Hot-injection Synthesis Research Articles

Colloidal hot injection synthesis of Cu2FeSnS4 nanoparticles towards an enhanced capacity anode material for Li-ion batteries

The increasing demand for portable energy storage devices has prompted a considerable exploration into advanced anode material with higher Li-ion battery capacities. Quaternary chalcopyrite semiconductors have generated significant attention as promising materials in applications such as optoelectronic devices, energy conversion, and energy storage devices. In this paper, Cu2FeSnS4 (CFTS) nanoparticles were prepared through a colloidal hot injection method (HIM). The structural analysis indicates that the CFTS nanoparticles exhibit a pure tetragonal structure characterized by high crystallinity. The morphological and elemental analysis shows the stoichiometric synthesis of CFTS nanoparticles with significant agglomeration of crystallites, accompanied by variation in size. The CFTS nanoparticles, employed as an anode material for Li-ion batteries, demonstrated significant performance characterized by high reversible capacity and stability at ambient temperature. The initial discharge capacity is achieved at 1181 mAhg−1 and retains 528 mAhg−1 during charge-discharge cycles within the voltage range of 0.005 to 3.0 V (versus Li/Li+) after 5 cycles. The CFTS nanoparticle performance findings indicate its promising implementation as an anode electrode in Li-ion batteries.

A high temperature in situ optical probe for colloidal nanocrystal synthesis.

We report on the fabrication and utilization of a robust high-temperature (>300 °C), adjustable-path-length, vacuum-tolerant, configurable, in situ optical probe, which interfaces with widely used chemical glassware via a 14/20 ground glass joint. This probe allows for high-speed reaction monitoring of colloidal semiconductor nanocrystal solutions at temperatures that were previously inaccessible. We demonstrate this capability by monitoring the hot-injection synthesis of CdSe quantum dots via UV-Vis absorption spectroscopy at 380 °C with a time resolution of ∼10ms, with the primary limitation being the acquisition and data saving rate of the commercial spectrometer used. We further demonstrate that this probe can also be used for in situ photoluminescence measurements. This system is generally applicable to harsh solution environments where optical monitoring of reaction progress is desirable and/or necessary.

Hot injection synthesis of CuS decorated CdS and ZnS nanomaterials from metal thiosemicarbazone complexes as single source precursors: Application in the photocatalytic degradation of methylene blue

CdS and ZnS are considered excellent semiconductors for photocatalysis, but photocorrosion and low photocatalytic activity limit their practical application. In order to improve on their photocatalytic activities, Copper sulfide-decorated CdS and ZnS (CuS@CdS and CuS@ZnS) nanocomposites were synthesized from Cu(II), Zn(II) and Cd(II) complexes of 2–(phenyl(pyridin–2–yl)methylene)hydrazine–1–carbothioamide, as single source precursors using a facile hot injection method at 250 °C, employing olive oil as capping agent. The structure, morphology, and optical properties of the as-prepared nanocomposites were determined using various analytical techniques. The results of powder X-ray diffraction (p-XRD), energy dispersive X-ray spectroscopy (EDX) and elemental mapping showed the presence of CuS, CdS and ZnS in CuS@CdS and CuS@ZnS, confirming the formation of nanocomposites. Transmission Electron Microscopy (TEM) images show agglomeration of CuS nanoparticles on the surface of CdS and ZnS nanoparticles. Scanning electron microscopy (SEM) images of CuS@CdS and CuS@ZnS nanocomposites revealed an agglomerated flower-like structure with porous surface. The band gap energies of 2.84 eV and 3.12 eV for CuS@CdS and CuS@ZnS, respectively, obtained from Tauc plots, demonstrate that combining CuS with single CdS and ZnS has an effect on their optical properties which probably account for the improved photocatalytic responses. The photocatalytic performance of the as-prepared materials was evaluated using the photodegradation of methylene blue (MB) dye under UV light irradiation. Results show that the degradation efficiencies for CuS@CdS (57 %) and CuS@ZnS (65 %) nanocomposites exhibited higher photocatalytic activity compared to those of pure CuS (42.0 %), CdS (35.1 %) and ZnS (57 %), suggesting that thiosemicarbazone complexes can be used as precursors for the development of metal sulphide nanocomposites as useful photocatalysts for the degradation of organic pollutants.

