PbS Nanocrystals Research Articles

Photodetectors: Inorganic UV–Visible–SWIR Broadband Photodetector Based on Monodisperse PbS Nanocrystals (Small 10/2016)

Synthesis of highly mono-dispersed large PbS nanocrystals (NCs) with low particle size dispersion is demonstrated by F. So and co-workers on page 1328, by controlling the sulfur concentration below the nucleation threshold during multiple injections of the sulfur precursor. These NCs are used to fabricate multi-spectral photodetectors and high detectivity values in the UV-Visible-SWIR (short-wave-IR) wavelength range from 350 nm to 2000 nm are demonstrated.

Facet-Dependent Electrical Conductivity Properties of PbS Nanocrystals

Large PbS protruded cubes, edge- and corner-truncated cubes and octahedra, and perfect octahedra with sizes over 200 nm have been synthesized in aqueous solution. By using two surface oxide-free tungsten probes to contact a clean particle, these PbS nanocrystals displayed facet-dependent electrical conductivity behaviors. Both {110} and {100} faces are highly conductive at applied voltages beyond 4 V, but the {111} faces can remain nonconductive even at 5 V. An asymmetric I–V curve was recorded when electrical contacts were made simultaneously on the {110} and {111} facets of a truncated cube. A modified band diagram of PbS is constructed to account for the observed facet-dependent effect. Density of states plots for varying numbers of PbS surface planes show larger areas of conduction band electron occupancy for the (110) and (100) planes than that for the (111) planes at a layer thickness of 3.0–3.4 nm. The work represents that, for the first time, the facet-dependent electrical properties of an n-type ...

Tuning of Coupling and Surface Quality of PbS Nanocrystals via a Combined Ammonium Sulfide and Iodine Treatment.

Surface states of colloidal nanocrystals are typically created when organic surfactants are removed. We report a chemical process that reduces surface traps and tunes the interparticle coupling in PbS nanocrystal thin films after the surfactant ligands have been stripped off. This process produces PbS/PbI2 core/shell nanocrystal thin films via a combined ammonium sulfide and iodine treatment. These all-inorganic nanocrystal thin films are air-stable and exhibit bright emission with optimum photoluminescence quantum yield close to that of pristine PbS nanocrystals passivated by oleate ligands. Interparticle coupling of post-treatment nanocrystal thin films is continuously tunable by varying the iodine treatment process. Optical studies reveal that this method can produce PbS nanocrystal thin films superior in both coupling and surface quality to nanocrystals linked by small molecules such as ethanedithiol or 3-mercaptopropionic acid.

Electrical conduction mechanisms in PbSe and PbS nano crystals 3D matrix layer

A simulation study and measurements of the electrical conductance in a PbSe and PbS spherical Nano-crystal 3D matrix layer was carried out focusing on its dependences of Nano-crystal size distribution and size gradient along the layer thickness (z-direction). The study suggests a new concept of conductance enhancement by utilizing a size gradient along the layer thickness from mono-layer to the next mono-layer of the Nano-crystals, in order to create a gradient of the energy levels and thus improve directional conductance in this direction. A Monte Carlo simulation of the charge carriers path along the layer thickness of the Nano-crystals 3D matrix using the Miller-Abrahams hopping model was performed. We then compared the conductance characteristics of the gradual size 3D matrix layer to a constant-sized 3D matrix layer that was used as a reference in the simulation. The numerical calculations provided us with insights into the actual conductance mechanism of the PbSe and PbS Nano-crystals 3D matrix and explained the discrepancies in actual conductance and the variability in measured mobilities published in the literature. It is found that the mobility and thus conductance are dependent on a critical electrical field generated between two adjacent nano-crystals. Our model explains the conductance dependents on the: Cathode-Anode distance, the distance between the adjacent nano-crystals in the 3D matrix layer and the size distribution along the current direction. Part of the model (current-voltage dependence) was validated using a current-voltage measurements taken on a constant size normal distribution nano-crystals PbS layer (330nm thick) compared with the predicted I-V curves. It is shown that under a threshold bias, the current is very low, while after above a threshold bias the conductance is significantly increased due to increase of hopping probability. Once reaching the maximum probability the current tend to level-off reaching the maximal conductance available through the sequential hopping and nano crystals based layer behaves as a resistor under bias.

