Lead Sulfide Quantum Dots Research Articles

Stable Monodisperse Pb1-x Cdx S Quantum Dots for NIR-II Bioimaging by Aqueous Coprecipitation of Bimetallic Clusters.

Aqueous lead sulfide (PbS) quantum dots (QDs) synthesized by traditional methods are unstable, so that they are usually coated with cadmium sulfide (CdS) to prevent oxidation, which are complicated and not satisfactory for mass production. Here, stable ternary Pb1-x Cdx S QDs were synthesized by in situ coprecipitation of Pb4-n Cdn O4 bimetallic clusters in an aqueous solution, which possess a uniform size of 4.0±0.2 nm and the second near-infrared (NIR-II) emission at 1100 nm with photoluminescence quantum yield (PLQY) as high as 17.72 %. Stored at 4 °C and in colloidal form, the PLQY of Pb1-x Cdx S QDs remained at 90.9 % of the initial value after 15 days, while stored as powder, the spectra did not change after 5 months. The high PLQY and good water compatibility of Pb1-x Cdx S QDs provide a good performance in vivo vasculature imaging and lymphatic system imaging at a very low power density (10 mW cm-2 ) in the NIR-II window.

Unraveling the Organic and Inorganic Passivation Mechanism of ZnO Nanowires for Construction of Efficient Bulk Heterojunction Quantum Dot Solar Cells.

Zinc oxide (ZnO) nanowire (NW) based lead sulfide (PbS) quantum dot solar cells (QDSCs), i.e., bulk heterojunction QDSCs, have been widely investigated because of the excellent photoelectronic properties of PbS QDs and ZnO NWs. To further improve the efficiency of this type of QDSCs, various passivation methods are applied to ZnO NWs to suppress interface recombination caused by trap defects. However, the comparison among passivation using organic, inorganic, and inorganic-organic hybrid materials with different properties has been less studied. In this work, the effect of passivation with inorganic Mg-doped ZnO (ZMO), organic 1,2-ethanedithiol (EDT) and both of them on ZnO NWs and PbS QDSCs are investigated. As a result, ZnO NWs purely passivated by organic material EDT show the best performance with fewer surface defects and better matched energy level with the PbS QD layer. A nearly 1.7 times larger power conversion efficiency (PCE) of 6.9% is achieved for the solar device using ZnO NW @EDT, compared with that (4.1%) of the untreated one. The work provides a promising way to impede interlayer charge recombination and facilitate carrier transport, thus enhancing the photovoltaic performance of the device.

Enhanced Surface Passivation of Lead Sulfide Quantum Dots for Short-Wavelength Photodetectors

Enhanced Surface Passivation of Lead Sulfide Quantum Dots for Short-Wavelength Photodetectors

Research on Photoelectric Detection Performance Based on Pb Se Quantum Dots

Quantum dot materials have the advantages of low cost, wide spectral response and good photostability, and are widely used in optoelectronic fields such as light-emitting diodes and photodetectors. Quantum dots are the key materials for the next generation of new semiconductor optoelectronic devices. The direct integration of nano-quantum dots with silicon-based materials can simplify the fabrication process of optoelectronic devices. The environmental stability of lead selenide (PbSe) quantum dots is poorer than that of lead sulfide (PbS) quantum dots, which limits its application in optoelectronic devices. In this paper, we combine lead selenide quantum dots with silicon-based photovoltaic junction field effect transistors, and introduce halides in the synthesis process to improve the stability of quantum dots in air. We analyze and study the performance of this new type of near-infrared quantum dot photodetector, and study the influence of factors such as channel area and quantum dot size on the performance of the detector, which provides ideas for further optimizing the photodetection performance.

Tuning the Frölich interactions in bismuth modified lead sulphide quantum dots to minimize the excitonic carrier energy dissipation

Tuning the Frölich interactions in bismuth modified lead sulphide quantum dots to minimize the excitonic carrier energy dissipation

Photodetectors Based on Lead Sulfide Quantum Dot and Organic Absorbers for Multispectral Sensing in the Visible to Short‐Wave Infrared Range

