Small Activation Energy Research Articles

Sonochemical synthesis of mesoporous ZnyCd1-yS quantum dots: Composition-dependent optical, electrical, dielectric, and hydrogen-generation characteristics

Mesoporous ZnyCd1-yS quantum dots (QDs) with mixed cubic–hexagonal phases prepared by sonochemical technique at varying Zn content. Incorporating Zn ions in the CdS lattice reduced the crystalline size and enhanced the corresponding surface areas at increasing Zn contents. The increase of Zn content in ZnyCd1-yS QDs increased the bandgap from 2.52 eV to 3.83 eV and enhanced the corresponding Urbach energy from 72 meV to 279 meV. ZnyCd1-yS QDs exhibited small electrical activation energies ranging from 249 mV to 361 mV. The effect of Zn content on the catalytic activity of ZnyCd1-yS QDs toward hydrogen production through NaBH4 hydrolysis was investigated at different temperatures. Ternary alloys ZnCdS QDs exhibited higher catalytic activity than pure ZnS and CdS QDs, with Zn0·5Cd0·5S QDs displaying the highest hydrogen generation rate of 96 mL∙min−1 g−1. The increase of reaction temperature from 30 °C to 60 °C enhanced the rate constant of hydrogen production from 0.071 to 0.36 min−1. Based on the pseudo-first-order equation, the estimated apparent activation energy of Zn0·5Cd0·5S QDs was 45.3 kJ mol−1. Overall, the obtained results underscored the potential of ZnyCd1-yS QDs as promising catalysts for hydrogen generation.

A Common Bottleneck for Metal Oxidation by Molecular Oxygen Across Size Regimes: Kinetics of Atomic Lanthanide Cations (La+-Lu+) with O2.

Kinetics of the lanthanide cations (Ln+ = La+-Lu+ excluding Pm+) reacting with molecular oxygen were measured in a selected-ion flow tube apparatus from 300 to 600 K. Where exothermic, these reactions occur efficiently, producing LnO+ + O. The reactions display positive temperature dependences consistent with Arrhenius equation behavior and show small activation energies (0-2 kJ mol-1) that are strongly correlated to promotion energies of the Ln+ atoms. Reanalysis of literature data on neutral Ln + O2 reactions show a similar correlation with slightly larger activation energies (0-10 kJ mol-1). The data are explained by a common mechanism controlling oxidation by molecular oxygen in these systems, as well as in gas-phase reactions of transition metal and posttransition metal cluster anions, neutral clusters deposited on surfaces, and for oxygen incident on metal surfaces. It is posited that across these systems, the height of an early barrier along the reaction coordinate is predictable based on knowledge of the electronic states of the reactants and may be used to either promote or inhibit oxygen activation.

Catalytic mechanism of Nb2O5 and Ni on hydrogen storage properties of CeMg12-type alloy for automatic weather station emergency fuel cell

In this paper, CeMg12/Ni/Nb2O5 was prepared by mechanical ball milling technology for the sake of probing into the impact of Ni and Nb2O5 on microstructure and hydrogen sorption properties of alloys. The microstructure research results indicate that adding Nb2O5 can promote the formation of nanocrystal structure; through ball milling the Nb2O5 dispersed on the surface of alloy particles uniformly enhances the surface activity of the alloy and improves the hydrogen absorption and releasing kinetics of the alloy. The research on hydrogen absorption performance shows that the addition of Nb2O5 can significantly increase the hydrogen release platform pressure of the alloy hydride, the enthalpy value of hydrogen releasing process drops from 74.82 kJ/mol to 71.07 kJ/mol when the content of Nb2O5 is increased from 0 wt% to 9 wt%, the above qualitative and quantitative discussion further proves that Nb2O5 is beneficial for amending the thermodynamic stability of alloy hydride. Besides, adding Nb2O5 can remarkably reduce the hydrogen dissociation activation energy of experimental alloy hydride, ameliorating the dynamic performances of hydrogen release. The alloy with 9 wt% Nb2O5 has the smallest activation energy and the best performances of hydrogen release.

