Single-Crystalline Silicon Frameworks: A New Platform for Transparent Flexible Optoelectronics

Centrifugal Inertia-Induced Directional Alignment of AgNW Network for Preparing Transparent Electromagnetic Interference Shielding Films with Joule Heating Ability

Transparent electromagnetic interference (EMI) shielding is highly desired in specific visual scenes, but the challenge remains in balancing their EMI shielding effectiveness (SE) and optical transmittance. Herein, this study proposed a directionally aligned silver nanowire (AgNW) network construction strategy to address the requirement of high EMI SE and satisfactory light transmittance using a rotation spraying technique. The orientation distribution of AgNW is induced by centrifugal inertia force generated by a high-speed rotating roller, which overcomes the issue of high contact resistance in random networks and achieves high conductivity even at low AgNW network density. Thus, the obtained transparent conductive film achieved a high light transmittance of 72.9% combined with a low sheet resistance of 4.5 Ω sq-1 and a desirable EMI SE value of 35.2 dB at X band, 38.9 dB in the K-band, with the highest SE of 43.4 dB at 20.4 GHz. Simultaneously, the excellent conductivity endowed the film with outstanding Joule heating performance and defogging/deicing ability, ensuring the visual transparency of windows when shielding electromagnetic waves. Hence, this research presents a highly effective strategy for constructing an aligned AgNW network, offering a promising solution for enhancing the performance of optical-electronic devices.

Freestanding Serpentine Silicon Strips with Ultrahigh Stretchability over 300% for Wearable Electronics

Well-functionalized electronic materials, such as silicon, in a stretchable format are desirable for high-performance wearable electronics. However, obtaining Si materials that meet the required stretchability of over 100% for wearable applications remains a significant challenge. Herein, a rational design strategy is proposed to achieve freestanding serpentine Si strips (FS-Si strips) with ultrahigh stretchability, fulfilling wearable requirements. The self-supporting feature makes the strips get rid of excessive constraints from substrates and enables them to deform with the minimum strain energy. Micrometer-scale thicknesses enhance robustness, and large diameter-to-width ratios effectively reduce strain concentration. Consequently, the FS-Si strips with the optimum design could withstand 300% stretch, bending, and torsion without fracturing, even under rough manual operation. They also exhibit excellent stability and durability over 50,000 cycles of 100% stretching cycles. For wearable applications, the FS-Si strips can maintain conformal contact with the skin and have a maximum stretchability of 120%. Moreover, they are electrically insensitive to large deformations, which ensure signal stability during their daily use. Combined with mature processing techniques and the excellent semiconductor properties of Si, FS-Si strips are promising core stretchable electronic materials for wearable electronics.

A Grating Interferometric Acoustic Sensor Based on a Flexible Polymer Diaphragm

This study presents a grating interferometric acoustic sensor based on a flexible polymer diaphragm. A flexible-diaphragm acoustic sensor based on grating interferometry (GI) is proposed through design, fabrication and experimental demonstration. A gold-coated polyethylene terephthalate diaphragm was used for the sensor prototype. The vibration of the diaphragm induces a change in GI cavity length, which is converted into an electrical signal by the photodetector. The experimental results show that the sensor prototype has a flat frequency response in the voice frequency band and the minimum detectable sound pressure can reach 164.8 µPa/√Hz. The sensor prototype has potential applications in speech acquisition and the measurement of water content in oil. This study provides a reference for the design of optical interferometric acoustic sensor with high performance.

Transparent and Stretchable Electromagnetic Interference Shielding Film with Fence-like Aligned Silver Nanowire Conductive Network

Flexible transparent conductive electrodes (TCEs) that can be used as electromagnetic interference (EMI) shielding materials have a great potential for use as electronic components in optical window and display applications. However, development of TCEs that display high shielding effectiveness (SE) and good stretchability for flexible electronic device applications has proven challenging. Herein, this study describes a stretchable polydimethylsiloxane (PDMS)/silver nanowire (AgNW) TCE with a fence-like aligned conductive network that is fabricated via pre-stretching method. The fence-like AgNW network endowed the PDMS/AgNW film with excellent optoelectronic properties, i.e., low sheet resistance of 7.68 Ω sq^-1 at 73.7% optical transmittance, thus causing an effective EMI SE of 32.2 dB at X-band. More importantly, the fence-like aligned AgNW conductive network reveals a high stability toward tensile deformation, thus gives the PDMS/AgNW film stretch-stable conductivity and EMI shielding property in the strain range of 0-100%. Typically, the film can reserve ≈70% or 80% of its initial EMI SE when stretching at 100% strain or stretching/releasing (50% strain) for 128 cycles, respectively. Additionally, the film exhibits a low-voltage driven and stretchable Joule heating performance. With these overall performances, the PDMS/AgNW film should be well suited for use in flexible and stretchable optical electronic devices.

