Latent heat storage (LHS) has emerged as a promising solution for addressing the challenges of large-scale and long-term energy storage, offering a clean and reusable system. Being in the developmental stage, and with only limited theoretical predictions being available, there is a need to enhance the efficiency of LHS systems. In this study, we use numerical simulations to study the melting process of a phase-change material (PCM) in a rectangular domain. A significant enhancement in the melt rate of the PCM is found by a simple inclination of the domain, with a 60% increase in melt rate compared to a standard square unit without inclination through enhanced heat transfer. We establish a theoretical relation for the optimal PCM melt rate, based on the inclination angle and the domain aspect ratio, outlining the optimal conditions for the PCM melt rate, which is solely dependent on the domain geometry. We further propose a heat-transfer model that predicts the optimal aspect ratio for achieving the maximum melt rate as a function of the Rayleigh and Prandtl numbers.

Aluminum-based foil anodes could enable lithium-ion batteries with high energy density comparable to silicon and lithium metal. However, mechanical pulverization and lithium trapping within aluminum tend to cause capacity fading. The complex interplay between these damage modes is not well understood, as well as the role of microstructure on reaction front evolution. Here, we investigate aluminum foils with different compositions and processing conditions to understand how microstructure influences chemo-mechanical degradation. Backscattered electron imaging of ion-milled foil cross sections is used to visualize reaction front evolution and chemo-mechanical degradation. We find that the shape of the reaction front during lithiation is strongly affected by foil composition, defect distribution, and grain size, which, in turn, affects the evolution of chemo-mechanical damage within the foils. Furthermore, a key finding is that the extent of fracture upon delithiation is inversely related to lithium trapping, with foil compositions that exhibit uniform lithiation, and therefore, less fracturing showing greater lithium trapping. Nonreactive precipitate inclusions within alloy foils are also found to induce void formation. This work shows that material design strategies designed to overcome the inverse fracture-lithium trapping relationship could be useful for improving performance.

Synchronization is essential for the operation of ac power systems: all generators in the power grid must rotate with fixed relative phases to enable a steady flow of electric power. Understanding the conditions for and the limitations of synchronization is of utmost practical importance. In this article, we propose a novel approach to computing and analyzing the stable stationary states of a power grid or a network of Kuramoto oscillators in terms of a convex optimization problem. This approach allows us to systematically compute all stable states where the phase difference across an edge does not exceed $\pi /2$. Furthermore, the optimization formulation allows us to rigorously establish certain properties of synchronized states and to bound the error in the widely used linear power flow approximation.

Singlet fission (SF) is an electronic transition that in the last decade has been under the spotlight for its applications in optoelectronics, from photovoltaics to spintronics. Despite considerable experimental and theoretical advancements, optimizing SF in materials like multichromophoric systems and molecular crystals remains a challenge, due to the complexity of its analysis beyond perturbative methods. Here, we tackle the case of one-dimensional rings, aiming to promote singlet fission and prevent its backreaction. We study ultrafast SF nonperturbatively, by numerically solving a spin-boson model, via exact propagation and tensor network methods. By optimizing over a parameter space relevant to organic molecular materials, we identify two classes of solutions that can take SF efficiency beyond 85% in the nondissipative (coherent) regime, and to 99% when exciton-phonon interactions can be tuned. After discussing the experimental feasibility of the optimized solutions, we conclude by proposing that this approach can be extended to a wider class of optoelectronic optimization problems.

