Lead Atoms Research Articles

Positive and Negative Contribution from Lead–Oxygen Groups and Halogen Atoms to Birefringence: A First Principles Investigation

Oxyhalides, containing oxygen and halogen atoms and combining the advantages of oxides and halides in geometry and optical response, have great potential in optical materials. In this study, the electronic structures and the optical properties of the Pb3O2X2 (X = Cl, Br, I) compounds have been investigated using the first principles method. The results show that these compounds have birefringence at 0.076, 0.078, and 0.059 @ 1064 nm, respectively. And, the asymmetric stereochemical active lone pair electrons were found around lead atoms, which were confirmed by the projected density of states, the electronic localization functions, and the crystal orbitals. The contribution of atoms and polyhedra to birefringence was further evaluated using the Born effective charge. The results show that halogen atoms give negative contribution, and lead—oxygen polyhedra give positive contribution. The spin—orbit coupling effect is also investigated, and the downshift of the conduction band and variation in the valence band are found after relevant spin—orbit coupling (SOC), which leads to a reduction in the band gap and birefringence.

Study of electron- and positron-induced elastic scattering cross sections of lead atoms

Study of electron- and positron-induced elastic scattering cross sections of lead atoms

Mechanism of the Anomalous Dependence between Spin-Orbit Coupling and Dimensionality in Lead Halide Perovskites.

The spin-orbit coupling (SOC) effect of lead (Pb) atoms is a consequential attribute of the unique optoelectronic and defect properties of lead halide perovskites (LHPs). It has been found that the SOC effect varies significantly as the structural dimensionality changes with an anomalous dependence; i.e., while the SOC strength monotonically decreases as structural dimensionality decreases from three-dimensional (3D) to two-dimensional (2D) and then to one-dimensional (1D), the zero-dimensional (0D) SOC strength is greater than the 1D SOC strength. The underlying mechanism of such a SOC dimensionality dependence anomaly remains elusive. In this work, we show that Pb 6p energy splitting increases from 3D to 2D and to 1D LHPs due to the increased degree of distortion, leading to a reduced SOC strength. However, the degree of distortion decreases for the 1D to 0D transformation, resulting in reverse SOC enhancement. The mechanism described in this work can be employed to regulate the SOC effect in the design of perovskite materials.

Three pseudo-dimeric lead halide complexes containing derivatives of 8-hydroxyquinoline, Cl2QPbX (X = Br, I), (Cl2Q)4Pb2:Synthesis, crystal structures, and fluorescence spectroscopic properties

Three new complexes, namely (5,7-Dichloro-8-hydroxyquinoline)PbX (X=Br, I) (1, 2) and Pb2(5,7-Dichloro-8-hydroxyquinoline)4 (3), were synthesized through solvent evaporation at ambient temperature. The crystal structures and fluorescence emission properties of these complexes were systematically investigated. An analysis using single crystal X-ray diffraction revealed that complexes 1-3 form pseudo-dimeric structures through the interaction between lead and neighboring oxygen via secondary contacts. A comparison between the structures of complex 2 and [Pb(μ-Q)I]2, a complex of PbI2 with 8-hydroxyquinoline, showed that the coordination polyhedron changed from a triangular pyramid to a distorted tetrahedron. This change may be attributed to the site resistance effect of the chlorine substituents coordinated to the quinoline ring. Complex 3 has a layered structure formed through secondary contacts and intramolecular hydrogen bonding C-H⋯O and C-H⋯Cl among the lamellar molecules. The maximum emission peak at 489 nm, 505 nm, and 543 nm for complex 1-3 can be assigned to the ligand-to-metal charge transfer (LMCT). The maximum emission peaks were red-shifted by 22 nm, 38 nm, and 75 nm, respectively, compared to the ligand. The number of ligands increases the conformational rigidity of the structure and the electron density on lead atoms causing the molecular structure to change, the energy alters, and the fluorescence peaks to move in the long-wave direction.