Hot-Injection Synthesis of Cesium Lead Halide Perovskite Nanowires with Tunable Optical Properties.

Metal halide perovskite semiconductors have emerged as promising materials for various optoelectronic applications due to their unique crystal structure and outstanding properties. Among different forms, perovskite nanowires (NWs) offer distinct advantages, including a high aspect ratio, superior crystallinity, excellent light absorption, and carrier transport properties, as well as unique anisotropic luminescence properties. Understanding the formation mechanism and structure-property relationship of perovskite NWs is crucial for exploring their potential in optoelectronic devices. In this study, we successfully synthesized all-inorganic halide perovskite NWs with high aspect ratios and an orthorhombic crystal phase using the hot-injection method with controlled reaction conditions and surface ligands. These NWs exhibit excellent optical and electrical properties. Moreover, precise control over the halogen composition through a simple anion exchange process enables the tuning of the bandgap, leading to fluorescence emission, covering a wide range of colors across the visible spectrum. Consequently, these perovskite NWs hold great potential for efficient energy conversion and catalytic applications in photoelectrocatalysis.

Room-temperature synthesis of full-component APbX3 perovskite nanocrystal inks for optoelectronic applications

Lead halide perovskite nanocrystals (PNCs) have received great research interests due to their excellent optoelectronic properties. However, high temperature, inert gas protection and insulating long-chain ligands are used during the conventional hot-injection synthesis of PNCs, which limits their practical applications. In this work, we first develop a simple and scalable polar-solvent-free method for the preparation of full-component APbX3 (A = Cs, methylammonium (MA), formamidinium (FA), X = Cl, Br, I) PNCs under ambient condition. Through an exothermic reaction between butylamine (BA) and propionic acid (PA) short ligands, the PbX2 precursors could be well dissolved without use of any polar solvent. Meanwhile, the relatively lower growth rate of PNCs in our room-temperature reaction enables us to modulate the synthetic procedure to enhance the scalability (40-fold) and achieve large-scale synthesis. The resultant short ligands passivated PNC inks are compatible with varying solution depositing technique like spray coating for large-area film. Finally, we showcase that adopting the as-prepared MAPbI3 PNC inks, a self-powered photodetector is fabricated and shows a high photoresponsivity. These results demonstrate that our ambient-condition synthetic approach can accelerate the preparation of tunable and ready-to-use PNCs towards commercial optoelectronic applications.

Synthesis of Metastable Silver-Lanthanide Double Perovskite Nanocrystals with White-Light Emission.

Four silver-lanthanide double perovskite nanocrystals, namely, Cs2AgSmCl6, Cs2AgEuCl6, Cs2AgGdCl6, and Cs2AgErCl6, were synthesized for the first time. These four double perovskites have yet to be reported in any form and are found to be metastable in the bulk phase. By using the colloidal hot-injection synthesis method, the metastable double perovskite phase can be arrested kinetically. These lead-free nanocrystals show a broadband emission owing to the self-trapped exciton recombination, with Cs2AgEuCl6 exhibiting the characteristic f-f emission from Eu3+.

Multinary light absorbing semiconductor nanocrystals with diversified electronic and optical properties

We report multinary CuZn2ASxSe4−x semiconductor nanocrystals in a wurtzite phase, achieved via hot-injection synthesis.

Fabrication of water-resistant fluorescent ink using the near-unity photoluminescence quantum yield of CsPbBr3 doped with NiBr2.

