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Colloidal quantum dots (QDs) are semiconductor nanocrystals (several to tens nm), whose size is smaller than the exciton Bohr radius of the bulk material. QDs exhibit discrete energy levels resulting from quantum confinement effect in all three spatial dimensions, rendering them unique size/composition/shape-dependent optoelectronic properties. Compared to bulk materials, QDs have unique properties such as tunable band gaps, broad absorption spectra, multiple exciton generation and high extinction coefficients. The controlled synthesis of colloidal semiconductor QDs has defined a new way to use them as potential building blocks in multiple emerging technologies such as biomedical labels, thermal sensors, light-emitting diodes, QDs sensitized solar cells (QDSCs), solar-driven photoelectrochemical (PEC) cells for hydrogen (H₂) generation and photodetectors. In this thesis, colloidal bare, doped and core/shell QDs are designed and synthesized with tunable size and narrow size distribution. Subsequently, their structural and optoelectronic properties are investigated systematically. A facile approach was designed for the synthesis of colloidal PbS QDs using thiourea and lead acetate as precursors for sulfur and lead, respectively. The sizes of the PbS QDs could be systematically controlled by simply adjusting the reaction parameters. Then, a Cd post-treatment on the bare PbS QDs via a cation exchange method was performed for increasing the stability of QDs, which is favorable for the fabrication of device under ambient environment. As a proof of concept, as-synthesized PbS QDs were employed as light harvesters for both (i) solar-driven PEC cells for H₂ generation and (ii) QDSCs. A saturated photocurrent density of ~2 mA/cm² under one sun illumination (AM 1.5G, 100 mW/cm²) is observed for PEC device based on PbS QDs synthesized using thiourea, which is comparable with that of PEC device based on PbS QDs synthesized using air-sensitive and unstable bis(trimethylsilyl) sul

Nature is an inexhaustible source of idea and materials. This time, chicken eggshell membrane, a nature product and waste material, has been discovered as a potential sulfur source for the production of sulfide. This is possible because of the presence of sulfur-containing amino acids in the proteins forming its fibers. In the present research eggshell membrane was high-energy ball milled with lead precursor to yield lead sulfide PbS, a semiconductor material suitable for the application in solar cells. Thus, a completely solid-state methodology (mechanochemical synthesis) without the need to use toxic precursors and solvents and evaluated temperatures has been successfully applied. The effect of rotation speed and the type of lead precursor (acetate and nitrate) on the reaction course was investigated. The as-received powders were washed with distilled water, filtered and the content of lead in the filtrate reaction was measured by means of atomic absorption spectrometry. This provided a direct information about the reaction progress (reactants are water-soluble whereas the produced PbS is not). The conversion reached 100 % after 120 min of treatment at 750 rpm, whereas only around 60 %conversion was achieved when milling at 500 rpm. The products were characterized by a vast number of characterization techniques, including XRD, low temperature N2 physisorption, SEM, TEM, XPS and electrochemical impedance spectroscopy using Mott-Schottky analysis. The nanocrystalline character of the products was confirmed by XRD and TEM. At the end, the photocatalytic activity to degrade selected organic dye of the products was tested.

Mine tailings containing trace metals arrived at the Doce River estuary, after the world’s largest mine tailings disaster (the Mariana disaster) dumped approximately 50 million m3 of Fe-rich tailings into the Doce River Basin. The metals in the tailings are of concern because they present a bioavailability risk in the estuary as well as chronic exposure hazards. Trace metal immobilization into sulfidic minerals, such as, pyrite, plays a key role in estuarine soils; however, this process is limited in the Doce River estuarine soil due to low sulfate inputs. Thus, to assess the use of gypsum amendment to induce pyritization in deposited tailings, a mesocosm experiment was performed for 35 days, with vinasse added as carbon source and doses of gypsum (as a sulfate source). Chemical and morphological evidence of Fe sulfide mineral precipitation was observed. For instance, the addition of 439 mg of S led to the formation of gray and black spots, an Fe2+ increase and decrease in sulfides in the solution, an increase in pyritic Fe, and a greater Pb immobilization by pyrite at the end of the experiment. The results show that induced pyritization may be a strategy for remediating metal contamination at the Doce River estuary