Cation vacancy modulated Cu3P-CoP heterostructure electrocatalyst for boosting hydrogen evolution at high current densities and coupling Zn-H2O battery

Exploiting highly efficient, cost-effective and stable electrocatalysts is key to decreasing hydrogen evolution reaction (HER) kinetics energy barrier. Herein, the alkaline HER kinetics energy barrier can greatly reduce by the joint strategies of the cation vacancy and heterostructure engineering, which is seldom explored and remains ambiguous. In this study, an efficient and stable copper foam-supported Cu3P-CoP heterostructure electrocatalyst with cation vacancy defects (defined as Cu3P-CoP-VAl/CF) was designed for HER via the successive coprecipitation, electrodeposition, alkali etching and phosphorization treatments. As anticipated, the as-obtained Cu3P-CoP-VAl/CF electrocatalyst reveals a remarkable catalytic activity for HER with a low overpotential of 205 mV at a current density of 100 mA·cm−2, a high turnover frequency value of 1.05 s−1 at an overpotential of 200 mV and a small apparent activation energy (Ea) of 9 kJ·mol−1, while shows superior long-term stability at large current densities of 100 and 240 mA·cm−2. Systematic experiment and characterization data demonstrate that the formed cation vacancy could optimize the Ea, leading to the decrease of the kinetic barriers of Cu3P-CoP/CF heterostructure, as well as the established heterogeneous interface induced a synergistic effect between biphasic components on boosting the kinetics toward HER. The results of density functional theory disclose that the synergistic effect of Cu3P-CoP heterostructure could decrease the energy barrier and optimize Gibbs free energy of hydrogen adsorption, resulting in the enhancement of intrinsic catalytic activity of Cu3P-CoP-VAl/CF. More significantly, the alkali-cell assembled by Cu3P-CoP-VAl/CF (cathode) and RuO2/CF (anode) behaves outstanding water splitting performance, delivering a current density of 10 mA·cm−2 at a relatively small applied voltage of 1.58 V, along with encouraging long-term durability. In addition, the alkaline Zn-H2O battery with Cu3P-CoP-VAl/CF as the cathode has been fabricated for the simultaneous generation of electricity and hydrogen, which displays a large power density of up to 4.1 mW·cm−2. The work demonstrates that rational strategy for the design of competent electrocatalysts can effectively accelerate the kinetics of HER, which supplies valuable insights for practical applications in overall water splitting.

Experimental Observation of a New Attenuation Mechanism in hcp‐Metals That May Operate in the Earth's Inner Core

AbstractSeismic observations show the Earth's inner core has significant and unexplained variation in seismic attenuation with position, depth and direction. Interpreting these observations is difficult without knowledge of the visco‐ or anelastic dissipation processes active in iron under inner core conditions. Here, a previously unconsidered attenuation mechanism is observed in zinc, a low pressure analog of hcp‐iron, during small strain sinusoidal deformation experiments. The experiments were performed in a deformation‐DIA combined with X‐radiography, at seismic frequencies (∼0.003–0.1 Hz), high pressure and temperatures up to ∼80% of melting temperature. Significant dissipation (0.077 ≤ Q−1(ω) ≤ 0.488) is observed along with frequency dependent softening of zinc's Young's modulus and an extremely small activation energy for creep (⩽7 kJ mol−1). In addition, during sinusoidal deformation the original microstructure is replaced by one with a reduced dislocation density and small, uniform, grain size. This combination of behavior collectively reflects a mode of deformation called “internal stress superplasticity”; this deformation mechanism is unique to anisotropic materials and activated by cyclic loading generating large internal stresses. Here we observe a new form of internal stress superplasticity, which we name as “elastic strain mismatch superplasticity.” In it the large stresses are caused by the compressional anisotropy. If this mechanism is also active in hcp‐iron and the Earth's inner‐core it will be a contributor to inner‐core observed seismic attenuation and constrain the maximum inner‐core grain‐size to ≲10 km.

