Lead Sulfide Quantum Dots Research Articles

Thiol-end-functionalized Regioregular Poly(3-hexylthiophene) for PbS Quantum Dot Dispersions

Inorganic nanoparticles hybridized with π-conjugated polymers were successfully synthesized by the ligand exchange reaction of thiol-end-functionalized regioregular poly(3-hexylthiophene) (P3HT-SH) with lead sulfide (PbS) quantum dots (QDs). The hybrid material (P3HT-SH/PbS-QD) shows good dispersibility in organic solvents even after 6 months due to the decreased intermolecular interaction of PbS nanoparticles coated by highly soluble P3HT. The ultraviolet–visible–near infrared absorption spectra show a clear difference in PbS-QDs hybridized with oleic acid and P3HT-SH, depending on the size of the PbS-QDs. By using transmission electron microscopy, small clusters of PbS-QDs are observed at the nanolevel when hybridized with P3HT-SH, indicating the formation of nanoscale aggregates of PbS-QDs in the hybrid material. Preliminary results for fullerene-free photovoltaic applications showed that P3HT-SH/PbS-QD can deliver almost two times higher power conversion efficiency (PCE) than P3HT when paired with an n-type naphthalene-diimide-based semiconducting polymer (N2200) as the photoactive system. Such an increase in PCE can be attributed to the increased dielectric constant exerted by PbS-QDs, which facilitates charge dissociation. This study not only describes a method for synthesizing PbS-QD-based organic–inorganic hybrids but also reveals an interesting design direction for photovoltaic materials.

The effect of synthesis situation on the structural, dielectric, linear and nonlinear optical properties of thiol-capped water-soluble lead sulfide (PbS) quantum dots

In this study, lead sulfide quantum dots (PbS QDs) have been prepared by an aqueous method with a mixture of TGL and DTG as a capping agent with different situations of synthesis. The XRD study defends mono-phase formation of PbS having a cubic system with a crystallite size of 2.9–3.6 nm. The SEM images show that the particles are at the nanoscale. The band gap energies of these samples were obtained 2.47–2.53 eV using UV–Vis absorption spectra. In addition, the optical limiting (OL) method was used to obtain linear absorption coefficient, α. The results of Kramers-Kronig (KK) relations show by increasing pH, the intensity increased in complex refractive index as well as complex dielectric constant. Moreover, regarding the transverse optical and longitudinal optical frequencies of PbS QDs, by increasing synthesized environment pH, both frequencies had significantly blue shifts. Owning the high dielectric constant of the sample, PbS QDs were revealed an appropriate candidate to employ in smart materials. Besides, standard single-beam Z-scan techniques with various laser powers have been employed for detecting nonlinear optical (NLO) characteristics. This research reports the relaxation time and pH-dependent third-order NLO properties of PbS QDs. The consequences have revealed that the nonlinear refractive (NLR) and nonlinear absorption (NLA) coefficients of PbS QDs have been improved by increasing laser power except at 55 mW, reaching values of 1.68 × 10−7 cm2/W and 6.8 × 10−4 cm/W in pH of 9.2 and relaxation time of 1 h at 45 mW, respectively.

Real-Time In Vivo Detection and Monitoring of Bacterial Infection Based on NIR-II Imaging.

Treatment according to the dynamic changes of bacterial load in vivo is critical for preventing progression of bacterial infections. Here, we present a lead sulfide quantum dots (PbS QDs) based second near-infrared (NIR-II) fluorescence imaging strategy for bacteria detection and real-time in vivo monitoring. Four strains of bacteria were labeled with synthesized PbS QDs which showed high bacteria labeling efficiency in vitro. Then bacteria at different concentrations were injected subcutaneously on the back of male nude mice for in vivo imaging. A series of NIR-II images taken at a predetermined time manner demonstrated changing patterns of photoluminescence (PL) intensity of infected sites, dynamically imaging a changing bacterial load in real-time. A detection limit around 102–104 CFU/ml was also achieved in vivo. Furthermore, analysis of pathology of infected sites were performed, which showed high biocompatibility of PbS QDs. Therefore, under the guidance of our developed NIR-II imaging system, real-time detection and spatiotemporal monitoring of bacterial infection in vivo can be achieved, thus facilitating anti-infection treatment under the guidance of the dynamic imaging of bacterial load in future.