Effect of the Diffusion of Copper Atoms in Polycrystalline CdTe Films Doped with Pb Atoms

The process of diffusion of labeled copper atoms in p-CdTe<Pb> coarse-block films with a columnar grain structure has been studied. The CdTe<Pb> film is a p-type semiconductor, where an increase in the Pb concentration in the composition of the CdTe films increases the resistivity ρ of the structure. When the Pb concentration in CdTe changes from 1018 to 5·1019 cm-3, the hole concentration decreases by more than 3 orders of magnitude at a constant operating level depth of EV + (0.4 ± 0.02) eV. This may indicate that the concentration of acceptor defects, which are formed in the films due to self-compensation upon doping with a PbCd donor, exceeds the number of the latter. Electrical measurements by the Hall method were carried out at a direct current and a temperature of 300 K. As a result, an increase in the temperature of films on a Mo-p-CdTe<Pb> substrate during annealing affects the electrical parameter of charge carrier mobility µ, it decreases significantly. X-ray diffraction analysis showed that on the diffraction patterns of samples of p-CdTe<Pb> films, all available reflections correspond to the CdTe phase and up to х = 0.08 do not contain reflections of impurity phases and have a cubic modification. Based on the results of the calculation, it was established that the low values of the diffusion coefficient of Cu atoms are due to the formation of associates of the A type , which are directly dependent on the concentration of atoms. Diffusion length Ln and lifetime τn of minority current carriers in large-block p-type cadmium telluride films, which can also be controlled by introducing lead atoms into cadmium telluride.

Effect of crystal structure on K shell binding energy of lead, mercury and tungsten using bremsstrahlung radiation

The K shell binding energies of lead, mercury, and tungsten in their pure elemental form and in some of their compounds have been measured for the first time by adopting a novel method. The method involves a weak beta source, an external bremsstrahlung converter, element and compound targets, and a high-resolution, high-purity germanium detector coupled to 16K multichannel analyzer. Continuous external bremsstrahlung photons produced by the interaction of beta particles from a 90Sr-90Y radioactive source with an iron foil are allowed to pass through the elemental and compound targets of lead, mercury, and tungsten. The spectrum of transmitted external bremsstrahlung photons is measured with a high-resolution high purity germanium detector spectrometer. The transmitted spectrum shows a sudden drop in intensity at K shell binding energy of the target. Such a sudden drop, which is due to the onset of the K shell photoelectric effect, has been used to determine the K shell binding energies. It has been investigated that the shifts in the K shell binding energies due to chemical environment of lead, mercury, and tungsten atoms is attributed to crystal structure.

Detection of high energy X-ray radiation following muon captures on Pb

Low background HPGe detector, shielded by lead, was used to collect background gamma spectra for more than 180 days. Three lines, originating from transitions of muons captured in orbitals of lead atoms were for the first time recognized in background spectra. Relative intensities of detected transitions were calculated and compared with the theoretical prediction.

Perovskite Films Regulation via Hydrogen-Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long-term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and carbonyl groups. The chemical bonding between polymer and perovskite could increase the growth activation energy of perovskite film and promote the preferential growth of high-quality perovskite film. Owing to the low defect density and gradient energy-level alignment, the corresponding device exhibited a champion efficiency of 23.10 %. Furthermore, due to the formation of the hydrogen-bonded polymer network in the perovskite film, the target devices demonstrated excellent air stability and enhanced flexibility for the flexible PSCs. More importantly, the polymer network could coordinate with Pb2+ ions, immobilizing lead atoms to reduce their release into the environment. This strategy paves the way for the industrialization of high-performance flexible PSCs.

Perovskite Films Regulation via Hydrogen‐Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long‐term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and carbonyl groups. The chemical bonding between polymer and perovskite could increase the growth activation energy of perovskite film and promote the preferential growth of high‐quality perovskite film. Owing to the low defect density and gradient energy‐level alignment, the corresponding device exhibited a champion efficiency of 23.10 %. Furthermore, due to the formation of the hydrogen‐bonded polymer network in the perovskite film, the target devices demonstrated excellent air stability and enhanced flexibility for the flexible PSCs. More importantly, the polymer network could coordinate with Pb2+ ions, immobilizing lead atoms to reduce their release into the environment. This strategy paves the way for the industrialization of high‐performance flexible PSCs.

Enhanced photostability of multication lead halide perovskites through the use of azaadamantane-based modifiers