Spherical nanoparticles (NPs) of cadmium and lead sulfides (diameter 37 ± 5 and 24 ± 4 nm, respectively) have been found to be cytotoxic for HL-1 cardiomyocytes as evidenced by decrease in adenosine triphosphate–dependent luminescence. Cadmium sulfide (CdS)-NPs were discovered to produce a much greater cytotoxic impact than lead sulphide (PbS)-NP. Given the same dose range, CdS-NP reduced the number of calcium spikes. A similar effect was observed for small doses of PbS-NP. In addition to cell hypertrophy under the impact of certain doses of CdS-NP and PbS-NP, doses causing cardiomyocyte size reduction were identified. For these 3 outcomes, we obtained both monotonic “dose–response” functions (well approximated by the hyperbolic function) and different variants of non-monotonic ones for which we found adequate mathematical expressions by modifying certain models of hormesis available in the literature. Data analysis using a response surface linear model with a cross-term provided new support to the previously established postulate that a diversity of types of joint action characteristic of one and the same pair of damaging agents is one of the important assertions of the general theory of combined toxicity. © The Author(s) 2020.

Steady-state access to intraband transitions in colloidal quantum dots (CQDs), via heavy doping, allows exploiting the electromagnetic spectrum at energies below the band gap. CQD intraband optoelectronics opens up a new path to cheap mid- and long-wavelength infrared photodetectors and light-emitting devices, which today employ mostly epitaxial materials. As a recent field of experimental research, thorough studies of the basic properties of intraband transitions in CQDs are still lacking. In this work, we investigate the size and temperature dependence of the intraband transition in heavily n-doped PbS quantum dot (QD) films. We measure the absorption coefficient of the intraband transition to be in the order of $10^4$ cm$^{-1}$, which is comparable to the value of the interband absorption coefficient. Additionally, we determine the size-dependence of the oscillator strength of the intraband transition. We demonstrate a negative dependence of the intraband energy with temperature, in contrast to the positive dependence of the interband transition., We thank Dr. Iacopo Torre for helpful discussions. The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the “Fondo Europeo de Desarrollo Regional” (FEDER) through grant TEC2017-88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Program for Centres of Excellence, Peer Reviewed, Postprint (published version)

Optical sensing in the mid- and long-wave infrared (MWIR, LWIR) is of paramount importance for a large spectrum of applications including environmental monitoring, gas sensing, hazard detection, food and product manufacturing inspection, and so forth. Yet, such applications to date are served by costly and complex epitaxially grown HgCdTe quantum-well and quantum-dot infrared photodetectors. The possibility of exploiting low-energy intraband transitions make colloidal quantum dots (CQD) an attractive low-cost alternative to expensive low bandgap materials for infrared applications. Unfortunately, fabrication of quantum dots exhibiting intraband absorption is technologically constrained by the requirement of controlled heavy doping, which has limited, so far, MWIR and LWIR CQD detectors to mercury-based materials. Here, we demonstrate intraband absorption and photodetection in heavily doped PbS colloidal quantum dots in the 5-9 µm range, beyond the PbS bulk band gap, with responsivities on the order of 10-4 A/W at 80 K. We have further developed a model based on quantum transport equations to understand the impact of electron population of the conduction band in the performance of intraband photodetectors and offer guidelines toward further performance improvement., I.R. acknowledges support from the Ministerio de Economiá , Industria y Competitividad of Spain via a Juan de la Cierva fellowship. The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the “Fondo Europeo de Desarrollo Regional” (FEDER) through Grant TEC2017- 88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0522). S.C. acknowledge support from a Marie Curie Standard European Fellowship (“NAROBAND”, H2020-MSCA-IF-2016-750600)., Peer Reviewed, Postprint (published version)