Colloidal PbS Quantum Dots for Visible-to-Near-Infrared Optical Internet of Things

The emergence of optical Internet of Things (optical-IoT) for sixth-generation (6G) networks has been envisaged to relieve the bandwidth congestion in the conventional radio frequency (RF) channel, and to support the ever-increasing number of smart devices. Among the plethora of device innovations deemed essential for fortifying the development, herein we report on the visible-to-near-infrared color-conversion luminescent-dyes based on lead sulphide quantum dots (PbS QDs), so as to achieve an eye-safe high-speed optical link. The solution-processed PbS QDs exhibited strong absorption in the visible range, radiative recombination lifetime of 6.4 $\mu$ s, as well as high photoluminescence quantum yield of up to 88%. Our proof-of-principle demonstration based on an orthogonal frequency-division multiplexing (OFDM) modulation scheme established an infrared data transmission of 0.27 Mbit/s, readily supporting an indoor optical-IoT system, and shed light on the possibility for PbS-integrated transceivers in supporting remote access control of multiple nodes. We further envisaged that our investigations could find applications in future development of solution-processable PbS-integrated luminescent fibers, concentrators, and waveguides for high-speed optical receivers.

Improving of Sensitivity of PbS Quantum Dot Based SWIR Photodetector Using P3HT.

In this study, we improved the photosensitivity of the lead sulfide quantum dot (PbS QD)-based shortwave infrared (SWIR: 1.0–2.5 μm) photodetector by blending poly(3-hexylthiophene-2,5-diyl) (P3HT) with PbS QD. The PbS QD used for SWIR photoactive layer showed an absorption peak at 1410 nm. In addition, by using zinc oxide nanoparticles (ZnO NPs) as an interlayer, we obtained the stable current characteristics of our device. To confirm the effectiveness of P3HT on the PbS QD-based SWIR photodetector, we compared the electrical characteristics of a PbS QD-based device with a hybrid P3HT:PbS QD-based device. In the reverse bias region, the current on/off ratio of the PbS QD-based device was 1.3, whereas the on/off ratio of the hybrid P3HT:PbS QD-based device was 2.9; 2.2 times higher than the PbS QD-based device. At −1 V, the on/off ratio of the PbS QD-based device was 1.3 and the on/off ratio of the hybrid P3HT:PbS QD-based device was 3.4; 2.6 times higher than the PbS QD-based device. The fabricated P3HT:PbS QD-based device had the highest on/off ratio when −1 V voltage was applied.

Probing Dynamics of Lead(II) Sulfide Quantum Dots in Solution Ligand Exchange by Voltammetry.

The ligand/quantum dots (QDs) ratio is crucial for the liquid state ligand exchange process to ensure a high-quality surface passivation and stable QDs ink. Herein we report an electrochemical method to investigate the ligand exchanged PbS-PbI2 QDs. It is found that the shell and core Pb(II) are distinguished by their reduction peak position in the cyclic voltammogram and the peak charge ratio gives the shell/core composition of the QDs. Combined with XPS analysis and UV-vis spectroscopy, it is further indicated that the shell/core ratio of PbS-PbI2 QDs varies as the ligand PbI2 concentration changes. Specifically, below a certain concentration, more PbI2 binds to the QD surface, leading to better passivation when the PbI2 concentration increases; however, beyond that concentration, decomposition of QDs likely occurs via an anion exchange process. The presented electrochemical method provides a new and powerful tool to investigate and optimize QD surface chemistry for boosting the scale up applications of QD devices.

Temperature-induced PbS quantum dots with tunable broadband wavelength grown by atomic layer deposition

Lead sulfide (PbS) quantum dots (QDs) were deposited onto silica substrates by atomic layer deposition (ALD). By controlling the number of growth cycles, the average size of the PbS nanocrystals (NCs) changed from approximately 6.3 to 95.4 nm. The crystalline phase of the PbS semiconductor materials was investigated via X-ray diffraction, and it was established that as the size of the NCs increased, the preferred growth orientation of the PbS films was (200). The obtained nanofilms were compact and continuous polycrystalline films with well-defined grain boundaries. To control the size of PbS QDs further, the temperature-induced characteristics of the ALD-fabricated PbS QD films were studied through annealing. Slow growth of the PbS QDs was observed for the nanofilms annealed at temperatures below 300 °C, whereas the QD size increased significantly at annealing temperatures above 300 °C. The broad near-infrared luminescence wavelength of the PbS nanofilms was tuned from 1000 to 1600 nm. Moreover, the photoluminescence lifetime of the annealed PbS QDs increased from 4.96 to 10.92 μs. The temperature-induced and size-controlled PbS QDs are ideal materials for application in wavelength-tunable optical devices.