Complex lead halides incorporating simultaneously a few univalent cations such as cesium (Cs+), methylammonium (MA+) and formamidinium (FA+) represent highly promising materials for perovskite solar cells, delivering record-high power conversion efficiencies. Unfortunately, these materials demonstrate insufficient stability, which limits their practical implementation; therefore, improving the photochemical and thermal stability of multication lead halide perovskites is an urgent task that needs to be addressed to achieve sufficiently long operational lifetimes of perovskite solar cells to facilitate their commercial real-life applications. Herein, we present a comparative study of two azaadamantane-based molecular modifiers as stabilizing additives for Cs0.10MA0.15FA0.75PbI3 and Cs0.12FA0.88PbI3 perovskite formulations. An iodide of N-methylated 1,3,5,7-tetraazaadamantane known as urotropine (MAdI) showed a modest stabilizing effect in Cs0.10MA0.15FA0.75PbI3, though it stabilized effectively Cs0.12FA0.88PbI3. On the contrary, 4,6,10-trihydroxy-3,5,7-trimethyl-1,4,6,10-tetraazaadamantane hydrochloride (NAdCl) strongly enhanced the stability of both lead halide perovskites and prevented the formation of metallic lead Pb0 as a photolysis product. Different stabilizing effects caused by MAdI and NAdCl were related to their different localization within the perovskite films, as evidenced by nanoscale infrared (IR) s-SNOM microscopy. Density functional theory (DFT) calculations confirmed the enhanced stability granted by NAdCl by demonstrating a much higher adsorption energy towards undercoordinated lead atoms on the surface of the perovskite. Finally, the optimal molecular modification of Cs0.10MA0.15FA0.75PbI3 and Cs0.12FA0.88PbI3 films with azaadamantanes made them completely tolerant to light and heat within at least 5000 and 16 000 h of aging, thus setting new perovskite stability records and presenting the newly-developed material formulations as highly promising absorbers for efficient and stable perovskite solar cells.

Lead Detection in a Gig-Lox TiO2 Sponge by X-ray Reflectivity.

The importance of lead analysis in environmental matrices becomes increasingly relevant due to the anthropogenic spread of toxic species in nature. Alongside the existing analytical methods to detect lead in a liquid environment, we propose a new dry approach for lead detection and measurement based on its capture from a liquid solution by a solid sponge and subsequent quantification based on X-ray analyses. The detection method exploits the relationship between the electronic density of the solid sponge, which depends on the captured lead, and the critical angle for total reflection of the X-rays. For this purpose, gig-lox TiO2 layers, grown by modified sputtering physical deposition, were implemented for their branched multi-porosity spongy structure that is ideal for capturing lead atoms or other metallic ionic species in a liquid environment. The gig-lox TiO2 layers grown on glass substrates were soaked into aqueous solutions containing different concentrations of Pb, dried after soaking, and finally probed through X-ray reflectivity analyses. It has been found that lead atoms are chemisorbed onto the many available surfaces within the gig-lox TiO2 sponge by establishing stable oxygen bonding. The infiltration of lead into the structure causes an increase in the overall electronic density of the layer and, thus, an increment of its critical angle. Based on the established linear relationship between the amount of lead adsorbed and the augmented critical angle, a standardized quantitative procedure to detect Pb is proposed. The method can be, in principle, applied to other capturing spongy oxides and toxic species.

Ultra-high-efficiency capture of lead ions over acetylenic bond-rich graphdiyne adsorbent in aqueous solution

A satisfactory material with high adsorption capacity is urgently needed to solve the serious problem of environment and human health caused by lead pollution. Herein, hydrogen-substituted graphdiyne (HsGDY) was successfully fabricated and employed to remove lead ions from sewage and lead-containing blood. The as-prepared HsGDY exhibits the highest adsorption capacity of lead among the reported materials with a maximum adsorption capacity of 2,390 mg/g, i.e., ~five times larger than that of graphdiyne (GDY). The distinguished hexagonal hole and stack mode of HsGDY allows the adsorption of more lead via its inner side adsorption mode in one single unit space. In addition, the Pb 6s and H 1s hybridization promotes the strong bonding of lead atom adsorbed at the acetylenic bond of HsGDY, contributing to the high adsorption capacity. HsGDY can be easily regenerated by acid treatment and showed excellent regeneration ability and reliability after six adsorption-regeneration cycles. Langmuir isotherm model, pseudo second order, and density functional theory (DFT) demonstrated that the lead adsorption process in HsGDY is monolayer chemisorption. Furthermore, the HsGDY-based portable filter can handle 1,000 μg/L lead-containing aqueous solution up to 1,000 mL, which is nearly 6.67 times that of commercial activated carbon particles. And, the HsGDY shows good biocompatibility and excellent removal efficiency to 100μg/L blood lead, which is 1.7 times higher than that of GDY. These findings suggest that HsGDY could be a promising adsorbent for practical lead and other heavy metal removal.

Thiourea-Derived Single-Source Molecular Precursor For Spin-Coated PbS Thin Films.