Efficient search for acetic acid synthesis pathway based on the bond disconnection process on Rh surface and Rh/metal oxide interface

The interfacial structure between Rh and the metal oxide support (or promoter) is thought to play an essential role in the synthesis of C2-oxygenated compounds such as acetic acid (CH3COOH). However, due to the complexity of the interface structure, the CH3COOH synthesis pathway has yet to be explored theoretically at the metal/metal oxide interface. In this study, we examined the CH3COOH synthesis pathway at the Rh surface and Rh/metal oxide interface based on the systematic investigation of bond disconnection of the CH3COOH molecule. First, CH3COOH synthesis pathways that include small activation energy Ea(c) were explored on the Rh(111) and it was shown that the reaction pathways CH + CO(H) → CHCO(H) → CH2CO(H) → CH3COH → CH3COOH were found [the rate-limiting step (RLS) is the C=O bond connection with Ea(c) = 1.41 eV]. After that, the CH3COOH synthesis pathway at the Rh/ZrO2 interface was investigated, and it was found that the CH3COOH synthesis pathway via the acetyl (CH3CO) generated from Rh–CH3 and Rh–CO with an oxygen atom in Rh–CO interacted with Zr cation (the RLS was the C–C bond connection with Ea(c) = 0.73 eV). This study provides guidelines for the design of a rational active metal/metal oxide interface for C2 oxygenates synthesis.

High capacity hydrogen storage structure based on a two-dimensional material (Ga2C6) with strong adsorption properties

The use of solid-state devices is a promising approach to address the current technological requirements for sustainable clean energy applications. Within this context, it has become apparent that density functional theory (DFT) has emerged as a powerful tool to study intrinsic electronic characteristics and shows great potential to lead the way to novel materials exploration. Here, we have investigated H2 adsorption on Ga2C6 monolayer, a prospective model for the storage of H2 molecule because of its structural stability. The hydrogen molecules favor being adsorbed at the carbon hexagon center with a binding energy of 0.39 eV. The thermodynamic stability of the Ga2C6 monolayer upon adsorption of 22H2 molecules was evaluated at room temperature using ab-initio molecular dynamics (AIMD) simulations. It is found from the electronic structure analysis that the semiconducting Ga2C6 sheet maintain its behavior after 22H2 molecules were adsorbed. Owing to the small activation energy of about 0.0198 eV, the process of H2 molecule migration at the surface easy proceeds. This investigation demonstrates a strong (GC) gravimetric capacity around 9.65 wt%, and a desorption temperature (TD) around 213.68 K. The above findings imply that the Ga2C6 monolayer may serve as a suitable medium for hydrogen adsorption.

Molecular motion of a nanoscopic moonlander via translations and rotations of triphenylphosphine on graphite

Mass transport at surfaces determines the kinetics of processes such as heterogeneous catalysis and thin-film growth, with the diffusivity being controlled by excitation across a translational barrier. Here, we use neutron spectroscopy to follow the nanoscopic motion of triphenylphosphine (P(C6H5)3 or PPh3) adsorbed on exfoliated graphite. Together with force-field molecular dynamics simulations, we show that the motion is similar to that of a molecular motor, i.e. PPh3 rolls over the surface with an almost negligible activation energy for rotations and motion of the phenyl groups and a comparably small activation energy for translation. While rotations and intramolecular motion dominate up to about 300 K, the molecules follow an additional translational jump-motion across the surface from 350-500 K. The unique behaviour of PPh3 is due to its three-point binding with the surface: Along with van der Waals corrected density functional theory calculations, we illustrate that the adsorption energy of PPh3 increases considerably compared to molecules with flat adsorption geometry, yet the effective diffusion barrier for translational motion increases only slightly. We rationalise these results in terms of molecular symmetry, structure and contact angle, illustrating that the molecular degrees of freedom in larger molecules are intimately connected with the diffusivity.