Plasma-facing materials (PFMs) represent one of the most significant challenges for the design of future nuclear fusion reactors. Inside the reactor, the divertor will experience the harshest material environment: intense bombardment of neutrons and plasma particles coupled with extremely large and intermittent heat fluxes. The material designated to cover this role in ITER is tungsten. While no other materials have shown the potential to match the properties of tungsten, many drawbacks associated with its application remain, including cracking and erosion induced by a low recrystallization temperature combined with a high ductile-brittle transition temperature and neutron-initiated embrittlement; surface morphology changes (helium bubbles and fuzz layer) due to plasma-tungsten interaction with subsequent risk of spontaneous material melting and delamination; and low oxidation resistance in the case of air contamination. Exploring alternatives to tungsten requires the design of a multivariable optimization problem. This work aims to produce a structured and comprehensive material screening of PFM candidates based on known inorganic materials. The method applied in this study to identify the most promising PFM candidates combines peer-reviewed data present in the PAULING FILE database and first-principles density-function theory calculations focusing on two key PFM defects—namely, the sputtering of surface atoms and the incorporation of interstitial hydrogen, respectively characterized by the surface binding energy and the interstitial formation energy. The crystal structures and their related properties, extracted from the PAULING FILE, are ranked according to the heat-balance equation of a PFM subjected to the heat loads in the divertor region of an ITER-like tokamak. The materials satisfying the requirements are critically compared with the state-of-the-art in plasma-facing materials research and in studies of refractory materials exposed to high temperatures, plasma, and neutron bombardment. This comparison assesses their thermo-mechanical properties under such conditions, identifying a subset of promising materials for first-principles electronic structure calculations. Most previously known and extensively studied PFMs, such as tungsten, molybdenum, and carbon-based materials, are captured by this screening process, confirming its reliability. Additionally, less familiar refractory materials suggest performance that calls for further investigations.

Considering its Venturi effect, long corridor terrain is considered as one of the outstanding wind-energy resources, but has not been developed due to unclear inflow turbulence effects on wind turbines. To advance the wind-power technology in long corridors and reveal the physics behind it, we conducted a series of data-fusion analyses combining field measurements in the Hexi Corridor, Gansu, China, and numerical simulations and summarize the effort here. In this study, the classical spectrum for the atmospheric boundary layer for wind-energy research, the IEC Kaimal spectrum (also known as IECKwind, International Elector technical Commission 61400-1) cannot describe the wind profile in corridors. Here, we proposed a new spectrum to describe the wind in the Hexi Corridor by modifying the IEC Kaimal spectrum, and we call it the IECK-HX spectrum. The results demonstrate that it preferentially resides at lower frequencies (larger spatial scales) compared with IECKwind. Large-scale motions (LSMs) and very large-scale motions (VLSMs) coexist in the Hexi Corridor atmospheric boundary layer, which can be well described by the IECK-HX spectrum, and these two dominate the large fluctuations in the power, thrust, and blade root flapwise moment of wind turbines, while the high-frequency small-scale coherent structures mainly cause high-frequency fluctuations in wind-turbine load. Furthermore, IEC Kaimal spectrum can not describe the VLSMs, and the generated flow presents significant fluctuations and thereby reduces the power output in high wind-speed regions. This study provides fundamental support for wind-energy scientists and engineers who are interested in wind energy in corridor terrains.

Crystalline alloys and related mixed systems make up a large family of materials with high tunability that have been proposed as the solution to a large number of energy-related material design problems. Because of the presence of chemical order and disorder in these systems, neither experimental efforts nor ab initio computational methods alone are sufficient to span the inherently large configuration space. Therefore, fast and accurate models are necessary. To this end, cluster expansions have been widely and successfully used for the past few decades. Cluster expansions are generalized Ising models designed to predict the energy of any atomic configuration of a system after training on a small subset of the available configurations. Constructing and sampling a cluster expansion consists of multiple steps that have to be performed with care. In this tutorial, we provide a comprehensive guide to this process, highlighting important considerations and potential pitfalls. The tutorial consists of three parts, starting with cluster expansion construction for a relatively simple system, continuing with strategies for more challenging systems such as surfaces, and closing with examples of Monte Carlo sampling of cluster expansions to study order-disorder transitions and phase diagrams.