Effect of nitrogen capture ability of quantum dots on resistive switching characteristics of AlN-based RRAM

This Letter studies the effect of the nitrogen capture ability of quantum dots on resistive switching characteristics of AlN-based resistive random access memory. We prepared a single layer AlN device and four types of AlN/PbS quantum dot stacked structure devices with different concentrations. Compared with the single layer AlN device, the AlN/PbS quantum dot stacked structure devices exhibit excellent resistive switching characteristics, such as forming-free, low power consumption, and excellent stability. We propose that the resistive switching process is determined by the migration of nitrogen ions and the lead sulfide (PbS) quantum dot layer as a natural nitrogen ion reservoir, which can improve the resistive switching characteristics. Moreover, the size of the natural nitrogen ion reservoir can be modulated by changing the concentration of quantum dots.

Synthesis and characterisation of N-gene targeted NIR-II fluorescent probe for selective localisation of SARS-CoV-2.

Tracking the viral progression of SARS-CoV-2 in COVID-19 infected body tissues is an emerging need of the current pandemic. Imaging at near infrared second biological window (NIR-II) offers striking benefits over the other technologies to explore deep-tissue information. Here we design, synthesise and characterise a molecular probe that selectively targets the N-gene of SARS-CoV-2. Highly specific antisense oligonucleotides (ASOs) were conjugated to lead sulfide quantum dots using a UV-triggered thiol-ene click chemistry for the recognition of viral RNA. Our ex vivo imaging studies demonstrated that the probe exhibits aggregation induced NIR-II emission only in presence of SARS-CoV-2 RNA which can be attributed to the efficient hybridisation of the ASOs with their target RNA strands.

Lead Sulfide Quantum Dots Mode Locked, Wavelength-Tunable Soliton Fiber Laser

We fabricate an oleic acid capped colloidal lead sulfide quantum dots (PbS QDs) by modified hot-injection method, and then drop them on the end of fiber connector to construct the fiber-based PbS QDs saturable absorber (SA). The modulation depth and saturation intensity of the PbS QDs SA are about 30% and 1.88 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The strong quantum confinement effect in PbS QDs enables wideband tunability. We get subpicosecond soliton pulses, wavelength-tunable between 1530 nm and 1560 nm, with stable mode-locking, by adjusting the orientations of the polarization controller. These results contribute to study the nonlinear optical properties of zero-dimensional nanomaterials and provide new opportunities for the applications of broadband photoelectronic devices.

Study on the performance of ZMO/PbS quantum dot heterojunction solar cells

In this work, the Mg-doped ZnO (ZMO)/Lead sulfide (PbS) quantum dot (QD) heterojunction solar cells are fabricated via layer-by-layer spin-coating method. The quantum dot solar cells (QDSCs) with structure of FTO/ZMO/PbS-EMII/PbS-EDT/Au and relatively larger area of 0.372 cm2 are prepared in ambient atmosphere. The effect of PbS active layer thickness on the photovoltaic performance of PbS QDSCs is investigated under room temperature of 293 K. It is concluded that seven spin-coating cycles of PbS active layers is the best choice for the device, and the cell with that achieves a power conversion efficiency (PCE) of 9.46%. Furthermore, the temperature dependent characteristics of PbS QDSCs are studied. It is exhibited that the power efficiency improves as the device temperature increases first then shows a decreasing trend as the temperature substantially rises. As a result, a highest PCE of 12% is shown at the working temperature of 273 K due to higher VOC and FF. Moreover, it is demonstrated the PbS QDSCs possess noticeably stability for over 30 days of storage in air.

Electrochemical DNA detection of hepatitis E virus genotype 3 using PbS quantum dot labelling.

The aim of this study was to develop a highly specific electrochemical DNA sensor using functionalized lead sulphide (PbS) quantum dots for hepatitis E virus genotype 3 (HEV3) DNA target detection. Functionalized-PbS quantum dots (QDs) were used as an electrochemical label for the detection of HEV3-DNA target by the technique of square wave anodic stripping voltammetry (SWASV). The functionalized-PbS quantum dots were characterized by UV-vis, FTIR, XRD, TEM and zeta potential techniques. As-prepared, functionalized-PbS quantum dots have an average size of 4.15 ± 1.35nm. The detection platform exhibited LOD and LOQ values of 1.23fM and 2.11fM, respectively. HEV3-DNA target spiked serum is also reported.Graphical abstract.