Redirecting the electron flow to coordinate oxidation and reduction reactions for efficient photocatalytic H2O2 production

Energy-efficient photocatalytic production of H2O2 from water holds the potential to replace the anthraquinone process. However, the impracticality of oxygen bubbling in such processes necessitates addressing the H2O2 production in oxygen-deficient environments. Here, we demonstrated the generation of singlet oxygen (1O2) as a highly active water oxidation derivative that redirects the electron flow for H2O2 production in oxygen-deficient environments. Ground-state oxygen was in-situ generated on photocatalysts and undergoes transition to 1O2, surpassing other competitive electron-consuming reactions. Self-generated 1O2 undergoes preferential photo-reduction to H2O2, benefiting from a small activation energy (0.2 eV), facilitated electron trapping rate, adjacent oxidation/reduction sites and suppressed competitive energy transfer from excited-states to air 3O2. A remarkable solar-to-chemical conversion (SCC) efficiency of 0.25 % was obtained for H2O2 generation in oxygen-deficient conditions. This work unveils a novel concept of redirecting electron flow towards H2O2 production, taking advantage of highly active in-situ generated 1O2.

Elucidating the Role of Ligand Engineering on Local and Macroscopic Charge‐Carrier Transport in NaBiS2 Nanocrystal Thin Films

AbstractTernary chalcogenides have emerged as potential candidates for ultrathin photovoltaics, and NaBiS2 nanocrystals (NCs) have gained appeal because of their months‐long phase‐stability in air, high absorption coefficients >105 cm−1, and a pseudo‐direct bandgap of 1.4 eV. However, previous investigations into NaBiS2 NCs used long‐chain organic ligands separating individual NCs during synthesis, which severely limits macroscopic charge‐carrier transport. In this work, these long‐chain ligands are exchanged for short iodide‐based ligands, allowing to understand the macroscopic charge‐carrier transport properties of NaBiS2 and evaluate its photovoltaic potential in more depth. It is found that ligand exchange results in simultaneous improvements in intra‐NC (microscopic) and inter‐NC (macroscopic) mobilities, while charge‐carrier localization still takes place, which places a fundamental limit on the transport lengths achievable. Despite this limitation, the high absorption coefficients enable ultrathin (55 nm thick) solar absorbers to be used in photovoltaic devices, which have peak external quantum efficiencies > 50%. In addition, temperature‐dependent transient current measurements uncover a small activation energy barrier of 88 meV for ion migration, which accounts for the strongly hysteretic behavior of NaBiS2 photovoltaic devices. This work not only reveals how the charge‐carrier transport properties of NaBiS2 NCs over several length and time scales are influenced by ligand engineering, but also unveils the facile ionic transport in this material, which limits the potential of NaBiS2 in photovoltaics. On the other hand, the discovery shows that there are opportunities to use this material in memristors, electrolytes, and other applications requiring ionic conduction.

Temperature Dependence of Charge Transport Properties of Quasi-2D Chiral Perovskite Thin-Film Field-Effect Transistors.

Chiral halide perovskite materials promise both superior light response and the capability to distinguish circularly polarized emissions, which are especially common in the fluorescence spectra of organic chiral materials. Herein, thin-film field-effect transistors (FETs) based on chiral quasi-two-dimensional perovskites are explored, and the temperature dependence of the charge carrier transport mechanism over the broad temperature range (80-300 K) is revealed. A typical p-type charge transport behavior is observed for both left-handed (S-C6H5(CN2)2NH3)2(CH3NH3)n-1PbnI3n+1 and right-handed (R-C6H5(CN2)2NH3)2(CH3NH3)n-1PbnI3n+1 chiral perovskites, with maximum carrier mobilities of 1.7 × 10-5 cm2 V-1 s-1 and 2.5 × 10-5 cm2 V-1 s-1 at around 280 K, respectively. The shallow traps with smaller activation energy (0.03 eV) hinder the carrier transport over the lower temperature regime (80-180 K), while deep traps with 1 order of magnitude larger activation energy than the shallow traps moderate the charge carrier transport in the temperature range of 180-300 K. From the charge carrier mechanism point of view, impurity scattering is established as the dominant factor from 80 K until around 280 K, while phonon scattering becomes predominant up to room temperature. Responsivities of 0.15 A W-1 and 0.14 A W-1 for left-handed and right-handed chiral perovskite FET devices are obtained.