AbstractMultispectral imaging in short‐wave infrared (SWIR) is a powerful analytical technique because of the distinctive spectral properties of many materials in this range. However, conventional SWIR image sensors are beyond the reach of many applications due to their high price. Image sensors based on colloidal quantum dots (CQDs) are expected to deliver affordable infrared image sensors to wider application scope. So far, the demonstrated CQD image sensors do not have a multispectral capability. Here, a dual‐band photodetector based on PbS CQDs is presented. By engineering the surface of CQDs, two oppositely facing pn junctions are fabricated in series, which enable sensing in two spectral channels. Furthermore, an optical cavity is designed that reduces the spectral crosstalk between the two channels and simultaneously enables wavelength‐tunability in one channel. Finally, an organic photodiode (OPD) is integrated with a PbS CQD photodiode in a single device, leveraging a high sensitivity in visible and near‐infrared (NIR) characteristics for OPDs. The presented photodetectors exhibit low dark current below 500 nA cm−2 at 1 V bias, a fast response measured in microseconds, as well as high external quantum efficiency, reaching 70% in NIR and 30% in SWIR.

Dye Enhanced Quantum Dot Sensitized Solar Cell

Third generation solar cells, such as dye and quantum dot sensitized solar cells are attracting attention of many research groups. In this investigation we explore the role of dye extract on the enhancement of the photovoltaic properties of quantum dot sensitized solar cells (QDSSCs). Lead sulfide quantum dots of different sizes have been used to sensitize a nanostructured titanium oxide electrode. We compare the open circuit voltage, the short circuit current, and power conversion efficiency of QDSSCs with the same quantities as obtained for dye-enhanced system using pomegranate dye extract. An open circuit voltage of 166 mV, a short circuit current of 0.1 mA, and an efficiency of 0.32% were obtained for 2.4 nm radius lead sulfide quantum dot sensitized solar cells. Using pomegranate dye extract reveals a considerable enhancement of the above characteristics. The combined dye-quantum dot system produces an open circuit voltage of 300 mV, a short circuit current of 0.55 mA, and an efficiency of 3.4%. For 3.2 nm radius QDs, the efficiency is substantially higher, reaching about 7%. A model describing the structure and processes leading to the above enhancement of the assembled solar cell characteristics is presented. In this model we explain the interplay between the transfer of electrons between the dye, quantum dots, and subsequent injection in the wide band gap titanium dioxide semiconductor.

Optically tunable split-ring resonators controlled lead sulfide quantum dots modulator for wide THz radiation

Abstract It is particularly appealing for efficient active terahertz (THz) modulators using photonic structures to enhance light–matter interaction. Here, an optical controlled THz modulator is proposed that combines lead sulfide (PbS) quantum dots with subwavelength metallic split-ring resonators (SRRs) for providing field enhancement. The modulation depth reaches 60.3%, which is approximately 3 times larger than the PbS quantum dots film without SRRs (as reference) in the frequency range of 0.1–1.1 THz. Such significant enhanced THz modulation is mainly due to the local THz field enhancement caused by the SRRs, which is consistent with the simulation result.

Study of the Electron-Phonon Coupling in PbS/MnTe Quantum Dots Based on Temperature-Dependent Photoluminescence.

The temperature dependence of photoluminescence (PL) emission is a valuable tool for investigating carrier localization, recombination, and carrier–phonon interactions. Herein, electron–phonon couplings in lead sulfide (PbS) quantum dots (QDs) and lead sulfide/manganese tellurite (PbS/MnTe) QDs is reported. The effect of temperature on the PL emission of PbS and PbS/MnTe was explored within a temperature range of 10 to 300 K. When temperature increased, PL emission was blue-shifted due to the confinement effect. The gradual broadening of the full width at half maximum (FWHM) with increasing temperature indicates electron–phonon interactions. An analysis based on the Boson model revealed that the values of the exciton acoustic phonon coupling coefficient, σ, and temperature-dependent linewidth, γ, for PbS/MnTe were larger than those for PbS, indicating stronger exciton longitudinal-optical–phonon coupling in the compound structure.

Pickering Emulsions of Self-Assembled Lead Sulfide Quantum Dots with Janus-Ligand Shells as Nanoreactors for Photocatalytic Reactions

Here we prepare Pickering emulsions with semiconductor quantum dots (QDs). Amphiphilic PbS QDs are prepared by constructing Janus-ligand shells comprised of lipophilic oleic acid and hydrophilic 4-(2,2-dicyanovinyl)cinnamic acid ligands. Upon homogenization, the QDs with Janus-ligand shells self-assemble at the water–dichloromethane interface, forming stable Pickering emulsions. The photocatalytic properties are evaluated by the photodegradation reaction of methyl orange (MO) dye molecules. Under the same conditions, MO was significantly degraded when photocatalyzed by the QD Pickering emulsions, while no degradation was observed when PbS QDs without Janus-ligand shells were employed. This work provides a guide to designing QD-based nanoreactors.