Establishing Multifunctional Interface Layer of Perovskite Ligand Modified Lead Sulfide Quantum Dots for Improving the Performance and Stability of Perovskite Solar Cells.

While organic-inorganic halide perovskite solar cells (PSCs) show great potential for realizing low-cost and easily fabricated photovoltaics, the unexpected defects and long-term stability against moisture are the main issues hindering their practical applications. Herein, a strategy is demonstrated to address the main issues by introducing lead sulfide quantum dots (QDs) on the perovskite surface as the multifunctional interface layer on perovskite film through establishing perovskite as the ligand on PbS QDs. Meanwhile, the multifunctions are featured in three aspects including the strong interactions of PbS QDs with perovskites particularly at the grain boundaries favoring good QDs coverage on perovskites for ultimate smooth morphology; an inhibition of iodide ions mobilization by the strong interaction between iodide and the incorporated QDs; and the reduction of the dangling bonds of Pb2+ by the sulfur atoms of PbS QDs. Finally, the device performances are highly improved due to the reduced defects and non-radiative recombination. The results show that both open-circuit voltage and fill factor are significantly improved to the high values of 1.13 V and 80%, respectively in CH3 NH3 PbI3 -based PSCs, offering a high efficiency of 20.64%. The QDs incorporation also enhances PSCs' stability benefitting from the induced hydrophobic surface and suppressed iodide mobilization.

Quantum Confinement Effect and Photoenhancement of Photoluminescence of PbS and PbS/MnS Quantum Dots

The quantum confinement effect and photoenhancement of photoluminescence (PL) of lead sulphide (PbS) quantum dots (QDs) and lead sulphide/manganese sulphide (PbS/MnS) core shell QDs capped with thiol ligands in aqueous solution were investigated. From PL results, the presence of MnS shells gives a strong confinement effect which translates to higher emission energy in PbS/MnS core shell QDs. Increasing MnS shell thickness from 0.3 to 1.5 monolayers (ML) causes a blueshift of PL peak energies as the charge carriers concentrated in the PbS core region. Enhancement of the PL intensity of colloidal PbS and PbS/MnS core shell QDs has been observed when the samples are illuminated above the band gap energy, under continuous irradiation for 40 min. Luminescence from PbS QDs and PbS/MnS core shell QDs can be strongly influenced by the interaction of water molecules and oxygen present in aqueous solution adsorbed on the QD surface. However, PbS/MnS core shell QDs with a shell thickness of 1.5 ML did not show a PL peak energy stability as it was redshifted after 25 min, probably due to wider size distribution of the QDs.

Current density improvement of colloidal PbS quantum dot solar cells by adding NaCl in ZnO electron transport layer

In this work, the effect of adding sodium chloride (NaCl) in zinc oxide (ZnO) electron transport layer (ETL) on the photovoltaic performance of lead sulfide (PbS) quantum dot (QD) solar cells is investigated. To elucidate that, PbS QD solar cells with pristine ZnO and NaCl passivated ZnO (ZnO–NaCl) as ETLs are fabricated, respectively. The current density–voltage (J–V)​ measurements are performed. The results show a considerable improvement in the current density of the device with ZnO–NaClas ETL, thus boosting the power conversion efficiency (PCE) from 7.278% to 9.149%. It is demonstrated that NaCl treatment benefits surface defects and series resistance (Rs) reduction in ZnO ETL, enhancing the carrier transport performance of the device. The strategy of adding NaCl in ZnO ETL provides a promising way for pushing solar cell performance to a high level.

Air-stable and ultrasensitive solution-cast SWIR photodetectors utilizing modified core/shell colloidal quantum dots

InGaAs-based photodetectors have been generally used for detection in the short-wave infrared (SWIR) region. However, the epitaxial process used to grow these materials is expensive; therefore, InGaAs-based photodetectors are limited to space exploration and military applications. Many researchers have expended considerable efforts to address the problem of SWIR photodetector development using lead sulfide (PbS) quantum dots (QDs). Along with their cost-efficient solution processability and flexible substrate compatibility, PbS QDs are highly interesting for the quantum-size-effect tunability of their bandgaps, spectral sensitivities, and wide absorption ranges. However, the performance of PbS QD-based SWIR photodetectors is limited owing to inefficient carrier transfer and low photo and thermal stabilities. In this study, a simple method is proposed to overcome these problems by incorporating CdS in PbS QD shells to provide efficient carrier transfer and enhance the long-term stability of SWIR photodetectors against oxidation. The SWIR photodetectors fabricated using thick-shell PbS/CdS QDs exhibited a high on/off (light/dark) ratio of 11.25 and a high detectivity of 4.0 × 1012 Jones, which represents a greater than 10 times improvement in these properties relative to those of PbS QDs. Moreover, the lifetimes of thick-shell PbS/CdS QD-based SWIR photodetectors were significantly improved owing to the self-passivation of QD surfaces.

