Study on Ag mesh/conductive oxide hybrid transparent electrode for film heaters

Thermal Profiles of Carbon Fiber Based Anisotropic Thin-Films: An Emerging Heat Management Solution for High-Current Flow Electrocatalysis and Electrochemical Applications

Carbon fiber has been extensively used in the photocatalysis, electrocatalysis and energy storage fields as supporting platform and conductive media. However, less attention has been paid with regards to its function in phonon transport and thermal management. We have investigated the effect of current flow direction on the heat management performance of carbon fiber based thin film heaters (CFTFHs) with anisotropic percolation network of carbon fibers (CFs). The anisotropic percolation network of carbon fibers (CFs) formed by roll-to-roll spray coating leads to the anisotropic electrical properties of CFs. As a result, CFs based thin films (CFTFs) have lower sheet resistance when measured parallel to the CFs alignment, compared to when they are aligned perpendicular. Because connectivity and current flow in CFs are critically dependent on the direction alignment of CFs, the saturation temperature (106.4 °C) of CFTFH with parallel aligned carbon fiber is higher than that (117.3 °C) of CFTFH with perpendicular alignment. Therefore, current flow in the same direction as the alignment of CFs is very important to achieve high-performance. Moreover, our study on thermal profile of anisotropic CFTFs under high current flows illustrates that carbon fiber thin films have great potential in thermal management solution for electrocatalytic and electrochemical energy storage applications.

Transparent heater with meshed amorphous oxide/metal/amorphous oxide for electric vehicle applications

For electric vehicle application, one of the problems to be solved is defrosting or defogging a windshield or a side mirror without gas-fired heaters. In this paper, we report on a high performance of transparent heater with meshed amorphous-SiInZnO (SIZO)/ Ag/ amorphous-SiInZnO (SIZO) (SAS) for pure electric vehicles. We have adopted amorphous oxide materials like SIZO since SIZO is well known amorphous oxide materials showing high transparency and smooth surface roughness. With the mesh processing technology, a transparent electrode with high transmittance of 91% and low sheet resistance of 13.8 Ω/ϒ was implemented. When a 10 V supply voltage is applied to transparent heater, the transparent heater on glass substrate was heated up to 130^oC in just 5 seconds and then reached to 250^oC after tens of seconds due to the low sheet resistance. In addition, the SAS transparent meshed heater (TMH) showed high stability under cycling test and long time working stability test.

Transparent Photothermal Heaters from a Soluble NIR-Absorbing Diimmonium Salt

While numerous near-infrared (NIR) materials have emerged, most of them are strongly colored or black due to the absorption band or tails in the visible region. Here, a highly transparent and soluble NIR-absorbing ionic salt, isobutyl-substituted diimmonium borate (IDI), is synthesized and fabricated, through a solution process, as a thin film that shows a transmittance of over 93% in the whole visible region. A transparent photothermal (PT) film heater is fabricated with the IDI-doped polymer solution, which shows a photothermal conversion efficiency (η_PT ) of 75.2%. Additionally, the prepared PT heater shows a high water evaporation conversion efficiency (η_w ) of 68.8% upon exposure to a 1064 nm laser. Furthermore, the transparent IDI film affords the development of a wireless transparent actuator for the first time, generating a bending angle over 75°, with over 2700 bending cycles. The transparent IDI film creates a hot transparent Venus flytrap and a colorful or fluorescent actuator upon the addition of colorants without losing the actuation properties.

Nickel-enhanced silver nanowire-based transparent heater with large size

An effective process for homogeneous electrodeposition of nickel was developed to improve the performance of silver nanowire-based transparent heaters (AgNW-THs). After electroplating Ni, the silver nanowires are uniformly coated by a layer Ni with 20-40 nm thickness, which has a small effect on the device transmittance, but significantly enhances its conductivity. Most excitingly, the nickel shell leads to a great increase of the temperature toleration of the AgNW-THs. A transparent tubular heater with large size of 3 cm in diameter and 20 cm in length is successfully fabricated, showing excellent heating properties in that the steady-state temperature can reach 284.3 °C and there is minimal variance in temperature after 10 heating cycles, and by using this tube, red Cu powder was oxidized into black CuO in a short time, which was visually observed. Additionally, two other shapes of transparent heaters with large size were constructed for dehydration of CuSO4·5H2O and burning of red phosphorus, respectively. This kind of transparent heater has wide applications requiring high transmittance, excellent temperature toleration and large size, especially for teaching experiment apparatus in a visual model.

