Structural organization of the toe pads in the amphibian Philautus annandalii (Boulenger, 1906)

We describe the morphology of toe pads in the Himalayan tree frog Philautus annandalii. These are expanded tips of digits and show modifications of their ventral epidermis for adhesion. The outer cells of toe pad epidermis (TPE) bear surface microstructures (0.7 × 0.2 μm), which are keratinized. Their cytoplasm contains no organelles, but pleomorphic nuclei and mucous granules (0.4–0.5 μm) that glue the keratin filaments. In the intermediate cell layer of TPE, similar keratinized microstructures as in the outer cells are present, so that when the outer layer is shed, it is ready with features for adhesion. These cells contain more keratin than the outer cells. The basal cell layer contains thin keratin bundles and usual cell organelles. The dermis contains mucous‐secreting glands, whose ducts open in the outer epidermal cell layer in channels. The dorsal epidermal cells lack surface microstructures and keratin bundles. Ultrastructural features suggest that toe pads utilize the surface microstructures for adhesion aided by mucus, in which the intermediate cell layer seems to bear the shear stress generated during locomotion. Further, TPE can expand and fit into an increased contact area of the substrate. The long, surface microstructures may also help in mechanical interlocking with rough surfaces on plants.     

On the Effect of the Amorphous Silicon Microstructure on the Grain Size of Solid Phase Crystallized Polycrystalline Silicon

In this paper the effect of the microstructure of remote plasma‐deposited amorphous silicon films on the grain size development in polycrystalline silicon upon solid‐phase crystallization is reported. The hydrogenated amorphous silicon films are deposited at different microstructure parameter values R* (which represents the distribution of SiH_x bonds in amorphous silicon), at constant hydrogen content. Amorphous silicon films undergo a phase transformation during solid‐phase crystallization and the process results in fully (poly‐)crystallized films. An increase in amorphous film structural disorder (i.e., an increase in R*), leads to the development of larger grain sizes (in the range of 700–1100 nm). When the microstructure parameter is reduced, the grain size ranges between 100 and 450 nm. These results point to the microstructure parameter having a key role in controlling the grain size of the polycrystalline silicon films and thus the performance of polycrystalline silicon solar cells.     

Flash Infrared Annealing for Antisolvent‐Free Highly Efficient Perovskite Solar Cells

Organic–inorganic perovskites have demonstrated an impressive potential for the design of the next generation of solar cells. Perovskite solar cells (PSCs) are currently considered for scaling up and commercialization. Many of the lab‐scale preparation methods are however difficult to scale up or are environmentally unfriendly. The highest efficient PSCs are currently prepared using the antisolvent method, which utilizes a significant amount of an organic solvent to induce perovskite crystallization in a thin film. An antisolvent‐free method is developed in this work using flash infrared annealing (FIRA) to prepare methylammonium lead iodide (MAPbI₃) PSCs with a record stabilized power conversion efficiency of 18.3%. With an irradiation time of fewer than 2 s, FIRA enables the coating of glass and plastic substrates with pinhole‐free perovskite films that exhibit micrometer‐size crystalline domains. This work discusses the FIRA‐induced crystallization mechanism and unveils the main parameters controlling the film morphology. The replacement of the antisolvent method and the larger crystalline domains resulting from flash annealing make FIRA a highly promising method for the scale‐up of PSC manufacture.     

Lithium Doping to Enhance Thermoelectric Performance of MgAgSb with Weak Electron–Phonon Coupling

Despite the unfavorable band structure with twofold degeneracy at the valence band maximum, MgAgSb is still an excellent p‐type thermoelectric material for applications near room temperature. The intrinsically weak electron–phonon coupling, reflected by the low deformation potential E_def ≈ 6.3 eV, plays a crucial role in the relatively high power factor of MgAgSb. More importantly, Li is successfully doped into Mg site to tune the carrier concentration, leading to the resistivity reduction by a factor of 3 and a consequent increase in power factor by ≈30% at 300 K. Low lattice thermal conductivity can be simultaneously achieved by all‐scale hierarchical phonon scattering architecture including high density of dislocations and nanoscale stacking faults, nanoinclusions, and multiscale grain boundaries. Collectively, much higher average power factor ≈25 μW cm^?1 K^?2 with a high average ZT ≈ 1.1 from 300 to 548 K is achieved for 0.01 Li doping, which would result in a high output power density ≈1.56 W cm^?2 and leg efficiency ≈9.2% by calculations assuming cold‐side temperature T_c = 323 K, hot‐side temperature T_h = 548 K, and leg length = 2 mm.     

