High-Efficiency Pure-Red CsPbI3 Quantum Dot Light-Emitting Diodes Enabled by Strongly Electrostatic Potential Solvent and Sequential Ligand Post-treatment Process.

Efficient pure-red emission light-emitting diodes (LEDs) are essential for high-definition displays, yet achieving pure-red emission is hindered by challenges like phase segregation and spectral instability when using halide mixing. Additionally, strongly confined quantum dots (QDs) produced through traditional hot-injection methods face byproduct contamination due to poor solubility of metal halide salts in the solvent octadecene (ODE) at low temperatures. Herein, we introduced a novel method using a benzene-series strongly electrostatic potential solvent instead of ODE to prevent PbI2 intermediates and promote their dissolution into [PbI3]-. Increasing methyl groups on benzene yields precisely sized (4.4 ± 0.1 nm) CsPbI3 QDs with exceptional properties: a narrow 630 nm PL peak with photoluminescence quantum yield (PLQY) of 97%. Sequential ligand post-treatment optimizes optical and electrical performance of QDs. PeLEDs based on optimized QDs achieve pure-red EL (CIE: 0.700, 0.290) approaching Rec. 2020 standards, with an EQE of 25.2% and T50 of 120 min at initial luminance of 107 cd/m2.

Gradient Alloy Shell Enabling Colloidal Quantum Wells Light-Emitting Diodes with Efficiency Exceeding 22.

Colloidal quantum well (CQW) based light emitting diodes (LEDs) possess extra-high theoretical efficiency, but their performance still lags far behind conventional LEDs due to severe exciton quenching and unbalanced charge injection. Herein, we devised a gradient composition CdxZn1-xS shell to address these issues. The epitaxial shell with gradient composition was achieved through controlling competition between Cd2+ and Zn2+ cations to preferentially bind to the anions S2-. Thus, exciton quenching was suppressed greatly by passivating defects and reducing nonradiative recombination, thereby achieving near-unity photoluminescence quantum yield (PLQY). The gradient energy level of the shell reduced the hole injection barriers and increased the hole injection efficiency to balance the charge injection of LEDs. As a result, the LEDs achieved a high external quantum efficiency (EQE) of 22.83%, luminance of 111,319 cd/m2 and a long operational lifetime (T95@100 cd/m2) over 6,500 h, demonstrating the state-of-the-art performance for the CQW based LEDs.

Strongly-Confined CsPbBr3 Perovskite Quantum Dots with Ultralow Trap Density and Narrow Size Distribution for Efficient Pure-Blue Light-Emitting Diodes.

The development of pure-blue perovskite light-emitting diodes (PeLEDs) faces challenges of spectral stability and low external quantum efficiency (EQE) due to phase separation in mixed halide compositions. Perovskite quantum dots (QDs) with strong confinement effects are promising alternatives to achieve high-quality pure-blue PeLEDs, yet their performance is often hindered by the poor size distribution and high trap density. A strategy combining thermodynamic control with a polishing-driven ligand exchange process to produce high-quality QDs is developed. The strongly-confined pure-blue (≈470 nm) CsPbBr3 QDs exhibit narrow size distribution (12% dispersion) and are achieved in Br-rich ion environment based on growth thermodynamic control. Subsequent polishing-driven ligand exchange process removes imperfect surface sites and replaces initial long-chain organic ligands with short-chain benzene ligands. The resulting QDs exhibit high photoluminescence quantum yield (PLQY) to near-unity. The resulting PeLEDs exhibit a pure-blue electroluminescence (EL) emission at 472 nm with narrow full-width at half-maximum (FWHM) of 25 nm, achieving a maximum EQE of 10.7% and a bright maximum luminance of 7697 cd m-2. The pure-blue PeLEDs show ultrahigh spectral stability under high voltage, a low roll-off of EQE, and an operational half-lifetime (T50) of 127 min at an initial luminance of 103 cd m-2 under continuous operation.