Hydrophobic and stretchable Ag nanowire network electrode passivated by a sputtered PTFE layer for self-cleaning transparent thin film heaters

We demonstrated hydrophobic, flexible/stretchable, and transparent electrodes made up of Ag nanowire (NW) networks passivated by a sputtered polytetrafluoroethylene (PTFE) layer to produce self-cleaning transparent thin film heaters (TFHs). Using carbon nanotubes and a PTFE mixed conducting target, we successfully sputtered a transparent PTFE layer on the Ag NW network using mid-frequency magnetron sputtering. The hydrophobic surface of the PTFE/Ag NW electrodes led to water-repelling and self-cleaning transparent Ag NW electrodes, which are beneficial for transparent TFH-based smart windows. Furthermore, hydrophobic PTFE/Ag NW electrodes coated on polyethylene terephthalate (PET) and polyurethane (PU) substrates showed outstanding flexibility and stretchability, respectively, due to the capping effect of the PTFE layer. Based on outer/inner bending and stretching test results, we demonstrated the superior mechanical properties of the PTFE/Ag NW electrode compared to a bare Ag NW electrode. Finally, we investigated the feasibility of the PTFE/Ag NW film coated on a PU substrate as a transparent and stretchable electrode for stretchable and self-cleaning transparent TFHs. The effective heat generation of the stretchable PTFE/Ag NW electrode indicates the potential for energy-efficient multi-functional PTFE/Ag NW-based TFHs attached to automobile windows.

We demonstrated hydrophobic, flexible/stretchable, and transparent electrodes made up of Ag nanowire networks passivated by a sputtered polytetrafluoroethylene layer to produce self-cleaning transparent film heaters.

Transparent Electrode Based on Silver Nanowires and Polyimide for Film Heater and Flexible Solar Cell

Transparent, conductive, and flexible Ag nanowire (NW)-polyimide (PI) composite films were fabricated by a facile solution method. Well-dispersed Ag NWs result in percolation networks on the PI supporting layer. A series of films with transmittance values of 53–80% and sheet resistances of 2.8–16.5 Ω/sq were investigated. To further verify the practicability of the Ag NWs-PI film in optoelectronic devices, we utilized it in a film heater and a flexible solar cell. The film heater was able to generate a temperature of 58 °C at a driving voltage of 3.5 V within 20 s, indicating its potential application in heating devices that require low power consumption and fast response. The flexible solar cell based on the composite film with a transmittance value of 71% presented a power conversion efficiency of 3.53%. These successful applications proved that the fabricated Ag NWs-PI composite film is a good candidate for application in flexible optoelectronic devices.

Thermally evaporated indium-free, transparent, flexible SnO2/AgPdCu/SnO2 electrodes for flexible and transparent thin film heaters

We investigated the characteristics of themally evaporated SnO₂/Ag-Pd-Cu (APC)/SnO₂ multilayer films for applications as damage-free, indium-free, flexible, and transparent electrodes for high performance flexible and transparent thin film heaters (TFHs). The top and bottom SnO₂ layers and APC interlayer were prepared by a multi-source evaporation process, and the effect of the thickness of each layer on the resistivity, optical transmittance, and mechanical flexibility of the SnO₂/APC/SnO₂ electrodes was investigated in detail. Based on a figure of merit value, we obtained a SnO₂/APC/SnO₂ electrode with a low sheet resistance of 9.42 Ohm/square and a high optical transmittance of 91.14%. In addition, we examined the mechanical properties of the SnO₂/APC/SnO₂ electrode using various bending tests such as inner bending, outer bending, dynamic fatigue, and a twisting test. By comparing the crack shape of the SnO₂/APC/SnO₂ electrode bent beyond the critical bending radius (2~3 mm), we suggest a possible crack formation mechanism for the SnO₂/APC/SnO₂ electrodes. Furthermore, we evaluated the feasibility of the SnO₂/APC/SnO₂ electrodes for flexible and transparent TFHs. By correlating the sheet resistance of the SnO₂/APC/SnO₂ electrode and the performance of TFHs, we show the importance of transparent electrodes for high performance flexible and transparent TFHs.

Microscopic Evaluation of Electrical and Thermal Conduction in Random Metal Wire Networks

Ideally, transparent heaters exhibit uniform temperature, fast response time, high achievable temperatures, low operating voltage, stability across a range of temperatures, and high optical transmittance. For metal network heaters, unlike for uniform thin-film heaters, all of these parameters are directly or indirectly related to the network geometry. In the past, at equilibrium, the temperature distributions within metal networks have primarily been studied using either a physical temperature probe or direct infrared (IR) thermography, but there are limits to the spatial resolution of these cameras and probes, and thus, only average regional temperatures have typically been measured. However, knowledge of local temperatures within the network with a very high spatial resolution is required for ensuring a safe and stable operation. Here, we examine the thermal properties of random metal network thin-film heaters fabricated from crack templates using high-resolution IR microscopy. Importantly, the heaters achieve predominantly uniform temperatures throughout the substrate despite the random crack network structure (e.g., unequal sized polygons created by metal wires), but the temperatures of the wires in the network are observed to be significantly higher than the substrate because of the significant thermal contact resistance at the interface between the metal and the substrate. Last, the electrical breakdown mechanisms within the network are examined through transient IR imaging. In addition to experimental measurements of temperatures, an analytical model of the thermal properties of the network is developed in terms of geometrical parameters and material properties, providing insights into key design rules for such transparent heaters. Beyond this work, the methods and the understanding developed here extend to other network-based heaters and conducting films, including those that are not transparent.

