Sterically Encumbered Tris(trialkylsilyl) Phosphine Precursors for Quantum Dot Synthesis

Suppression of Interfacial Oxidation in Core/Shell InP Quantum Dots through Solvent Assisted Core-Etching Strategy for Efficient Green Light-Emitting Diodes

Indium phosphide (InP) quantum dots (QDs) are promising alternative heavy-metal CdSe QDs for light-emitting diode (LED) application. However, their highly reactive core surface is prone to oxidation, which reduces the photoluminescence quantum yield (PL QY) and impedes subsequent shell growth. Traditional etching methods using HF aqueous solution are problematic as water can induce reoxidation during or after etching. Herein, we present HF pyridine solution as a more effective etching reagent to enhance luminous properties of InP QDs. Pyridine molecules replace the bulky carboxyl ligand, reducing steric hindrance and allowing HF easier access to the core for removing surface oxides. This ligand exchange promotes rapid shell growth, minimizing core exposure to the reaction environment and thereby reoxidation risk. Consequently, the as-prepared core/shell QDs exhibit a high PL QY of ∼90%, and the corresponding LEDs achieve an external quantum efficiency of 15.4% along with a long operational lifetime of 6819 h, outperforming the control devices.

Asymmetric Metal-Carboxylate Complexes for Synthesis of InGaP Alloyed Quantum Dots with Blue Emission

Indium phosphide (InP) quantum dots (QDs) have attracted significant interest as next-generation light-emitting materials. However, the synthesis of blue-emitting InP-based QDs has lagged behind that of established green- and red-emitting InP QDs. Herein, we present a strategy to synthesize blue-emitting QDs by forming an InGaP alloy composition. The introduction of asymmetric In-carboxylate and Ga-carboxylate complexes resulted in a balanced synthetic reactivity between In-P and Ga-P, leading to the formation of InGaP alloyed QDs. The resultant In1-xGaxP alloyed QDs exhibited a broad range of photoluminescence (PL) tunability, spanning from 535 nm (InP) to 465 nm (In0.62Ga0.38P), depending on the In/Ga ratio used in the synthesis. In contrast, synthesis with symmetric In-carboxylate and Ga-carboxylate complexes produced a core/shell structure of InP/GaP QDs, which did not exhibit a blue shift of the PL peak with Ga addition. By employing a core/shell structure of In0.62Ga0.38P/ZnS QDs, we achieved a PL quantum yield of 42% at 475 nm. This work highlights the material-processing strategy essential for forming alloyed structures in III-V ternary systems.

Metal Fluorides Passivate II-VI and III-V Quantum Dots

Quantum dots (QDs) with metal fluoride surface ligands were prepared via reaction with anhydrous oleylammonium fluoride. Carboxylate terminated II-VI QDs underwent carboxylate for fluoride exchange, while InP QDs underwent photochemical acidolysis yielding oleylamine, PH3, and InF3. The final photoluminescence quantum yield (PLQY) reached 83% for InP and near unity for core-shell QDs. Core-only CdS QDs showed dramatic improvements in PLQY, but only after exposure to air. Following etching, the InP QDs were bound by oleylamine ligands that were characterized by the frequency and breadth of the corresponding ν(N-H) bands in the infrared absorption spectrum. The fluoride content (1.6-9.2 nm-2) was measured by titration with chlorotrimethylsilane and compared with the oleylamine content (2.3-5.1 nm-2) supporting the formation of densely covered surfaces. The influence of metal fluoride adsorption on the air stability of QDs is discussed.

Surface Passivation toward Multiple Inherent Dangling Bonds in Indium Phosphide Quantum Dots

Indium phosphide (InP) quantum dots (QDs) have become the most recognized prospect to be less-toxic surrogates for Cd-based optoelectronic systems. Due to the particularly dangling bonds (DBs) and the undesirable oxides, the photoluminescence performance and stability of InP QDs remain to be improved. Previous investigations largely focus on eliminating P-DBs and resultant surface oxidation states; however, little attention has been paid to the adverse effects of the surface In-DBs on InP QDs. This work demonstrates a facile one-step surface peeling and passivation treatment method for both In- and P-DBs for InP QDs. Meanwhile, the surface treatment may also effectively support the encapsulation of the ZnSe shell. Finally, the generated InP/ZnSe QDs display a narrower full width at half-maximum (fwhm) of ∼48 nm, higher photoluminescence quantum yields (PLQYs) of ∼70%, and superior stability. This work enlarges the surface chemistry engineering consideration of InP QDs and considerably promotes the development of efficient and stable optoelectronic devices.