Triple-junction solar cells with cyanate in ultrawide-bandgap perovskites.

Perovskite bandgap tuning without quality loss makes perovskites unique among solar absorbers, offering promising avenues for tandem solar cells1,2. However, minimizing the voltage loss when their bandgap is increased to above 1.90 eV for triple-junction tandem use is challenging3-5. Here we present a previously unknown pseudohalide, cyanate (OCN-), with a comparable effective ionic radius (1.97 Å) to bromide (1.95 Å) as a bromide substitute. Electron microscopy and X-ray scattering confirm OCN incorporation into the perovskite lattice. This contributes to notable lattice distortion, ranging from 90.5° to 96.6°, a uniform iodide-bromide distribution and consistent microstrain. Owing to these effects, OCN-based perovskite exhibits enhanced defect formation energy and substantially decreased non-radiative recombination. We achieved an inverted perovskite (1.93 eV) single-junction device with an open-circuit voltage (VOC) of 1.422 V, a VOC × FF (fill factor) product exceeding 80% of the Shockley-Queisser limit and stable performance under maximum power point tracking, culminating in a 27.62% efficiency (27.10% certified efficiency) perovskite-perovskite-silicon triple-junction solar cell with 1 cm2 aperture area.

One-dimensional single atom arrays on ferroelectric nanosheets for enhanced CO2 photoreduction.

Single-atom catalysts show excellent catalytic performance because of their coordination environments and electronic configurations. However, controllable regulation of single-atom permutations still faces challenges. Herein, we demonstrate that a polarization electric field regulates single atom permutations and forms periodic one-dimensional Au single-atom arrays on ferroelectric Bi4Ti3O12 nanosheets. The Au single-atom arrays greatly lower the Gibbs free energy for CO2 conversion via Au-O=C=O-Au dual-site adsorption compared to that for Au-O=C=O single-site adsorption on Au isolated single atoms. Additionally, the Au single-atom arrays suppress the depolarization of Bi4Ti3O12, so it maintains a stronger driving force for separation and transfer of photogenerated charges. Thus, Bi4Ti3O12 with Au single-atom arrays exhibit an efficient CO production rate of 34.15 µmol·g-1·h-1, ∼18 times higher than that of pristine Bi4Ti3O12. More importantly, the polarization electric field proves to be a general tactic for the syntheses of one-dimensional Pt, Ag, Fe, Co and Ni single-atom arrays on the Bi4Ti3O12 surface.

Recent advances in in-situ transmission electron microscopy techniques for heterogeneous catalysis.

The process of heterogeneous catalytic reaction under working conditions has long been considered a "black box", which is mainly because of the difficulties in directly characterizing the structural changes of catalysts at the atomic level during catalytic reactions. The development of in situ transmission electron microscopy (TEM) techniques offers opportunities for introducing a realistic chemical reaction environment in TEM, making it possible to uncover the mystery of catalytic reactions. In this article, we present a comprehensive overview of the application of in situ TEM techniques in heterogeneous catalysis, highlighting its utility for observing gas-solid and liquid-solid reactions during thermal catalysis, electrocatalysis, and photocatalysis. in situ TEM has a unique advantage in revealing the complex structural changes of catalysts during chemical reactions. Revealing the real-time dynamic structure during reaction processes is crucial for understanding the intricate relationship between catalyst structure and its catalytic performance. Finally, we present a perspective on the future challenges and opportunities of in situ TEM in heterogeneous catalysis.

A General Dual-Metal Nanocrystal Dissociation Strategy to Generate Robust High-Temperature-Stable Alumina-Supported Single-Atom Catalysts.

