Hot-injection Method Research Articles

Zwitterionic Block Copolymers for the Synthesis and Stabilization of Perovskite Nanocrystals.

Traditional hot injection methods for the preparation of cesium lead halide perovskite nanocrystals (CsPbX3 PNCs, where X=Cl, Br, or I) rely on small molecule surfactants to produce PNCs with cube, plate, or rod-like morphologies. Here, we describe a new method whereby zwitterionic block copolymers are employed as macromolecular ligands in PNC synthesis, affording PNCs with excellent colloidal stability, high photoluminescence quantum yield, and in some cases distinctly non-cubic shapes. The block copolymers used in this study - composed of a poly(n-butyl methacrylate) hydrophobic block and zwitterionic methacrylate hydrophilic blocks - dissolve in useful solvents for PNC growth despite containing large mole percentages of zwitterionic groups. PNCs prepared with block copolymer ligands were found to disperse and retain their fluorescence in a range of polar organic solvents and were amenable to direct integration into optically transparent nanocomposite thin films with high PNC content.

Bi3+ and Eu3+ co-doped CsPbCl3 perovskite quantum dots with efficient controllable blue emission via energy transfer

Halide perovskite quantum dots (QDs) are considered to be an outstanding optoelectronic and photonic materials. However, the heavy usage of toxic Pb element is still a serious problem, which can greatly hinder their practical application. Herein, co-doping of different metal ions pairs in perovskite QDs host can solve this problem without affecting their optical properties. The highly monodisperse low-Pb content Cs(Pb1-xBix)Cl3 (x = 0.02–0.1) and Cs(Pb0.95-yBi0.05Euy)Cl3 (y = 0.05–0.50) perovskite QDs with cubic morphologies are successfully obtained by using the improved hot-injection method in the present work. The metal ions (Bi3+ and Eu3+)-doped do not alter the crystal structure, maintaining the tetragonal crystalline structure of the CsPbCl3 host, but has an effect on the particle size owing to the difference in the ionic radius. Under the UV excitation wavelength of 380 nm, the perovskite QDs after doping with metal ions all display their respective typical emission bands, including the band-edge emission of CsPbCl3 host, the 3P1 → 1S0 transition of Bi3+, and the 5D0 → 7F2 transition of Eu3+. The relative intensities and the positions of their typical emission bands can be tuned by changing the Bi3+ or Eu3+ content, indicating the emission color of samples can be controlled. The interesting spectroscopic behaviour benefits from the efficient energy transfers between the CsPbCl3 host and doped metal ions, and the energy transfers are owing to the differences in intrinsic energy levels of Bi3+ or Eu3+. The metal ions-doped CsPbCl3 perovskite QDs developed in this work can reduce the toxicity of perovskite QDs while improving the optical performance, which can provide a novel platform for the application in optoelectronic device applications.

Enhanced optical properties of ZnSexS1-x and Mn-doped ZnSexS1-x QDs via non-toxic synthetic approach

A tunable approach for the non-phosphine synthesis of monodisperse, highly photoluminescent ZnSexS1-x and Mn-doped ZnSe0.1S0.9 quantum dots (QDs) using (Z)-1-(octadec-9-enyl)-3-phenylselenourea and (Z)-1-(octadec-9-enyl)-3-phenylthiourea as novel sources of selenium and sulphur is provided. QDs syntheses were performed in an organic disperse medium at 280 °C using environmentally friendly and at the same time highly reactive N,N'-disubstituted thio- and selenoureas.By varying the molar ratios of sulphur and selenium sources, ZnSexS1-x QDs, where х = 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, and 0.75, were obtained. Mn-doped ZnSe0.1S0.9 QDs (0.5–15 molar %) have been synthesized by the low cost hot-injection method. The presence of manganese in ZnSe0.1S0.9 QDs resulted in the appearance of the expected second emission band (579 nm), the maximum intensity of which was determined for Mn(5%):ZnSe0.1S0.9 QDs. According to the analytical data, ZnSexS1-x and Mn-doped ZnSe0.1S0.9 QDs are consistent with the desired elemental composition and uniform in size. The chemical composition, morphology and crystal structure of prepared undoped ZnSexS1-x and Mn-doped ZnSe0.1S0.9 QDs were studied by X-Ray diffraction (XRD), energy dispersive X-Ray spectroscopy (EDS), X-Ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) analyses. The optical properties of nanocomposite materials based on synthesized ZnSexS1-x and Mn-doped ZnSe0.1S0.9 QDs in a polymer matrix of polyvinyl toluene (PVT) were also studied. It should be noted that transparent monoliths have the same photoluminescent characteristics as QDs. These results give proof of the chemical stability of the resulting nanomaterials and can contribute to their possible transfer in the photodetectors and LEDs production.