In search of a suitable single-source precursor for the deposition of nanostructured PbS thin films at moderate temperatures under ambient conditions, we have synthesized the ligand N-(thiomorpholine-4-carbothioyl)benzamide and its corresponding lead(II) complex. The structures of both compounds were determined by single-crystal X-ray diffraction. In the complex, two ligands coordinate to a lead(II) atom in hemi-directed geometry through S and O atoms. Secondary intermolecular Pb⋅⋅⋅S interactions group the complexes into pairs. As bulk powders, both the ligand and complex show nominal composition and purity as evidenced by elemental analysis, 1 H NMR and IR spectroscopy. Thermal analysis of the lead(II) complex was carried out to understand its thermal decomposition behaviour for establishing a thin film fabrication protocol. Thin films of phase-pure PbS were fabricated using this new molecular precursor at the comparatively low annealing temperature of 250 °C. The film showed nanoparticles with cuboidal morphology and a blue-shifted optical absorption.

Electronic structures and molecular dynamics of gadolinium-doped FAPbI3 perovskite crystals

The additive effect of a gadolinium ion into a formamidinium lead iodide (FAPbI3) perovskite crystal on electronic structures and molecular dynamics was investigated for improving photovoltaic performance with stability. The electronic structures, band structure, partial density of state, and molecular dynamics were determined by first-principles calculation. The band distribution and charge transfer between the 5d orbital of the gadolinium atom, the 5p orbital of the iodine atom, and the 6p orbital of the lead atom promoted the carrier generation and diffusion related to short-circuit current density. The enthalpy and kinetic energy prompted stabilization of the gadolinium-doped crystal with a slight distortion of coordination structure, as compared with the decomposition of the FAPbI3 crystal. Diffusion coefficients of iodine and lead ions in the FAPbI3 crystal with defect were increased, predicting decomposition. The gadolinium-doped FAPbI3 perovskite crystal has great potential for applications in photovoltaic devices by improving photovoltaic performance.

Manipulating Ionic Behavior with Bifunctional Additives for Efficient Sky‐Blue Perovskite Light‐Emitting Diodes

AbstractPerovskite Light‐emitting diodes (PeLEDs) have emerged as a promising technique for future high‐definition displays due to their outstanding electroluminescent characters. However, the development of blue PeLEDs toward practical applications is seriously hindered by their inferior performance, which mainly arises from the detrimental halide ionic behavior and thus severe nonradiative recombination in mixed‐halide blue perovskite materials. Herein, efficient sky‐blue PeLEDs featuring spectrally stable emission at 483 nm are realized by employing bifunctional passivators of Lewis‐base benzoic acid anions and alkali metal cations to simultaneously passivate the under‐coordinated lead atoms and suppress halide ion migration. A decent external quantum efficiency (EQE) of 16.58% and a maximum EQE of 18.65% are achieved, which is further boosted to 28.82% through the optical outcoupling enhancement. This work demonstrates unique insight into the generality and individuality of this category of benzoates and puts forward a feasible guidance in choosing appropriate additives for efficient perovskite materials.

Rational design of Lewis base molecules for stable and efficient inverted perovskite solar cells.

Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.5 illumination at the maximum power point and at ~40°C for >3500 hours. DPPP-treated devices showed a similar increase in PCE after being kept under open-circuit conditions at 85°C for >1500 hours.

Investigating the Potential of Alkali Metal Plumba-closo-Dodecaborate (B11H11Pb2–) Salts as Solid-State Battery Electrolytes

Metal dodecaborate salts have been identified as a new class of ion conductors that are highly tunable. A [B–H] unit within the dodecaborate anion can be replaced with a Pb atom to create a dipole and anisotropy within the anion to tune the crystal structure of alkali metal salts, enhancing ion conductivity for solid-state electrolyte (SSE) applications in batteries. Li2B11H11Pb·xH2O shows superionic conductivity up to ∼7 mS cm–1 at 120 °C, proving it comparable to state-of-the-art LiCB11H12 at these temperatures. Dehydration of the Li salt occurs above 120 °C, causing changes in the crystal structure and a decrease in the ion conductivity. Na2B11H11Pb·xH2O shows modest ion conductivity (0.01 mS cm–1 at 170 °C), whereas the potassium salt shows conductivities below 1 × 10–5 mS cm–1. The B11H11Pb2– analogues are proposed to be inferior ion conductors to the CB11H12– varieties due to the divalent B11H11Pb2– anion causing stronger bonding between the cation and anion, possibly higher energy required to move from position to position within the crystal structure. Despite this, the insertion of a lead atom into the dodecaborate cage shows promise in allowing high ion conductivity in the solid state.