Designing new synthesis routes to fabricate highly thermally durable precious metal single-atom catalysts (SACs) is challenging in industrial applications. Herein, a general strategy is presented that starts from dual-metal nanocrystals (NCs), using bimetallic NCs as a facilitator to spontaneously convert a series of noble metals to single atoms on aluminum oxide. The metal single atoms are captured by cation defects in situ formed on the surface of the inverse spinel (AB2O4) structure, which process provides numerous anchoring sites, thus facilitating generation of the isolated metal atoms that contributes to the extraordinary thermodynamic stability. The Pd1/AlCo2O4-Al2O3 shows not only improved low-temperature activity but also unprecedented (hydro)thermal stability for CO and propane oxidation under harsh aging conditions. Furthermore, our strategy exhibits a small scaling-up effect by the simple physical mixing of commercial metal oxide aggregates with Al2O3. The good regeneration between oxidative and reductive atmospheres of these ionic palladium species makes this catalyst system of potential interest for emissions control.

Thermal-Induced Dopant Precipitation Enabling High-Quality Surface Modification of LiCoO2.

Surface modification is an effective approach for overcoming the interfacial degradations to enable high electrochemical performance of battery materials, yet it is still challenging to realize high-quality surface modification with simple processing, low cost, and mass production. Herein, a thermal-induced surface precipitation phenomenon is reported in a Ti-dopped LiCoO2 , which can realize an ultrathin (≈5 nm) and uniform surface modification by a simple annealing process. It is revealed that surface Li-deficiency enables bulk Ti to precipitate and segregate on the non-(003) surface facets, forming a Ti-enriched disordered layered structure. Such a surface modification layer can not only stabilize the interfacial chemistry but also significantly improve the charge/discharge reaction kinetics, leading to much-improved cycling stability and rate capability. Dopants surface precipitation is a unique outward diffusion process, which differs from the current surface modification techniques and further diversifies these approaches for realizing high-quality surface modification of battery materials.

Ferroelectricity in layered bismuth oxide down to 1 nanometer.

Atomic-scale ferroelectrics are of great interest for high-density electronics, particularly field-effect transistors, low-power logic, and nonvolatile memories. We devised a film with a layered structure of bismuth oxide that can stabilize the ferroelectric state down to 1 nanometer through samarium bondage. This film can be grown on a variety of substrates with a cost-effective chemical solution deposition. We observed a standard ferroelectric hysteresis loop down to a thickness of ~1 nanometer. The thin films with thicknesses that range from 1 to 4.56 nanometers possess a relatively large remanent polarization from 17 to 50 microcoulombs per square centimeter. We verified the structure with first-principles calculations, which also pointed to the material being a lone pair-driven ferroelectric material. The structure design of the ultrathin ferroelectric films has great potential for the manufacturing of atomic-scale electronic devices.

Determination of Crystallographic Orientation and Exposed Facets of Titanium Oxide Nanocrystals.

Titanium dioxide (TiO2 ) nanocrystals have attracted great attention in heterogeneous photocatalysis and photoelectricity fields for decades. However, contradicting conclusions on the crystallographic orientation and exposed facets of TiO2 nanocrystals frequently appear in the literature. Herein, using anatase TiO2 nanocrystals with highly exposed {001} facets as a model, the misleading conclusions that exist on anatase nanocrystals are clarified. Although TiO2 -001 nanocrystals are recognized to be dominated by {001} facets, in fact, anatase nanocrystals with both dominant {001} and {111} facets always co-exist due to the similarities in the lattice fringes and intersection angles between the two types of facets (0.38 nm and 90° in the [001] direction, 0.35 nm and 82° in the [111] direction). A paradigm for determining the crystallographic orientation and exposed facets based on transmission electron microscopy (TEM) analysis, which provides a universal methodology to nanomaterials for determining the orientation and exposed facets, is also given.

Hydrogenated Cs2AgBiBr6 for significantly improved efficiency of lead-free inorganic double perovskite solar cell.