The chalcogenide perovskite ${\mathrm{Ba}\mathrm{Zr}\mathrm{S}}_3$ has attracted much attention as a promising solar absorber for thin-film photovoltaics. Here we use first-principles calculations to evaluate its carrier transport and defect properties. We find that ${\mathrm{Ba}\mathrm{Zr}\mathrm{S}}_3$ has a phonon-limited electron mobility of $37{\mathrm{cm}}^2/$V s, which is comparable to that in halide perovskites, but lower hole mobility of $11{\mathrm{cm}}^2/$V s. The defect computations indicate that ${\mathrm{Ba}\mathrm{Zr}\mathrm{S}}_3$ is intrinsically $n$-type due to shallow sulfur vacancies, but that strong compensation by sulfur vacancies will prevent attempts to make it $p$-type. We also establish that ${\mathrm{Ba}\mathrm{Zr}\mathrm{S}}_3$ shows some degree of defect tolerance, presenting only few low formation energy, deep intrinsic defects. Among the deep defects, sulfur interstitials are the dominant nonradiative recombination centers but exhibit a moderate capture coefficient. Our work highlights the material’s intrinsic limitations in carrier mobility and $p$-type doping, and suggests focusing on suppressing the formation of sulfur interstitials to achieve longer carrier lifetime.

Power electronics are critical for a sustainable energy future, playing a key role in electrification and integration of renewable energy sources into the grid. Advances in ultrawide band gap materials are needed to handle higher powers in smaller form factors while reducing electrical and thermal losses. High $\mathrm{Al}$ content ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ is theoretically capable of meeting these demands, but its impact in power electronics has been severely restricted by a lack of substrates that can satisfy conductivity, lattice matching, and/or thermal expansion requirements. We demonstrate that electrically conductive $\mathrm{Ta}\mathrm{C}$ can be used as a virtual substrate for ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ heteroepitaxy. Scaleably sputtered $\mathrm{Ta}\mathrm{C}$ grown on ${\mathrm{Al}}_2{\mathrm{O}}_3$, followed by high-temperature face-to-face annealing, produces a thin film $\mathrm{Ta}\mathrm{C}$ template with an effective hexagonal lattice constant matched to ${\mathrm{Al}}_{0.70}{\mathrm{Ga}}_{0.30}\mathrm{N}$. Annealing of the $\mathrm{Ta}\mathrm{C}$ promotes recrystallization, significantly improving crystallinity and reducing crystalline defects from as-deposited columnar grains to a step-and-terrace surface morphology, enabling the subsequent growth of high-quality ${\mathrm{Al}}_{0.70}{\mathrm{Ga}}_{0.30}\mathrm{N}$ by molecular beam epitaxy. X-ray diffraction and scanning transmission electron microscopy confirm that the ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ layer is heteroepitaxially aligned, strain-free, and lattice-matched, transitioning abruptly from $\mathrm{Ta}\mathrm{C}$ to ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ without intermediate phases. These results demonstrate $\mathrm{Ta}\mathrm{C}$ virtual substrates as electrically conductive, lattice-matched, and thermally compatible templates for vertical ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ devices that can meet the growing power needs of a sustainable energy future.

Heusler compounds with semiconducting properties represent an important class of functional materials. Usually, research on these systems is guided by simple electron-counting rules, such as the Slater-Pauling principle. Here, we report on the discovery of Heusler-type semiconductors, significantly deviating from the Slater-Pauling rule. We theoretically predict the occurrence of nonmagnetic semiconducting ground states in various highly off-stoichiometric full-Heusler alloys, where self-substitution leads to a band-gap opening. This unexpected trend is confirmed experimentally by thermoelectric transport measurements on a multitude of $\mathrm{Fe}$${}_{2-2x}$$\mathrm{V}$${}_{1-x}$$\mathrm{Al}$${}_{1+3x}$ samples with up to 20% substitution of $\mathrm{Fe}$ and $\mathrm{V}$ atoms. The band-gap opening leads to an exceptionally large Seebeck coefficient in $p$-type $\mathrm{Fe}$${}_2$$\mathrm{VAl}$ thermoelectrics, previously limited by bipolar conduction and low-density-of-states effective mass. Consequently, our work presents a paradigm to tune the band gap of Heusler compounds by self-substitution and introduces a hitherto unexplored class of semiconductors with exceptional thermoelectric properties, offering significant potential for advancements in energy science and sustainable-energy technologies.