Highly efficient tin oxide‐based colloidal lead sulfide quantum dot solar cell

AbstractThis work presents the assessment of tin oxide (SnO2) electron transport layer (ETL)‐based quantum dot solar cell for improved efficiency (>20%). The proposed solar cell consists of a solid layer of lead sulfide (PbS) treated with PbS‐TBAI (tetrabutylammonium iodide) as absorber layer and PbS CQD treated with 1,2‐ethanedithiol (PbS‐EDT) as hole transport layer (HTL). The high level of efficiencies is achieved by varying the doping concentration of ETL and HTL, which affect the mobility of carriers (both electrons and holes). The optimization is carried out with a doping concentration (for ETL and HTL) of 1 × 1019 cm−3. The said doping reflected >20% conversion efficiency. PCE, fill‐factor (FF), Voc, and Jsc were analyzed for all the performed variations.

Sensitive and simultaneous detection of multi-index lung cancer biomarkers by an NIR-Ⅱ fluorescence lateral-flow immunoassay platform

The simultaneous detection of multiple serum biomarkers of cancer with high sensitivity and point-of-care manner is of great significance for facile and early screening of cancers. In this work, the sensitivity of lateral-flow immunoassay (LFIA) platform was improved by two strategies. The NIR-Ⅱ emitting lead sulfide quantum dots (PbS QDs) were employed to replace common visible region fluorophores to reduce background interference from sample matrix. Meanwhile, numerous hydrophobic PbS QDs were concentrated and assembled within single dendritic scaffold via three-dimensional distribution manner to enhance the fluorescence intensity of individual colloidal label. The LFIA strips with multi-testing lines were performed to realize simultaneous diagnosis of carcino-embryonic antigen (CEA), cytokeratin 19 fragment (Cyfra21-1) and neuron-specific enolase (NSE). The multi-target LFIA could be completed within 12 min with precise quantitative results by a portable NIR-Ⅱ strip scanner. The analytical data illustrated wide linear detection ranges of 0.11–100 ng mL−1, 0.18–100 ng mL−1 and 0.28–100 ng mL−1 and limit of detection of 0.11, 0.18 and 0.28 ng mL−1 for CEA, Cyfra21-1 and NSE, respectively. The multi-target LFIA revealed minor cross-reactivity of three specific antibodies conjugated labels with non-specific cancer biomarkers and interfering proteins in human serum. For real serums of lung cancer patients and healthy persons, the combination detection of the three biomarkers exhibited an improved sensitivity up to 92.7%, which was significantly higher than any individual biomarker detection, with a satisfactory specificity of 92.0%. The multi-target LFIA platform with high sensitivity and specificity holds great significance for point-of-care and simultaneous diagnosis of multiple cancer biomarkers.

The impact of chemical composition of halide surface ligands on the electronic structure and stability of lead sulfide quantum dot materials.

There is a high fundamental interest in the surface and bulk chemistry of quantum dot (QD) solids, as they have proven to be very promising materials in optoelectronic devices. The choice of surface ligands for quantum dots in solid devices determines many of the film properties, as the ligands influence for example the doping density, chemical stability and charge transport. Lead halide ligands have developed as the main ligand of choice for lead sulfide quantum dots, as they have been shown to passivate quantum dot surfaces and enhance the chemical stability. In this study, we successfully varied the ligand composition on the surface of PbS quantum dot films from pure lead iodide to pure lead bromide and investigated its influence on the chemical and electronic structure of the QD solids using hard X-ray photoelectron spectroscopy (HAXPES). Furthermore, we developed a surface treatment to prevent the surface oxidation of a bulk PbS reference sample. Through measurements of this sample and of lead halide reference samples, we were able to assign the contributions of different chemical bonding to the Pb 4f core level and of different atomic orbitals to the valence band spectral shape of the QD materials. Overall, we found that the valence band edge position was very similar for all different iodide:bromide ratios and that all investigated compositions were able to protect the quantum dot surfaces within solid films from oxidation. However, the ligand composition significantly influences the sample stability under X-rays. The iodide rich QD solids showed the highest stability with very little to no chemical changes over several hours of X-ray exposure, while the bromide rich QD solids changed already within the first hour of exposure.