Development of lead-free inorganic perovskite material, such as Cs2AgBiBr6, is of great importance to solve the toxicity and stability issues of traditional lead halide perovskite solar cells. However, due to a wide bandgap of Cs2AgBiBr6 film, its light absorption ability is largely limited and the photoelectronic conversion efficiency is normally lower than 4.23%. In this text, by using a hydrogenation method, the bandgap of Cs2AgBiBr6 films could be tunable from 2.18 eV to 1.64 eV. At the same time, the highest photoelectric conversion efficiency of hydrogenated Cs2AgBiBr6 perovskite solar cell has been improved up to 6.37% with good environmental stability. Further investigations confirmed that the interstitial doping of atomic hydrogen in Cs2AgBiBr6 lattice could not only adjust its valence and conduction band energy levels, but also optimize the carrier mobility and carrier lifetime. All these works provide an insightful strategy to fabricate high performance lead-free inorganic perovskite solar cells.

Direct Synthesis of Stable 1T-MoS2 Doped with Ni Single Atoms for Water Splitting in Alkaline Media.

Metallic MoS2 (i.e., 1T-MoS2 ) is considered as the most promising precious-metal-free electrocatalyst with outstanding hydrogen evolution reaction (HER) performance in acidic media comparable to Pt. However, sluggish kinematics of HER in alkaline media and its inability for the oxygen evolution reaction (OER), hamper its development as bifunctional catalysts. The instability of 1T-MoS2 further impedes its applications for scaling up, calling an urgent need for simple synthesis to produce stable 1T-MoS2 . In this work, the challenge of 1T-MoS2 synthesis is first addressed using a direct one-step hydrothermal method by adopting ascorbic acid. 1T-MoS2 with flower-like morphology is obtained, and transition metals (Ni, Co, Fe) are simultaneously doped into 1T-MoS2 . Ni-1T-MoS2 achieves an enhanced bifunctional catalytic activity for both HER and OER in alkaline media, where the key role of Ni doping as single atom is proved to be essential for boosting HER/OER activity. Finally, a Ni-1T-MoS2 ||Ni-1T-MoS2 electrolyzer is fabricated, reaching a current density of 10 mA cm-2 at an applied cell voltage of only 1.54 V for overall water splitting.

Recent Progress on Revealing 3D Structure of Electrocatalysts Using Advanced 3D Electron Tomography: A Mini Review.

Electrocatalysis plays a key role in clean energy innovation. In order to design more efficient, durable and selective electrocatalysts, a thorough understanding of the unique link between 3D structures and properties is essential yet challenging. Advanced 3D electron tomography offers an effective approach to reveal 3D structures by transmission electron microscopy. This mini-review summarizes recent progress on revealing 3D structures of electrocatalysts using 3D electron tomography. 3D electron tomography at nanoscale and atomic scale are discussed, respectively, where morphology, composition, porous structure, surface crystallography and atomic distribution can be revealed and correlated to the performance of electrocatalysts. (Quasi) in-situ 3D electron tomography is further discussed with particular focus on its impact on electrocatalysts' durability investigation and post-treatment. Finally, perspectives on future developments of 3D electron tomography for eletrocatalysis is discussed.

Mesoporous Single-Crystal Lithium Titanate Enabling Fast-Charging Li-Ion Batteries.

There remain significant challenges in developing fast-charging materials for lithium-ion batteries (LIBs) due to sluggish ion diffusion kinetics and unfavorable electrolyte mass transportation in battery electrodes. In this work, a mesoporous single-crystalline lithium titanate (MSC-LTO) microrod that can realize exceptional fast charge/discharge performance and excellent long-term stability in LIBs is reported. The MSC-LTO microrods are featured with a single-crystalline structure and interconnected pores inside the entire single-crystalline body. These features not only shorten the lithium-ion diffusion distance but also allow for the penetration of electrolytes into the single-crystalline interior during battery cycling. Hence, the MSC-LTO microrods exhibit unprecedentedly high rate capability, achieving a specific discharge capacity of ≈174 mAh g-1 at 10 C, which is very close to its theoretical capacity, and ≈169 mAh g-1 at 50 C. More importantly, the porous single-crystalline microrods greatly mitigate the structure degradation during a long-term cycling test, offering ≈92% of the initial capacity after 10 000 cycles at 20 C. This work presents a novel strategy to engineer porous single-crystalline materials and paves a new venue for developing fast-charging materials for LIBs.