Doping with transition and alkaline earth metal ions into all-inorganic perovskite nanocrystals (NCs) has attracted attention recently for tuning the photoluminescence quantum yield (PLQY). We report on the hot injection synthesis of nickel ion-doped CsPbBr3 NCs with near-unity PLQYs. Nickel ions were successfully incorporated into the octahedral environment of CsPbBr3 NCs, replacing the lead ions. The introduction of nickel ions into CsPbBr3 NCs substantially eliminates intrinsic defects and halide vacancies for improved structural order and near-unity PLQYs. Benefiting from these unique properties, nickel ion-doped CsPbBr3 NCs were dispersed in a polymer to prepare an efficient fluorescent ink. The fluorescent ink shows excellent thermal and water stability under harsh environmental conditions. Moreover, the usefulness of the fluorescent ink for security purposes was demonstrated by designing and recognizing a fluorescent QR code. This study reveals that doped CsPbBr3 NCs can be used to prepare efficient water-resistant fluorescent ink for anti-counterfeiting applications, widening the usefulness of doped all-inorganic perovskite NCs.

Electrophoretic assisted fabrication of additive-free WS2 nanosheet anodes for high energy density lithium-ion batteries.

2D WS2 nanosheets (NSs) are gaining popularity in the domain of Li-ion batteries (LIBs) due to their unique structures, which can enable reversible insertion and extraction of alkali metal ions. While synthesis methods have mostly relied on the exfoliation of bulk materials or direct growth on substrates, here we report an alternative approach involving colloidal hot-injection synthesis of 2D WS2 in 2H and 1T' crystal phases followed by their electrophoretic deposition (EPD) on the current collector. The produced 2D WS2 NSs' films do not require any additional additives during deposition, which boosts the energy density of the additive-free LIBs produced. The 1T' and 2H NSs exhibit long-term stable cyclic performance at C/5 for 600 cycles. At a high cycling rate (1C), the 2H NSs outperform the 1T' NSs, delivering a 1st cycle reversible capacity of 513 mA h g-1 with capacity retention of 73% after 100 cycles (compared to 205 mA h g-1, and 84 mA h g-1 respectively for NS-1T'). Post-cycling investigation confirms that there is no leaching or cracking of the active material on the surface of anodes after 100 cycles at C/5, which enables mechanical stability, and impressive battery performance of the WS2 NS electrodes.

Potential usage of cesium manganese halide for multi-functional optoelectronic devices: Display & photodetector application

The composition of manganese, which exhibits tetrahedral coordination with halogen ligands, makes it excellent for use in green light-emitting materials. In particular, zero-dimensional Cs3MnBr5 material has continuously been researched as a lead-free all-inorganic light emitting material. It has excellent optical properties such as center wavelength and full width at half maximum. The most recent studies on Cs3MnBr5 have synthesized it using a bottom-up method. However, the problem of notably poor particle uniformity or efficiency remains. The aim of this study was to develop sub-micron-sized Cs3MnBr5 particles with octahedron or truncated shapes by modifying the existing hot-injection synthesis method. Sub-micron Cs3MnBr5 particles showed 60% photoluminescence quantum yield (PLQY) under blue light excitation and absorbed light in the entire visible light region, including the absorption edge by PLE. Therefore, we explored existing research on light conversion films for LED & micro-LED and photodetector applications with a focus on optical properties of Cs3MnBr5 particles.

Hot-injection synthesis of lead-free pseudo-alkali metal-based perovskite (TlSnX3) nanoparticles with tunable optical properties

The commercialization of organo-inorganic hybrid perovskite materials for optoelectronic applications is limited owing to the restriction of lead (Pb) usage in consumer electronics and the instability of organic cations in the perovskite structure. To address these challenges, we synthesize TlSnX3 (X = Cl, Br, and I) perovskite nanoparticles (NPs) with high crystallinity and uniformity using the hot-injection method. The optical properties of TlSnX3 NPs are fine-tuned by substituting the halide ions of TlSnX3. In addition, the oxidation of Sn in TlSnX3 NPs is effectively prevented by the strong reducing ligands such as dioleamide (DOA) and trioctylphosphine (TOP). Furthermore, TlSnX3 NPs-based perovskite solar cells (PSCs) are fabricated by a spin-coating method; they exhibited a high open-circuit voltage (∼1.4 V). These results demonstrate that TlSnX3 NPs can be an attractive candidate for solution-processable optoelectronic devices.

