Synthesis of Ultralong Copper Nanowires for High-Performance Flexible Transparent Conductive Electrodes: The Effects of Polyhydric Alcohols

Formation of Self-Assembled Nanowires from Copper Nanoparticles Synthesized by the Electro-Explosion of Wires Technique-Study of the Time-Dependent Structural and Functional Evolution

We report here the formation of Cu nanowires (CuNWs) from Cu nanoparticles (CuNPs) by a self-assembly process. The CuNPs were synthesized by the electro-explosion of wire (EEW) technique that included nonequilibrium processes for the synthesis. Structural evolution in terms of aggregation or nanowire formation in the samples was observed when the CuNPs were kept for a month after synthesis in a glass vial without the application of any external driving force. The emergence of tangled CuNWs was noticed at the bottom of the vials only when no agitation or aeration was allowed. The nanowires were characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Thermal oxidation of the nanowire samples implied that they could convert into rod-shaped structures. Loss of functionality was also observed in the hemoglobin precipitation study conducted to compare the activity of freshly prepared CuNPs and CuNWs. From the above observations, we conclude that the CuNP, after synthesis, possesses a huge amount of energy, and attainment of equilibrium occurs through either aggregation (clustering) or ordered self-assembly, depending on the conditions applied.

Synthesis of Ni Nanosheets by Template-Free Method and Their Application in Conductive and Magnetic Flexible Electrons

Two-dimensional Ni nanosheets are synthesized by the template-free method using Na₃CA as an orientation agent in liquid phase, and then the conductive Ni nanosheet ink is prepared for conductive circuits on flexible electronics. The thickness of the Ni nanosheets is about 800 nm, and the diameter is about 100 μm. Na₃CA plays a structural guiding role to form Ni nanocrystals, promoting the self-assembly of Ni nanocrystals into Ni nanosheets effectively. The laminar stackable patterns of the Ni nanosheet circuits increase the contact area of the Ni nanosheets and improve the stability of the conductors under stress. Ni nanosheets can bend with the folding of the structure, while the mutual constraints between their layers promote the circuit to remain stable during the bending state. Therefore, the Ni nanosheet circuits display excellent conductive performance during the tiled and bent stages. In addition, Ni nanosheet/Ag nanowire composites are prepared to enhance conductivity to meet higher demands. Moreover, the experimental results of its application in magnetic guided switch closure circuits show that Ni nanosheet/Ag nanowire composites have the potential to participate in both conductive and magnetic field applications simultaneously.

Thermochromic Energy Efficient Windows: Fundamentals, Recent Advances, and Perspectives

Thermochromic energy efficient windows represent an important protocol technology for advanced architectural windows with energy-saving capabilities through the intelligent regulation of indoor solar irradiation and the modulation of window optical properties in response to real-time temperature stimuli. In this review, recent progress in some promising thermochromic systems is summarized from the aspects of structures, the micro-/mesoscale regulation of thermochromic properties, and integration with other emerging energy techniques. Furthermore, the challenges and opportunities in thermochromic energy-efficient windows are outlined to promote future scientific investigations and practical applications in building energy conservation.

van der Waals integration of mixed-dimensional CeO2@Bi heterostructure for high-performance self-powered photodetector with fast response speed

Heterostructures have been extensively investigated for optoelectronic devices owing to their fantastic physicochemical properties. Herein, a mixed-dimensional van der Waals heterostructure (vdWH) CeO₂@Bi, 1D ceria (CeO₂) loaded with 0D bismuth quantum dots (Bi QDs), is synthesized through a facile hydrothermal bottom-up method. It is found that the fabricated CeO₂@Bi-based photoelectrochemical (PEC)-type photodetector (PD) shows self-powered photodetection capability with a fast photoresponse speed of 0.02 s. Besides, a photocurrent of 2.00 μA cm^-2 and a photoresponsivity of 888.89 μA W^-1 under 365 nm illumination are obtained. Furthermore, good long-term cycle stability is also observed after 1 month in a harsh environment, indicating the great potential for practical applications. These results are further supported by density functional theory (DFT) calculations. We believe that the presented work is expected to provide a new pathway for the future utilization of vdWHs for high-performance optoelectronics.

