Composite Technology Research Articles

Focus on perovskite emitters in blue light-emitting diodes.

Blue perovskite light-emitting diodes (PeLEDs) are essential in pixels of perovskite displays, while their progress lags far behind their red and green counterparts. Here, we focus on recent advances of blue PeLEDs and systematically review the noteworthy strategies, which are categorized into compositional engineering, dimensional control, and size confinement, on optimizing microstructures, energy landscapes, and charge behaviors of wide-bandgap perovskite emitters (bandgap >2.5 eV). Moreover, the stability of perovskite blue emitters and related devices is discussed. In the end, we propose a technical roadmap for the fabrication of state-of-the-art blue PeLEDs to chase and achieve comparable performance with the other two primary-color devices.

Advances to Stabilize Photoactive Phase of FAPbI3 Perovskite†

Comprehensive SummaryRecently, hybrid organic–inorganic perovskite materials have drawn widespread attention because of their outstanding optoelectrical properties (i.e., high absorption coefficient, long carrier diffusion distance), hence they are suitable light‐absorbing materials for photovoltaic application. Among all perovskite materials, formamidinium lead iodide (FAPbI3) based solar cells exhibit impressive power conversion efficiency (PCE) at laboratory stage, showing great potential to compete with silicon‐based solar cell. However, FAPbI3 still suffers from poor phase stability which is the prior problem that needs to be addressed before its further commercialization. To be precise, the photoactive phase (α phase) is thermodynamically metastable at room temperature, which not only makes α phase tend to transform into photoinactive phase (δ phase), but also causes competitive crystallization between two phases during the film preparation process, making it hard to fabricate pure α‐FAPbI3 films. In our review, we summarized key factors that are vital for obtaining high‐quality FAPbI3 perovskite thin films and enhancing the stability of FAPbI3 photoactive phase. First of all, precursor solution stability is of great importance since the conditions of precursor solution determine the nucleation and crystal growth process of perovskite. By introducing coordinating additives, using FAPbI3 single crystal as raw material or applying co‐solution strategy, the impurities formed by side reaction during precursor solution aging can be effectively suppressed, thus the stability of FAPbI3 solution can be greatly prolonged. Second, the crystallization kinetics of FAPbI3 have been systematically manipulated to obtain dense and large grain size perovskite films. Through introducing intermediate phase, regulating the surface energy, and retarding the crystal growth of FAPbI3 in crystallization process, not only films without pinholes and fewer grain boundaries can be obtained, the pre‐formed δ phase at room temperature can also be well‐suppressed, thus high‐quality α‐FAPbI3 films can be obtained. Third, how to thermodynamically enhance the phase stability of acquired FAPbI3 film has been extensively studied. The Gibbs free energy of FAPbI3 photoactive phase can be reduced through composition engineering, dimension engineering and external additives engineering, hence the phase transition barrier from α phase to δ phase has been significantly improved, which further enhance the phase stability of α‐FAPbI3. Lastly, we pointed out challenges of each method and proposed potential applications of mentioned strategies on improving the stability of all kinds of perovskite materials, thus further boost the commercialization of perovskite solar cell devices.

Band alignment and crystal stability of Y3Al5−xGaxO12 garnets using density functional theory with hybrid functional