In-situ crosslinking of a novel conjugated dialkynyl-based polyimide for high performance carbon molecular sieve membrane

High-performance and reliable membranes for efficient gas separation and their design strategies are key points for membrane-based carbon capture. Here, we reported a high-performance carbon membrane design protocol from a microporous, highly rigid polyimide precursor (6FBD1-CR), which was produced by in-situ crosslinking a polyimide (6FBD1) containing conjugated dialkynyl group at 300 °C. The possible crosslinking mechanisms are the [2+2+2] trimerization of three ethynyl groups to form a benzene ring and the Diels-Alder reaction between the ethynyl bond and phenylacetylene to generate the fused naphthalene ring. After crosslinking, the membrane shows a ∼ 8-fold improved microporosity (37.1–298 m2 g−1). When pyrolyzed at 550 °C, the resulting 6FBD1-CMS demonstrates very high pure- and mixed-gas separation performance. E.g., the CO2 permeability reaches 7661 Barrer and CO2/CH4 selectivity of 44, additionally, even at the CO2/CH4 mixed-gas pressure of 30 bar, the PCO2 can still reach 4920 Barrer combined with a αCO2/CH4 of 28, which is well above the latest CO2/CH4 mixed-gas Upper Bound line. We consider this is due to the acetylene crosslinking induced a very stable microporous structure composed of rigid fused rings that alleviate the micropore collapse during the carbonization process, and thus, resulting in a relatively higher BET surface area, larger d-spacing, relatively higher concentration of continuous disordered phase (higher sp3/sp2) and small activation energy (Ep) for gas transport than the CMSM derived from polyimide without pre-crosslinking. This finding provides new opportunity for the structural design of high-performance CMSMs.

High‐Efficiency Solution‐Processed Hyperfluorescent Organic Light‐Emitting Diodes Enabled by Novel Triazatruxene‐Based Exciplexes with High Up‐Conversion Efficiency

AbstractAlthough sensitizing traditional fluorescent dyes with thermally activated delayed fluorescence (TADF) exciplexes has been extensively studied, the device performance of solution‐processed organic light‐emitting diodes (OLEDs) still lags far behind in this regard. Herein, the novel exciplex with high up‐conversion efficiency composed of a triazatruxene‐based donor and a triazine‐based acceptor is employed as a TADF sensitizer to fluorescent dye in solution‐processed hyperfluorescent OLEDs. Benefiting from the small activation energy for triplet up‐conversion and less non‐radiative recombination of triplet excitons, the new TADF exciplex can up‐convert efficiently non‐radiative triplet excitons through reverse intersystem crossing. Besides, expeditious up‐conversion processes also shorten the residence time of triplet excitons, giving rise to significant suppression of detrimental Dexter energy transfer from the exciplex sensitizer to the dopant. By maximizing the triplet up‐conversion efficiency of exciplex sensitizers, the optimized OLEDs achieve a maximum external quantum efficiency (EQEmax) of 16.0%, which is the first report for the solution‐processed exciplex‐sensitized hyperfluorescent OLEDs with EQEmax exceeding 15%. These results validate that the up‐conversion efficiency of triplet excitons in the exciplexes strongly affects the performance of exciplex‐sensitized fluorescent devices, and the triazatruxene‐based molecules are promising donor candidates for constructing the exciplexes with high up‐conversion efficiency.

Constructing Ultra-Shallow Near-Edge States for Efficient and Stable Perovskite Solar Cells.

Electronic band structure engineering of metal-halide perovskites (MHP) lies at the core of fundamental materials research and photovoltaic applications. However, reconfiguring the band structures in MHP for optimized electronic properties remains challenging. This article reports a generic strategy for constructing near-edge states to improve carrier properties, leading to enhanced device performances. The near-edge states are designed around the valence band edge using theoretical prediction and constructed through tailored material engineering. These states are experimentally revealed with activation energies of around 23 milli-electron volts by temperature-dependent time-resolved spectroscopy. Such small activation energies enable prolonged carrier lifetime with efficient carrier transition dynamics and low non-radiative recombination losses, as corroborated by the millisecond lifetimes of microwave conductivity. By constructing near-edge states in positive-intrinsic-negative inverted cells, a champion efficiency of 25.4% (25.0% certified) for a 0.07-cm2 cell and 23.6% (22.7% certified) for a 1-cm2 cell is achieved. The most stable encapsulated cell retains 90% of its initial efficiency after 1100 h of maximum power point tracking under one sun illumination (100mW cm-2) at 65 °C in ambient air.