Inserting underlying reduced graphene oxide ($\mathrm{rGO}$) into $\mathrm{Co}$ aims to regulate the chemical integrity and catalytic ability of the $\mathrm{Co}$ upper layer for hydrogen evolution reaction (HER) as a green-hydrogen goal. Principally, an operando mass spectrometer indicates 3.8 times more considerable hydrogen generation in $\mathrm{Co}/\mathrm{rGO}$ than in $\mathrm{Co}$. The spectroscopical approaches, combining operando soft and hard X-ray probing, illustrate the chemical oxidation evolution of electronic $\mathrm{Co}$-3d and $\mathrm{Co}$-4p states differently regarding the underlying $\mathrm{rGO}$ contribution. A unique examination is regarded as the phase transition from the initial middle to high oxidation and to deoxidation, related to the intermediate ${\mathrm{Co}}^0$ existence and ${\mathrm{H}}_2$ generation. The chemical adsorption of $\mathrm{Co}$–$\mathrm{O}(\mathrm{H})$, $\mathrm{Co}$–${\mathrm{H}}_{\mathrm{ads}}$, and ${\mathrm{H}}_2$ molecules desorption have been assigned their spectral significances. The $\mathrm{rGO}$ mediation indicates two significant metal $\mathrm{Co}$ and $\mathrm{Co}$–$\mathrm{O}(\mathrm{H})$ blocks in the two-dimensional R-k domain. Density-functional-theory (DFT) calculation provides the regeneration, sustained stability, and decreasing energy barrier of $\mathrm{Co}$–${\mathrm{H}}_{\mathrm{ads}}$ catalysts due to the $\mathrm{rGO}$ incorporation, thereby augmenting the HER enhancement through the alternative Volmer-Heyrovsky process. The in-situ experiment, including mass spectrometer, soft, and hard X-ray, provides evidence regarding the catalyst’s HER enhancement. This study offers insights into the chemical composition, electronic structure, and active role of $\mathrm{Co}$ bonded with or without the extinct $\mathrm{OH}$ and H bonds, advancing our comprehension of electrocatalytic reactions, thus taking our knowledge of composite materials to stepwise electrocatalytic reactions forward. This cutting-edge experiment under in-situ environment and DFT studies gives critical information regarding the catalytic mechanism and chemical stability of the $\mathrm{Co}$ and $\mathrm{rGO}$ materials.

Solid-state electrolytes offer a promising avenue for energy storage in the context of lithium-based batteries, not only from an energy density perspective, but also by eliminating issues such as freezing of the liquid electrolyte at low temperatures and the performance limitations associated with that. In solid-state batteries, solid electrolytes are not only used in separators but are also needed in composite electrodes. However, the transport properties of solid-state battery composites are often investigated at room temperature, while the temperature dependence of effective ion transport as a function of volume fraction remains underexplored. Therefore, this work investigates the effective ionic transport in composites of multiple sulfide-based solid electrolytes with $\mathrm{Si}/\mathrm{C}$ as the active material, as a function of composition and temperature. Analyzing impedance spectra with a transmission line model, this work reveals changes in activation barrier and with that the temperature dependence of ion transport upon varying the volume ratios. This finding emphasizes the importance of considering the activation energy in solid-state battery design to tailor battery performance to the temperature range of application.

The stability of ac power grids relies on ancillary services that mitigate frequency fluctuations. The electromechanical inertia of large synchronous generators is currently the only resource to absorb frequency disturbances on subsecond time scales. Replacing standard thermal power plants with inertialess new renewable sources of energy (NREs) therefore jeopardizes grid stability against, e.g., sudden power-generation losses. To guarantee system stability and compensate the lack of electromechanical inertia in grids with large penetrations of NREs, virtual synchronous generators, which emulate conventional generators, have been proposed. Here, we propose a novel control scheme for virtual synchronous generators, where the provided inertia is large at short times—thereby absorbing faults as efficiently as conventional generators—but decreases over a tunable time scale to prevent coherent frequency oscillations from setting in. We evaluate the performance of this adaptive-inertia scheme under sudden power losses in large-scale transmission grids. We find that it systematically outperforms conventional electromechanical inertia and that it is more stable than previously suggested schemes. Numerical simulations show how a quasioptimal geographical distribution of adaptive-inertia devices not only absorbs local faults efficiently but also significantly increases the damping of interarea oscillations. Our results show that the proposed adaptive-inertia control scheme is an excellent solution to strengthen grid stability in future low-inertia power grids with large penetrations of NREs.

