Thermoresponsive Complex Coacervate‐Based Underwater Adhesive

Sandcastle worms have developed protein‐based adhesives, which they use to construct protective tubes from sand grains and shell bits. A key element in the adhesive delivery is the formation of a fluidic complex coacervate phase. After delivery, the adhesive transforms into a solid upon an external trigger. In this work, a fully synthetic in situ setting adhesive based on complex coacervation is reported by mimicking the main features of the sandcastle worm's glue. The adhesive consists of oppositely charged polyelectrolytes grafted with thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) chains and starts out as a fluid complex coacervate that can be injected at room temperature. Upon increasing the temperature above the lower critical solution temperature of PNIPAM, the complex coacervate transitions into a nonflowing hydrogel while preserving its volume—the water content in the material stays constant. The adhesive functions in the presence of water and bonds to different surfaces regardless of their charge. This type of adhesive avoids many of the problems of current underwater adhesives and may be useful to bond biological tissues.     

Directed Vertical Diffusion of Photovoltaic Active Layer Components into Porous ZnO‐Based Cathode Buffer Layers

Cathode buffer layers (CBLs) can effectively further the efficiency of polymer solar cells (PSCs), after optimization of the active layer. Hidden between the active layer and cathode of the inverted PSC device configuration is the critical yet often unattended vertical diffusion of the active layer components across CBL. Here, a novel methodology of contrast variation with neutron and anomalous X‐ray reflectivity to map the multicomponent depth compositions of inverted PSCs, covering from the active layer surface down to the bottom of the ZnO‐based CBL, is developed. Uniquely revealed for a high‐performance model PSC are the often overlooked porosity distributions of the ZnO‐based CBL and the differential diffusions of the polymer PTB7‐Th and fullerene derivative PC₇₁BM of the active layer into the CBL. Interface modification of the ZnO‐based CBL with fullerene derivative PCBE? OH for size‐selective nanochannels can selectively improve the diffusion of PC₇₁BM more than that of the polymer. The deeper penetration of PC₇₁BM establishes a gradient distribution of fullerene derivatives over the ZnO/PCBE‐OH CBL, resulting in markedly improved electron mobility and device efficiency of the inverted PSC. The result suggests a new CBL design concept of progressive matching of the conduction bands.     

Citrate‐Induced Nanocubes: A Re‐Examination of the Role of Citrate as a Shape‐Directing Capping Agent for Ag‐Based Nanostructures

Seed‐mediated syntheses utilizing facet‐selective surface passivation provide the necessary chemical controls to direct noble metal nanostructure formation to a predetermined geometry. The foremost protocol for the synthesis of (111)‐faceted Ag octahedra involves the reduction of metal ions onto pre‐existing seeds in the presence of citrate and ascorbic acid. It is generally accepted that the capping of (111) facets with citrate dictates the shape while ascorbic acid acts solely as the reducing agent. Herein, a citrate‐based synthesis is demonstrated in which the presence or absence of ascorbic acid is the shape‐determining factor. Reactions are carried out in which Ag⁺ ions are reduced onto substrate‐immobilized Ag, Au, Pd, and Pt seeds. Syntheses lacking ascorbic acid, in which citrate acts as both the capping and the reducing agent, result in a robust nanocube growth mode able to withstand wide variations in the concentration of reactants, reaction rates, seed material, seed orientation and faceting, pH, and substrate material. If, however, ascorbic acid is included in these syntheses, then the growth mode reverts to one that advances the octahedral geometry. The implication of these results is that citrate, or one of its oxidation products, selectively caps (100) facets, but where this capability is compromised by ascorbic acid.     

Metallic Nanowire‐Based Transparent Electrodes for Next Generation Flexible Devices: a Review

Transparent electrodes attract intense attention in many technological fields, including optoelectronic devices, transparent film heaters and electromagnetic applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO's lack of flexibility and the relatively high manufacturing costs have a prompted search into alternative materials. With their outstanding physical properties, metallic nanowire (MNW)‐based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution‐based processing, and are compatible with large area deposition techniques. Estimations of cost of the technology are lower, in particular thanks to the small quantities of nanomaterials needed to reach industrial performance criteria. The present review investigates recent progress on the main applications reported for MNW networks of any sort (silver, copper, gold, core‐shell nanowires) and points out some of the most impressive outcomes. Insights into processing MNW into high‐performance transparent conducting thin films are also discussed according to each specific application. Finally, strategies for improving both their stability and integration into real devices are presented.     

Improved SERS Intensity from Silver‐Coated Black Silicon by Tuning Surface Plasmons

An economical method of fabricating large‐area (up to a 100‐mm wafer) silver (Ag)‐coated black silicon (BS) substrates is demonstrated by cryogenic deep reactive ion etching with inductively coupled plasma. This method enables a simple adjustment of the spike structure (e.g., height, width, sidewall slope and density of the spikes) on the silicon substrate, which thus offers the advantages of accurate tuning the density and amplitude of the localized surface plasmons after Ag coating. Using this method, an enhancement factor of 10⁹ is achieved for the probe molecule of rhodamine 6G (around two orders of magnitude higher than previous results based on Ag‐coated BS) in surface‐enhanced Raman scattering (SERS) measurement. The presented results pave the way to make Ag‐coated BS substrates as economic and large‐area platforms for diverse surface plasmon related applications (such as SERS and surface plasmon based biosensors).     