In this study, the dependence of band gap, band alignment, and structural stability of Y3Al5−xGaxO12 garnet (YAGG) solid solutions on Ga content (x) have been investigated using density functional theory (DFT) with PBE0 hybrid functional. The most stable model of YAGG for each x is identified using evolutionary algorithm-based USPEX method. The band alignment was determined by connecting valence band maximum (VBM) and conduction band minimum (CBM) to vacuum level via macroscopic average electrostatic potential of the slab model. Solid solution formation energy as a function of x indicates that YAGG with x = 3.0 (Y3Al2Ga3O12) exhibits remarkable structural stability. At x = 3.0, the analysis of the formation energy contribution shows a dominant contribution from electronic charge redistribution energy while there is no contribution from distortion energy. Bader charge, electron localization function, as well as the projected density of state analysis reveal a strong covalent character of Ga under oxygen tetragonal environment. The calculated PBE0 band gap as a function of x agrees well with the experimental results. Ga admixing significantly lowers the CBM, which exhibits a potential to envelop the shallow electron traps from the forbidden gap. The YAGG band alignment calculated using the proposed vacuum-connecting method is consistent with VRBE results from experiment. The proposed methods used to model site-preferred solid solution and calculate the vacuum-connected band alignment are viable in predicting structural stability and band edge modification via compositional engineering of garnet solid solutions. We expect that this work provides a promising strategy for material design through compositional engineering in obtaining high stability and enhanced performance in garnet compounds.

On the Roles of Cellulose Nanocrystals in Fiber Cement: Implications for Rheology, Hydration Kinetics, and Mechanical Properties.

Fiber cement reinforced with pulp fibers is one of the key drivers for the decarbonization of nonstructural building materials, where the inclusion of sustainable pulp fibers at high proportions (i.e., > 8 wt %) renders poor workability of fiber-cement slurry with a concomitant loss in mechanical strength. Petrochemical-derived superplasticizers, i.e., polycarboxylates (PCEs), are predominantly used in fiber cement (including cement mortars) because they dramatically improve (content <0.5 wt %) the slurry rheology but reduce the rate of hydration and weaken the strength of the cured composite. Thus, it is crucial to explore renewable and bio-based superplasticizers devoid of any negative traits (if possible) of the conventional PCEs. In this study, we examined wood-derived cellulose nanocrystals (CNCs) as a multifunctional additive in fiber cement (bleached pulp fiber content: 8 wt %). In fiber cement, variation of the content (0.02-4 wt %) of CNCs resulted in improvement in the shear thinning behavior of the fiber-cement slurry and thereafter increased the hydration kinetics at high CNC contents (2-4 wt %). Notably, the flexural strength of the composite also exhibited improvement upon the addition of CNCs; the maximum strength was observed at 4 wt % of CNCs. Overall, the beneficial roles of CNCs afforded >10 wt % (in-total) bio-based content in fiber cement without compromising the mechanical strength and curing time (compared to PCEs); hence, the findings of this study could unravel new avenues in interface engineering of cement composites leveraging the multifunctional features of biomaterials, thus enhancing sustainability.

Mixed-Halide Perovskites with Halogen Bond Induced Interlayer Locking Structure for Stable Pure-Red PeLEDs.

Mixed-halide perovskites enable precise spectral tuning across the entire spectral range through composition engineering. However, mixed halide perovskites are susceptible to ion migration under continuous illumination or electric field, which significantly impedes the actual application of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate a novel approach to introduce strong and homogeneous halogen bonds within the quasi-two-dimensional perovskite lattices by means of an interlayer locking structure, which effectively suppresses ion migration by increasing the corresponding activation energy. Various characterizations confirmed that intralattice halogen bonds enhance the stability of quasi-2D mixed-halide perovskite films. Here, we report that the PeLEDs exhibit an impressive 18.3% EQE with pure red emission with CIE color coordinate of (0.67, 0.33) matching Rec. 2100 standards and demonstrate an operational half-life of ∼540 min at an initial luminance of 100 cd m-2, representing one of the most stable mixed-halide pure red PeLEDs reported to date.

Chemical Modulation of Metal-Insulator Transition toward Multifunctional Applications in Vanadium Dioxide Nanostructures.