Few-layer bismuth selenide cathode for low-temperature quasi-solid-state aqueous zinc metal batteries.

The performances of rechargeable batteries are strongly affected by the operating environmental temperature. In particular, low temperatures (e.g., ≤0 °C) are detrimental to efficient cell cycling. To circumvent this issue, we propose a few-layer Bi2Se3 (a topological insulator) as cathode material for Zn metal batteries. When the few-layer Bi2Se3 is used in combination with an anti-freeze hydrogel electrolyte, the capacity delivered by the cell at -20 °C and 1 A g-1 is 1.3 larger than the capacity at 25 °C for the same specific current. Also, at 0 °C the Zn | |few-layer Bi2Se3 cell shows capacity retention of 94.6% after 2000 cycles at 1 A g-1. This behaviour is related to the fact that the Zn-ion uptake in the few-layer Bi2Se3 is higher at low temperatures, e.g., almost four Zn2+ at 25 °C and six Zn2+ at -20 °C. We demonstrate that the unusual performance improvements at low temperatures are only achievable with the few-layer Bi2Se3 rather than bulk Bi2Se3. We also show that the favourable low-temperature conductivity and ion diffusion capability of few-layer Bi2Se3 are linked with the presence of topological surface states and weaker lattice vibrations, respectively.

A High-Performance In-Memory Photodetector Realized by Charge Storage in a van der Waals MISFET.

The emerging data-intensive applications in optoelectronics are driving innovation toward the fused integration of sensing, memory, and computing to break through the restrictions of the von Neumann architecture. However, the present photodetectors with only optoelectronic conversion functions cannot satisfy the growing demands of the multifunctions required in single devices. Here, a novel route for the integration of non-volatile memory into a photodetector is proposed, with a WSe2 /h-BN van der Waals heterostructure on a Si/SiO2 substrate to realize in-memory photodetection. This photodetector exhibits an ultrahigh readout photocurrent of 3.4 µA and photoresponsivity of 337.8 A W-1 in the solar-blind wavelength region, together with an extended retention time of more than 10 years. Furthermore, the charge-storage-based non-volatile mechanism of h-BN/SiO2 is successfully proven through a novel analysis of in situ optoelectronic electron energy-loss spectroscopy. These results represent a leap forward to future applications and insightful mechanisms of in-memory photodetection.

Understanding liquefaction in halide perovskites upon methylamine gas exposure.

Methylamine (CH3NH2, MA) gas-induced fabrication of organometal CH3NH3PbI3 based perovskite thin films are promising photovoltaic materials that transform the energy from absorbed sunlight into electrical power. Unfortunately, the low stability of the perovskites poses a serious hindrance for further development, compared to conventional inorganic materials. The solid-state perovskites are liquefied and recrystallized from CH3NH2. However, the mechanism of this phase transformation is far from clear. Employing first principles calculations and ab initio molecular dynamics simulations, we investigated the formation energy of primary defects in perovskites and the liquefaction process in CH3NH2 vapor. The results indicated that defect-assisted surface dissolution leads to the liquefaction of perovskite thin films in CH3NH2 vapor. Two primary defects were studied: one is the Frenkel pair defect (including both negatively charged interstitial iodide ion (Ii -) and iodide vacancy (VI +) at the PbI2-termination surface, and the other is the Schottky defects (methylammonium vacancy, VMA) at the MAI-termination surface. Moreover, the defect-induced disorder in the microstructure reduces the degeneration of energy levels, which leads to a blue shift and broader absorption band gap, as compared to the clean perovskite surface. The mechanism of how defects impact the surface dissolution could be applied for the further design of high-stability perovskite solar cells.

In CH3 NH3 PbI3 Perovskite Film, the Surface Termination Layer Dominates the Moisture Degradation Pathway.