Phase-selective synthesis of lead-free CsMnBr3 and Cs3MnBr5 nanocrystals dependent on solvent concentration.

We demonstrate the crystal phase-selective synthesis for lead-free cesium manganese bromine perovskite nanocrystals synthesized by the modified hot-injection method due to changing the concentration of solvent (trioctylphosphine; TOP). The compositions synthesized were determined by the amount of TOP solvent, and the structure phase of the nanocrystals was selected from hexagonal CsMnBr3 to tetragonal Cs3MnBr5 as the amount of TOP solvent increased. The emission peaks of CsMnBr3 and Cs3MnBr5 nanocrystals were observed at 650 nm (red) and 520 nm (green), respectively. After a durability test at 85°C and 85% humidity for 24 h, the lead-free perovskite CsMnBr3 nanocrystal powder maintained its initial emission intensity, and the metal halide Cs3MnBr5 nanocrystal powder exhibited an increase in red emission due to the post-synthesis of CsMnBr3 nanocrystals.

Boosted luminescence efficiency and stability of Mn-doped perovskite nanoplatelets via incorporating Cd2+ ions

Mn-doped two-dimensional lead halide perovskites nanoplatelets (NPLs) possess promising application in solid state lighting. The Mn:L2[CsPbBr3]PbBr4 NPLs with corporation of Cd2+ were prepared via a hot injection method. The photoluminescence (PL) properties the NPLs with different Mn/Pb/Cd molar ratio from 0.5/1/0 to 5/1/3 were investigated by steady-state and time-resolved PL spectroscopy, indicating that the doping efficiency of Mn2+ can be boosted by adding Cd2+ to the NPLs. After thermal annealing, the PL quantum yield of Mn2+ ions reached up to 75%, which is Cd2+ content dependent. The temperature-dependent PL spectra demonstrated that the thermal activation energies of the NPLs could be increased by incorporating Cd2+, meaning that the nonradiative defect/trap states were effectively suppressed. These experimental results suggested the PL properties of Mn:L2[CsPbBr3]PbBr4 NPLs were optimized by adding Cd2+ ions.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Highly Stable and Efficient Mn2+ Doping Zero-Dimension Cs2ZnxPb1-xCl4 Alloyed Nanorods toward White Electroluminescent Light-Emitting Diodes.

Zero-dimensional (0D) crystal structure perovskite NCs have reemerged as promising materials owing to their superior long-term stability; however, their poor conductivity leads to the inferior electrical performances and critically restricts the optoelectronic application of 0D perovskite materials. Herien, the alloyed 0D crystal structure Cs2ZnxPb1-xCl4 nanorods (NRs) have been synthesized by the modified hot-injection method, which emits bright blue-violet light at 408 nm, and the optimized photoluminescence quantum yield (PLQY) reaches 26%. The Cs2Zn0.88Pb0.12Cl4 NRs display more excellent air stability and an order of magnitude higher conductivity than CsPbCl3 nanocube films. In addition, we dope Mn2+ ions into the Cs2Zn0.88Pb0.12Cl4 NRs, which accomplished the optimized PLQY of 40.3% and polarized emission with r = 0.19. The light-emitting diodes (LEDs) based on Mn2+ ion doped Cs2Zn0.88Pb0.12Cl4 NRs exhibit a chromaticity coordinate (CIE) of (0.36, 0.33), an EQE of 0.3%, and a maximum luminance of 98 cd m-2. This work has enriched ideas for the production of white light perovskite LEDs.