Strain effect on the field-effect sensing property of Si wires

Silicon-based field effect transistor (FET) sensors with high sensitivity are emerging as powerful sensors for detecting chemical/biological species. Strain engineering has been demonstrated as an effective means to improve the performance of Si-based devices. However, the strain effect on the field-effect sensing property of silicon materials has not been studied yet. Here, we investigate the strain effect on the field-effect sensing property of silicon wires by taking humidity sensing as an example. The humidity sensitivity of FET sensors based on silicon wires increases with increasing tensile strain but decreases with increasing compressive strain. The sensitivity is very responsive to strain with an enhancement factor of 67 for tensile strain. Theoretical analysis shows that the sensitivity variation under different strains is mainly attributed to the change in adsorption energy between silicon wires and water molecules. This work indicates that strain engineering can be an effective route to modulate the field-effect sensing property of Si wires for constructing highly sensitive Si-based FET sensors.

Flexible and Semi-Transparent Silicon Solar Cells as a Power Supply to Smart Contact Lenses

Supplying electric power to wearable IoT devices, particularly smart contact lenses (SCLs), is one of the main obstacles to widespread adoption and commercialization. In the present study, we have successfully designed, fabricated, and characterized semi-transparent, self-supported, and flexible single crystalline silicon solar cells using a single-sided micromachining procedure. Optical, mechanical, and electrical simulations, together with the practical measurements, verify the application of our developed solar cells to be mounted on a limited-footprint and flexible SCL. The 15 μm-thick silicon solar cells conformally fit on a dome-shaped contact lens (ROC = 8 mm) without any mechanical and electrical degradation. This homojunction photovoltaic device containing an array of micro-holes exhibits a V _oc, J _sc, and maximum power density of 504 mV, 6.48 mA cm^-2, and 1.67 mW cm^-2, respectively, at 25% visible light transparency under an AM1.5 one sun condition. Furthermore, the measurements were conducted under low-intensity indoor light conditions and resulted in a maximum power output of 25 and 42 μW cm^-2 for the 50 and 25% transparent solar cells, respectively.

Multifunctional Textile Electronic with Sensing, Energy Storing, and Electrothermal Heating Capabilities

The development of wearable devices has stimulated significant engineering and technologies of textile electronics (TEs). Improving sensing, energy-storing, and electro-heating capabilities of TEs is still challenging but crucial for their practical applications. Herein, a drip-coating method that constructs a dense β-FeOOH scaffold on a nylon strip for enhancing polypyrrole loading is proposed, which facilitates the fabrication of highly conductive and hydrophobic PFCNS (polypyrrole/β-FeOOH/nylon strip). The space provided by the β-FeOOH scaffold increases the mass of polypyrrole on fibers from 1.1 (polypyrrole/nylon strip) to 3.0 mg cm^-2 (polypyrrole/β-FeOOH/nylon strip), which decreases the resistance from 104.96 to 34.29 Ω cm^-1. The PFCNS exhibits a linear elastic modulus of 0.758 MPa within 150% strain, performs a unique resistance variation mechanism, and enables great sensing capability with rapid response time (140 ms), long durability (10,000 stretching-recovering), and effective movement monitoring (e.g., breathing, back bending, jumping). The sensing signals for knee bending have been analyzed in detail by combining with both stretching and pressing response mechanisms. The PFCNS electrode attains a diffusion-controlled capacitance of 574 mF cm^-2 and discharging-capacitance of 916 mF cm^-2. Furthermore, an interdigitally parallel connection is proposed, which assists the PFCNS heater in achieving high temperature (84 °C) at a low voltage (4 V). This work provides a simple route for nylon-based TEs and promises satisfactory application in wearable sensors, power sources, and heaters.