Temperature-Dependent Kinetics for the Reactions of Fen- (n = 2-17) and FexNiy- (x + y = 3-9) with O2: Comparison of Pure and Mixed Metal Clusters with Relevance to Meteor Radio Afterglows and Surface Oxidation.

Rate constants and product branching fractions were measured from 300-600 K for Fen- + O2 (n = 2-17) and for 300-500 K for FexNiy- + O2 (x + y = 3-9) using a selected-ion flow tube (SIFT) apparatus. Rate constants for 46 species are reported. All rate constants increased with increasing temperature, and several were in excess of the Langevin-Gioumousis-Stevenson (LGS) capture rate at elevated temperatures. As with previously studied transition metal anion oxidation reactions, the collision limit is treated as the sum of the LGS limit along with a hard-sphere contribution, allowing for determination of activation energies. These values are compared to each other along with previous results for Nin-. Measured rate constants for all three series (Fen-, Nin-, and FexNy-) vary over a relatively narrow range (1-5 × 10-10 cm3 s-1 at 300 K) being at least 15% of the collision rate constant. All reaction rate constants increase with temperature, described by small activation energies of 0.5-4 kJ mol-1. The data are consistent with an anticorrelation between the electron binding energy and rate constant, previously noted in other systems. The Fen- reaction produces a larger population of higher energy electrons than do the Nin- reactions, with FexNiy- producing an intermediate amount. The results suggest that the overall rate constant is limited by a small energetic barrier located at a large internuclear distance where electrostatic forces dominate, causing the potentials to be similar across systems, while the product formation is determined by the shorter-range, valence portion of the potential, which varies widely between systems.

Glycoside-metabolizing oxidoreductase D3dgpA from human gut bacterium.

The Gfo/Idh/MocA family enzyme DgpA was known to catalyze the regiospecific oxidation of puerarin to 3"-oxo-puerarin in the presence of 3-oxo-glucose. Here, we discovered that D3dgpA, dgpA cloned from the human gut bacterium Dorea sp. MRG-IFC3, catalyzed the regiospecific oxidation of various C-/O-glycosides, including puerarin, in the presence of methyl β-D-3-oxo-glucopyranoside. While C-glycosides were converted to 3"- and 2"-oxo-products by D3dgpA, O-glycosides resulted in the formation of aglycones and hexose enediolone from the 3"-oxo-products. From DFT calculations, it was found that isomerization of 3"-oxo-puerarin to 2"-oxo-puerarin required a small activation energy of 9.86 kcal/mol, and the O-glycosidic bond cleavage of 3"-oxo-products was also thermodynamically favored with a small activation energy of 3.49 kcal/mol. In addition, the reaction mechanism of D3dgpA was discussed in comparison to those of Gfo/Idh/MocA and GMC family enzymes. The robust reactivity of D3dgpA was proposed as a new general route for derivatization of glycosides.

Effective aerobic oxidative denitrogenation of model fuel with metal-free porous carbon derived from phytic acid-loaded polyaniline

Aerobic oxidative denitrogenation (ODN) of a model fuel was first done with metal-free P and O co-doped carbon catalysts. The catalysts, phytic acid (PA)-loaded polyaniline-derived carbons (PPDCs), were firstly prepared by high-temperature pyrolysis of polyaniline with phytic acid (as P/O sources). One material, PPDC-2 showed a conversion of 95 % and 86 % for indole (IND) and quinoline (500 ppm each), respectively, at 100 °C, with O2 as an oxidant. A very small activation energy of 26.6 kJ mol−1 was observed in the IND oxidation. Radical trapping experiments and electron spin resonance spectroscopy analyses supported the formation of superoxide anion radicals (O2−) from the fed O2, which was responsible for the IND oxidation. A plausible reaction mechanism was proposed by analyzing the experimental results and DFT calculations on charge separations on carbons. Defect sites also could play an important role in the activation of O2 since PPDC-2 showed higher defect sites compared to the non-doped carbon. PPDC-2 was also found to be recyclable for the ODN, by simple acetone soaking, without a considerable loss in performance.