Cation-Disorder Engineering Promotes Efficient Charge-Carrier Transport in AgBiS2 Nanocrystal Films.

Efficient charge-carrier transport is critical to the success of emergent semiconductors in photovoltaic applications. So far, disorder has been considered detrimental for charge-carrier transport, lowering mobilities, and causing fast recombination. This work demonstrates that, when properly engineered, cation disorder in a multinary chalcogenide semiconductor can considerably enhance the charge-carrier mobility and extend the charge-carrier lifetime. Here, the properties of AgBiS2 nanocrystals (NCs) are explored as a function of Ag and Bi cation-ordering, which can be modified via thermal-annealing. Local Ag-rich and Bi-rich domains formed during hot-injection synthesis are transformed to induce homogeneous disorder (random Ag-Bi distribution). Such cation-disorder engineering results in a sixfold increase in the charge-carrier mobility, reaching ≈2.7 cm2 V-1 s-1 in AgBiS2 NC thin films. It is further demonstrated that homogeneous cation disorder reduces charge-carrier localization, a hallmark of charge-carrier transport recently observed in silver-bismuth semiconductors. This work proposes that cation-disorder engineering flattens the disordered electronic landscape, removing tail states that would otherwise exacerbate Anderson localization of small polaronic states. Together, these findings unravel how cation-disorder engineering in multinary semiconductors can enhance the efficiency of renewable energy applications.

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.

Hot-Injection Synthesis of HgTe Nanoparticles: Shape Control and Growth Mechanisms.

Understanding the growth mechanisms of HgTe nanoparticles (NPs) with varied shapes is crucial for their applications in infrared photodetection. Here, we investigated the growth mechanisms of HgTe NPs with nanorod, sphere, and tetrahedral shapes in depth. The HgTe NPs with a nanorod shape are obtained at low reaction temperatures and formed by breaking tetrapod branches, while HgTe NPs with sphere and tetrahedron shapes have been further achieved at increased reaction temperatures. The systematic crystal analyses demonstrate this effective shape control is related to the synergic effect among the anisotropic passivation of oleylamine, surface free energy, and reaction temperatures. Our findings have deepened the understanding of shape control of the HgTe NPs and inspired a growing passion in the design and engineering of infrared photodetectors using HgTe NPs.

Surface Chemistry and Band Engineering in AgSbSe2: Toward High Thermoelectric Performance.

AgSbSe2 is a promising thermoelectric (TE) p-type material for applications in the middle-temperature range. AgSbSe2 is characterized by relatively low thermal conductivities and high Seebeck coefficients, but its main limitation is moderate electrical conductivity. Herein, we detail an efficient and scalable hot-injection synthesis route to produce AgSbSe2 nanocrystals (NCs). To increase the carrier concentration and improve the electrical conductivity, these NCs are doped with Sn2+ on Sb3+ sites. Upon processing, the Sn2+ chemical state is conserved using a reducing NaBH4 solution to displace the organic ligand and anneal the material under a forming gas flow. The TE properties of the dense materials obtained from the consolidation of the NCs using a hot pressing are then characterized. The presence of Sn2+ ions replacing Sb3+ significantly increases the charge carrier concentration and, consequently, the electrical conductivity. Opportunely, the measured Seebeck coefficient varied within a small range upon Sn doping. The excellent performance obtained when Sn2+ ions are prevented from oxidation is rationalized by modeling the system. Calculated band structures disclosed that Sn doping induces convergence of the AgSbSe2 valence bands, accounting for an enhanced electronic effective mass. The dramatically enhanced carrier transport leads to a maximized power factor for AgSb0.98Sn0.02Se2 of 0.63 mW m-1 K-2 at 640 K. Thermally, phonon scattering is significantly enhanced in the NC-based materials, yielding an ultralow thermal conductivity of 0.3 W mK-1 at 666 K. Overall, a record-high figure of merit (zT) is obtained at 666 K for AgSb0.98Sn0.02Se2 at zT = 1.37, well above the values obtained for undoped AgSbSe2, at zT = 0.58 and state-of-art Pb- and Te-free materials, which makes AgSb0.98Sn0.02Se2 an excellent p-type candidate for medium-temperature TE applications.