Broadband emission originating from the stereochemical expression of 6s2 lone pairs in two-dimensional lead bromide perovskites.

The stereochemical expression of the 6s2 lone pair on the lead atom has a significant impact on the crystal structures and physical properties of lead halide perovskites. Two-dimensional (2D) lead bromide perovskites often exhibit a broadband emission, yet the structural origin of the broadband emission has been under debate. Here, we report the synthesis and characterization of a 2D lead bromide hybrid (4-chlorophenylammonium)2PbBr4 that consists of a combination of the octahedral unit PbBr6 and the rarely observed capped octahedral unit PbBr7 through corner-sharing and edge-sharing linkages. The seven-coordination geometry indicates a strong stereo-active lone pair on the Pb2+ cation. By comparing this structure with two representative 2D perovskites, (benzylammonium)2PbBr4 and (4-aminotetrahydropyran)2PbBr4, we establish how the lone pair expression affects the local coordination geometry of the Pb2+ cation and the resulting optical and electronic properties. As the Pb-Br bond length increases, the lone pair expression leads to off-centering displacement of Pb2+ within the octahedra and then the formation of seven-coordination capped octahedra. Density functional theory calculations indicate that the off-centering distorted octahedra and capped octahedra are due to the asymmetric distribution of the Pb electrons that have both s and p orbital characteristics. Spectroscopic studies show the photoluminescence spectra evolving from narrowband emission to broadband emission with increasing LPE, as well as softer and more anharmonic lattice vibrations that facilitate exciton self-trapping. Our results demonstrate that lone pairs could be a powerful design rule for developing light emitting materials.

A moderate intensity ligand works best: a theoretical study on passivation effects of pyridine-based molecules for perovskite solar cells.

Improving battery stability while maintaining high photoelectric conversion efficiency remains the bottleneck in the current development of perovskite solar cells (PSCs). Three π-conjugated pyridine-based molecules, pyridine (Py), bipyridine (Bpy), and terpyridine (Tpy), were adopted to passivate the PSCs in recent experiments (J. Chen, S.-G. Kim, X. Ren, H. S. Jung and N.-G. Park, J. Mater. Chem. A, 2019, 7, 4977-4987; J. Zhang, J. Duan, Q. Zhang, Q. Guo, F. Yan, X. Yang, Y. Duan and Q. Tang, Chem. Eng. J., 2022, 431, 134230), in which Bpy works best in terms of photovoltaic properties and moisture tolerance. In this work, based on density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, we demonstrate that Bpy displays the least structural fluctuation when adsorbed on the perovskite surface, enlarges the bandgap suppressing electron-hole recombination, and exhibits remarkable shielding effects against moisture. The appropriate anchoring ability of Bpy retains robust binding strength and preferable charge transfer ability compared to Py at the interfaces between the passivation molecules (PMs) and MAPbI3. In contrast, although Tpy possesses the strongest charge-transfer capability, it introduces midgap states owing to intense electronegativity, providing additional pathways for nonradiative charge relaxation. Besides, Tpy triggers rapid diffusions of water and larger atomic fluctuations, destroying the structures of the perovskite through the removal of lead atoms. Our computational results not only rationalize the experimental observations but also provide valuable guidance at the atomic level to design novel PMs that endow PSCs with outstanding photovoltaic performance as well as stability against moisture.

Exo‐ and endo‐Isomers of Plumbylenes Supported by 1,3‐Diethers of Calix[4]arene

AbstractCalix[4]arene‐plumbylene complexes Pb[Calixt‐Bu(O)2(OR)2], where R=benzyl, 9‐fluorenyl, SitBuMe2, and SiiPr3, have been synthesized by the reaction of Lappert's plumbylene Pb[N(SiMe3)2]2 with the corresponding 1,3‐diethers of calix[4]arene. The products have been fully characterized by 1H, 13C{1H}, and 207Pb NMR spectroscopy, elemental analysis, and X‐ray diffraction analysis. The products adopt two different forms depending on the R groups: the alkyl derivatives were obtained as exo‐isomers in which the lead atom resides outside the cavity of the calix[4]arene, while the silyl derivatives were isolated as endo‐isomers where the lead atom is situated inside the cavity. X‐ray diffraction studies revealed that the lead(II) atoms in the exo‐ and endo‐isomers are coordinated by the ethereal oxygen atoms (OR) and the aromatic rings (ArOR), respectively, which are maintained in solution as evidenced by 207Pb NMR studies.