Synthesis, dielectric and impedance spectroscopy study of temperature stable Ta2O5 modified 0.85BaTiO3-0.15Bi(Mg0.5Ti0.5)O3 ceramics

In the present study, 0.85BaTiO3–0.15Bi(Mg0.5Ti0.5)O3-xTa2O5 (x = 0, 0.01, 0.015, 0.02, 0.025) processed via the conventional mix oxide route. The phase, microstructure, and dielectric properties were studied. Single perovskite phase developed and studied via XRD. A Dense microstructure for each composition was developed with the pseudo-crystal structure. Low grain size <3 μm is achieved for each composition. A high dielectric constant (εr) > 1000 and low dielectric loss (tanδ <2.5 %) is obtained for x ≤ 0.020, with high stability over a broad range of temperatures (<0 °C to 180 °C). These compositions are considered to be suitable for designing X9R capacitors. In complex impedance analysis, the decreasing value of the bulk impedance upon increasing the temperature revealed the negative temperature coefficient of resistance (NTCR) behavior. The small conductivity and high activation energy value for x = 0.01 demonstrate the temperature stability of this ceramic.

Tailored multi-functional molecular chain-based ferrocene derivative for efficient and stable perovskite solar cells

Under the stimulation of external factors, the ions with small activation energies could escape from the surface of perovskite, aggravating the defects at the interfaces and deteriorating the perovskite solar cells (PSCs). Here, we report a novel strategy utilizing a tailored organometallic molecule (bis-ferrocenyl-carboxylate-hexadecafluorodecyl, namely Fc-16 F) interlayer to functionalize the perovskite/hole transport layer interface, which simultaneously blocks the migration pathways of ions and facilitate the charge extraction at the interface. The electron-absorbing substituents (carboxyl groups and a long C-F chain) are introduced to strengthen the redox properties of ferrocene units, limit self-migration, and enhance hydrophobicity. With the strengthened oxidation driving force and the tight and dense hydrogen bond networks formed between Fc-16 F and organic cations, Fc-16 F could efficiently recover the Pb, I vacancies, inhibit the diffusion of defect-induced by-products (I2), and stabilize the components on the surface. The champion device modified with Fc-16 F interlayer yields a remarkable power conversion efficiency (PCE) of 23.02% as well as superior humidity and long-term stabilities. The Fc-16 F-modified PSCs retain an outstanding 83.3% of its initial PCE over 1200 h under high humidity (60% RH) and retain over 90% of its initial PCE after aging in the N2 atmosphere for over 2000 h.

Optical and temperature-dependent electrical and dielectric properties of ultrasound-synthesized CdS quantum dots

CdS quantum dots (QDs) were synthesized by the ultrasound-assisted chemical precipitation technique. The structure analysis revealed the presence of bi-structural cubic and hexagonal phases with an average crystallite size of 3 nm. The N2-adsorption isotherm exhibited the evolution of meso-/macro-porous interfaces with a pore size of 7.56 nm and a surface area of 44.41 m2·g−1. The improvement of the quantum size effect in CdS QDs resulted in the increase of optical bandgap to 2.52 eV compared with the corresponding bulk phase. However, the analysis of long-tail states absorption revealed a very small Urbach energy of about 76 meV compared with CdS QDs prepared by other techniques. The as-synthesized CdS QDs revealed high room-temperature DC conductivity of 2.56 × 10–6 Ω−1 · m−1 and very small activation energy of 268 meV facilitating tunnelling of the thermionically excited carrier through the high bandgap of CdS QDs. The frequency-dependent behavior of AC conductivity (σ AC) and dielectric constant (ε r) of CdS QDs were investigated at different temperatures in the range from 303 K to 453 K. It was observed that both σ AC and ε r were improved with increasing temperature up to 363 K followed by a sudden decrease at higher temperatures.