The metal-insulator transition (MIT) of vanadium dioxide (VO2 ) has been of great interest in materials science for both fundamental understanding of strongly correlated physics and a wide range of applications in optics, thermotics, spintronics, and electronics. Due to the merits of chemical interaction with accessibility, versatility, and tunability, chemical modification provides a new perspective to regulate the MIT of VO2 , endowing VO2 with exciting properties and improved functionalities. In the past few years, plenty of efforts have been devoted to exploring innovative chemical approaches for the synthesis and MIT modulation of VO2 nanostructures, greatly contributing to the understanding of electronic correlations and development of MIT-driven functionalities. Here, this comprehensive review summarizes the recent achievements in chemical synthesis of VO2 and its MIT modulation involving hydrogen incorporation, composition engineering, surface modification, and electrochemical gating. The newly appearing phenomena, mechanism of electronic correlation, and structural instability are discussed. Furthermore, progresses related to MIT-driven applications are presented, such as the smart window, optoelectronic detector, thermal microactuator, thermal radiation coating, spintronic device, memristive, and neuromorphic device. Finally, the challenges and prospects in future research of chemical modulation and functional applications of VO2 MIT are also provided.

In Situ and Operando Characterization Techniques in Stability Study of Perovskite-Based Devices

Metal halide perovskite materials have demonstrated significant potential in various optoelectronic applications, such as photovoltaics, light emitting diodes, photodetectors, and lasers. However, the stability issues of perovskite materials continue to impede their widespread use. Many studies have attempted to understand the complex degradation mechanism and dynamics of these materials. Among them, in situ and/or operando approaches have provided remarkable insights into the degradation process by enabling precise control of degradation parameters and real-time monitoring. In this review, we focus on these studies utilizing in situ and operando approaches and demonstrate how these techniques have contributed to reveal degradation details, including structural, compositional, morphological, and other changes. We explore why these two approaches are necessary in the study of perovskite degradation and how they can be achieved by upgrading the corresponding ex situ techniques. With recent stability improvements of halide perovskite using various methods (compositional engineering, surface engineering, and structural engineering), the degradation of halide perovskite materials is greatly retarded. However, these improvements may turn into new challenges during the investigation into the retarded degradation process. Therefore, we also highlight the importance of enhancing the sensitivity and probing range of current in situ and operando approaches to address this issue. Finally, we identify the challenges and future directions of in situ and operando approaches in the stability research of halide perovskites. We believe that the advancement of in situ and operando techniques will be crucial in supporting the journey toward enhanced perovskite stability.

Interfacial Engineering of CFRP Composites and Temperature Effects: A Review

Interfacial Engineering of CFRP Composites and Temperature Effects: A Review

Over-18%-Efficiency Quasi-2D Ruddlesden-Popper Pb-Sn Mixed Perovskite Solar Cells by Compositional Engineering.

Quasi-two-dimensional (2D) Pb-Sn mixed perovskites show great potential in applications of single and tandem photovoltaic devices, but they suffer from low efficiencies due to the existence of horizontal 2D phases. Here, we obtain a record high efficiency of 18.06% based on 2D ⟨n⟩ = 5 Pb-Sn mixed perovskites (iso-BA2MA4(PbxSn1-x)5I16, x = 0.7), by optimizing the crystal orientation through a regulation of the Pb/Sn ratio. We find that Sn-rich precursors give rise to a mixture of horizontal and vertical 2D phases. Interestingly, increasing the Pb content can not only entirely suppress the unwanted horizontal 2D phase in the film but also enhance the growth of vertical 2D phases, thus significantly improving the device performance and stability. It is suggested that an increase of the Pb content in the Pb-Sn mixed systems facilitates the incorporation of iso-butylammonium (iso-BA+) ligands in vertically oriented perovskites because of the reduced lattice strain and increased interaction between the organic ligands and inorganic framework. Our work sheds light on the optimal conditions for fabricating stable and efficient 2D Pb-Sn mixed perovskite solar cells.