Charge Transfer from Lead Sulfide Quantum Dots to MoS2 Nanoplatelets

The research interest in the transition metal dichalcogenides (TMD) has been reborn a few years ago. This had happened due to the remarkable properties of monolayered TMD (e.g., high carrier mobility and high exciton binding energy) and due to the development of the exfoliation methods. Photoconductive MoS2-based devices spectral range can be expanded to the NIR by coupling them with PbS QDs. However, this requires extensive knowledge about the charge and energy transfer processes in such systems. In this paper, we investigate charge transfer between PbS QDs and MoS2 nanoplatelets (NPls). Using the PL decay analysis, we show how the charge transfer efficiency changes with the distance between the QDs and NPls, as well as with QD size. Last, we demonstrate that the addition of the MoS2 NPLs increases the photoconductive response for up to an order of magnitude, as compared to the bare QD.

In Vivo Dynamic Monitoring of Bacterial Infection by NIR-II Fluorescence Imaging.

Time window of antibiotic administration is a critical but long-neglected point in the treatment of bacterial infection, as unnecessary prolonged antibiotics are increasingly causing catastrophic drug-resistance. Here, a second near-infrared (NIR-II) fluorescence imaging strategy based on lead sulfide quantum dots (PbS QDs) is presented to dynamically monitor bacterial infection in vivo in a real-time manner. The prepared PbS QDs not only provide a low detection limit (104 CFU mL-1 ) of four typical bacteria strains in vitro but also show a particularly high labeling efficiency with Escherichia coli (E. coli). The NIR-II in vivo imaging results reveal that the number of invading bacteria first decreases after post-injection, then increases from 1 d to 1 week and drop again over time in infected mouse models. Meanwhile, there is a simultaneous variation of dendritic cells, neutrophils, macrophages, and CD8+ T lymphocytes against bacterial infection at the same time points. Notably, the infected mouse self-heals eventually without antibiotic treatment, as a robust immune system can successfully prevent further health deterioration. The NIR-II imaging approach enables real-time monitoring of bacterial infection in vivo, thus facilitating spatiotemporal deciphering of time window for antibiotic treatment.

Tuning the Quantum Dot (QD)/Mediator Interface for Optimal Efficiency of QD-Sensitized Near-Infrared-to-Visible Photon Upconversion Systems.

Lead sulfide (PbS) quantum dots (QDs) have shown promising performance as a sensitizer in infrared-to-visible photon upconversion systems. To investigate the key design rules, we compare three PbS-sensitized upconversion systems using three mediator molecules with the same tetracene triplet acceptor at different distances from the QD. Using transient absorption spectroscopy, we directly measure the triplet energy-transfer rates and efficiencies from the QD to the mediator and from the mediator to the emitter. With increasing distance between the mediator and PbS QD, the efficiency of the first triplet energy transfer from the QD to the mediator decreases because of a decrease in the rate of this triplet energy-transfer step, while the efficiency of the second triplet energy transfer from the mediator to the emitter increases because of a reduction in the QD-induced mediator triplet state decay. The latter effect is a result of the slow rate constant of the second triplet energy-transfer process, which is 3 orders of magnitude slower than the diffusion-limited value. The combined results lead to a net decrease of the steady-state upconversion quantum yield with distance, which could be predicted by our kinetic model. Our result shows that the QD/mediator interface affects both the first and second triplet energy transfer processes in the photon upconversion system, and the QD/mediator distance has an opposite effect on the efficiencies of the first and second triplet energy transfer. These findings provide important insight for the further rational improvement of the overall efficiency of QD-based upconversion systems.

Double‐Layer electron transporting layer for efficient lead sulfide quantum dots solar cells

Herein, for the first time, the role of double-layer electron transporting layer (ETL), i.e. ZnO/SnO 2 on the efficiency of lead sulfide quantum dots solar cells is demonstrated. Using this approach, a device with power conversion efficiency of 10.6% is achieved mainly due to the enhancement of open circuit voltage ( V OC ). The authors reduce the loss-in-potential by 80 mV using ZnO/SnO 2 double-layer ETL.