High-performance Transparent Heaters Research Articles

Heat-driven self-cleaning glass based on fast thermal response for automotive sensors

High-performance transparent heaters, which can prevent a camera lens from frosting/icing and evaporate droplets on the surface of the lens, are one of the promising self-cleaning devices for automotive optical sensors such as an automotive camera and Light Detection and Ranging (LiDAR) sensor. However, many previous studies on transparent heaters have mainly focused on advanced materials and manufacturing technologies. For the commercialization of transparent heaters, practical methods to improve thermal response and evaluate the cleaning performance of contaminants must be investigated. Hence, we propose a heat-driven self-cleaning glass based on fast thermal response using overdrive voltage for automotive sensors. The proposed device was designed as a mesh-type patterned electrode for high transmittance and fabricated using the Micro-electro-mechanical-systems (MEMS) process. The proposed device generated heat when voltage was applied and reached 85 °C in approximately 4 sec when driven using an overdrive driving method. In addition, performing a test to remove droplets of various volumes generated on the surface of the proposed device, it was confirmed that droplets of various volumes could be removed within 30 sec. For a demonstration of the proposed concept, the heat-driven self-cleaning glass was applied to an automotive camera, and the image distorted by rainwater on the camera lens became clear when the glass was operated. We believe these experimental results are useful to commercialize transparent heaters for the next-generation automotive optical sensors.

Efficient Protection of Silver Nanowire Transparent Electrodes by All-Biorenewable Layer-by-Layer Assembled Thin Films.

An efficient protection strategy for silver nanowire-based transparent electrodes (AgNW TEs) is developed to enhance their poor adhesion force on substrates and thermal, optical, chemical, and electrical stabilities. Chitin nanofibers (CNFs) and alkali lignin (AL), which possess high mechanical property, a gas/moisture barrier, and UV absorption properties, are successively assembled on AgNW TEs through layer-by-layer (LBL) assembly based on their oppositely charged surfaces. The formation of LBL-assembled CNFs and AL (CNF/AL)10 bilayers, where 10 is the optimized number of bilayers, on the aldehyde-modified AgNW (Al-AgNW) TEs does not deteriorate their electrical conductivity (17.3 ± 2.1 Ω/□) and transmittance (90.1 ± 0.3% at 550 nm), and the (CNF/AL)10 bilayer-coated Al-AgNW [(CNF/AL)10@Al-AgNW] TEs present considerable enhancement in their adhesion force and thermal, optical, chemical, and electrical durability. In detail, their optoelectrical properties are stable over 200 cycles of the scotch peel-off test, for 10 h sonication, up to 350 °C, under UV/O3 treatment for 100 min, in 10% HCl and 28% NH3 for 6 and 12 h, and at an electrical potential up to 14 V, respectively. These features make (CNF/AL)10@Al-AgNW TEs suitable as a durable high-performance transparent heater.

High-performance transparent heater with Ag paste-based nanomesh electrodes

Transparent heaters have attracted significant attention in recent years because of their wide range of potential applications, including defogging and defrosting windshields, thermochromic smart windows, and wearable heating devices. This paper presents a comparison of the performances of a transparent heater with nanomesh electrodes and that with micromesh electrodes. Both transparent heaters exhibit excellent basic characteristics, with an optical transmittance of more than 90%, and sheet resistance of less than 2 Ω/□. From the thermal response time tests, we observed a shorter thermal response time of 30 s for the nanomesh heater. This is because the heater must warm the transparent area; hence, the smaller transparent area of the nanomesh is more advantageous for a transparent heater. Furthermore, the nanomesh transparent heater exhibited excellent heating stability and performance at various sizes. The promising results of this study can facilitate significant and practical applications of transparent heaters, such as windshields for vehicles.

Flexible Transparent Heater Fabricated from Spray-Coated In:ZnO/Ag-NWs/In:ZnO Multilayers on Polyimide Foil.

A flexible transparent heater is presented, based on an all-sprayed composite architecture of indium-doped zinc oxide (IZO) layers that sandwich a network of silver nanowires, on a polyimide-foil substrate. This architecture could be materialized through the development of a low-temperature (240 °C) spray-pyrolysis process for the IZO layers, which is compatible with the thermal stability of the transparent polyimide substrate and allows for the formation of compact and transparent layers, without precipitates. The IZO layers entirely embed the silver nanowires, offering protection against environmental degradation and decreasing the junction resistance of the nanowire network. The resulting transparent heaters have a high mean transmittance of 0.76 (including the substrate) and sheet resistance of 7.5 Ω/sq. A steady-state temperature of ~130 °C is achieved at an applied bias of 3.5 V, with fast heater response times, with a time constant of ~4 s The heater is mechanically stable, reaching or surpassing 100 °C (at 3.5 V), under tensile, respectively, compressive-bending stress. This work shows that high-performance transparent heaters can be fabricated using all-sprayed oxide/silver-nanowire composite coatings, that are compatible with large-scale and low-cost production.

