeS/ZnS quantum dots (QDs) through ensemble and single-dot spectroscopic analyses. Employing gradient shells is discovered to suppress Auger recombination to a high degree, allowing charged QDs to be luminescent comparatively with neutral QDs. The “lifetime blinking” phenomenon is observed as evidence of suppressed Auger recombination. Furthermore, single-QD measurements reveal that gradient shells in QDs reduce spectral diffusion and elevate the energy barrier for charge trapping. Shell composition dependency in the gradience effect is observed. An increase in the ZnS composition (ZnS >50%) in the gradient shell introduces lattice mismatch between the core and the shell and therefore rather reverses the effect and reduces the QD performance

Cation-Exchange-Derived InGaP Alloy Quantum Dots toward Blue Emissivity

In contrast to a substantial progress of heavy metal-free green and red emitters exclusively from indium phosphide (InP) quantum dots (QDs), the development of non-Cd blue QDs remains nearly unexplored. The synthesis of blue InP QDs with a bright, deep-blue emissivity is not likely viable, which is primarily associated with their intrinsic size limitation. To surmount this challenge, herein, the first synthesis of blue-emissive ternary InGaP QDs through In3+-to-Ga3+ cation-exchange strategy is implemented. Pregrown InP QDs turn out to be efficiently Ga-alloyed at a relatively low temperature of 280 °C in the presence of Ga iodide (GaI3), and the degree of Ga alloying is also found to be systematically adjustable by varying GaI3 amounts. Such cation-exchanged InGaP cores are surface-passivated sequentially with ZnSeS inner and ZnS outer shells. As the amount of GaI3 added for cation exchange increases, the resulting double-shelled InGaP/ZnSeS/ZnS QDs produce consistent blue shifts in photoluminescence (PL) from 475 to 465 nm, while maintaining high PL quantum yield in the range of 80–82%. Among a series of QD samples, above 465 nm emitting InGaP/ZnSeS/ZnS QDs are further employed as an emitting layer of an all-solution-processed electroluminescent device. This unprecedented InGaP QD-based blue device generates maximum values of 1038 cd/m2 in luminance and 2.5% in external quantum efficiency