The Dynamic Interaction of Surfactants with Colloidal Molybdenum Disulfide Nanosheets Calls for Thermodynamic Stabilization by Solvents.

Top-down liquid-phase exfoliation (LPE) and bottom-up hot-injection synthesis are scalable methods to produce colloids of two-dimensional (2D) van der Waals (vdW) solids. Generally thought off as two entirely different fields, we show that similar stabilization mechanisms apply to colloids of molybdenum disulfide (MoS2) produced by both methods. By screening the colloidal stability of MoS2 produced in a hot-injection synthesis in a wide range of solvents, we observe that colloidal stability can be understood based on solution thermodynamics, wherein matching the solubility parameter of solvent and nanomaterial maximizes colloidal stability. Identical to MoS2 produced through LPE, optimal solvents to disperse MoS2 produced from the bottom-up have similar solubility parameters of ≈22 MPa1/2 and include aromatic solvents with polar functionalities, such as o-dichlorobenzene, and polar aprotic solvents, such as N,N-dimethylformamide. We further complemented our findings by nuclear magnetic resonance (NMR) spectrscopy, highlighting that organic surfactants, such as oleylamine and oleic acid, have a minimal affinity toward the nanocrystal surface and engage in a highly dynamic adsorption/desorption equilibrium. We thus conclude that hot injection yields MoS2 colloids with comparable surfaces as those produced by LPE. These similarities might offer the prospect of using established procedures developed for LPE nanomaterials to postprocess colloidally synthesized dispersions of 2D colloids as processable inks.

OPTICAL CHARACTERIZATION of STEARIC ACID POWDER and ITS USE for THE SYNTHESIS of NANOPARTICLES

Fatty acids are found in the structure of triglycerides and phospholipids which have vital importance for the life. Stearic acid is an important member of the fatty acids. It is used in the manufacturing of various products such as soaps, detergents, and rubbers. It is valuable to provide a thermal and optical characterization database of stearic acid. In this study, a comprehensive database has been prepared by studying thermogravimetric analysis, X-ray powder diffraction, dispersive Raman and Fourier transform infrared spectroscopies of stearic acid. Its thermal decomposition temperature, X-ray diffraction angles and infrared vibrational modes have been determined. Stearic acid has been used at the synthesis of cadmium selenide quantum dots, bismuth nanoparticles and mixed copper/zinc nanocrystals. Hot-injection and one-pot synthesis methods have been utilized to synthesize these nanostructures. Their sizes, distributions, shapes, elemental compositions, and crystalline structures have been investigated by transmission electron microscopy and energy dispersive X-ray analysis. Mixed copper/zinc nanocrystals have also been examined by X-ray diffraction spectroscopy.

SOĞURMA SPEKTROSKOPİSİ ve GEÇİRİMLİ ELEKTRON MİKROSKOPİ ile KADMİYUM SELENÜR KUANTUM NOKTALARININ OPTİK TESPİTİ

Quantum dots are tiny semiconductor nanocrystals. Their dimensions are between about 2 and 10 nm. They have attracted much attention due to their unique electronic and optical properties. These particles can be synthesized in a variety of ways. Synthesis methods of quantum dots can be classified into top-down and bottom-up. Top-down approach is a fragmentation process of bulk material. In contrast to top-down, quantum dots are constructed from atoms and molecules of the material at bottom-up procedure. Ball milling, optical lithography, laser ablation and arc-discharge are some top-down methods. However, chemical reduction, thermal decomposition, sol-gel and ultrasonic spray pyrolysis are bottom-up methods. In this study, chemical hot-injection synthesis method of cadmium selenide quantum dots which is a kind of bottom-up procedure will be explained. Cadmium selenide quantum dots have been grown in hot solvent at 259oC. Concentration of cadmium selenide quantum dots dispersed in toluene has been adjusted by observing their first exciton peak. First excitonic absorbance peak of cadmium selenide quantum dots has been measured at around 2.18 eV. Transmission electron microscope photo of these growth quantum dots has been shown. The average diameter of cadmium selenide quantum dots has been found to be approximately 3.48 nm. Lattice fringe spacing of cadmium selenide quantum dots has been measured as ~0.35 nm.

