Molecular-Additive-Assisted Tellurium Homogenization in ZnSeTe Quantum Dots

Suppressing Colloidal Quantum Dot Multimer Fusion Leads to High-Performance InSb Infrared Photodetectors

Environmentally friendly InSb colloidal quantum dots (CQDs) short-wave infrared (SWIR) photodetectors feature characteristics of low-cost, high-volume scalability, CMOS integrability, and compliance with RoHS regulations, and hold great commercial potential. Yet, their performance falls short of commercially relevant specifications. In this work, it is posited that CQD fusion observed in these dots leads to the formation of band-tail trap states and it is further demonstrated that avoidance of such band-tail trap states is crucial for device performance. By doing so, InSb CQDs SWIR photodetectors are reported with compelling performance metrics, including a dark current of 4 µA cm-2, EQE of ≈20% (at -1 V), a linear dynamic range over 140 dB and a response time of 90 ns. This represents a more than ten-fold reduction in dark current compared to previously report InSb CQD photodetectors in the SWIR range. The record high PLQY of 10% for InSb/InP CQDs taken together with the high EQE of the device at zero bias confirm the achievement of high-quality InSb CQDs through the suppression of band-tail trap states and passivation of surface defects.

Highly efficient light-emitting diodes via self-assembled InP quantum dots

Heavy-metal-free quantum dot light-emitting diodes (QLEDs) face commercialization challenges due to low efficiency and poor stability. Spin-coated quantum dot films often create charge leakage areas, limiting device performance. Here, we develop an evaporative-driven self-assembly strategy that enables the preparation of uniform and dense InP-based quantum dot films. During device operation, these films effectively suppress performance degradation caused by charge leakage. QLEDs with uniform and dense InP-based quantum dot films achieve high external quantum efficiency (26.6%) and luminance (1.4 × 105 cd m-2), along with considerable stability (extrapolated T50 lifetime of 4026 hours at 1000 cd m-2). For a 2 × 3 cm2 InP-based device, the peak external quantum efficiency reaches 21.1%. By combining high-performance QLEDs with lithography technology, we fabricate miniaturized QLEDs with a minimum pixel size of 3 μm, achieving a resolution as high as 5080 pixels per inch and a peak external quantum efficiency of 22.6%.

Mitigating Surface Energy and Core-Shell Interface Strain of Yb3+-Doped ZnSe-Based Quantum Dots for Pure-Blue Emission QLED Devices

Large ZnSe quantum dots (QDs) with an emission peak ≈450 nm hold significant promise for display technologies. However, achieving efficient pure-blue emission through the enlargement of ZnSe nanocrystals remains a significant challenge. In this study, a breakthrough is reported in growing large-size ZnSe QDs well beyond the exciton Bohr radius through Yb3+ doping strategy. Yb3+ doping reduces the surface energy of the ZnSe (220) crystal plane and alleviates interface strain in the ZnSe/ZnS structure, enabling the QDs to grow larger while maintaining enhanced crystal stability. The resulting Yb: ZnSe/ZnS QDs exhibit pure-blue emission at 453 nm, with a full width at half maximum (FWHM) of 46 nm and a high photoluminescence quantum yield (PLQY) of 67.5%. When integrated into quantum dot light-emitting diodes (QLEDs), the devices display electroluminescence (EL) at 455 nm, with an external quantum efficiency (EQE) of 1.35%, and a maximum luminance of 1337.08 cd m-2.

Strategies for Stabilizing Metal Halide Perovskite Light-Emitting Diodes: Bulk and Surface Reconstruction of Perovskite Nanocrystals

Light-emitting colloidal lead halide perovskite nanocrystals (PeNCs) are considered promising candidates for next-generation vivid displays. However, the operational stability of light-emitting diodes (LEDs) based on PeNCs is still lower than those based on polycrystalline perovskite films, which requires an understanding of defect formation in PeNCs, both inside the crystal lattice ("bulk") and at the surface. Meanwhile, uncontrollable ion redistribution and electrochemical reactions under LED operation can be severe, which is also related to the bulk and surface quality of PeNCs, and a well-designed device architecture can boost carrier injection and balance radiative recombination. In this review, we consider bulk and surface reconstruction of PeNCs by enhancing the crystal lattice rigidity and rationally selecting the surface ligands. Degradation pathways of PeNCs under applied voltage are discussed, and strategies are considered to avoid both undesirable ion migration and electrochemical reactions in the PeNC films. Subsequently, other critical issues hindering the commercial application of PeNC LEDs are discussed, including the toxicity of Pb in lead halide perovskites, scale-up deposition of PeNC films, and design of active-matrix prototypes for high-resolution LED modules.