Lead sulphide nanocrystal photodetector technologies

Light detection is the underlying principle of many optoelectronic systems. For decades, semiconductors including silicon carbide, silicon, indium gallium arsenide and germanium have dominated the photodetector industry. They can show excellent photosensitivity but are limited by one or more aspects, such as high production cost, high-temperature processing, flexible substrate incompatibility, limited spectral range or a requirement for cryogenic cooling for efficient operation. Recently lead sulphide (PbS) nanocrystals have emerged as one of the most promising new materials for photodetector fabrication. They offer several advantages including low-cost manufacturing, solution processability, size-tunable spectral sensitivity and flexible substrate compatibility, and they have achieved figures of merit outperforming conventional photodetectors. We review the underlying concepts, breakthroughs and remaining challenges in photodetector technologies based on PbS nanocrystals.

Rapid and facile synthesis of high-quality, oleate-capped PbS nanocrystals

A convenient method for the synthesis of high quality PbS nanocrystals is studied and reported.

Facet engineering of monodisperse PbS nanocrystals with shape- and facet-dependent photoresponse activity

Monodisperse PbS nanocrystals with three different shapes for designing optoelectronic devices.

The effect of alkyl chain length on the structure of lead(ii) xanthates and their decomposition to PbS in melt reactions.

A series of lead(ii) alkylxanthates, [Pb(S2COR)2] (R = ethyl (1), n-propyl (2), n-butyl (3), n-hexyl (4) or n-octyl (5)) have been prepared and explored as single source precursors for use in melt reactions to form lead sulfide. X-ray single crystal structures of (2), (3) and (4) were used along with previously reported structures to investigate the influence of structure and chain length on the materials produced. The complexes were decomposed at 150, 175 or 200 °C forming PbS nanocrystals as confirmed by XRD and TEM. Analysis by SEM shows that the choice of precursor had an influence on nanocrystal size with longer alkyl chains resulting in smaller cubic nanocrystals. In addition to cubes, anisotropic growth was observed from decomposition of compound (5).

Toward Conductive Mesocrystalline Assemblies: PbS Nanocrystals Cross-Linked with Tetrathiafulvalene Dicarboxylate

We use the organic semiconductor tetrathiafulvalene dicarboxylate (TTFDA) to assemble PbS nanocrystals into conductive mesocrystals. Density functional theory calculations predict a size-tunable, near-resonant alignment between the PbS 1Sh state and the TTFDA HOMO with the potential to form a conductive channel for holes. We test this hypothesis with transport measurements on TTFDA-functionalized PbS nanocrystals of different sizes and find a pronounced modulation of the field-effect hole mobilities. Photothermal deflection spectroscopy reveals unchanged Urbach energies after ligand exchange, whereas further surface modification by colloidal-atomic layer deposition leads to a strong increase in the density of in-gap states. Hole transport in PbS-TTFDA is unusually robust against such surface modification. Our structural analysis of the mesocrystals suggests that TTFDA induces a defined interparticle spacing, the orientation of atomic lattices, and the angle within the mesocrystal unit cell. The results of...

X-ray structural analysis of two-dimensional assembling lead sulfide nanocrystals of different sizes

We report on the structural investigation of self-organized assemblies of PbS nanocrystals (NCs) of different sizes, which were deposited on a glass substrate or embedded in a porous matrix. Regardless of the NC size and the type of the substrate and matrix, the assemblies were ordered in two-dimensional superlattices with densely packed NCs.

Modifying Thermal Transport in Colloidal Nanocrystal Solids with Surface Chemistry.

We present a systematic study on the effect of surface chemistry on thermal transport in colloidal nanocrystal (NC) solids. Using PbS NCs as a model system, we vary ligand binding group (thiol, amine, and atomic halides), ligand length (ethanedithiol, butanedithiol, hexanedithiol, and octanedithiol), and NC diameter (3.3-8.2 nm). Our experiments reveal several findings: (i) The ligand choice can vary the NC solid thermal conductivity by up to a factor of 2.5. (ii) The ligand binding strength to the NC core does not significantly impact thermal conductivity. (iii) Reducing the ligand length can decrease the interparticle distance, which increases thermal conductivity. (iv) Increasing the NC diameter increases thermal conductivity. (v) The effect of surface chemistry can exceed the effect of NC diameter and becomes more pronounced as NC diameter decreases. By combining these trends, we demonstrate that the thermal conductivity of NC solids can be varied by an overall factor of 4, from ∼0.1-0.4 W/m-K. We complement these findings with effective medium approximation modeling and identify thermal transport in the ligand matrix as the rate-limiter for thermal transport. By combining these modeling results with our experimental observations, we conclude that future efforts to increase thermal conductivity in NC solids should focus on the ligand-ligand interface between neighboring NCs.

