Ligand Effect in 1-Octanethiol Passivation of InP/ZnSe/ZnS Quantum Dots-Evidence of Incomplete Surface Passivation during Synthesis

Enhanced Quantum Yield and Long-Term Stability of Eco-Friendly Water-Dispersed InP/ZnSe/ZnS Quantum Dots via Photochemical Surface Passivation

Quantum dots (QDs) are essential in fields such as bioimaging and electronics due to their unique optical properties. However, traditional cadmium (Cd)-based QDs pose significant environmental and health risks. This study aimed to develop efficient, Cd-free QDs suitable for water dispersion and long-term stability. We synthesized InP/ZnSe/ZnS multi-shell QDs and employed a photochemical surface passivation method using a halogen lamp to enhance their photoluminescence. For water dispersion, we used ligand exchange with hydrophilic agents, such as 3-mercaptopropionic acid (3-MPA) and 11-mercaptoundecanoic acid (11-MUA). This process facilitated the dispersion of QDs in water while maintaining their quantum yield (QY). The results revealed that the water-dispersed QDs retained 92.5% of their initial QY after 2 months, a notable improvement compared to the 47.3% retention of QDs dispersed in chloroform solvents. This demonstrates that our photochemical passivation method and ligand exchange effectively stabilize QDs in aqueous environments. These Cd-free, water-dispersed QDs offer significant advantages for sustainable electronics, water treatment, and biomedical applications. The study highlights the potential for broader commercialization and further research into optimizing QD performance through advanced ligand and synthesis techniques.

Green InP Quantum Dots with High Brightness and Narrow Emission through Layer-by-Layer Modification with Aluminum

InP quantum dots (QDs) show a unique promise for display and lighting applications. However, the synthesis of InP QDs with high optical quality is much more difficult compared to that of Cd-based QDs and Pb-based perovskites. Here, we established a layer-by-layer modification approach to improve the optical properties of the InP QDs. InP QDs with green emission were prepared using tris(dimethylamino)phosphine ((DMA)3P). By introducing aluminum isopropoxide (AIP) twice during the formation of the ZnSeS and ZnS shell layers, we increased the photoluminescence quantum yield (PLQY) of the resulting Al-modified InP/ZnSeS/ZnS QDs to 96%. The full-width-at-half-maximum (fwhm) could be narrowed to 37 nm. It was speculated that the introduction of Al could alleviate the charge mismatch between the cores and shells and passivate surface defects. In addition, AIP might form oxides on the outer layers of QDs, thus enhancing their stability. Moreover, the green light-emitting diode (LED) based on Al-modified InP/ZnSeS/ZnS QDs performed well with a maximum power efficiency of 28 lm/W. This work finds a way to obtain InP QDs of high brightness and narrow emission by modification in the midsynthetic process, which will inspire the synthesis of better InP QDs.

Recent Advances and Challenges of Colloidal Quantum Dot Light-Emitting Diodes for Display Applications

Colloidal quantum dots (QDs) exhibit tremendous potential in display technologies owing to their unique optical properties, such as size-tunable emission wavelength, narrow spectral linewidth, and near-unity photoluminescence quantum yield. Significant efforts in academia and industry have achieved dramatic improvements in the performance of quantum dot light-emitting diodes (QLEDs) over the past decade, primarily owing to the development of high-quality QDs and optimized device architectures. Moreover, sophisticated patterning processes have also been developed for QDs, which is an essential technique for their commercialization. As a result of these achievements, some QD-based display technologies, such as QD enhancement films and QD-organic light-emitting diodes, have been successfully commercialized, confirming the superiority of QDs in display technologies. However, despite these developments, the commercialization of QLEDs is yet to reach a threshold, requiring a leap forward in addressing challenges and related problems. Thus, representative research trends, progress, and challenges of QLEDs in the categories of material synthesis, device engineering, and fabrication method to specify the current status and development direction are reviewed. Furthermore, brief insights into the factors to be considered when conducting research on single-device QLEDs are provided to realize active matrix displays. This review guides the way toward the commercialization of QLEDs.

Tuning the Shades of Red Emission in InP/ZnSe/ZnS Nanocrystals with Narrow Full Width for Fabrication of Light-Emitting Diodes

While Cd-based luminescent nanocrystals (NCs) are the most mature NCs for fabricating efficient red light-emitting diodes (LEDs), their toxicity related limitation is inevitable, making it necessary to find a promising alternative. From this point of view, multishell-coated, red-emissive InP-based NCs are excellent luminescent nanomaterials for use as an emissive layer in electroluminescent (EL) devices. However, due to the presence of oxidation states, they suffer from a wide emission spectrum, which limits their performance. This study uses tris(dimethylamino)phosphine (3DMA-P) as a low-cost aminophosphine precursor and a double HF treatment to suggest an upscaled, cost-effective, and one-pot hot-injection synthesis of purely red-emissive InP-based NCs. The InP core structures were coated with thick layers of ZnSe and ZnS shells to prevent charge delocalization and to create a narrow size distribution. The purified NCs showed an intense emission signal as narrow as 43 nm across the entire red wavelength range (626-670 nm) with an emission quantum efficiency of 74% at 632 nm. The purified samples also showed an emission quantum efficiency of 60% for far-red wavelengths of 670 nm with a narrow full width of 50 nm. The samples showed a relatively long average emission lifetime of 50-70 ns with a biexponential decay profile. To demonstrate the practical ability of the prepared NCs in optoelectronics, we fabricated a red-emissive InP-based LEDs. The best-performing device showed an external quantum efficiency (EQE) of 1.16%, a luminance of 1039 cd m-2, and a current efficiency of 0.88 cd A-1.

Ligand-Crosslinking Strategy for Efficient Quantum Dot Light-Emitting Diodes via Thiol-Ene Click Chemistry

While solution-processable colloidal quantum dots (QDs) offer cost-effective and large-scale manufacturing, they can be susceptible to subsequent solution processes, making continuous processing challenging. To enable complex and integrated device architectures, robust QD films with subsequent patterning are necessary. Here, we report a facile ligand-crosslinking strategy based on thiol-ene click chemistry. Thiol molecules added to QD films react with UV light to form radicals that crosslink with QD ligands containing carbon double bonds, enabling microscale photo-patterning of QD films and enhancing their solvent resistance. This strategy can also be extended to other ligand-capped nanocrystals. It is found that the swelling of QD films during the process of binding with the thiol molecules placed between the ligands contributes to the improvement of photoluminescence and electroluminescence properties. These results suggest that the thiol-ene crosslinking modifies the optoelectronic properties and enables direct optical patterning, expanding the potential applications of QDs.