Porous MoS2/Carbon Spheres Anchored on 3D Interconnected Multiwall Carbon Nanotube Networks for Ultrafast Na Storage

The performance of lithium and sodium‐ion batteries is partly determined by the microstructures of the active materials and anodes. Much attention has been paid to the construction of various nanostructured active materials, with emphasis on optimizing the electronic and ionic transport kinetics, and structural stability. However, less attention has been given to the functionalization of electrode microstructure to enhance performance. Therefore, it is significant to study the effect of optimized microstructures of both active materials and electrodes on the performance of batteries. In this work, porous MoS₂/carbon spheres anchored on 3D interconnected multiwall carbon nanotube networks (MoS₂/C‐MWCNT) are built as sodium‐ion battery anodes to synergistically facilitate the sodium‐ion storage process. The optimized MoS₂/C‐MWCNT possesses favorable features, namely few‐layered, defect‐rich, and interlayer‐expanded MoS₂ with abundant mesopores/macropores and carbon incorporation. Notably, the presence of 3D MWCNT network plays a critical role to further improve interparticle and intraparticle conductivity, sodium‐ion diffusion, and structural stability on the electrode level. As a result, the electrochemical performance of optimized MoS₂/C‐MWCNT is significantly improved. This study suggests that rational design of microstructures on both active material and electrode levels simultaneously might be a useful strategy for designing high performance sodium‐ion batteries.     

Correlation Between Microstructure and Na Storage Behavior in Hard Carbon

Hard carbons are considered among the most promising anode materials for Na‐ion batteries. Understanding their structure is of great importance for optimizing their Na storage capabilities and therefore achieving high performance. Herein, carbon nanofibers (CNFs) are prepared by electrospinning and their microstructure, texture, and surface functionality are tailored through carbonization at various temperatures ranging from 650 to 2800 °C. Stepwise carbonization gradually removes the heteroatoms and increases the graphitization degree, enabling us to monitor the corresponding electrochemical performance for establishing a correlation between the CNFs characteristics and Na storage behavior. Outstandingly, it is found that for CNFs carbonized at above 2000 °C, a single voltage Na uptake plateau at ≈0.1 V with a capacity of ≈200 mAh g^‐1. This specific performance may be nested in the higher degree of graphitization, lower active surface area, and different porous texture of the CNFs at such temperatures. It is demonstrated via the assembly of a CNF/Na₂Fe₂(SO₄)₃ cell the benefit of such CNFs electrode for enhancing the energy density of full Na‐ion cells. This finding sheds new insights in the quest for high performance carbon based anode materials.     

The Role of Sodium as a Surfactant and Suppressor of Non‐Radiative Recombination at Internal Surfaces in Cu2ZnSnS4

It is well‐known that sodium improves the performance of Cu₂ZnSnS₄ (CZTS) devices, yet the mechanism of the enhancement is still not fully understood. This work aims to present a unified account of the relationships between grain boundaries in CZTS, sodium content at these boundaries, non‐radiative recombination, and surfactant effects that produce large microstructural changes. Using temperature‐dependent photoluminescence measurements, it is demonstrated that samples containing dramatically different grain sizes display identical radiative and non‐radiative decay characteristics when sufficient sodium is present in the film. It is also shown that the sodium concentration needed to efficiently passivate non‐radiative defects is significantly less that the quantity needed to obtain micrometer‐sized CZTS grains. Finally, the high densities of donor‐acceptor pairs that are observed in CZTS films appear to reside within the grains themselves, rather than at grain boundaries.     

Tuning Multiscale Microstructures to Enhance Thermoelectric Performance of n‐Type Bismuth‐Telluride‐Based Solid Solutions

Microstructure manipulation plays an important role in enhancing physical and mechanical properties of materials. Here a high figure of merit zT of 1.2 at 357 K for n‐type bismuth‐telluride‐based thermoelectric (TE) materials through directly hot deforming the commercial zone melted (ZM) ingots is reported. The high TE performance is attributed to a synergistic combination of reduced lattice thermal conductivity and maintained high power factor. The lattice thermal conductivity is substantially decreased by broad wavelength phonon scattering via tuning multiscale microstructures, which includes microscale grain size reduction and texture loss, nanoscale distorted regions, and atomic scale lattice distotions and point defects. The high power factor of ZM ingots is maintained by the offset between weak donor‐like effect and texture loss during the hot deformation. The resulted high zT highlights the role of multiscale microstructures in improving Bi₂Te₃‐based materials and demonstrates the effective strategy in enhancing TE properties.