Lead sulfide quantum dot assembly with biocompatible mechanical property and tunable hydrophilicity

The outstanding optical and electronic properties of lead sulfide (PbS) colloidal quantum dots have broad applications in nanotechnology. They are composed of an inorganic semiconductor core and organic ligands. Here, using 2,3-dimercaptosuccinic acid (DMSA) as a reactant, we synthesized PbS nanoparticles and assembled them on a pigeon feather substrate through a self-assembled monolayer process. This assembly process results in a significantly higher increase in the modulus and hardness of the synthesized PbS material compared to that of the PbS materials reported previously. Particularly, there is only a slight increase in the mechanical properties of the PbS layer compared with the bio-template, indicating the compatibility between the coating and base material, demonstrating its potential for biological applications, such as wearable flexible electronic devices. In addition, the DMSA of the rich carboxylic groups as a passivator promoted the tunability of the PbS surface from hydrophilic to superhydrophilic. The influence of the surface roughness of the PbS layer on the wetting behavior conforms to the Cassie–Baxter model.

A new innovative real-time tracking method for flying insects applicable under natural conditions

BackgroundSixty percent of all species are insects, yet despite global efforts to monitor animal movement patterns, insects are continuously underrepresented. This striking difference between species richness and the number of species monitored is not due to a lack of interest but rather to the lack of technical solutions. Often the accuracy and speed of established tracking methods is not high enough to record behavior and react to it experimentally in real-time, which applies in particular to small flying animals.ResultsOur new method of real-time tracking relates to frequencies of solar radiation which are almost completely absorbed by traveling through the atmosphere. For tracking, photoluminescent tags with a peak emission (1400 nm), which lays in such a region of strong absorption through the atmosphere, were attached to the animals. The photoluminescent properties of passivated lead sulphide quantum dots were responsible for the emission of light by the tags and provide a superb signal-to noise ratio. We developed prototype markers with a weight of 12.5 mg and a diameter of 5 mm. Furthermore, we developed a short wave infrared detection system which can record and determine the position of an animal in a heterogeneous environment with a delay smaller than 10 ms. With this method we were able to track tagged bumblebees as well as hawk moths in a flight arena that was placed outside on a natural meadow.ConclusionOur new method eliminates the necessity of a constant or predictable environment for many experimental setups. Furthermore, we postulate that the developed matrix-detector mounted to a multicopter will enable tracking of small flying insects, over medium range distances (>1000 m) in the near future because: a) the matrix-detector equipped with an 70 mm interchangeable lens weighs less than 380 g, b) it evaluates the position of an animal in real-time and c) it can directly control and communicate with electronic devices.

Self-assembly, stability, and photoresponse of PbS quantum dot films capped with mixed halide perovskite ligands

The type of passivating ligands and the ligand exchange method influence the quality of lead sulfide quantum dot films. This imparts on the efficiency of optoelectronic devices. To get a compact arrangement of the nanocrystals in a thin film (⁓100 nm) via self-assembling, we used organic-inorganic perovskites with mixed halides for the solid-state exchange of oleic acid ligands on PbS QDs (⁓ 4 nm). Formamidinium lead halides FAPbIxBr3-x (x= 3,2,1,0) were used. X-ray spectroscopy shows that successful replacement of oleic acid with FA happens by short immersion of the films (2 min) in the solution. Transmission electron microscopy shows that nano-scale cracks, short-range ordering, and fusion of the nanocrystals happen during the exchange with FAPbI3. Gradual substitution of I− with Br− ions improves the film homogeneity with fewer defects (nano-scale holes and cracks). Uniform cubic assembly of the nanocrystals without defects and high coverage density is obtained with FAPbBr3. The findings are applied to the fabrication of field effect phototransistors on Si/SiO2/graphene wafers. Photoresponse of the devices indicates that the stability of the films in humidified air (26 °C and 51% humidity) is improved from less than 14 days for iodine to more than 60 days for bromine. The ILIGHT/IDARK ratio, responsivity, and specific detectivity increase by 64%, 55%, and 60%, respectively, with FAPbBr3. Prevention of lead sulfide nanocrystal aggregation and the formation of large-scale self-assemblies with perovskite ligands is of technical importance for next-generation optoelectronic applications.