Theoretical studies have shown that surface terminations, such as MAI or PbI layers, greatly affect the environmental stability of organic-inorganic perovskite. However, until now, there has been little effort to experimentally detect the existence of MAI or PbI terminations on MAPbI3 grains, let alone disclose their effects on the humidity degradation pathway of perovskite solar cell. Here, we successfully modified and detected the surface terminations of MAI and PbI species on polycrystalline MAPbI3 films. MAI-terminated perovskite film followed the moisture degradation process from MAPbI3 to hydrate MAPbI3 ⋅H2 O and then into PbI2 , with penetration of water molecules being the main driving force leading to the degradation of MAPbI3 layer by layer. In contrast, for the PbI-terminated perovskite film in a humid atmosphere, a deprotonation degradation pathway was confirmed, in which the film preferentially degraded directly from MAPbI3 into PbI2 , here the iodine defects played a key role in promoting the dissociation of water molecules into OH- and further catalyzing the decomposition of perovskite.

Facet-Dependent Cobalt Ion Distribution on the Co3O4 Nanocatalyst Surface.

Co3O4 is an important catalyst widely used for CO oxidation or electrochemical water oxidation near room temperature and was also recently used as support for single-atom catalysts (SACs). Co3O4 with a spinel structure hosts dual oxidation states of Co2+ and Co3+ in the lattice, leading to the complexity of its surface structure as the exposure of Co2+ and Co3+ has a significant impact on the performance of the catalysts. Although it is acknowledged that different facets exhibit varied catalytic activities and different abilities in hosting single atoms to provide active centers in SACs, the Co3O4 surface structure remains under-investigated. In this study, major facets of {111}, {110}, and {100} were studied down to subangstrom scale using advanced electron microscopy. We noticed that each facet has its own most stable surface configuration. The distribution of Co2+ and Co3+ on each facet was quantified, revealing a facet-dependent distribution of Co2+ and Co3+. Co3+ was found to be preferentially exposed on {100} and {110} as well as surface steps. Surface reconstruction was revealed, where a subangstrom scale shift of Co2+ was confirmed on facets of {111} and {100} due to polarity compensation and oxygen deficiency on the surface. This work not only improves our fundamental understanding of the Co3O4 surface structure but also may promote the design of Co3O4-based catalysts with tunable activity and stability.

Precipitation kinetics, microstructure evolution and mechanical behavior of a developed Al-Mn-Sc alloy fabricated by selective laser melting.

The dynamic metallurgical characteristics of the selective laser melting (SLM) process offer fabricated materials with non-equilibrium microstructures compared to their cast and wrought counterparts. To date, few studies on the precipitation kinetics of SLM processed heat-treatable alloys have been reported, despite the importance of obtaining such detailed knowledge for optimizing the mechanical properties. In this study, for the first time, the precipitation behavior of an SLM fabricated Al-Mn-Sc alloy was systematically investigated over the temperature range of 300-450 °C. The combination of in-situ synchrotron-based ultra-small angle X-ray scattering (USAXS), small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) revealed the continuous evolution of Al6Mn and Al3Sc precipitates upon isothermal heating in both precipitate structure and morphology, which was confirmed by ex-situ transmission electron microscopy (TEM) studies. A pseudo-delay nucleation and growth phenomenon of the Al3Sc precipitates was observed for the SLM fabricated Al-Mn-Sc alloy. This phenomenon was attributed to the preformed Sc clusters in the as-fabricated condition due to the intrinsic heat treatment effect induced by the unique layer-by-layer building nature of SLM. The growth kinetics for the Al6Mn and Al3Sc precipitates were established based on the in-situ X-ray studies, with the respective activation energies determined to be (74 ± 4) kJ/mol and (63 ± 9) kJ/mol. The role of the precipitate evolution on the final mechanical properties was evaluated by tensile testing, and an observed discontinuous yielding phenomenon was effectively alleviated with increased aging temperatures.