Highly stretchable electroluminescent device based on copper nanowires electrode

Although stretchable electroluminescent (EL) devices have been the research hotspots for decades because of their enormous market value in lighting sources and displays, fabrication of the stretchable EL device through a simple, cost-effective, and scalable method still remains an open issue. Here, a novel all solution-processed method is developed to fabricate a high-performance alternative current electroluminescent (ACEL) device based on copper nanowires (Cu NWs). The Cu NW-based electrode exhibited a low resistance change of less than 10% after 1000 stretching cycles at a tensile strain of 30% and the resistance variation of the electrode in one stretching-releasing cycle was less than 1% at the 1000th. To substantiate suitability for the wearable application, the ACEL device was stretched at a tensile strain of 100% and it retained a luminance of 97.6 cd/m². Furthermore, the device works well under different deformations such as bending, folding, rolling, and twisting. To the best of our knowledge, this is the first demonstration of Cu NWs applied in a stretchable ACEL, promising cost-effective electrode materials for various wearable electronics applications.

3D Printed High Performance Silver Mesh for Transparent Glass Heaters through Liquid Sacrificial Substrate Electric-Field-Driven Jet

Transparent glass with metal mesh is considered a promising strategy for high performance transparent glass heaters (TGHs). However, the realization of simple, low-cost manufacture of high performance TGHs still faces great challenges. Here, a technique for the fabrication of high performance TGHs is proposed using liquid sacrificial substrate electric-field-driven (LS-EFD) microscale 3D printing of thick film silver paste. The liquid sacrificial substrate not only significantly improves the aspect ratio (AR) of silver mesh, but also plays a positive role in printing stability. The fabricated TGHs with a line width of 35 µm, thickness of 12.3 µm, and pitch of 1000 µm exhibit a desirable optoelectronic performance with sheet resistance (R_s ) of 0.195 Ω sq^-1 and transmittance (T) of 88.97%. A successful deicing test showcases the feasibility and practicality of the manufactured TGHs. Moreover, an interface evaporator is developed for the coordination of photothermal and electrothermal systems based on the high performance TGHs. The vapor generation rate of the device reaches 10.69 kg m^-2 h^-1 with a voltage of 2 V. The proposed technique is a promising strategy for the cost-effective and simple fabrication of high performance TGHs.

Copper Nanowires for Transparent Electrodes: Properties, Challenges and Applications

Transparent electrodes are essential elements of devices bearing a screen or display, as well as solar cells, LEDs etc. To overcome the drawbacks presented by indium tin oxide, nanomaterials have been proposed for a long time as alternatives. Metal nanowires are particularly interesting for their high intrinsic electrical conductivity. Copper nanowires have attracted wide interest due to the low cost and high abundancy of the starting material. However, they are easily oxidized thus suitable strategies must be devised to prevent it. This review discusses the fundamental properties and challenges of copper nanowires, focusing on the efforts made to make them longer and thinner then the strategies to prevent oxidation and to join them in the network are presented. After that, mechanical properties are summarized and applications are presented, before conclusions and perspectives are finally given.

High-Performance Flexible Transparent Conductive Films Enabled by a Commonly Used Antireflection Layer

Recently, silver nanowire-based transparent conductive films (AgNW-based TCFs) with excellent comprehensive performance have aroused wide and great interest. However, it is always difficult to simultaneously improve the performances of TCFs in all aspects. In this work, by introducing silica nanoparticles (SiO₂-NPs) with a smaller particle size, several properties of AgNW-based TCFs were optimized successfully. The transmittance and conductivity were improved simultaneously, and smaller particle size was proven to be more suitable to achieve TCFs with excellent optoelectrical properties. Typically, an AgNW/SiO₂-based TCF with a sheet resistance of 250 Ω/sq and transmittance of 93.6% (including the poly (ethylene terephthalate) substrate, abbreviated as PET) could be obtained by using SiO₂-NPs with a size of ∼21 nm, and this transmittance is even higher than that of the bare PET (91.8%) substrate. We demonstrated that the layer formed through self-assembly of SiO₂-NPs can cut down the light scattering on the AgNW surface through total reflection, thus leading to a low haze of AgNW/SiO₂-based TCFs. Very interestingly, the SiO₂-NPs conducted away most of the heat generated during laser ablation, protecting the AgNWs from excessive melt and PET from empyrosis, and thus ensuring the TCFs with high transmittance and patterning accuracy. Besides, AgNW/SiO₂-based TCFs have smaller surface roughness, better flexibility, and adhesive force. To the best of our knowledge, the comprehensive performance of the AgNW/SiO₂-based TCFs reaches the highest level among recently reported novel TCFs.