Scalable fabrication of efficient p-n junction lead sulfide quantum dot solar cells

Nowadays, the best lead sulfide (PbS) colloidal quantum dot (CQD) solar cells are primarily demonstrated in the n-p structure, while the p-n structure is significantly less developed. This technological gap between the n-p and p-n structures is much more distinct than in cases of other solution-processable photovoltaic technologies like perovskites and polymers. Here, we propose a scalable fabrication strategy for efficient PbS QD solar cells with p-n structure. An industrially suited blade-coating technique has been used to deposit both n-type and p-type QD layers. The obtained solar cells demonstrated power conversion efficiency of 9%, thus, commensurate to the record device efficiency with this architecture fabricated with a non-scalable technique. The availability of both p-n and n-p structures fabricated from scalable methods may promote the future integration of the PbS QDs into tandem devices together with other solution-processable materials to exploit the most prominent benefits of the PbS QDs, such as infrared absorption.

Near-infrared PbS quantum dots functionalized with affibodies and ZnPP for targeted imaging and therapeutic applications

We report a new theranostic device based on lead sulfide quantum dots (PbS QDs) with optical emission in the near infrared wavelength range decorated with affibodies (small 6.5 kDa protein-based antibody replacements) specific to the cancer biomarker human epidermal growth factor receptor 2 (HER2), and zinc(II) protoporphyrin IX (ZnPP) to combine imaging, targeting and therapy within one nanostructure. Colloidal PbS QDs were synthesized in aqueous solution with a nanocrystal diameter of ∼5 nm and photoluminescence emission in the near infrared wavelength range. The ZHER2:432 affibody, mutated through the introduction of two cysteine residues at the C-terminus (Afb2C), was used as capping ligand to form Afb2C-PbS QDs that have a high binding affinity for HER2, which is overexpressed in several types of cancer including breast cancer. Afb2C-PbS QDs were further modified by conjugation with ZnPP, which acts as an anticancer agent. The biological activity of these QDs was tested against SKBR3 (HER2-positive) and MDA-MB-231 (HER2-normal) breast cancer cells, with results showing that ZnPP-Afb2C-functionalized PbS QDs were successfully targeted to the HER2-overexpressing cancer cells and induced cell apoptosis thanks to the conjugation with ZnPP. These results expand the use of the QD nanoplatform with the formulation of novel nanomaterials for targeted delivery and combined imaging and therapy via direct surface-protein interaction.

Influence of Ligand Structure on Excited State Surface Chemistry of Lead Sulfide Quantum Dots.

The ligand-nanocrystal boundaries of colloidal quantum dots (QDs) mediate the primary energy and electron transfer processes that underpin photochemical and photocatalytic transformations at their surfaces. We use mid-infrared transient absorption spectroscopy to reveal the influence that ligand structure and bonding to nanocrystal surfaces have on the changes of the excited state surface chemistry of this boundary in PbS QDs and the corresponding impact on charge transfer processes between nanocrystals. We demonstrate that oleate ligands undergo marked changes in their bonding to surfaces in the excitonic excited states of the nanocrystals, indicating that oleate passivated PbS surfaces undergo significant structural changes following photoexcitation. These changes can impact the surface mobility of the ligands and the ability of redox shuttles to approach the nanocrystal surfaces to undergo charge transfer in photocatalytic reactions. In contrast, markedly different transient vibrational features are observed in iodide/mercaptoproprionic acid passivated PbS QD films that result from charge transfer between neighboring nanocrystals and localization of holes at the nanocrystal surfaces near MPA ligands. This ability to distinguish the influence that excitonic excited states vs charge transfer processes have on the surface chemistry of the ligand-nanocrystal boundary lays the groundwork for exploration of how this boundary can be understood and controlled for the design of nanocrystalline materials tailored for specific applications in solar energy harvesting and photocatalytic reactions.

Pyroelectricity of Lead Sulfide (PbS) Quantum Dot Films Induced by Janus-Ligand Shells.

Asymmetry is an essential property to control. To do that in nanocrystalline systems we have developed methods to produce Janus-ligand shells on otherwise symmetric PbS quantum dots (QDs). Here, we demonstrate that control by constructing a system that exhibits pyroelectricity built from spherical PbS QDs. We observed a pyroelectric current in two different configurations. In one configuration, the QDs are self-assembled into close-packed arrays while in the second configuration, the QDs are dispersed into an electro-inactive polymer, polydimethylsiloxane. Both exhibit a pyroelectric response. In the first configuration we estimate a lower limit of the pyroelectric coefficient to be 1.97 × 10-7 C/m2·K, which is likely limited by the degree of QD alignment during film formation but is already on par with common pyroelectric systems. Compared with inorganic ceramic-like and polymeric pyroelectric materials, pyroelectric films self-assembled from polar QDs are easier to prepare, responsive to light with different energies based on QD exciton energy, and the polarization of each QD could be easily tuned by constructing different Janus-ligand shells.