To decrease the world’s energy dependence on fossil fuels, energy production and specifically electricity production needs to shift to more sustainable alternatives. One such alternative is solar cells as they directly convert energy emitted from the sun into electricity. Silicon and thin film solar cells which are commercialized today are either expensive to make and rigid, or utilizes rare and toxic materials. This has resulted in an increase in the field of solar cell research to find cheaper alternatives which are also based on abundant materials. Colloidal quantum dot (CQD) solar cells are third generation solar cells which has received much focus in the last decade due to the property of the quantum confinement effects. This makes it possible to increase the band gap by decreasing the size of the crystallites.CQDs made of PbS were in this thesis developed for high PCE (power conversion efficiency), low weight and flexible CQD solar cells. By applying the PbS CQDs on flexible and durable substrates, light weight solar cells with a high power-per-weight of 15.2 W g-1 value were accomplished. Other PbS CQD solar cells were covered and passivated by a mid-high band gap perovskite semiconductor with good lattice matching to facilitate improved stability and PCE, with the latter reaching 10.7 %. By shifting the focus towards more low-toxic and more environmentally friendly materials, materials such as PbS could be phased out. In this thesis, Ag2S and AgBiS2 were investigated as alternatives. By utilizing a heat-up synthesis method for the production of Ag2S CQDs, a proof-of-concept PCE of 0.34 % was accomplished for solar cells based on these CQDs. To improve the PCE, a hot-injection method was utilized to produce Ag2S CQDs with a surface better suited for solar cell applications. This resulted in an improved PCE of 2.2 %. In a final study, AgBiS2 CQDs were investigated by changing the composition of the precursor ratio Ag:Bi:S. The final composition was linearly de

Lead sulfide thin films were grown by means of chemical bath deposition using thermostatically controlled conditions, microwave and ultrasonic irradiation. The film was characterized by means of XRD, SEM and EDX methods. According to XRD deposited film has a cubic structure of PbS. SEM confirmed nanosize nature of thin film that depend on deposition conditions. The dark resistance and photosensitivity of PbS film is shown to correlate with deposition time, concentration of ammonium iodide in reaction mixture, ultrasound and microwave influences. © 2018 Chemical Publishing Co. All rights reserved.

From a niche field over 30 years ago, quantum dots (QDs) have developed into viable materials for many commercial optoelectronic devices. We discuss the advancements in Pb-based QD solar cells (QDSCs) from a viewpoint of the pathways an excited state can take when relaxing back to the ground state. Systematically understanding the fundamental processes occurring in QDs has led to improvements in solar cell efficiency from ~3% to over 13% in 8 years. We compile data from ~200 articles reporting functioning QDSCs to give an overview of the current limitations in the technology. We find that the open circuit voltage limits the device efficiency and propose some strategies for overcoming this limitation., ChemE/Opto-electronic Materials

type:Journal Article, Using spatial energy-level gradient engineering with quantum dots (QDs) of different sizes to increase the generated carrier collection at the junction of a QD heterojunction solar cell (QDHSC) is a hopeful route for improving the energy-conversion efficiency. However, the results of current related research have shown that a variable band-gap structure in a QDHSC will create an appreciable increase, not in the illumination current density, but rather in the fill factor. In addition, there are a lack of studies on the mechanism of the effect of these graded structures on the photovoltaic performance of QDHSCs. This study presents the development of air atmosphere solution-processed TiO2/PbS QDs/Au QDHSCs by engineering the energy-level alignment (ELA) of the active layer via the use of a sorted order of differently sized QD layers (four QD sizes). In comparison to the ungraded device (without the ELA), the optimized graded architecture (containing the ELA) solar cells exhibited a great increase (21.4%) in short-circuit current density (Jsc). As a result, a Jsc value greater than 30 mA/cm2 has been realized in planar, thinner absorption layer (∼300 nm) PbS QDHSCs, and the open-circuit voltage (Voc) and power-conversion efficiency (PCE) were also improved. Through characterization by the light intensity dependences of the Jsc and Voc and transient photovoltage decay, we find that (i) the ELA structure, serving as an electron-blocking layer, reduces the interfacial recombination at the PbS/anode interface, and (ii) the ELA structure can drive more carriers toward the desirable collection electrode, and the additional carriers can fill the trap states, reducing the trap-assisted recombination in the PbS QDHSCs. This work has clearly elucidated the mechanism of the recombination suppression in the graded QDHSCs and demonstrated the effects of ELA structure on the improvement of Jsc. The charge recombination mechanisms characterized in this work would be able to shed ligh, source:DOI: 10.1021/acsami.7b06552