Control Over Metal-Halide Reactivity Enables Uniform Growth of InSb Colloidal Quantum Dots for Enhanced SWIR Light Detection

InSb colloidal quantum dots (CQDs) hold promise in short-wave infrared sensing; however, their synthesis presents ongoing challenges, particularly in achieving precise size control - this is the result of poorly controlled reactivity among the precursors. Herein, the use of alkyl-phosphine and amine-based organic additives to control the reactivity of In and Sb precursors during the nucleation and growth of CQDs is developed. This interplay between organic additive and precursors enables the synthesis of InSb CQDs having narrowed size distributions; and bandgaps tunable across the 1.2-1.5 µm spectral range; all this leading to peak-to-valley ratios >1.4 in absorption spectra. The CQDs are surface-terminated with a mixture of oleylamine, halides, and oxide-like species, and this hinders ligand exchange reactions and subsequent integration into photodiodes. We therefore resurface the CQDs with alkanethiols, displacing the native ligands via an acid-base mechanism, an approach that removes oxide species. Using a layer-by-layer fabrication process, the ligands of the resurfaced InSb CQDs are exchanged with short organic and halide ligands and incorporated films into n-i-p photodiode structures. The resultant devices exhibit a detectivity of 10¹2 Jones, an external quantum efficiency (EQE) of 33% at 1380 nm, and T90 operating stability of >19 h under continuous illuminated operation.

Homogeneous ZnSeTeS quantum dots for efficient and stable pure-blue LEDs

The electroluminescence performance of heavy-metal-free blue quantum dot (QD) light-emitting diodes (QLEDs) is much lower than that of state-of-the-art cadmium-based counterparts. Ecofriendly ZnSeTe QDs are an ideal alternative to cadmium-based blue QDs1,2, but face issues with colour impurity and inferior stability caused by the aggregated tellurium (Ten≥2) that dominates compositional inhomogeneity3,4. Here we developed an isoelectronic control strategy using congeneric sulfur coordinated with triphenyl phosphite (TPP-S) to construct homogeneous ZnSeTeS QDs with pure-blue emissions and near-unity photoluminescence quantum yield. TPP with low electron-donating capability promotes the reactivity balance among anionic precursors, favouring the growth of QDs with uniform composition. The acceptor-like S with high electronegativity weakens the hole localization of the Te atoms by interfering with their surrounding carriers, thereby suppressing the formation of Ten≥2 isoelectronic centres. Furthermore, the congeneric S increases the configurational entropy of the QDs and eliminates the stacking faults and oxygen defects, leading to improved structural stability and reduced non-radiative carrier density. Consequently, the resulting pure-blue QLEDs based on core-shell ZnSeTeS/ZnSe/ZnS QDs emitting at 460 nm show a high external quantum efficiency of 24.7%, a narrow linewidth of 17 nm, and long operational half-lifetime (T50) close to 30,000 hours at 100 cd cm-2, rivalling state-of-the-art cadmium-based blue QLEDs.

Defect passivation engineering of chalcogenide quantum dots via in situ fluorination treatment

Efficient carrier transport through reducing the traps in chalcogenide quantum dots (QDs) is crucial for their application in optoelectronic devices. This study introduces an innovative in situ fluorination treatment to remove the whole-body traps of metal chalcogenide QDs, further accelerating the carrier transport process. The selected benzene carbonyl fluoride (BF) molecular additive can efficiently peel off the caused oxide traps and dangling bonds of chalcogenide QDs in real-time through the continuous release of the HF gas of BF decomposition. Experimental results revealed that the obtained chalcogenide QDs with in situ fluorination treatment can accelerate the charge extraction and hinder the charge recombination. Finally, two types of photo-electrical conversion devices, consisting of photodetectors and sensitized solar cells, are fabricated to reveal the advantages of in situ fluorination treatment of QDs. Our findings highlight in situ fluorination treatment towards chalcogenide QDs as a viable approach to reduce the traps of QDs and improve the performance in optoelectronic technologies, offering hope for the practical application of this technology in the near future.