Screen-Printed Fabrication of PEDOT:PSS/Silver Nanowire Composite Films for Transparent Heaters

A transparent and flexible film heater was fabricated; based on a hybrid structure of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and silver nanowires (Ag NWs) using a screen printing; which is a scalable production technology. The resulting film integrates the advantages of the two conductive materials; easy film-forming and strong adhesion to the substrate of the polymer PEDOT:PSS; and high conductivity of the Ag NWs. The fabricated composite films with different NW densities exhibited the transmittance within the range from 82.3% to 74.1% at 550 nm. By applying 40 V potential on the films; a stable temperature from 49 °C to 99 °C was generated within 30 s to 50 s. However; the surface temperature of the pristine PEDOT:PSS film did not increase compared to the room temperature. The composite film with the transmittance of 74.1% could be heated to the temperatures from 41 °C to 99 °C at the driven voltages from 15 V to 40 V; indicating that the film heater exhibited uniform heating and rapid thermal response. Therefore; the PEDOT:PSS/Ag NW composite film is a promising candidate for the application of the transparent and large-scale film heaters.

High-performance graphene-based flexible heater for wearable applications

A graphene-based flexible heater with low driving voltage and ultrafast response time.

Large Pulsed Electron Beam Welded Percolation Networks of Silver Nanowires for Transparent and Flexible Electrodes

Mechanical properties of transparent electrodes, including flexibility, are important in flexible electronics for sustaining electrical conductivity under bending with small radius of curvature. Low contact resistance of junctions in metal nanowire percolation networks is the most important factor to produce electrodes with excellent optical, electrical and mechanical performance. Here, we report the fabrication of welded silver nanowire percolation networks using large pulsed electron beam (LPEB) irradiation as a welding process of silver nanowires (AgNWs). It results in modification of electrical and mechanical properties because of the low contact resistance at welded junctions. Consequently, the flexible and transparent AgNW electrodes fabricated by LPEB irradiation showed lower sheet resistance of 12.63 Ω sq(-1) at high transmittance of 93% (at 550 nm), and superb mechanical flexibility, compared with other AgNW electrodes prepared by thermal treatement and without any treatment. Polymer light-emitting diodes (PLEDs) using AgNWs by LPEB irradiation were fabricated to confirm that the AgNW electrode by LPEB irradiation was able to become alternative to indium tin oxide (ITO) and they showed good device performance as a maximum luminous efficiency of 7.37 cd A(-1), and excellent mechanical flexibility under bending with small radius of curvature.

Visibly Transparent Heaters

Heater plates or sheets that are visibly transparent have many interesting applications in optoelectronic devices such as displays, as well as in defrosting, defogging, gas sensing and point-of-care disposable devices. In recent years, there have been many advances in this area with the advent of next generation transparent conducting electrodes (TCE) based on a wide range of materials such as oxide nanoparticles, CNTs, graphene, metal nanowires, metal meshes and their hybrids. The challenge has been to obtain uniform and stable temperature distribution over large areas, fast heating and cooling rates at low enough input power yet not sacrificing the visible transmittance. This review provides topical coverage of this important research field paying due attention to all the issues mentioned above.

Nano-sized Ag inserted into ITO films prepared by continuous roll-to-roll sputtering for high-performance, flexible, transparent film heaters

We demonstrate high-performance, flexible, transparent film heaters fabricated on a conductive Ag layer inserted into ITO films prepared by pilot-scale roll-to-roll (RTR) sputtering.

A facile method for transparent carbon nanosheets heater based on polyimide

Transparent carbon nanosheet film heaters are fabricated by spin-coating of poly(amic acid) on quartz substrates following by carbonization process. These thin films show the transparency of 55–90% at 550 nm and sheet resistance of 14.7 to 1.6 kΩ sq⁻¹.

Highly flexible and transparent film heaters based on polyimide films embedded with silver nanowires

Highly flexible AgNW/PI transparent film heaters with superior mechanical and thermal response behavior were fabricated using an all solution-coating method.