The solubility of iron sulfide and of lead sulfide in water was determined experimentally in the temperature range from 25 to 80 °C and at atmospheric pressure. The solubility of iron sulfide was determined by bringing precipitated iron sulfide in equilibrium with water and determining the concentration of iron ions and of total sulfur after the equilibration. The same method was used for determining the lead sulfide solubility in water. In both cases, a difference between the concentrations of metal ion and of total sulfur was observed. The concentrations were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The time required for equilibration was studied. The particle size distribution was examined to select a proper membrane for separating saturated solution from solid material.

We present in this work density functional theory calculations of the structural and electronic properties of (PbS)n nanoparticles with n=4-32. Particular care has been taken on the correct description of their electronic structure by using a hybrid functional including the spin-orbit coupling effects. We demonstrate that the bonding in PbS nanoparticles is quite different from bulk PbS as the six Pb-S bonds around a single Pb atom are found to have a different character while in bulk PbS all Pb-S distances are equivalent. We also relate the geometric structure to the evolution of the HOMO-LUMO gaps and show how the computed electronic properties strongly depend on the functional used. Finally, based on an extrapolation of our results we predict that to obtain the onset of absorption in the infrared region of the spectrum a cubic nanoparticle of ~1.96 nm side length is needed, a result that is in agreement with existing experimental information

Recently, hybrid graphene–quantum dot systems have attracted increasing attention for the next-generation optoelectronic devices such as ultrafast photo-detectors and solar energy harvesting. In this paper, a novel, one-step, reproducible, and solution-processed method is introduced to prepare hybrid graphene–PbS colloids by employing supercritical ethanol. In the hybrid nanocomposite, PbS quantum dots (~3 nm) are decorated on the reduced graphene oxide (rGO) nanosheets (~1 nm thickness and less than 1 micron lengths). By employing X-ray photoelectron and Raman and infrared spectroscopy techniques, it is shown that the rGO nanosheets are bonded to PbS nanocrystals through carboxylic bonds. Passivation of {111} planes of PbS quantum dots with rGO nanosheets is demonstrated by employing density function theory. Quenching of the photoluminescence emission of PbS nanocrystals through coupling with graphene sheets is also shown. In order to illustrate that the developed preparation method does not impair the quantum efficiency of the PbS nanocrystals, the photovoltaic efficiency of solar cell device is reported and compared with oleic acid-capped PbS colloidal quantum dot solar cells. By employing the “Hall effect” measurement, it is shown that the carrier mobility is significantly increased (by two orders of magnitudes) in the presence of graphene nanosheets.

В данной работе изучались состав, структура и морфология многофазных полупроводниковых пленок свежеосажденного сульфида кадмия и пленок CdS, выдержанных в растворе ацетата свинца Pb(CH3COO)2. Композиции на основе сульфида кадмия, образовавшиеся на межфазной границе CdSтв/Pb2+(aqua), исследовались методами, электронной микроскопии, а также был проведен сравнительный анализ спектров комбинационного рассеяния полученных образцов и индивидуальных сульфидов кадмия и свинца. Впервые показана возможность получения твердых растворов замещения в халькогенидных системах путем ионного обмена на межфазной границе «пленка халькогенида металла – водный раствор»., In this paper we studied the composition, structure and morphology of the multi-phase semiconductor thin films of cadmium sulfide films and CdS, which aged in a solution of lead acetate Pb (CH3COO)2 . The composition based on cadmium sulfide, which formed at the interface CdS(sol)/Pb2 + (aqua), were studied by electron microscopy and comparative analysis of the Raman spectra of the samples. For the first time the possibility of obtaining solid solutions in chalcogenide systems by ion exchange at the interface " metal chalcogenide film - water solution " was shown.

