Supporting Information Inorganically Coated Colloidal Quantum Dots in Polar Solvents by Microemulsion-Assisted Method (original) (raw)
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Inorganically coated colloidal quantum dots in polar solvents using a microemulsion-assisted method
Physical chemistry chemical physics : PCCP, 2016
The dielectric nature of organic ligands capping semiconductor colloidal nanocrystals (NCs) makes them incompatible with optoelectronic applications. For this reason, these ligands are regularly substituted through ligand-exchange processes by shorter (even atomic) or inorganic ones. In this work, an alternative path is proposed to obtain inorganically coated NCs. Differently to regular ligand exchange processes, the method reported here produces core-shell NCs and the removal of the original organic shell in a single step. This procedure leads to the formation of connected NCs resembling 1D worm-like networks with improved optical properties and polar solubility, in comparison with the initial CdSe NCs. The nature of the inorganic shell has been elucidated by X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Photoelectron Spectroscopy (XPS). The 1D morphology along with the lack of long insulating organic ligands and the higher...
Acid-Assisted Ligand Exchange Enhances Coupling in Colloidal Quantum Dot Solids
Nano letters, 2018
Colloidal quantum dots (CQDs) are promising solution-processed infrared-absorbing materials for optoelectronics. In these applications, it is crucial to replace the electrically insulating ligands used in synthesis to form strongly coupled quantum dot solids. Recently, solution-phase ligand-exchange strategies have been reported that minimize the density of defects and the polydispersity of CQDs; however, we find herein that the new ligands exhibit insufficient chemical reactivity to remove original oleic acid ligands completely. This leads to low CQD packing and correspondingly low electronic performance. Here we report an acid-assisted solution-phase ligand-exchange strategy that, by enabling efficient removal of the original ligands, enables the synthesis of densified CQD arrays. Our use of hydroiodic acid simultaneously facilitates high CQD packing via proton donation and CQD passivation through iodine. We demonstrate highly packed CQD films with a 2.5 times increased carrier mo...
SYNTHESIS AND CHARACTERIZATION OF CdSe COLLOIDAL QUANTUM DOTS IN ORGANIC SOLVENT
In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the range 2.28-2.92 nm which is in good agreement with PL measurements.
The Role of Organic Ligand Shell Structures in Colloidal Nanocrystal Synthesis
Nature Synthesis, 2022
Organic ligands are essential in the growth of monodisperse colloidal inorganic nanocrystals and can be leveraged to create a wide variety of shapes and sizes. Inorganic nanocrystals coated with surfactant-like organic molecules have a vast range of properties that arise from the combination of the individual components. In this Review, we discuss the role that the tails of the organic ligands play in the synthesis and properties of colloidal nanocrystals, particularly the collective effects of the organic ligands on the surface. Ligand–ligand interactions influence the thermodynamic and kinetic properties of the nanocrystals, as well as alter their colloidal stability. These interactions should inform the conceptualization of new nanocrystal syntheses as they influence the surface energy of the colloid, and these interactions should play a role in subsequent assembly strategies to prepare nanocrystal superlattices, which are driven by interparticle interactions.
Surfactant Ligand Removal and Rational Fabrication of Inorganically Connected Quantum Dots
Nano Letters, 2011
b S Supporting Information I norganic colloidal nanocrystals (NCs) have attracted much attention in the past decade due to their unique size and shapedependent properties. 1 Thin films of semiconductor NCs have emerged as promising new materials for electronic and optoelectronic devices. 2À11 In most successful synthetic routes to colloidal NCs, the use of bulky hydrocarbon (C 8 ÀC 18 ) molecules with coordinating functional groups (such as ÀCOOH, ÀNH 2 , etc.) as surfactant ligands is crucial for stabilization, for prevention of aggregation, and for size and shape control of NCs. 12À15 The presence of these large organic molecules, however, creates highly insulating barriers which block electronic communication between NCs, limiting the usefulness of colloidal NCs assemblies in applications. Thermal removal of surfactant ligands has proven to be difficult because NCs become unstable at temperatures well below those required for the pyrolysis of surfactant ligands. Research into surface modification of NCs has thus mainly focused on replacing the long chain ligands with small molecules, such as amines, 3,16 thiols, 17 and hydrazine. 4 More recently, the ligand exchange reactions have been extended to use inorganic surfactant ligands, including BF 4 3 NO, 18 metal chalcogenides, 19À21 and metal-free chalcogenides. 22 These surfactant ligand modifications have decreased the interparticle distances and, in several cases, introduced conductive inorganic ligands, resulting in NCs thin films with increased conductance.