Enhancement of electrothermal performance in single-walled carbon nanotube transparent heaters by room temperature post treatment

High-performance transparent heaters were fabricated on glass substrate using spray coating the solution processed single walled carbon nanotubes (SWCNT). Transparent heaters were treated with acid and alcohol mixture (10:1) to display high heating performance. The post treated SWCNT heater with 81% transmittance at 550nm reached a steady-state temperature of 424K with a heating rate of 0.6K/s when 60V is applied. The enhancement of electrothermal performance was studied in terms of heating rate, input power density and applied voltage. The enhanced heating performance attributed due to the effective wetting of the SWCNT network which intern reduce the sheet resistance of the conducting films. Defrosters realized using the post treated heater able to remove frost within a minute when 30V was applied. The excellent power dependent heating performance with high stability indicates that the SWCNT heaters can be used in the temperature controlled heaters, smart windows and defrosters.

Recyclable patterning of silver nanowire percolated network for fabrication of flexible transparent electrode

Recent studies have revealed that silver nanowires (AgNWs) are a promising material for highly flexible transparent electrodes. Here we introduce a novel photoinduced recyclable approach to AgNW patterning to overcome the issue of loss of material during fabrication of AgNW patterns, which is a leading factor in the high fabrication costs of AgNW-based electrodes. Our patterning scheme involves the selective irradiation of an AgNW/polymer composite with high-intensity pulsed light, followed by immersion of the sample in a liquid and an ultrasonication treatment. The nanowires that detach during sonication could be recycled, and the recycled AgNWs achieved comparable performance to that of pristine AgNWs. The recycled AgNWs were also superior to commercial indium tin oxide films and other competing materials. We successfully demonstrated a high performance transparent heater by employing the recyclable patterning method and recycled AgNWs.

Area-Selective Lift-Off Mechanism Based on Dual-Triggered Interfacial Adhesion Switching: Highly Facile Fabrication of Flexible Nanomesh Electrode.

With the recent emergence of flexible and wearable optoelectronic devices, the achievement of sufficient bendability and stretchability of transparent and conducting electrodes (TCEs) has become an important requirement. Although metal-mesh-based structures have been investigated for TCEs because of their excellent performances, the fabrication of mesh or grid structures with a submicron line width is still complex due to the requirements of laborious lithography and pattern transfer steps. Here, we introduce an extremely facile fabrication technique for metal patterns embedded in a flexible substrate based on submicron replication and an area-selective delamination (ASD) pattern. The high-yield, area-specific lift-off process is based on the principle of solvent-assisted delamination of deposited metal thin films and a mechanical triggering effect by soft wiping or ultrasonication. Our fabrication process is very simple, convenient, and cost-effective in that it does not require any lithography/etching steps or sophisticated facilities. Moreover, their outstanding optical and electrical properties (e.g., sheet resistances of 0.43 Ω sq-1 at 94% transmittance), which are markedly superior to those of other flexible TCEs, are demonstrated. Furthermore, there is no significant change of resistance over 1000 repeated bending cycles, with a bending radius of 5 mm, and immersion in various solvents such as salt water and organic solvents. Finally, we demonstrate high-performance transparent heaters and flexible touch panels fabricated using the nanomesh electrode, confirming the long-range electrical conduction and reliability of the electrode.

Observation of convection phenomenon by high-performance transparent heater based on Pt-decorated Ni micromesh

In this study, we report for the first time on the convection phenomenon for the consistent and sensitive detection of target materials (particulate matter (PM) or gases) with a high-performance transparent heater. The high-performance transparent heater, based on Pt-decorated Ni micromesh, was fabricated by a combination of transfer printing process and Pt sputtering. The resulting transparent heater exhibited excellent mechanical durability, adhesion with substrates, flexibility, and heat-generating performance. We monitored the changes in the PM concentration and temperature in an airtight chamber while operating the heater. The temperature in the chamber was increased slightly, and the PM2.5 concentration was increased by approximately 50 times relative to the initial state which PM is deposed in the chamber. We anticipate that our experimental findings will aid in the development and application of heaters for sensors and actuators as well as transparent electrodes and heating devices.

Electron beam irradiated silver nanowires for a highly transparent heater.

Transparent heaters have attracted increasing attention for their usefulness in vehicle windows, outdoor displays, and periscopes. We present high performance transparent heaters based on Ag nanowires with electron beam irradiation. We obtained an Ag-nanowire thin film with 48 ohm/sq of sheet resistance and 88.8% (substrate included) transmittance at 550 nm after electron beam irradiation for 120 sec. We demonstrate that the electron beam creates nano-soldering at the junctions of the Ag nanowires, which produces lower sheet resistance and improved adhesion of the Ag nanowires. We fabricated a transparent heater with Ag nanowires after electron beam irradiation, and obtained a temperature of 51 °C within 1 min at an applied voltage of 7 V. The presented technique will be useful in a wide range of applications for transparent heaters.