Correction to Interparticle Spacing and Structural Ordering in Superlattice PbS Nanocrystal Solids Undergoing Ligand Exchange

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Interparticle Spacing and Structural Ordering in Superlattice PbS Nanocrystal Solids Undergoing Ligand ExchangeMark C. Weidman, Kevin G. Yager, and William A. Tisdale*Cite this: Chem. Mater. 2015, 27, 21, 7546Publication Date (Web):October 27, 2015Publication History Published online27 October 2015Published inissue 10 November 2015https://doi.org/10.1021/acs.chemmater.5b03933Copyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views785Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (137 KB) Get e-Alerts Get e-Alerts

Tuning light emission of PbS nanocrystals from infrared to visible range by cation exchange

Colloidal semiconductor nanocrystals, with intense and sharp-line emission between red and near-infrared spectral regions, are of great interest for optoelectronic and bio-imaging applications. The growth of an inorganic passivation layer on nanocrystal surfaces is a common strategy to improve their chemical and optical stability and their photoluminescence quantum yield. In particular, cation exchange is a suitable approach for shell growth at the expense of the nanocrystal core size. Here, the cation exchange process is used to promote the formation of a CdS passivation layer on the surface of very small PbS nanocrystals (2.3 nm in diameter), blue shifting their optical spectra and yielding luminescent and stable nanostructures emitting in the range of 700–850 nm. Structural, morphological and compositional investigation confirms the nanocrystal size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Absorption and photoluminescence spectroscopy demonstrate the growth of a passivation layer with a decrease of the PbS core size, as inferred by the blue-shift of the excitonic peaks. The surface passivation strongly increases the photoluminescence intensity and the excited state lifetime. In addition, the nanocrystals reveal increased stability against oxidation over time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such highly luminescent nano-objects can find interesting applications in sensitized photovoltaic cells and light-emitting devices.

Influence of ligand exchange on the electrical transport properties of PbS nanocrystals

In this work, FETs are used as a research tool to study charge carrier mobilities in PbS nanocrystals (NCs) thin‐films employed as semiconducting layer in bottom‐gate bottom‐contact (BGBC) field‐effect transistors (FETs). The as‐synthesised NCs are surrounded by long alkyl chain ligands which act as electrical insulators. Therefore, a ligand exchange process with shorter molecules is necessary to enhance the free charges generation and transport. We used two different ligands: 1,2 ethandithiol (EDT) and 1,2,3,4‐tetrabutylammonium iodide (TBAI) and studied the charge mobility of PbS NCs comparing the electrical characteristics of FETs made by exchanged NCs. We analysed also the contemporary presence of both exchanged nanocrystals on the device. All the transistors showed p‐type transport behaviour, enhanced by an annealing process at 100 °C for 10 min. After this, only the TBAI‐treated NCs devices showed a n‐type transport, resulting in an ambipolar behaviour. Inkjet printing deposition techniques was also successfully used to deposit PbS‐(TBAI) NCs and ambipolar devices were obtained. In addition, for printed devices it was found that it is possible to modulate the charge transport properties by applying surface treatment to the substrate with a pentafluorothiophenol (PFTP). Indeed in this case, the p‐type transport was suppressed while n‐type behaviour was induced.

Colloidal nanocomposite of reduced graphene oxide and quantum dots for enhanced surface passivation in optoelectronic applications

Colloidal graphene/PbS quantum dots (QDs) hybrid nanostructures are fabricated with chemical grafting in one-pot solution methods. In the hybrid nanocomposites, PbS QDs are decorated on the reduced graphene oxide (rGO) nanosheets (NSs). By employing X-ray photoelectron spectroscopy (XPS) analysis, it is shown that the rGO NSs are bonded to PbS nanocrystals through oxygen functional groups, leading to improved surface passivation and electrical conductivity in the hybrids. The results obtained by the recordings of time-resolved photoluminescence spectra, field effect mobility, and photovoltaic performance revealed that rGO grafted to PbS QD composite structures provided better charge transport by 16 times compared to PbS alone, which is attributed to suppressed charge recombination and improved interfacial charge transport processes. Thus, the developed hybrid photoactive film enhanced open circuit current (Jsc) and power conversion efficiency (PCE) by 12% and 14% correspondingly.