Recent Advances in Transition Metal Phosphide Nanocatalysts for H2 Evolution and CO2 Reduction

Green hydrogen energy has captivated researchers and is regarded as a feasible option for future energy-related aspirations. The emerging awareness of renewable energy-driven hydrogen generation and carbon dioxide reduction calls for the use of unconventional schematic tools in the fabrication of nanocatalyst systems. Transition metal phosphides are state-of-art, cost-effective, noble-metal-free materials that have been comprehensively examined for sustainable energy-driven applications. Recent reports on these advanced functional materials have cemented their candidature as high-performance catalytic systems for hydrogen production and for carbon dioxide conversion into value-added chemical feedstock. Bimetallic NiCoP (238.2 mmol g−1 h−1) exhibits top-notch catalytic competence toward photocatalytic HER that reveals the energy-driven application of a pristine class of TMPs, whereas heterostructured Ni2P/CdS was found to be fit for photochemical CO2 reduction, as well as for HER. On the other hand, pristine Ni2P was recently ascertained as an efficient electrocatalytic system for HER and CO2RR applications. A wide array of physicochemical modulations, such as compositional and structural engineering, defect generation, and facet control, have been used for improving the catalytic efficiency of transition metal phosphide nanostructures. In this review, we succinctly discuss the proficiency of transition metal phosphides in green hydrogen production and carbon dioxide conversion via photochemical and electrochemical pathways. We detail the significance of their structural properties and brief the readers about the synthetic advancements without deviating from our goal of summarizing the recent achievements in energy-driven applications.

Effect and Application of Different Amendments on Salinized Soil Remediation

At present, China's saline-alkali soil area is very large. In the saline-alkali soil, the salinity will affect the growth of plants in the severe areas, so the plants cannot survive. How to maintain soil quality and prevent soil salt from being high has become an important research goal of soil improvement. Soil amendments can combine many small soil particles together to form large water stable aggregates. And it is widely used to prevent soil erosion, reduce soil water evaporation or excessive evaporation, save the amount of irrigation and promote the healthy growth of plants. This study through the use of homemade iron han ecological amendments, phosphogypsum, garden waste decay secondary materials, five materials mixed polyacrylamide and microbial amendments, combined with the water salt engineering comparison experiment, the whole experiment for three, respectively is composite amendments and water salt engineering comprehensive improvement measures (TG1, TG2), the traditional composite amendments (G 1, G 2) and tai tian shallow water conservancy salt project (T) single measures. In the above experiments, the best effects are TG 1 (comprehensive improvement measures of Tiehan ecological amendments) and TG 2 (comprehensive improvement measures of Heka amendments). Although the amount of reagent applied is different, the treatment effect is very good. The results show that different improvement measures significantly reduced the salt content and reduced the PH value of soil, and improved the soil nutrients. This measurement data provides a certain theoretical basis for the repair and study of salinized soil. It also shows that soil amendments have obvious guidance for the application of salinized soil.

Comprehensively enhanced strain performance in PIN-PMN-PT ferroelectric ceramics via composition and orientation engineering

Excellent overall strain performances (i.e., low hysteresis, giant strain, and wide temperature span) are highly desirable in commercial high-precision displacement actuators to satisfy different application scenarios. However, any single means, e.g., compositional design or orientation engineering can hardly achieve the overall improvement of strain properties in ceramics. In this work, an approach of integrating compositional design (Sm and Mn co-doping) and orientation engineering (<001>-textured) is proposed to enhance the strain performance of 0.27Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PIN-PMN-PT) comprehensively. Initially, with the co-doping of Sm and Mn, the hysteresis of PIN-PMN-PT is substantially decreased to approximately 0.43 times that of the undoped material. Subsequently, 5 wt% BaTiO3 (BT) templates were added during the tape-casting process to orient the grains in 1 mol% Sm and Mn-doped PIN-PMN-PT ceramics. This resulted in a unique "4R" domain configuration with a reduced domain size of 0.13 µm. As a result, the domain wall energy was lowered, and the strain strength was increased to 0.35% at 70 kV/cm with low hysteresis to 8.94%. Moreover, the "clamping effect" in textured ceramics generates additional stress due to the lattice mismatch between the matrix grains and the BaTiO3 template, which inhibits the rhombohedral to the tetragonal phase transition. In addition, the fluctuation of strain value was only 8.5% over a wide temperature range of 30–150 °C, demonstrating excellent temperature stability. As a result of the combined effect of ion doping and orientation engineering, the overall strain performance in PIN-PMN-PT has been improved, providing a novel approach to designing superior and practical displacement actuators.

