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.

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.

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.

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.

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.

Genuine Active Species Generated from Fe3 N Nanotube by Synergistic CoNi Doping for Boosted Oxygen Evolution Catalysis.

The surface reconstruction of oxygen evolution reaction (OER) catalysts has been proven favorable for enhancing its catalytic activity. However, what is the active site and how to promote the active species generation remain unclear and are still under debate. Here, the in situ synthesis of CoNi incorporated Fe3 N nanotubes (CoNi-Fe3 N) on the iron foil through the anodization/electrodeposition/nitridation process for use of boosted OER catalysis is reported. The synergistic CoNi doping induces the lattice expansion and up shifts the d-band center of Fe3 N, which enhances the adsorption of hydroxyl groups from electrolyte during the OER catalysis, facilitating the generation of active CoNi-FeOOH on the Fe3 N nanotube surface. As a result of this OER-conditioned surface reconstruction, the optimized catalyst requires an overpotential of only 285 mV at a current density of 10 mA cm-2 with a Tafel slope of 34 mV dec-1 , outperforming commercial RuO2 catalysts. Density functional theory (DFT) calculations further reveal that the Ni site in CoNi-FeOOH modulates the adsorption of OER intermediates and delivers a lower overpotential than those from Fe and Co sites, serving as the optimal active site for excellent OER performance.

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.

Dimension Engineering of High-Quality InAs Nanostructures on a Wafer Scale.

Low-dimensional narrow-band-gap III-V semiconductors are key building blocks for the next generation of high-performance nanoelectronics, nanophotonics, and quantum devices. Realizing these various applications requires an efficient methodology that enables the material dimensional control during the synthesis process and the mass production of these materials with perfect crystallinity, reproducibility, low cost, and outstanding electronic and optoelectronic properties. Although advances in one- and two-dimensional narrow-band-gap III-V semiconductors synthesis, the progress toward reliable methods that can satisfy all of these requirements has been limited. Here, we demonstrate an approach that provides a precise control of the dimension of InAs from one-dimensional nanowires to wafer-scale free-standing two-dimensional nanosheets, which have a high degree of crystallinity and outstanding electrical and optical properties, using molecular-beam epitaxy by controlling catalyst alloy segregation. In our approach, two-dimensional InAs nanosheets can be obtained directly from one-dimensional InAs nanowires by silver-indium alloy segregation, which is much easier than the previously reported methods, such as the traditional buffering technique and select-area epitaxial growth. Detailed transmission electron microscopy investigations provide solid evidence that the catalyst alloy segregation is the origination of the InAs dimensional transformation from one-dimensional nanowires to two-dimensional nanosheets and even to three-dimensional complex crosses. Using this method, we find that the wafer-scale free-standing InAs nanosheets can be grown on various substrates including Si, MgO, sapphire, GaAs, etc. The InAs nanosheets grown at high temperature are pure-phase single crystals and have a high electron mobility and a long time-resolved terahertz kinetics lifetime. Our work will open up a conceptually new and general technology route toward the effective controlling of the dimension of the low-dimensional III-V semiconductors. It may also enable the low-cost fabrication of free-standing nanosheet-based devices on an industrial scale.

A Strategy toward New Low-Dimensional Hybrid Halide Perovskites with Anionic Spacers.