Highly efficient and eco-friendly green quantum dot light-emitting diodes through interfacial potential grading

As next-generation display technologies, eco-friendly colloidal quantum dot light-emitting diodes have drawn great attention due to their excellent luminescence properties, along with their rapid development. However, practical applications of eco-friendly quantum dot light-emitting device remain challenging, primarily due to the inferior performance of green device, which still lag behind their red and blue counterparts. Herein, we present efficient green device based on interfacial potential-graded ZnSeTe quantum dots. Our findings show that this potential-graded structure alleviates interfacial lattice mismatch and strain, reducing structural deformation and misfit defects. The smoothed interfacial potential suppresses the nonradiative recombination processes, particularly Auger recombination revealed by excitation-intensity dependent ultrafast transient absorption kinetics. Consequently, the interfacial potential-graded quantum dots demonstrate highly efficient green quantum dot light-emitting diodes, with a peak external quantum efficiency of 21.7% at 520 nm and a corresponding current efficiency of 75.7 cd A-1.

Blue Quantum Dot Light-Emitting Diodes toward Full-Color Displays: Materials, Devices, and Large-Scale Fabrication

Quantum dots (QDs) light-emitting diodes (QLEDs) are gaining significant interest for the next generation of display and lighting applications because of their wide color gamut, cost-effective solution processability, and good stability. The last decades have witnessed rapid advances in improving their efficiency and lifetime. So far, among the three primary colors of QLEDs devices, the performance of blue QLEDs is considerably inferior to that of green and red ones including Cd-based and Cd-free devices, which is a key bottleneck hindering QLEDs' application. This mini-review describes recent advances of blue Cd-based and Cd-free QLEDs from materials to device engineering, in particular, elaborating the essential factors that limit their performance and the degradation mechanisms. We also discuss the progress and challenges of large-scale displays. Finally, we propose possible approaches to improve the performance of the blue QLEDs, including QDs materials and device architecture optimization, and summarize potential applications in this stimulating field.

X-Type Ligands Effect on the Operational Stability of Heavy-Metal-Free Quantum Dot Light-Emitting Diodes

ZnSeTe quantum dots (QDs) offer an efficient avenue for realizing heavy-metal-free light-emitting diodes (LEDs) that meet the Rec.2100 blue standard. Synthetic core-shell engineering has enabled big advances in the external quantum efficiency (EQE) of ZnSeTe QD-LEDs. However, the mechanisms behind the degradation of the operational stability of ZnSeTe QD-LEDs remain relatively unexplored. In this study, we explore the impact of ligand density and composition on both material and device stability. We developed a solid-film ligand exchange utilizing an inorganic X-type ligand (zinc chloride), revealing that the substitution of inorganic ligands for organic counterparts significantly influences the stability of both materials and devices.

Organoborane Se and Te Precursors for Controlled Modulation of Reactivity in Nanomaterial Synthesis

To exploit the distinctive optoelectrical properties of nanomaterials, precise control over the size, morphology, and interface structure is essential. Achieving a controlled synthesis demands precursors with tailored reactivity and optimal reaction temperatures. Here, we introduce organoborane-based selenium and tellurium precursors borabicyclononane-selenol (BBN-SeH) and tellurol (BBN-TeH). The reactivity of these precursors can be modified by commercially available additives, covering a wide range of intermediate reactivity and filling significant reactivity gaps in existing options. By allowing systematic adjustment of growth conditions, they achieve the controlled growth of quantum dots of various sizes and materials. Operating via a surface-assisted conversion mechanism, these precursors rely on surface coordination for activation and undergo quantitative deposition on coordinating surfaces. These properties allow precise control over the radial distribution and density of different chalcogenide atoms within the nanoparticles. Diborabicyclononanyl selane ((BBN)2Se), an intermediate from the BBN-SeH synthesis, can also serve as a selenium precursor. While BBN-SeH suppresses nucleation, (BBN)2Se exhibits efficient nucleation under specific conditions. By leveraging these distinct activation behaviors, we achieved a controlled synthesis of thermally stable nanoplates with different thicknesses. This study not only bridges critical reactivity gaps but also provides a systematic methodology for precise nanomaterial synthesis.