Effect of Dispersion Solutions on Optical Properties and Stability of CsPbBr3 Perovskite Nanocrystals

Long-term storage stability of cesium lead-based perovskite nanocrystals, especially at ambiance conditions is a vital challenge that deters their advancement in photovoltaic applications. Herein, CsPbBr3 perovskite nanocrystals are synthesized by hot injection method and the stability of CsPbBr3 nanocrystals is investigated when dispersed in individual solvents such as Toluene, Acetone, and Ethanol as well as the combination of solvents. The synergistic effect of toluene- non-polar molecule and acetone-a polar molecule was studied and their effect on the stability of CsPbBr3 in terms of retention of optical absorption and emission is investigated. A combination of toluene and acetone as solvents is found to be the best medium for dispersion of CsPbBr3 perovskite nanocrystals which remain stable for two weeks with 63%, 60% retention of luminescence and absorbance. Further, by the addition of PVP polymer (0.05 wt%) in dispersion solution, the luminescence and absorbance are retained up to ∼77% and ∼70% for more than two months of storage time. The storage stability of a combination of mix solvents is important for the applications in which stable dispersion of perovskite materials ought to prepare in polar or non-polar solvents.

Investigation on the structural and magnetic properties of MxBi2–xTe3 (M = Gd, Fe, Cr) (x = 0, 1) using colloidal hot-injection method

Investigation on the structural and magnetic properties of MxBi2–xTe3 (M = Gd, Fe, Cr) (x = 0, 1) using colloidal hot-injection method

Thiophene Derivatives as Ligands for Highly Luminescent and Stable Manganese-Doped CsPbCl3 Nanocrystals.

Ligands on the surface of perovskite nanocrystals are important to stabilize the nanocrystal structure. However, the research of ligands on Mn2+ ion-doped CsPbCl3 nanocrystals (Mn: CsPbCl3 NCs), a promising candidate family for the lightning community, is relatively rare. Here, we demonstrate a new ligand modification strategy for preparing high-quality Mn: CsPbCl3 NCs by a simple hot-injection method. Thiophene derivative, for the first time, is applied as ligands for perovskite nanocrystals. The new ligands of thiophene derivatives passivate defects on the surface of NCs and enhance optical properties, originating from the sulfur in thiophene additives binding to the uncoordinated lead ions. The photoluminescence quantum yield of the modified Mn: CsPbCl3 NCs is 93% in comparison with 46% of the pristine counterparts, whose value is the highest to date for ligand-modified Mn: CsPbCl3 NCs. Meanwhile, the thermal, storage, and purification stability are also significantly improved. The performance of related LEDs is also investigated.

Luminescence temperature anti-quenching in CdSe/CdS core/shell and CdSe/CdS/ZnS core/double shell nanostructures

Luminescence temperature anti-quenching (LTAQ) was investigated on CdSe/CdS core/shell and CdSe/CdS/ZnS core/double shell nanostructures prepared by hot injection method. They have the same core size, CdS shell thickness ranging from 1 to 5 monolayer (ML) and ZnS shell thickness of 2 ML. Temperature-dependent photoluminescence (PL) spectra of the purified core, core/shell, and core/double shell samples were comparatively investigated over a temperature range of 79 - 460 K. The LTAQ phenomenon was observed for the core/shell and core/double shell nanostructures and is reversible. The fluorescence recovery magnitude and the temperature range in which the LTAQ process occurs depends on the thickness and composition of the shell surrounding the core. Analysis of the temperature-dependent spectral characteristics shows an increase in compression strain in the CdSe core when increasing the shell thickness. The cause of the LTAQ phenomenon is attributed to the rearrangement of the atoms at the core/shell and shell/shell interfaces in the investigated nanostructures due to thermal expansions of the core and shell crystalline lattices. The linear dependence of integrated emission intensities of CdSe/CdS (1 ML) and CdSe/CdS (3 ML) samples on temperature in the ranges of 220 - 360 K and 270 - 340 K, respectively, opens up the prospect of creating temperature sensors for biomedical applications.