The low-dimensional halide perovskites have received enormous attention due to their unique photovoltaic and optoelectronic performances. Periodic spacers are used to inhibit the growth of 3D perovskite and fabricate a 2D counterpart with layered structure, mostly based on organic/inorganic cations. Herein, by introducing organic anions (e.g., pentanedioic acid (PDA) and hexanedioic acid (HDA) simultaneously), leaf-shaped (Cs3 Pb2 Br5 )2 (PDA-HDA) microplates with low-dimensional structure are synthesized. They also exhibit significant photoluminescence (PL) centered at 540 nm with a narrow emission peak. The synthesis of single crystals of Pb(PDA) and Pb(HDA) allows to further clarify the crystal structure of (Cs3 Pb2 Br5 )2 (PDA-HDA) perovskite and its structural evolution mechanism. Moreover, the cooperative introduction of dicarboxylic acid pairs with appropriate lengths is thermodynamically favored for the low-dimensional perovskite crystallization. The temperature-dependent PL indicates a V-shaped Stokes shift with elevated temperature that could be associated with the localization of excitons in the inorganic layers between organic dicarboxylic acid molecules. This work demonstrates low-dimensional halide perovskite with anionic spacers, which also opens up a new approach to the growth of low-dimensional organic-inorganic hybrid perovskite crystals.

Well-Dispersed Ruthenium in Mesoporous Crystal TiO2 as an Advanced Electrocatalyst for Hydrogen Evolution Reaction.

TiO2 mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO3 as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption-desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO2 can be attained by the same process using Ru-doped precursor SrTi1- xRu xO3. Ru is doped into lattice of TiO2, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO2 accept an electron from Ru and become Ti3+, which is observed for the first time. This Ru-doped TiO2 performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO2:Ru with Ru5+ and Ti3+ holds high HER activity with appropriate hydrogen-adsorption Gibbs free energies (Δ GH).

Growth of Black Phosphorus Nanobelts and Microbelts.

Black phosphorus nanobelts are fabricated with a one-step solid-liquid-solid reaction method under ambient pressure, where red phosphorus is used as the precursor instead of white phosphorus. The thickness of the as-fabricated nanobelts ranges from micrometers to tens of nanometers as studied by scanning electron microscopy. Energy dispersive X-ray spectroscopy and X-ray diffraction indicate that the nanobelts have the composition and the structure of black phosphorus, transmission electron microscopy reveals a typical layered structure stacked along the b-axis, and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy analysis demonstrates the doping of bismuth into the black phosphorus structure. The nanobelt can be directly measured in scanning tunneling microscopy in ambient conditions.

Nanoscale Engineering in VO2 Nanowires via Direct Electron Writing Process.

Controlling phase transition in functional materials at nanoscale is not only of broad scientific interest but also important for practical applications in the fields of renewable energy, information storage, transducer, sensor, and so forth. As a model functional material, vanadium dioxide (VO2) has its metal-insulator transition (MIT) usually at a sharp temperature around 68 °C. Here, we report a focused electron beam can directly lower down the transition temperature of a nanoarea to room temperature without prepatterning the VO2. This novel process is called radiolysis-assisted MIT (R-MIT). The electron beam irradiation fabricates a unique gradual MIT zone to several times of the beam size in which the temperature-dependent phase transition is achieved in an extended temperature range. The gradual transformation zone offers to precisely control the ratio of metal/insulator phases. This direct electron writing technique can open up an opportunity to precisely engineer nanodomains of diversified electronic properties in functional material-based devices.

Surficial Reconstruction of Pt-Ni/NiS and Its Effect on Electrocatalytic Hydrogen Evolution in Alkaline Medium.

Cyclic voltammetry pretreatment of Pt-based electrocatalysts has been proven to be a normal activation process on achieving the optimal alkaline hydrogen evolution performance. Until now, the congruent relationship between the microstructural evolution and performance improvement during this process has rarely been reported. Herein, when the in situ transmission electron microscopy and in situ Raman analyses are employed, a self-reconstruction process from crystalline NiS into amorphous nickel hydroxide hydrate [Ni(OH)2-x·H2O, where x ≈ 0.3] on the surface of platinum-nickel nanowires has first been captured, which is the critical water dissociation active site to offer a sufficient proton supply. Furthermore, such a surficial reconstruction triggers an increase in the current density from -2.3 to -38.8 mA/cm2 (at -70 mV), which is nearly 17 times. These observations point to the fact that it is essential to consider the fundamental mechanisms of hydrogen evolution on the active sites when the process is scaled up.

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.

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.

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.