Crystallographic and Photophysical Analysis on Facet-Controlled Defect-Free Blue-Emitting Quantum Dots

The burgeoning demand for commercializing self-luminescing quantum dot (QD) light-emitting diodes (LEDs) has stimulated extensive research into environmentally friendly and efficient QD materials. Hydrofluoric acid (HF) additive improves photoluminescence (PL) properties of blue-emitting ZnSeTe QDs, ultimately reaching a remarkable quantum yield (QY) of 97% with an ultranarrow peak width of 14 nm after sufficient HF addition. The improvement in optical properties of the QDs is accompanied by a morphology change of the particles, forming cubic-shaped defect-free ZnSeTe QDs characterized by a zinc blende (ZB) crystal structure. This treatment improves the QD-emitting properties by facilitating facet-specific growth, selectively exposing stabilized (100) facets, and reducing the lattice disorders. The facet-specific growth process gives rise to defect-free monodispersed cubic dots that exhibit remarkably narrow and homogeneous PL spectra. Meticulous time-resolved spectroscopic studies allow an understanding of the correlation between ZnSeTe QDs' particle shape and performance following HF addition. These investigations shed light on the intricacies of the growth mechanism and the factors influencing the PL efficiency of the resulting QDs. The findings significantly contribute to understanding the role of HF treatment in tailoring the optical properties of ZnSeTe QDs, thereby bringing it closer to the realization of highly efficient and bright QD-LEDs for various practical applications.

Blue-Emissive ZnSeTe Quantum Dots and Their Electroluminescent Devices

Over the last two decades, quantum-dot light-emitting diodes (QLEDs), also known as quantum dot (QD) electroluminescent devices, have gained prominence in next-generation display technologies, positioning them as potential alternatives to organic light-emitting diodes. Nonetheless, challenges persist in enhancing key device performances such as efficiency and lifetime, while those of blue QLEDs lag behind compared with green and red counterparts. In this Perspective, we discuss key factors affecting the photoluminescence characteristics of environmentally benign blue-emissive ternary ZnSeTe QDs, including composition, core/shell heterostructure, and surface ligand. Notably, we highlight the recent progress in breakthrough strategies to enhance blue QLED performance, examining the effects of the ZnSeTe QD attribute and device architecture on device performance. This Perspective offers insights into integrated aspects of QD material and device structure in overcoming challenges toward a high-performance blue ZnSeTe QLED.

Arresting Ion Migration from the ETL Increases Stability in Infrared Light Detectors Based on III-V Colloidal Quantum Dots

III-V colloidal quantum dots (CQDs) are of interest in infrared photodetection, and recent developments in CQDs synthesis and surface engineering have improved performance. Here this work investigates photodetector stability, finding that the diffusion of zinc ions from charge transport layers (CTLs) into the CQDs active layer increases trap density therein, leading to rapid and irreversible performance loss during operation. In an effort to prevent this, this work introduces organic blocking layers between the CQDs and ZnO layers; but these negatively impact device performance. The device is then, allowing to use a C60:BCP as top electron-transport layer (ETL) for good morphology and process compatibility, and selecting NiOX as the bottom hole-transport layer (HTL). The first round of NiOX -based devices show efficient light response but suffer from high leakage current and a low open-circuit voltage (Voc) due to pinholes. This work introduces poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) with NiOX NC to form a hybrid HTL, an addition that reduces pinhole formation, interfacial trap density, and bimolecular recombination, enhancing carrier harvesting. The photodetectors achieve 53% external quantum efficiency (EQE) at 970 nm at 1 V applied bias, and they maintain 95% of initial performance after 19 h of continuous illuminated operation. The photodetectors retain over 80% of performance after 80 days of shelf storage.

Interface defects repair of core/shell quantum dots through halide ion penetration

The interface defects of core-shell colloidal quantum dots (QDs) affect their optoelectronic properties and charge transport characteristics. However, the limited available strategies pose challenges in the comprehensive control of these interface defects. Herein, we introduce a versatile strategy that effectively addresses both surface and interface defects in QDs through simple post-synthesis treatment. Through the combination of fine chemical etching methods and spectroscopic analysis, we have revealed that halogens can diffuse within the crystal structure at elevated temperatures, acting as "repairmen" to rectify oxidation and significantly reducing interface defects within the QDs. Under the guidance of this protocol, InP core/shell QDs were synthesized by a hydrofluoric acid-free method with a full width at half-maximum of 37.0 nm and an absolute quantum yield of 86%. To further underscore the generality of this strategy, we successfully applied it to CdSe core/shell QDs as well. These findings provide fundamental insights into interface defect engineering and contribute to the advancement of innovative solutions for semiconductor nanomaterials.