CuInSe2 quantum dots doped MAPbI3 films with reduced trap density for perovskite solar cells

The organic-inorganic halide perovskite (OIHP) materials are becoming promising, but there is still inherent defect-mediated-carrier recombination in hybrid perovskite materials, thus, leading to inefficient power conversion efficiency (PCE). The defect states, which act as the recombination centers, are usually formed during crystallization process. Here, by a hot injection method, Na2S ligand exchange is applied to synthesize copper indium selenium quantum dots (CuInSe2 QDs), which are well dispersed in N,N-dimethylformamide (DMF) and then added into perovskite precursor solution. The resulted QD-in-perovskite structure is found to be beneficial for enlarging grain size, and thus exhibits an improved crystallinity and absorption due to the passivation of trap states. Hence, the perovskite solar cell (PSC) based on the MAPbI3-CuInSe2 QD hybrid film show an improved carrier lifetime from 58.17 ns to 243.23 ns and an enhanced PCE from 16.3% to 18.4% due to higher open-circuit voltage, compared to the cell device based on the pure perovskite film. Additionally, the optimized cell device presents better stability, which can still keep 75% of the initial PCE after 20-day storage. Such a simple Na2S ligand exchange to introduce QD into perovskite provides strong potential for preparing other hybrid materials.

Synthesis of KNN nanoblocks through surfactant-assisted hot injection method and fabrication of flexible piezoelectric nanogenerator based on KNN-PVDF nanocomposite

With the tremendous growth of flexible piezoelectric nanogenerators, alkali niobates have gained considerable attention and are perceived to be the eco-friendly substitute for the unsustainable lead based piezoelectric systems. However, successful realization of potassium sodium niobate (KNN) based devices with appreciable piezoelectricity requires tailored molecular level organization. Herein, we have developed a lead-free flexible piezoelectric nanogenerator based on KNN-PVDF nanocomposite, in which the KNN nanoblocks were synthesized using a novel non-aqueous surfactant-assisted hot injection method. Also, the synthesis of KNN employed non-toxic surface stabilizer, oleic acid and reaction catalyst, oleyl amine respectively, making the preparation environmental benign. The KNN nanoblocks homogeneously dispersed in the PVDF matrix up to 10 wt% filler loading, enhanced the piezoelectric and dielectric properties of the composite. Further, the fabricated flexible piezoelectric nanogenerator without any external poling process exhibits an output open circuit voltage of ∼ 2.1 V and a short circuit current of ~ 42 nA on a gentle finger tapping force (~3 N). The results demonstrate the potential of chemically engineered KNN nanoblocks dispersed in PVDF for large-scale sustainable piezoelectric nanogenerator applications.

Structural Reconstruction in Lead-Free Two-Dimensional Tin Iodide Perovskites Leading to High Quantum Yield Emission

We report a structural reconstruction-induced high photoluminescence quantum yield of 25% in colloidal two-dimensional tin iodide nanosheets that are synthesized by a hot-injection method. The as-synthesized red-colored nanosheets of octylammonium tin iodide perovskites at room temperature transform to white hexagonal nanosheets upon washing or exposure to light. This structural change increases the bandgap from 2.0 eV to 3.0 eV, inducing a large Stokes shift and a broadband emission. Further, a long photoluminescence lifetime of about 1 microsecond is measured for the nanosheets. Such long-lived broad and intense photoluminescence with large Stokes shift is anticipated to originate from tin iodide clusters that are formed during the structural reconstruction. Stereoactive 5s2 lone pair of tin (II) ions perturbs the excited state geometry of the white hexagonal nanosheets and facilitates the formation of self-trapped excitons. Such broadband and intensely emitting metal halide nanosheets are promising for white light-emitting diodes.