A high-performance $p$-type transparent conductor (TC) does not yet exist but could lead to advances in a wide range of optoelectronic applications and enable new architectures for, e.g., next-generation photovoltaic (PV) devices. High-throughput computational material screenings have been a promising approach to filter databases and identify new $p$-type TC candidates and some of these predictions have been experimentally validated. However, most of these predicted candidates do not have experimentally achieved properties on par with $n$-type TCs used in solar cells and therefore have not yet been used in commercial devices. Thus, there is still a significant divide between transforming predictions into results that are actually achievable in the laboratory and an even greater lag in scaling predicted materials into functional devices. In this perspective, we outline some of the major disconnects in this materials discovery process—from scaling computational predictions into synthesizable crystals and thin films in the laboratory to scaling laboratory-grown films into real-world solar devices—and share insights to inform future strategies for TC discovery and design.

We propose a multijunction configuration for an electroluminescent cooling system, incorporating multiple semiconductor layers with different band gaps. Through theoretical analysis focusing on cooling power density and coefficient of performance, we show that increasing the number of semiconductor layers results in an enhanced performance of electroluminescent cooling. We highlight the reduction of operating voltage as a pivotal factor contributing to this improvement. Furthermore, we show that the enhancement can persist in the presence of nonradiative recombination. Our work indicates the potential of multijunction configurations in advancing the capabilities of electroluminescent cooling.

Variations in local strain, defect densities, and composition of hybrid metal-halide perovskites have been reported to create heterogeneous energy landscapes in thin films, which impact charge-carrier diffusion and recombination dynamics. Here, we employ one- and two-photon transient absorption spectroscopy to selectively probe the dynamics of charge carriers from surface and bulk regions of methylammonium lead bromide thin films. Differences in the transient absorption spectra indicate that an energy gradient of approximately 100 meV is formed between the higher band-gap surface and lower band-gap bulk regions. Thus, during their lifetime, photoexcited carriers move away from the surface to recombine in the bulk, where our experiments detect long-lived charge populations despite the significant band splitting that has conventionally been assumed to inhibit efficient radiative recombination. Supported by first-principles calculations, we demonstrate that bright emission can still arise from the bulk with states that occupy a wide range of momenta in the vicinity of the band extrema, which show strong dipole transitions. Our results report that photoexcitations in the hybrid perovskites avoid defect-rich surface regions, and that particularly strong emission is generated from accumulated excitation populations in the bulk.

In photosymbiotic giant clams, vertical columns of single-celled algae absorb sunlight that has first been forward scattered from a superficial layer of light-scattering cells called iridocytes. In principle, this arrangement could lead to a highly efficient system but it has been unclear how to calculate a productivity denominator to normalize the performance of the system. Inspired by the geometry observed in the clam, we have created an analytical model that calculates the idealized performance of a system with a geometry similar to the clam. In our model, photosynthesis-irradiance behavior obeys that of algal cells isolated from clams. Using a standard rate of eight photons of photosynthetically active radiation required to create one molecule of $\mathrm{O}$${}_2$, we find that a fixed geometry of the “light-dilution” strategy employed by the clams can reach a quantum efficiency of 43% relative to the solar resource in intense tropical sunlight. In comparing the performance of the model to published photosynthesis-irradiance relations of living clams, we have observed that the living system easily exceeds the performance of the static model. Therefore, we have next considered a model in which the system geometry changes dynamically to optimize the quantum efficiency as a function of the solar irradiance. In this scenario, with changes in irradiance typical of a sunny tropical day, the performance of the model was consistent with that of large mature living clams and had a quantum efficiency of 67%. We also show that a similar dynamic modulation of the clam-tissue geometry could plausibly occur in the living animals. We have considered the possibility that efficiency gains in the living system could also occur via further optimization of per-cell absorbance of multiply scattered light within the highly absorbing system. However, a numerical model of radiative transfer within clam tissue that captures realistic multiple scattering has not located efficiency gains relative to the simpler single-pass analytical model. Therefore, we infer that additional resource efficiency over the dynamic, large-clam-like model would require nontrivial organization among cells at small length scales. We also observe that boreal spruce forests coupled to atmospheric haze may realize the same scale-invariant scattering-and-absorbance strategy as the clams but at a different, larger, length scale. Given these results, our model may demonstrate the maximum realizable light-use efficiency of a large photosynthetic system relative to the solar resource. The general principles here also readily generalize to any photosynthetic cell type or organic photoconversion material and solar-irradiance regime. They could therefore provide inspiration both for engineering novel efficient photoconversion processes and materials and inform optimal land-use estimates for efficient industrial biomass production.