Composition engineering strategy of carbon–coated bimetallic phosphide for high energy density hybrid supercapacitors

Bimetallic phosphides hold great promise for using in hybrid supercapacitors (HSCs) as electrode material due to their synergistic effect of hetero-metal ions in ameliorating specific capacity and electrical conductivity. The production of bimetallic Ni1-xCoxP nanocrystals based on carbon-coated (Ni1-xCoxP@C) is described, and their potential application as positive electrodes in HSCs is also discussed. We give an insight into the significance of composition engineering for nickel-cobalt bimetallic phosphides in obtaining excellent electrochemical performance for supercapacitors. Ni0.9Co0.1P@C electrode reaches a maxima specific capacity as high as 4250 ± 48 mC cm−2 at 1 mA cm−2 (1327 ± 15 C g−1 at 1 A g−1), outperforming most transition metal phosphides (TMP)-based electrodes reported recently. Utilizing Ni0.9Co0.1P@C as electrode, the obtained HSC device provides a desired energy density of 46.9 ± 2.2 Wh kg−1 at 1600 W kg−1 and continues to sustain 26.2 ± 1.3 Wh kg−1 at a significant power density of 8000 W kg−1, capacitance retention remaining at 89.4 % after 10,000 cycles. It is believed that the Ni0.9Co0.1P@C has significant promise for application in extremely effective and affordable HSCs, as well as probably in other energy storage devices.

Composition, additive, and process engineering of halide perovskite green photodetector for enhanced responsivity and detectivity

Si-based materials have been successfully adapted for photodiode (PD) sensing applications. However, their micrometer-scale thickness requirement and parasitic light absorption limit color discrimination. In this study, we developed halide-perovskite-based thin films through composition engineering and process optimization for green-light sensing with high detectivity and responsivity. First, composition engineering studies, i.e., ratio control of methylammonium (MA) and formamidinium (FA) precursors and subsequent annealing condition optimization, were conducted to control the bandgap and phase formation of green-targeted perovskite absorber films. Next, we studied the effect of the CH3NH3Cl (MACl) additive on reducing the dark current and enhancing phase stability. Notably, space-charge-limited current measurements revealed that MACl could effectively reduce the trap density. Furthermore, simultaneous optimization of the cationic site composition, annealing conditions, and additive significantly affected the perovskite film morphology, phase stability, and defect formation, enabling the fabrication of high-performance green PDs. Our optimized, green-targeted PD exhibits a superior responsivity of 55.24 A·W−1 (under 7.17 × 10−7 W·cm−2 excitation), an average external quantum efficiency of 86%, and a high on/off ratio, thereby providing a feasible approach for future PD commercialization.

High-entropy transition metal disulfide colloid clusters: synergistic atomic scale interaction and interconnected network for ultra-stable potassium ion storage

High-entropy metal disulfide (HES2) colloid clusters were synthesized through a two-step templated solvothermal method for used as anode materials for potassium-ion storage devices. HES2’s large configuration entropy stabilizes its crystal structure and promotes chemical diversity by introducing multiple cations, thus reducing the impact of the shuttle effect, retaining active materials and extending cycling life up to 1800 cycles. During cycling, crystalline-amorphous grain boundaries formed in situ enhance electrochemical reaction activities and ensure the exposure of active sites. Elements with lower electronegativity allow S to bring more negative charges, improving the electrostatic force between S and K+ and enabling better anchoring of potassium polysulfide. Meanwhile, the retained close-packed cluster structure of HES2 provides a large contact area to accelerate the reduction reaction of the electrolyte in the sphere during the repeating K+ insertion/extraction. We further demonstrate the excellent performance of HES2 anodes on practical potassium-ion full battery and hybrid capacitor applications. The pioneering concept in atomic compositional engineering and structural design of transition metal sulfide electrodes presented in this work marks a significant step forward in the development of chalcogenide electrode systems for energy storage devices.