Phosphinecarboxamide based InZnP QDs - an air tolerant route to luminescent III-V semiconductors

We describe a new synthetic methodology for the preparation of high quality, emission tuneable InP-based quantum dots (QDs) using a solid, air- and moisture-tolerant primary phosphine as a group-V precursor. This presents a significantly simpler synthetic pathway compared to the state-of-the-art precursors currently employed in phosphide quantum dot synthesis which are volatile, dangerous and air-sensitive, e.g. P(Si(CH3)3)3.

Reeling them in: Ph2PSiMe3 in the sequential formation of InP magic-sized clusters

Indium phosphide magic-sized clusters (MSCs) have been identified as a key step in the growth of InP quantum dots (QDs). However, the need for elevated temperatures to form QDs from MSCs has limited our understanding of this transformation. Herein, we utilize Ph₂PSiMe₃ to identify additional MSC intermediate species, which absorb from 365 nm to 490 nm. Excitingly, particle growth was carried out at 100 °C without the use of acidic surfactants. We show that despite being discrete, stable, and isolable sizes of MSCs, they form a reaction continuum, thus providing further insight into the growth mechanism of InP.

ZnF2-Assisted Synthesis of Highly Luminescent InP/ZnSe/ZnS Quantum Dots for Efficient and Stable Electroluminescence

High-quality InP-based quantum dots (QDs) have become very promising, environmentally benign light emitters for display applications, but their synthesis generally entails hazardous hydrofluoric acid. Here, we present a highly facile route to InP/ZnSe/ZnS core/shell/shell QDs with a near-unity photoluminescence quantum yield. As the key additive, the inorganic salt ZnF₂ mildly reacts with carboxylic acid at a high temperature and in situ generates HF, which eliminates surface oxide impurities, thus facilitating epitaxial shell growth. The resulting InP/ZnSe/ZnS QDs exhibit a narrower emission line width and better thermal stability in comparison with QDs synthesized with hydrofluoric acid. Light-emitting diodes using large-sized InP/ZnSe/ZnS QDs without replacing original ligands achieve the highest peak external quantum efficiency of 22.2%, to the best of our knowledge, along with a maximum brightness of >110 000 cd/m² and a T₉₅ lifetime of >32 000 h at 100 cd/m². This safe approach is anticipated to be applied for a wide range of III-V QDs.

Highly luminescent red-emitting In(Zn)P quantum dots using zinc oxo cluster: synthesis and application to light-emitting diodes

Despite the importance of separating nucleation steps from growth steps for the production of monodisperse highly luminescent In(Zn)P quantum dots (QDs), the practical implementation of this strategy is hindered by the high reactivity and fast depletion of conventional P precursors. This problem can be mitigated through the use of (i) Zn oxo clusters, which effectively regulate the kinetics of QD growth and prevent the fast depletion of conventional P precursors in the nucleation step, or (ii) seed-mediated continuous growth methods, which avoid secondary nucleation in the growth step and yield red-emitting InP QDs. Herein, we combine approaches (i) and (ii) to synthesize red-emitting In(Zn)P QDs with a high photoluminescence quantum yield (>93%) and a low emission bandwidth (full width at half maximum = 38 nm), revealing that our strategy hinders the carboxylate ketonization-induced generation of byproducts and suppresses the surface oxidation of In(Zn)P QDs during growth steps. The prepared In(Zn)P QDs are used to fabricate QD light-emitting diodes with a maximum brightness of 1164 cd m^-2 and an external quantum efficiency of 3.61%. Thus, our results pave the way to the replacement of toxic Cd- and Pb-based QDs with more eco-friendly Zn- and In-based analogs for a variety of applications.