Study on chemical synthesis of SnSSe nanosheets and nanocrystals

Two kinds of raw material combinations for the hot injection method were investigated for the chemical synthesis of SnSSe nanosheets and nanocrystals, which are low-toxic optoelectronic materials. When SnSe quantum dots were synthesized by mainly using oleic acid as the Se precursor solvent, the quantum dots changed from spherical to cubic as the size increased. The growth condition dependence of the nanocrystal formation process was discussed. When SnSSe nanocrystals were synthesized by mainly using trioctylphosphine as the S Se precursor solvent, it was found that the nanocrystal shape changed from dot to rod or sheet by reducing the proportion of S. The bandgap energy did not simply depend on the composition ratio of S but was affected by the change in the nanocrystal shape depending on the quantum confinement effect.

Cu2AgInS4 quantum dot sensitized zinc doped Titania nanoparticles film as the high efficient photoanode for photovoltaic cells

In this work, Cu, Ag, In, and S based qu aternary quantum dots (Cu2AgInS4 QDs) were synthesized by a hot-injection method, and Zinc doped (0, 1, and 2 wt%) Titania nanoparticles (Zn-TiO2 NPs) were synthesized by a sol-gel method. The synthesized QDs were anchored onto Zn-TiO2 NPs film through a linker-based assembly method to form Cu2AgInS4 QDs/Zn-TiO2 NPs to use as the photoanodes for Quantum dot sensitized solar cells (QDSCs). The physio-chemical behavior of the Cu2AgInS4 QDs, Zn-TiO2 NPs, and Cu2AgInS4 QDs/Zn-TiO2 photoanodes was examined by various spectroscopic analyses. Optical analysis of the fabricated photoanodes revealed that Cu2AgInS4 QDs/Zn-TiO2 NPs photoanode has a high redshift of light absorbance than Zn-TiO2 NPs. Moreover, due to the proper band alignment of Cu2AgInS4 QDs and 2 wt% Zn-TiO2 NPs, Cu2AgInS4 QDs/Zn-TiO2 NPs has high electron transfer ability than Cu2AgInS4 QDs/TiO2 NPs. On the other hand, the electrochemical impedance analysis confirms that Cu2AgInS4 QDs/Zn-TiO2 photoanode has lower charge transfer resistance (9.53 Ω) with high photocatalytic behavior than that of Cu2AgInS4 QDs/ TiO2 NPs as the photoanode. Hence Cu2AgInS4 QDs/Zn-TiO2 NPs photoanode based QDSC shows 36% improvement in the photoconversion efficiency (5.43%) than that of Cu2AgInS4 QDs/TiO2 NPs (3.92%) based QDSC.

Vacuum-Free Quantum Dots Planar Hybrid Solar Cells: Improving Charge Transport Using Reduced Graphene Oxide and PEO as the Buffer Layer

In this work, reduced graphene oxide (rGO) was synthesized using a modified Hummer method and its morphological and structural properties were investigated using transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and X-ray diffraction (XRD). The rGO was used as the hole transport buffer layer (HTBL) and poly(ethylene oxide) (PEO) was used as the electron transport buffer layer (ETBL) for the vacuum-free quantum dot planar hybrid (VFQPH) solar cells (SCs) fabrication. PbS quantum dots (Qdots) were prepared using a hot-injection method, which was used as the p-type material and PCBM ([6,6]-Phenyl-C61-butyric acid methyl ester) was used as the n-type material. The effects of the hole transport buffer layer and electron transport buffer layer on the morphological and electrical properties of the device were investigated. A device with a structure of glass/indium tin oxide (ITO)/HTBL/PbS: PCBM/ETBL/E-GaIn was fabricated and the maximum power conversion efficiency of about 4.34% was obtained.

