Ultra‐Low Resistivity Copper Mesh as Embedded Current Collector Layer for Inkjet‐Printed Flexible Electrochromic Device Realizing Fast Response and Uniform Coloration

Abstract

such as bendable touch screen displays, [1] organic light-emitting diodes (OLEDs), [2] organic photovoltaics (OPVs) [3] and electrochromic devices (ECDs). [4] Among the devices mentioned above, flexible electrochromic devices (FECDs) hold great promise for versatile applications owing to the ability to change optical properties reversibly in response to applied voltages and can be attached to the curved surface due to their flexibility. [5] However, the main challenge presently for scaling up FECDs is the nonuniform coloration from the edge to the center of a large-area device during operation because of the undesirable voltage variation across the device caused by high sheet resistance of electrode material, which is mainly PET-ITO. [6] As the most widely used transparent conductive material, indium tin oxide (ITO) stands out for its high optical transmittance and chemical stability. [7] Despite the matured large-area ITO sputtering process on flexible substrates such as polyethylene terephthalate (PET) or polyimide (PI), brittleness and relatively high sheet resistance are still the two drawbacks of flexible ITO substrates which cannot be solved simultaneously because the sheet resistance of ITO film directly relates to its thickness.In order to overcome the inherent limitations of ITO-based electrodes, several alternatives have been developed as FTEs such as conducting polymers, [8] carbon materials, [5a,9] metallic nanowires, and nanostructures. [10] Notably, silver nanowire (Ag NW) has been widely studied as the electrode material for the fabrication of FECDs owing to its outstanding flexibility and simplicity for scalable processing. [4c] However, the sheet resistances of reported Ag NWs are usually limited in the range of 10 Ω □ −1 , [3a,4c,11] which is not a significant breakthrough in conductivity compared to PET-ITO (typically ≥30 Ω □ −1 without metallic modification), hindering their further applications in large-area FECDs. Considering all the FTE technologies reported so far, metal-mesh is believed to be the only technology that can easily reach a sheet resistance of less than 1 Ω □ −1 by adjusting mesh pitch, line width, and metal thickness. [12] However, owing to the high mobility of silver and the poor electrochemical stability of copper, bare Ag or Cu mesh is practically not suitable as the electrode material for traditional ECDs. [10a,13] Liu et. reported Flexible electrochromic devices (FECDs) hold great promise for energysaving static displays. As the most widely used flexible transparent electrode (FTE) material for FECDs, the indium tin oxide (ITO) coated on polyethylene terephthalate (PET-ITO) suffers from relatively high sheet resistance which can cause nonuniform coloration during the device operation, hindering the development of large-area FECDs. Herein, a hybrid FTE is developed in which an additional copper (Cu) mesh as an embedded current collector layer underneath the ITO film to achieve ultra-low sheet resistance (<0.2 Ω □ −1 ) compared to that of PET-ITO (≈35 Ω □ −1 )...

Photolithographically patterned and highly stable electrochromic displays enabled by a photo-assisted cross-linker

“…The b -values are 0.91 and 0.86, respectively, indicating that the kinetics for charge storage of the two films were mainly surface-controlled, and the electrode material tends to be capacitive. 30 As shown in Fig. 3d, X-PProDOT exhibits an almost identical transmittance to PProDOT, in both the colored (reduced) and bleached (oxidized) states.…”

Fabrication strategies for metallic nanowire flexible transparent electrodes with high uniformity

“…10(a)). Hu et al 173 effectively improved the uniformity of the electric field by introducing a copper mesh within the flexible ITO electrode, achieving a more uniform coloring process (Fig. 10(c)).…”

Hybrid Ag/Ni mesh/PH 1000 transparent electrodes for high performance flexible electrochromic devices with exceptional stability

“…Patterned FECDs were made by inkjet printing the PProDOT, for which the PProDOT ink was formulated by mixing o-xylene and 1,2,3,4tetrahydronaphthalene in a weight ratio of 2:1 [17]. The prepared ink was inkjet printed on the surface of Ag/Ni mesh/PH 1000 (Fujifilm Dimatix DMP2831 inkjet printer) and annealed on a hot plate at 80 • C for 30 min.…”

“…Although metal oxide films have been reported with high electrochemical stability, their brittleness makes them hard to apply for FECDs [14,15]. In addition, the high sheet resistance (>10 sq −1 ) at high transmittance (>85%) leads to non-uniform color changes and slow response time in large-area electrochromic devices owing to the high ohmic losses [9,16,17]. In order to overcome those issues, several alternative materials, including conductive polymer [18][19][20],…”