Highly conductive Ag-SiNx composite thin film anode engineering for transparent battery

Silicon nitride-based electrodes (SiNx), have been proposed as promising candidates for high-capacity transparent anode electrodes in earlier studies. Unfortunately, they have low electrical conductivity, resulting in some disadvantages such as power density for application in thin film batteries. To improve electrical conductivity, bulk batteries use conductive carbon additives, which also impair transmittance. Thus, we conducted this research to enhance the electrochemical properties by improving the conductivity without compromising the transmittance by uniformly dispersed Ag nanoparticles in SiNx thin film. We obtained an Ag-SiNx composite thin-film anode via continuous composition spread sputtering and investigated the effect of the Ag concentration. The capacity of the thin-film battery raised to 242.8 μAh/cm2·μm with Ag0.236SiO0.7N anode compared to the SiO0.7N anode which had a capacity of 37.2 μAh/cm2·μm. In addition, while SiO0.7N was operated only up to 2 C, Ag0.236SiO0.7N has driven up to 5 C and 10 C, which are high C rates, was also possible. AgxSiO0.7N thin film with less than 0.236 mol content demonstrates an optical transmittance of over 60% in the visible area. These results indicate that improving the electrical conductivity by the addition of an Ag during the silicon nitride deposition can increase its electrochemical performance while maintaining its applicability to transparent batteries.

Composition engineering of lead-free double perovskites towards efficient warm white light emission for health and well-being

Lead-free halide double perovskites (DPs) [A2B(I)B(III)X6] (A: monovalent cation, B(I): monovalent cation, B(II): trivalent cation, X: halide anion) has drawn tremendous attention because of their environmental-friendliness and high stability compared to traditional lead-based perovskites ABX3 (A: monovalent cation; B: Pb2+; X: halide anion). The optoelectronic properties of DPs are, however, compromised. This work provides a methodology for improving the photophysical properties of DPs and achieving high-efficiency warm white light emission. First principles density functional theory (DFT) was used in material design and the ligand-free synthesis of halide DP Cs2Ag1−xKxIn0.875Bi0.125Cl6 (x ≤ 0.60) via a facile recrystallization process was demonstrated. The compositional tuning of K+ to Ag+ resulted in an improvement in photophysical properties. Independent of K+ content, all the samples exhibit strong absorption at a wavelength of λmax ∼ 375 nm with a direct bandgap which is consistent with our DFT calculation results. Broadband photoluminescence (PL) emission profiles covering the spectra from blue to deep red (405–820 nm at λmax ∼ 629 nm) were observed. Besides, with an optimized K+ alloying content of 0.20, the optical performance of these halide DPs was impressively regulated, demonstrating improved photoluminescence quantum yield (PLQY) of host Cs2AgInCl6 crystals from ∼ 2.70 % (x = 0) to ∼15.96 % (x = 0.20), due to increased radiative recombination of self-trapped excitons. the highest report for such structures. It also shows high stability over 180 days. Furthermore, the use of blue-emitting CsPbBr3 and DP Cs2Ag0.80K0.20In0.875Bi0.125Cl6 as color conversion layers in white light-emitting diodes (LEDs) demonstrates that high-quality white light emission with the CIE color coordinate of (0.387, 0.385) and a correlated color temperature (CCT) of 3878 K, color rendering index (CRI) of 85, and luminous efficacy of radiation (LER) of 214 lm/W. Hence, the research work provides insight into realizing environmentally friendly and high-efficiency white light emission with high color quality by using earth-abundant elements and the low-cost synthesis method.