In situ siloxane passivation of colloidal lead halide perovskite via hot injection for light-emitting diodes.

All-inorganic cesium lead halide perovskite (CsPbX3; X = Cl, Br) nanocrystals (NCs) are synthesized via a modified hot injection method using 3-mercaptopropyltrimethoxysilane (MPTMS), together with oleic acid and oleylamine, for in situ passivation of the surface defects. The surface chemistry, revealed by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) techniques, shows an absence of Si-O-Si network and C-O groups on these in situ passivated CsPbX3 NCs, denoted as InMP-CsPbX3, which is in strong contrast to the counterpart NCs obtained via a postsynthesis exchange strategy. The x-ray diffraction (XRD) pattern indicates a lattice structure significantly strained from the cubic structure. The synthesis of these InMP-CsPbX3 NCs is highly reproducible, and the colloids are stable in nonpolar solvents. The emission wavelength of CsPb(Cl/Br)3 mixed halide perovskite NCs is tuned from 405 nm to 508 nm by reducing the nominal Cl/Br ratio, while the photoluminescence quantum yield (PLQY) is greatly enhanced over the whole spectral range. More importantly, the InMP-treatment is among the few strategies that are promising for electroluminescence in light-emitting diodes.

Highly efficient and stable Eu3+-doped two-dimensional perovskites

Compared to the three-dimensional (3D) counterparts, single-layered two-dimensional (2D) perovskites show high stability, high exciton binding energy and structural flexibility that are beneficial for light-emitting diodes (LEDs) applications. Yet, the emission peaks of single-layered 2D perovskites are strongly limited to the blue-green region due to their very strong quantum confined effect, hampering their application. Doping ions has been recognized as a promising way to tune emission wavelengths. In this work, we have prepared Eu3+ doped PEA2PbCl4 perovskites by a hot-injection method. Its Eu3+ emission is not stable, which disappears after exposed in the air due to the coordination of Eu3+ with H2O or O2. By exploiting strong ligands of thenoyltrifluoroacetone (TTA), the H2O or O2 can be replaced, resulting in a rigid coordination environment for Eu3+. Besides, energy level alignment can be modified by the passivation of TTA, leading to effective energy transfer from exciton to Eu3+. In the end, stable red-emitting perovskite is acquired with a photoluminescence quantum yield (PLQY) up to 83%. This work provides new synthetic strategies for the design of high-performance perovskite/lanthanide composites.

High-yield synthesis of CsPbBr3 nanoparticles: diphenylphosphine as a reducing agent and its effect in Pb-seeding nucleation and growth

Based on the reported nucleation mechanisms for CsPbX3 and II–VI/IV–VI quantum dots, CsPbBr3 nanoparticles with a higher reaction-yield (up to 393% mass-increment) were synthetized by the hot-injection method. The introduction of diphenylphosphine (DPP) as a reducing agent improved nanoparticle nucleation and growth, giving out evidence for Pb-seeding in CsPbBr3 nanoparticles formation. Additionally, a clear influence of the DPP in a CsPbBr3-Cs4PbBr6 incomplete phase transformation was observed, marked by the appearance of several PbBr2 nanoparticles. This indicated the need for an improved ratio between the stabilizing agents and the precursors, due to the increased number of nucleation sites produced by DPP. The resulting CsPbBr3 nanoparticles showed high quality, as they displayed 70%–90% photoluminescence quantum yield; narrow size distribution with an average nanoparticle size of ∼10 nm; and the characteristic cubic morphology reported in previous works. This increment in CsPbBr3 nanoparticles’ reaction yield will contribute to making them a more attractive option for different optoelectronic applications.