Van der Waals Integration of Bismuth Quantum Dots-Decorated Tellurium Nanotubes (Te@Bi) Heterojunctions and Plasma-Enhanced Optoelectronic Applications

Van der Waals (vdW)-integrated heterojunctions have been widely investigated in optoelectronics due to their superior photoelectric conversion capability. In this work, 0D bismuth quantum dots (Bi QDs)-decorated 1D tellurium nanotubes (Te NTs) vdW heterojunctions (Te@Bi vdWHs) are constructed by a facile bottom-up assembly process. Transient absorption spectroscopy suggests that Te@Bi vdWH is a promising candidate for new-generation optoelectronic devices with fast response properties. The subsequent experiments and density functional theory calculations demonstrate the vdW interaction between Te NTs and Bi QDs, as well as the enhanced optoelectronic characteristics owing to the plasma effects at the interface between Te NTs and Bi QDs. Moreover, Te@Bi vdWHs-based photodetectors show significantly improved photoresponse behavior in the ultraviolet region compared to pristine Te NTs or Bi QDs-based photodetectors. The proposed integration of vdWHs is expected to pave the way for constructing new nanoscale heterodevices.

Recent progress of solution-processed Cu nanowires transparent electrodes and their applications

Research on next-generation transparent electrode (TE) materials to replace expensive and fragile indium tin oxide (ITO) is crucial for future electronics. Copper nanowires (Cu NWs) are considered as one of the most promising alternatives due to their excellent electrical properties and low-cost processing. This review summarizes the recent progress on the synthesis methods of long Cu NWs, and the fabrication techniques and protection measures for Cu NW TEs. Applications of Cu NW TEs in electronics, such as solar cells, touch screens, and light emitting diodes (LEDs), are discussed.

Fabrication of High-Performance Silver Mesh for Transparent Glass Heaters via Electric-Field-Driven Microscale 3D Printing and UV-Assisted Microtransfer

Great challenges remain concerning the cost-effective manufacture of high-performance metal meshes for transparent glass heaters (TGHs). Here, a high-performance silver mesh fabrication technique is proposed for TGHs using electric-field-driven microscale 3D printing and a UV-assisted microtransfer process. The results show a more optimal trade-off in sheet resistance (R_s = 0.21 Ω sq^-1 ) and transmittance (T = 93.9%) than for indium tin oxide (ITO) and ITO substitutes. The fabricated representative TGH also exhibits homogeneous and stable heating performance, remarkable environmental adaptability (constant R_s for 90 days), superior mechanical robustness (R_s increase of only 0.04 in harsh conditions-sonication at 100 °C), and strong adhesion force with a negligible increase in R_s (2-12%) after 100 peeling tests. The practical viability of this TGH is successfully demonstrated with a deicing test (ice cube: 21 cm³ , melting time: 78 s, voltage and glass thickness: 4 V, 5 mm). All of these advantages of the TGHs are attributed to the successful fabrication of silver meshes with high resolution and high aspect ratio on the glass substrate using the thick film silver paste. The proposed technique is a promising new tool for the inexpensive fabrication of high-performance TGHs.

Mechanically Flexible Conductors for Stretchable and Wearable E-Skin and E-Textile Devices

Considerable progress in materials development and device integration for mechanically bendable and stretchable optoelectronics will broaden the application of "Internet-of-Things" concepts to a myriad of new applications. When addressing the needs associated with the human body, such as the detection of mechanical functions, monitoring of health parameters, and integration with human tissues, optoelectronic devices, interconnects/circuits enabling their functions, and the core passive components from which the whole system is built must sustain different degrees of mechanical stresses. Herein, the basic characteristics and performance of several of these devices are reported, particularly focusing on the conducting element constituting them. Among these devices, strain sensors of different types, energy storage elements, and power/energy storage and generators are included. Specifically, the advances during the past 3 years are reported, wherein mechanically flexible conducting elements are fabricated from (0D, 1D, and 2D) conducting nanomaterials from metals (e.g., Au nanoparticles, Ag flakes, Cu nanowires), carbon nanotubes/nanofibers, 2D conductors (e.g., graphene, MoS₂ ), metal oxides (e.g., Zn nanorods), and conducting polymers (e.g., poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate), polyaniline) in combination with passive fibrotic and elastomeric materials enabling, after integration, the so-called electronic skins and electronic textiles.