Separating the Effects of Nonorthogonal Variables on the Hot-Injection Synthesis of Core/Thick-Shell (“Giant”) CdTe/CdS Quantum Dots

“Giant” core/thick-shell quantum dot (QD) nanostructures are of interest due to their unusual optical properties and importance as components of more advanced heterostructures tailored to achieve increasingly complex optical functions. However, reliable one-step seeded growth of these structures poses a significant challenge: one must balance multiple competing reaction processes to find the growth regime that realizes spherical shells of both the target size and high crystalline quality. Adjusting synthesis conditions in thicker-shelled reactions is further complicated by multiple nonorthogonal variables that impact the reaction mechanism. These variables include the reaction volume, reaction concentration, and oleic acid (ligand) concentration. Here, we investigate the seeded growth of core/thick-shell CdTe/CdS QDs by adapting a “flash” shelling method. We systematically vary three key reaction parameters (particle concentration, oleic acid:Cd ratio, and Cd–S:CdTe core ratio) over 30+ different thick-shelling reactions to elucidate the separate and intersecting impacts of these parameters on shell growth. Our analysis of the resulting particle quality reveals that the particle concentration of the reaction plays a critical role in the shell growth mechanism. We find the impact of oleic acid to be dependent on the particle concentration for a given shell thickness. We also find that the optimal conditions shift when targeting increasingly thick shells. The results demonstrate the importance of testing and controlling for synthesis variables across a multidimensional parameter space. We develop and present general experimental design criteria to help guide efficient development of new seeded growth reactions that enable reliable synthesis of thick-shelled nanostructures.

Cu+ → Mn2+ Energy Transfer in Cu, Mn Coalloyed Cs3ZnCl5 Colloidal Nanocrystals.

In this work, we report the hot-injection synthesis of Cs3ZnCl5 colloidal nanocrystals (NCs) with tunable amounts of Cu+ and Mn2+ substituent cations. All the samples had a rodlike morphology, with a diameter of ∼14 nm and a length of ∼30–100 nm. Alloying did not alter the crystal structure of the host Cs3ZnCl5 NCs, and Cu ions were mainly introduced in the oxidation state +1 according to X-ray photoelectron and electron paramagnetic resonance spectroscopies. The spectroscopic analysis of unalloyed, Cu-alloyed, Mn-alloyed, and Cu, Mn coalloyed NCs indicated that (i) the Cs3ZnCl5 NCs have a large band gap of ∼5.35 eV; (ii) Cu(I) aliovalent alloying leads to an absorption shoulder/peak at ∼4.8 eV and cyan photoluminescence (PL) peaked at 2.50 eV; (iii) Mn(II) isovalent alloying leads to weak Mn PL, which intensifies remarkably in the coalloyed samples, prompted by an energy transfer (ET) process between the Cu and Mn centers, favored by the overlap between the lowest (6A1 → 4T1) transition for tetrahedrally coordinated Mn2+ and the PL profile from Cu(I) species in the Cs3ZnCl5 NCs. The efficiency of this ET process reaches a value of 61% for the sample with the highest extent of Mn alloying. The PL quantum yield (QY) values in these Cu, Mn coalloyed NCs are lower at higher Mn contents. The analysis of the Mn PL dynamics in these samples indicates that this PL drop stems from inter-Mn exciton migration, which increases the likelihood of trapping in defect sites, in agreement with previous studies.