Journal of the American Chemical Society, 2015
Colloidal quantum dots (QDs) stand among the most attractive lightharvesting materials to be exploited for solution-processed optoelectronic applications. To this aim, quantitative replacement of the bulky electrically insulating ligands at the QD surface coming from the synthetic procedure is mandatory. Here we present a conceptually novel approach to design light-harvesting nanomaterials demonstrating that QD surface modification with suitable short conjugated organic molecules permits us to drastically enhance light absorption of QDs, while preserving good long-term colloidal stability. Indeed, rational design of the pendant and anchoring moieties, which constitute the replacing ligand framework leads to a broadband increase of the optical absorbance larger than 300% for colloidal PbS QDs also at high energies (>3.1 eV), which could not be predicted by using formalisms derived from effective medium theory. We attribute such a drastic absorbance increase to ground-state ligand/QD orbital mixing, as inferred by density functional theory calculations; in addition, our findings suggest that the optical band gap reduction commonly observed for PbS QD solids treated with thiol-terminating ligands can be prevalently ascribed to 3p orbitals localized on anchoring sulfur atoms, which mix with the highest occupied states of the QDs. More broadly, we provide evidence that organic ligands and inorganic cores are inherently electronically coupled materials thus yielding peculiar chemical species (the colloidal QDs themselves), which display arising (opto)electronic properties that cannot be merely described as the sum of those of the ligand and core components.
Effect of Ligands and Solvents on the Stability of Electron Charged CdSe Colloidal Quantum Dots
The Journal of Physical Chemistry C
Many colloidal quantum dot (QD)-based devices involve charging of the QD, either via intentional electronic doping or via electrical charge injection or photoexcitation. Previous research has shown that this charging can give rise to undesirable electrochemical surface reactions, leading to the formation of localized in-gap states. However, little is known about the factors that influence the stability of charged QDs against surface oxidation or reduction. Here, we use density functional theory to investigate the effect of various ligands and solvents on the reduction of surface Cd in negatively charged CdSe QDs. We find that X-type ligands can lead to significant shifts in the energy of the band edges but that the in-gap state related to reduced surface Cd is shifted in the same direction. As a result, shifting the band edges to higher energies does not necessarily lead to less stable electron charging. However, subtle changes in the local electrostatic environment lead to a clear correlation between the position of the in-gap state in the bandgap and the energy gained upon surface reduction. Binding ligands directly to the Cd sites most prone to reduction was found to greatly enhance the stability of the electron charged QDs. We find that ligands bind much more weakly after reduction of the Cd site, leading to a loss in binding energy that makes charge localization no longer energetically favorable. Lastly, we show that increasing the polarity of the solvent also increases the stability of QDs charged with electrons. These results highlight the complexity of surface reduction reactions in QDs and provide valuable strategies for improving the stability of charged QDs.
Environmental Science and Engineering, 2013
Colloidal core and core shell Quantum Dots (QD's) are unique and important optoelectronic materials because properties of these QD's can be tailored by configuring core and optimizing shell thickness. In this research work, lead selenide (PbSe) core and PbSe-CdSe (Core-shell) QD's are synthesized using oleic acid as a capping ligand by colloidal route. This simpler, cost-effective and rapid single pot synthesis route for colloidal core-shell quantum dots unlike conventional double-pot approach like cationexchange and SILAR process has been reported for the very first time. Phase formation of prepared quantum dots is confirmed by XRD analysis, capping ligand presence by IR spectroscopy and morphological information by Scanning electron microscopy respectively. These synthesized inorganic quantum dots are dispersed in Poly (3-hexyl thiophene) polymer for formation of their respective nanocomposites. From PL quenching studies, it was inferred that PbSe-CdSe coreshell quantum dots showed enhanced rate of PL quenching and hence higher value of Stern-Volmer constant (K SV) than PbSe Core QD's. This confirms that CdSe shell formation on PbSe core significantly passivates the core-surface, increases the stability and enhances the charge transfer mechanism for its potential application in Hybrid Solar cells.
Chemistry of Materials, 2013
Gold(III)chloride, Oleic acid, Oleylamine, (TMS) 2 S, Tetrakis(acetonitrile)copper(I) hexafluorophosphate (97%), dodecyldimethylammonium bromide (DDAB), Ammonium bromide, o-dichlorobenzene (ODCB) and water free toluene, methanol, acetonitrile (MeCN) and ethanol were purchased from Sigma while trioctylphosphine (TOP, 97%), Lead acetate trihydrate, Platinum chloride, Trioctylphosphine oxide (TOPO, 99%), Tributylphosphine, (TBP, 97%), were purchased from Strem. Octadecylphosphonic acid (ODPA, 99%) and Hexylphosphonic acid (HPA, 99%) and Octylphosphonic acid (OPA, 99%) were purchased from Polycarbon Industries. Propyiltrichlorosilane (PTCS, 97%) and Hydrazine monohydrate (98%) were purchased from Alpha Aesar. Ammonium hydroxide (33%) was purchased from J.T. Baker. All the chemicals were used as shipped. CdSe, CdS, CdSe/CdS core/shell rods and dots were synthesized following already reported procedures [1] with slight modifications. Synthesis of CdSe dots TOPO (3.0g), ODPA (0.280g) and CdO (0.060g) were mixed in a 50mL flask, heated to 120°C and put under vacuum for about 1 hour. Then, under nitrogen, the solution was heated to 300-350°C to dissolve the CdO until it turned optically clear and colorless. At this point, 1.5g of TOP was injected in the flask Average Diameter (nm) Average length (nm)