Quantum dot light-emitting diodes (QLEDs) show great potential in high-definition displays due to their narrow emission and high color purity. However, the imperfect quantum dots (QDs) with high trap density are difficult to be removed from QD solution, which could cause serious nonradiative recombination, thereby suppressing the improvement of QLEDs. Here, we devise a novel chemical filtering strategy with a bidentate coordination to remove the imperfect QDs. The bidentate ligand of ethanolamine (EA) with an amidogen and a carboxyl was directly added into the CdSe/CdS/ZnS core/shell/shell QD solution. Then, uncoordinated sites such as S2– and Zn2+ on the surface of QDs were bonded with the amidogen and carboxyl of EA, respectively, resulting in aggregations of the imperfect QDs with high defect density, which were precipitated from the solution. As a result, the photoluminescence quantum yield (PLQY) of the filtered QD solution increased to 93% because of the decrease in trap density. The size distribution of QDs was also improved after filtration. QLEDs fabricated with filtered QDs show a high external quantum efficiency (EQE) of 15.76% and luminance of 19,640 cd/m2, greater than those of the control devices. This strategy shows a great potential to be used in the large-scale treatment and production of QDs and QLEDs.
Kanghong Wang,Yi Tao,Zikun Tang,Daniele Benetti,François Vidal,Haiguang Zhao,Federico Rosei,Xuhui Sun
Colloidal Quantum dots (QDs) are considered promising light harvesters for photoelectrochemical (PEC) hydrogen generation devices due to their size tunable optoelectronic properties. However, the solar-to-hydrogen (STH) efficiency and long-term stability of devices based on QDs are still relatively low, thus limiting the commercial development. These limitations are attributed to the limited absorption range of QDs, unfavorable band energy alignment and photo-oxidation. Here we propose and realize two core/multiple-shell architecture based on CdSe/CdS/ZnS QDs. The shell composition is optimized with gradient layers, forming CdSe/CdSe x S 1−x /CdS/Zn y Cd 1−y S/ZnS core/multiple-shell structures, which reduces the surface traps and defects of QDs and simultaneously suppresses exciton recombination by providing intermediated alloyed interlayers . The PEC device based on a mesoporous TiO 2 sensitized with two types of core/multiple-shell QDs exhibited an outstanding saturated photocurrent density of 20.5 mA/cm 2 for alloyed core/multiple-shell QDs, under one sun illumination (AM 1.5 G, 100 mW/cm 2 ). To our knowledge, this is comparable to the highest value reported so far for the PEC devices based on colloidal QDs. In addition, the as-prepared PEC devices exhibited excellent stability, maintaining ~93.4 % of the initial photocurrent density after 2-hour continuous illumination (100 mW/cm 2 ). This work provides an efficient approach for improving the performance of PEC devices through QDs structure engineering.
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