The thermal expansion of a lead sulfide nanofilm produced by chemical bath deposition was determined by X-ray diffraction (XRD). The thickness of the synthesized film was about 100 nm, and the average size of the coherent scattering regions as determined from XRD was about 40 nm. The lattice constant of the PbS nanofilm was measured as a function of the annealing temperature from 293 to 473 K and as a function of the annealing time at a constant temperature of 423 K. The thermal expansion coefficient derived was found almost twice as large as that for coarse-grained PbS. © 2013 Elsevier B.V. All rights reserved. All rights reserved.

We propose a technique for wet-chemical codeposition of lead sulfide and selenide using thiourea and selenourea to form films of PbSe yS 1-y substitutional solid solutions. The synthesized nanocrystalline layers with NaCl (B1) structure simultaneously contain both PbS-based and PbSe-based PbSe yS 1-y solid solutions (0 < y < 0.9). © 2012 Springer Science+Business Media, Inc.

We studied the emission properties of colloidal PbS quantum dots (QDs) (5.3 nm) dispersed on semi-insulating GaAs in the temperature range of 5-300 K by employing Fourier transform infrared photoluminescence spectroscopy. The results reveal that the PbS QDs alter and notably enhance the emission features of the GaAs substrate itself. The dependence of the QD emission peak position on temperature is modeled equivalently well with the well-known empirical Varshni equation and with a relation based on thermodynamics. The work reveals that emission properties of PbS QDs do not follow predictably general rules but are determined sensitively by the preparation method and substrate used., Published in Journal of Applied Physics, 108, 013525 (2010).

Size- and shape-controlled nanocrystal growth is intensely researched for applications including electro-optic, catalytic, and medical devices. Chemical transformations such as cation exchange overcome the limitation of traditional colloidal synthesis, where the nanocrystal shape often reflects the inherent symmetry of the underlying lattice. Here we show that nanocrystals, with established synthetic protocols for high monodispersity, can be templates for independent composition control. Specifically, controlled interconversion between wurtzite CdS, chalcocite Cu2S, and rock salt PbS occurs while preserving the anisotropic dimensions unique to the as-synthesized materials. Sequential exchange reactions between the three sulfide compositions are driven by the disparate solubilites of the metal ion exchange pair in specific coordinating molecules. Starting with CdS, highly anisotropic PbS nanorods are created, which serve as an important material for studying strong 2-dimensional quantum confinement, as well as for optoelectronic applications. Furthermore, interesting nanoheterostructures of CdS|PbS are obtained by precise control over ion insertion and removal.

A highly regular hexapod-like structure of PbS with six symmetric arms has been synthesized by a simple and mild chemical solution route. The hexapod-like PbS structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results show that each arm is perpendicular to the other four, and opposite to the last one. The arms are about 0.3-0.6 mu m long, which have about 40-60 nm tips and 150-200 nm base. And the arm shows an icicle-like structure and some clear steps, and grows along (100) directions. The most possible growth mechanism discussed herein is based on the characterization results. The Raman spectra of the hexapod-like PbS structure were investigated. The results show that our products are sensitive to the laser and can be photodegraded easily.

This review for the first time systematizes the results of our investigations into the influence of magnetic effects on the mechanical properties and the real structure of nonmagnetic crystals. It is found that the preliminary magnetic treatment of alkali halide crystals leads to a decrease in their solubility and a change in the microhardness and yield stress. The magnetic field strongly affects the macroplasticity of LiF, NaCl, and PbS crystals under deformation in a magnetic field. This is accompanied by a change in the shape of stress-strain curves, a shortening of deformation stages, a change in the hardening coefficients, and a decrease in the yield stress. It is revealed that the magnetic effects exhibit threshold behavior. The yield stress is measured as a function of the magnetic induction and the strain rate. It is established that the magnetic and electric fields have a joint effect on the kinetics of plastic deformation. A kinematic model of the macroscopic magnetoplastic effect is proposed. © 2003 MAIK "Nauka/ Interperiodica".