Localized Surface Plasmon Induced Position‐Sensitive Photodetection in Silicon‐Nanowire‐Modified Ag/Si

Surface plasmon‐based approaches are widely applied to improve the efficiency of photoelectric devices such as photosensors and photocells. In order to promote the light absorption and electron–hole pair generation in devices, metallodielectric nanostructures are used to boost the growth of surface plasmons. Here, silicon nanowires (SiNWs) are used to modify a metal–semiconductor structure; thus, Ag/SiNWs/Si is manufactured. In this system, a large increased lateral photovoltaic effect (LPE) is detected with a maximum positional sensitivity of 65.35 mV mm^?1, which is ≈53‐fold and 1000‐fold compared to the conventional Ag/Si (1.24 mV mm^?1) and SiNWs/Si (0.06 mV mm^?1), respectively. It is demonstrated that localized surface plasmons (LSPs) contribute a lot to the increment of LPE. Furthermore, through the surface‐enhanced Raman scattering spectra of rhodamine‐6G and finite‐difference time‐domain simulation, it is illustrated that silver‐coated SiNWs support strong LSPs. The results propose an enhancement mechanism based on LSPs to facilitate the photoelectric conversion in LPE and offer an effective way to improve the sensitivity of photodetectors.     

Ultrahigh Rate and Long‐Life Sodium‐Ion Batteries Enabled by Engineered Surface and Near‐Surface Reactions

To achieve the high‐power sodium‐ion batteries, the solid‐state ion diffusion in the electrode materials is a highly concerned issue and needs to be solved. In this study, a simple and effective strategy is reported to weaken and degrade this process by engineering the intensified surface and near‐surface reactions, which is realized by making use of a sandwich‐type nanoarchitecture composed of graphene as electron channels and few‐layered MoS₂ with expanded interlayer spacing. The unique 2D sheet‐shaped hierarchical structure is capable of shortening the ion diffusion length, while the few‐layered MoS₂ with expanded interlayer spacing has more accessible surface area and the decreased ion diffusion resistance, evidenced by the smaller energy barriers revealed by the density functional theory calculations. Benefiting from the shortened ion diffusion distance and enhanced electron transfer capability, a high ratio of surface or near‐surface reactions is dominated at a high discharge/charge rate. As such, the composites exhibit the high capacities of 152 and 93 mA h g^?1 at 30 and 50 A g^?1, respectively. Moreover, a high reversible capacity of 684 mA h g^?1 and an excellent cycling stability up to 4500 cycles can be delivered. The outstanding performance is attributed to the engineered structure with increased contribution of surface or near‐surface reactions.     

Regulating Bulk‐Heterojunction Molecular Orientations through Surface Free Energy Control of Hole‐Transporting Layers for High‐Performance Organic Solar Cells

Interface properties are of critical importance for high‐performance bulk‐heterojunction (BHJ) organic solar cells (OSCs). Here, a universal interface approach to tune the surface free energy (γ_S) of hole‐transporting layers (HTLs) in a wide range through introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is reported. Based on the optimal γ_S of HTLs and thus improved face‐on molecular ordering in BHJs, enhanced fill factor and power conversion efficiencies in both fullerene and nonfullerene OSCs are achieved, which is attributed to the increased charge carrier mobility and sweepout with reduced recombination. It is found that the face‐on orientation‐preferred BHJs (PBDB‐TF:PC₇₁BM, PBDB‐T:PC₇₁BM, and PBDB‐TF:IT‐4F) favor HTLs with higher γ_S while the edge‐on orientation‐preferred BHJs (PDCDT:PC₇₁BM, P3HT:PC₇₁BM and PDCBT:ITIC) are partial to HTLs with lower γ_S. Based on the surface property–morphology–device performance correlations, a suggestion to select a suitable HTL in terms of γ_S for a specific BHJ with favored molecular arrangement is provided. This work enriches the fundamental understandings on the interface characteristics and morphological control toward high‐efficiency OSCs based on a wide range of BHJ materials.     

On‐Surface Synthesis of Graphyne‐Based Nanostructures

The successful synthesis of stacking graphdiynes has stimulated numerous fascinating applications. However, it still remains challenging to prepare atomically precise 2D graphdiyne and other graphyne‐based structures. The development of on‐surface synthesis has contributed to many secondary graphyne‐based structures that are directive in fabricating extended graphyne networks. Herein, the recent progress concerning on‐surface synthesis of graphyne‐based nanostructures, especially atomically precise graphdiyne nanowires, is summarized.