Enhanced Charge-Transport Behavior on PbS Nanocrystals Capped with Atomic Ligands

In order to enhance charge-transport nanocrystal (NC) arrays, long and insulating ligands have to be replaced by short and electronically transparent ligands. Traditionally, benzene dithiol or mercaptopropionic acid have been frequently used as such surface ligands to overcome low charge-carrier mobility issues that affect colloidal NCs. However, the resulting devices usually exhibit a limited enhanced mobility of ~0.01 cm2/Vs. In this study, to realize a high charge-carrier mobility over 0.1 cm2/Vs, we demonstrate the utilization of atomic ligands such as halide anions (X-, X : Cl, Br, I) as electrically transparent ligands for lead chalcogenide NCs. We discuss the origin of such improved charge-transport behavior, which results from the introduction of atomic ligands, as well as various characterization results.

Induced synthesis of toroid-like lead sulfide nanocomposites in ethanol solution through a protein templating route

The toroid-like PbS nanocrystals have been prepared in zein ethanol solution based on self-assembly template of protein molecules. From transmission electron microscopy observation, the obtained samples were monodispersed with an average size of about 47 nm. The chemical composition and crystal structure of nanocomposites were determined by X-ray diffraction and energy-dispersive X-ray spectrum measurements. The interaction between PbS and zein was investigated through Fourier transform infrared, photoluminescence, circular dichroism (CD) spectra, and thermogravimetric analysis. The PbS nanocrystals could react with nitrogen and oxygen atoms of zein molecules through coordination and electrostatic force. The CD spectra results suggested that PbS nanocrystals induced the conformational transition of protein from α-helix to β-sheet and then self-assembled into ring or toroid nanostructure. The quenching of zein fluorescence induced by PbS nanocrystals also showed the change in the chemical microenvironments of the fluorescent amino acid residues in the protein structure. The key step of this facile, biomimetic route was the formation of self-assembly nanostructure of zein, which could regulate the nucleation and growth of toroid-like PbS nanocrystals.

PbS nanocrystals in microstructured fibers: Peculiarities of synthesis and optical properties

The results are presented on an investigation into the peculiarities of the lead sulfide (PbS) nanocrystal formation in a glass matrix under different temperature regimes based on an analysis of absorption and luminescence spectra in the near-infrared region. The possibility of controlled synthesis of such particles in optical fibers is shown. The effective sensitization of the liquid medium is demonstrated using proposed and fabricated microstructured fiber containing PbS nanocrystals as an example, which could be used either as a microcuvette or a broadband infrared source.

Highly Efficient Dual-Color Electrochemiluminescence from BODIPY-Capped PbS Nanocrystals.

Electrochemiluminescence (ECL) of a hybrid system consisting of PbS nanocrystals (NCs) and a BODIPY dye (BDY) capping ligand was discovered to produce highly efficient dual emissions with tri-n-propylamine as a coreactant. By means of spooling ECL spectroscopy, the strong dual ECL emission peaks of 984 and 680 nm were attributed to the PbS and BDY moieties, respectively, and found to be simultaneous during the light evolution and devolution. The ECL of the PbS was enhanced via NC collisions with the electrode and reached an efficiency of 96% relative to that of Ru(bpy)3(2+), which is the highest among the semiconductor NCs.

Optical and Magnetic Properties of PbS Nanocrystals Doped by Manganese Impurities

We study the effect of manganese impurities on optical and magnetic properties of PbS quantum dots (QDs) of different sizes. We find that at low Mn concentrations, the manganese atoms slightly change the absorption spectra of pure PbS nanocrystals. A soon as the number of Mn atoms increases a QD energy gap expands. In a PbS QD there is a distinct exciton peak. With the presence of Mn impurities this peak is smeared over and almost disappears for larger Mn concentrations. This effect indicates the strong sp–d hybridization. We also study how an Mn location inside a QD can affect the absorption spectra. We find that if the Mn atoms are spread over the surface, there is no significant influence on the absorption. If the Mn atoms are clustered, there is no difference where such a cluster is located, whether in the middle of a QD or on a QD surface. We also study the magnetic properties of Pbn–xMnxSn nanocrystals. We find that such a system is always in an antiferromagnetic order. This indicates that at short ...