Insight into mechanism of boosted oxygen reduction reaction in mixed-conducting composite cathode of solid oxide fuel cell via a novel open-source pore-scale model

Composite engineering is one of the most practical strategies for mitigating thermo-mechanical instability in state-of-the-art cobalt-based mixed ionic-electronic conducting electrodes for solid oxide cells. Nevertheless, the mechanism underlying improved performance and durability of composite electrodes is not substantially examined and understood. Pore-scale modeling can effectively bridge the gap between material property, microstructure discovery, and performance evaluation. However, most of the previous pore-scale models are built on in-house codes or commercial software that is closed-source to the public, limiting customization and community involvement. Here we report for the first time a microstructure-resolved 3D pore-scale model based on an open-source Lattice Boltzmann library, implementing a well-validated electrochemical module that considers gas, ion and electron transport, as well as electrochemical reaction at triple-phase-boundary (TPB) and double-phase-boundary (DPB). The pure La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and 50/50 vol% composite LSCF/GDC (Gd-doped ceria) cathodes are reconstructed using focused ion beam-scanning electron microscopy and then are investigated under various current densities, temperatures, oxygen concentrations, and thicknesses. Results reveal the advantages of boosted TPB density and ionic conductivity outweigh the disadvantages of lower DPB density and electronic conductivity for the composite cathode. Furthermore, the composite cathode performs better at low temperatures and low oxygen concentrations due to the presence of more macropores, the stable bulk ion conductivity of GDC, and higher TPB density. Local current distribution at active sites indicates a thickness of 20 to 40 μm is favorable for reduced overpotential and moderate reaction homogeneity.

Negligible Bowing Effect of Bandgap and Lattice Constant in a Variety of Compositions using Large Tilt Distortion in a Cesium–Lead Mixed‐Halide System

AbstractHalide perovskites have broad bandgap tunability, making them suitable for diverse applications in optoelectronics and photovoltaics. The optical bandgap of halide perovskites varies almost linearly with the halide ionic size, and therefore, it can be controlled through compositional engineering. However, the mechanism underlying this low‐bandgap variation is not yet fully understood. Thus, this study comprehensively investigates the bandgap bowing of cesium–lead mixed‐halide perovskites using compositional engineering and demonstrates that bandgap bowing is extremely small in a variety of compositions including Cl, Br, and I. Subsequently, through density functional theory calculations, it is suggested that the antibonding character of the valence band maximum, tilt distortion of halide ions, and entropy effect leading to equal participation of various halide ions around Pb are collectively responsible for the small bandgap bowing.

Multielectron Conversion: Peculiar Transition Metal Sulfides with Mixed Vulcanized States toward High‐Capacity Metal‐Ion Storage

AbstractTransition metal sulfides with mixed vulcanized states (TMS‐mVs) possess tremendous potential to realize highcapacity, superior redox reactions, and structural reversibility for metal‐ion (Mn+) storage owing to their multielectron reactions caused by the simultaneous participation of transition metal (TM) cations and S22−anions as well as multifarious TM or S valence states. Here, recent advances are systematically introduced regarding the mainstream TMS‐mVs that can be applied to Mn+storage. These TMS‐mVs can be divided into two categories of TMS, those with mixed sulfur‐valence states (TMS‐mSs) and those with mixed metal‐valence states (TMS‐mMs). It is found that TMS‐mV anodes mainly experience three reaction mechanisms, inculding insertion‐accompanied conversion, insertion, and conversion reactions. During the reversible charge process, Li2S is possibly oxidized into polysulfides or even S. TMS‐mVs have the ability to transfer more electrons than other homogeneous TMSs. TMS‐mS anodes usually present higher theoretical specific capacities than TMS‐mM anodes. In these TMS‐mV anodes, Mo‐based, V‐based, and Co‐based TMS‐mM anodes exhibit good electrochemical reversibility, Ni‐based TMS‐mM anodes exhibit moderate electrochemical reversibility, and Fe‐based TMS‐mM and TMS‐mS anodes exhibit poor electrochemical reversibility. The strategies for enhancement of their electrochemical performance are classified into composite, coating, nanostructure, heterointerface, and lattice engineering.