The development of perovskite solar cells (PSCs) has ushered in a new era of solar technology, characterized by its exceptional efficiency and cost-effective production. However, the soft and fragile nature of perovskites makes module encapsulation challenging. Polyolefin elastomers (POEs) have been reported to be promising encapsulants for perovskite modules. However, little research exists on identifying criteria among different types of POEs as encapsulants. Here, two POEs with different morphologies were compared as encapsulants. The first POE crystallizes during encapsulation (crystal content ∼40%), and the resulting shrinkage or warpage leads to delamination, causing minimodule failure. In contrast, perovskite minimodules encapsulated with a mostly amorphous POE exhibited better reliability and reproducibility. The best perovskite minimodules passed the thermal cycling test for 240 cycles between −40 and 85 °C and the damp heat test for 1419 h, according to the IEC 61215 standard. This study highlights the importance of the morphology of encapsulants in achieving high-quality encapsulation.

Layered halide perovskites have emerged as potential alternatives to three-dimensional (3D) halide perovskites due to their improved stability and larger material phase space, allowing fine tuning of structural, electronic, and optical properties. However, their charge carrier mobilities are significantly smaller than those of 3D halide perovskites, which has a considerable impact on their application in optoelectronic devices. Here, we employ state-of-the-art ab initio approaches to unveil the electron-phonon mechanisms responsible for the diminished transport properties of layered halide perovskites. Starting from a prototypical $AM{X}_3$ halide perovskite, we model the case of $n=1$ and $n=2$ layered structures and compare their electronic and transport properties to the 3D reference. The electronic and phononic properties are investigated within density functional theory (DFT) and density functional perturbation theory (DFPT), while transport properties are obtained via the ab initio Boltzmann transport equation. The vibrational modes contributing to charge carrier scattering are investigated and associated with polar-phonon scattering mechanisms arising from the long-range Fröhlich coupling and deformation-potential scattering processes. Our investigation reveals that the lower mobilities in layered systems primarily originate from the increased electronic density of states at the vicinity of the band edges, while the electron-phonon coupling strength remains similar. Such an increase is caused by the dimensionality reduction and the break in octahedra connectivity along the stacking direction. Our findings provide a fundamental understanding of the electron-phonon coupling mechanisms in layered perovskites and highlight the intrinsic limitations of the charge carrier transport in these materials.

Multimodal x-ray microscopy is key to assessing the property-functionality relationships of semiconductor devices with the utmost sensitivity and spatial resolution. Here, we report on a novel setup—the “Analyzer of X-ray excited Optical Luminescence Offering Temporal and spectraL resolution” (AXOLOTL)—and demonstrate its use by investigating a series of triple-cation mixed-halide perovskite solar cells (PSCs) with varying $\mathrm{Cs}$ content. These PSCs exhibit spatially varying performance and are thus ideally probed by multimodal x-ray microscopy to elucidate the origin of the performance variations. Specifically, our nanoscale characterization of the wrinkled perovskite photoabsorber unveils a segregation of $\mathrm{I}$ and $\mathrm{Br}$, which is accompanied by a narrowed band gap and an increased charge-carrier lifetime in thick absorber areas. Overall, we demonstrate with this technique the spatial correlation of compositional inhomogeneities, topography, electrical performance, and optical performance, which is of highest interest for identifying loss mechanisms at the nanoscale in high-performance electronic device development, including solar cells.