Fabrication of embedded metal-mesh flexible transparent conductive film via electric-field-driven jet microscale 3D printing and roller-assisted thermal imprinting

Abstract

Transparent conductive films play a pivotal role in advanced optoelectronic devices, especially the flexible optoelectronic devices. The next-generation transparent conductive films require not only an optimal trade-off between the sheet resistance and optical transparency, but also an excellent flexibility. Although indium tin oxide (ITO) has been widely used in conventional transparent conductive films, the scarcity of indium, the brittleness and high sheet resistance of ITO hinder the further application in the emerging flexible optoelectronic devices. Among all the ITO substitutes, metal-mesh flexible transparent conductive film could be an ideal candidate due to its good flexibility and excellent photoelectric properties. However, the metal-mesh usually forms on the surface of the film, leading to high surface roughness, poor adhesion of the metal-mesh to the flexible substrate, and potential electrical short-circuits between the metal-mesh and a top electrode, which limits its applications for highly flexible electronic devices and optoelectronic devices. All these defects can be mitigated or optimized with embedded metal-mesh flexible transparent conductive films to achieve higher performance. Additionally, the embedded nature of the metal-mesh can make it have favorable resistance against moisture, oxygen, and chemicals. But the fabrication of embedded metal-mesh flexible transparent conductive film is more challenging. Despite some recent efforts to address these challenges, existing fabrication methods are still complex, with long cycles, high production costs and waste generation, especially they are difficult to realize the fabrication of large-area transparent conductive film. Therefore, new technologies to achieve high-efficiency, low-cost fabrication of large-area, high-performance embedded metal-mesh flexible transparent conductive film are needed. This paper proposes a new method for fabricating embedded metal-mesh flexible transparent conductive film based on electric-field-driven jet microscale 3D printing and roller-assisted thermal imprinting technology. First, the basic principle and process flow of the fabrication process are explained. Then, the effects and rules of the main process parameters (printing voltage, printing speed, printing pressure, imprinting temperature and imprinting force) on the precision and quality of the embedded metal-mesh flexible transparent conductive film are revealed via experiments for optimization of the process window. Finally, by using the optimized parameters on the electric-field-driven jet deposition micro-nano 3D printer and composite nanoimprint lithography machine independently developed by the research group, an embedded square metal-mesh flexible transparent conductive film with a pattern area of 70 mm ×70 mm, a line width of 20 μm and a pitch of 1000 μm is fabricated. It has a sheet resistance of 3.62 Ω/sq and a transmittance of 92.3% at a wavelength of 550 nm. In addition, the contact level of the metal-mesh to the substrate is up to 5B, the surface roughness value is 18.81 nm, and the change rate of the sheet resistance of the fabricated embedded metal-mesh flexible transparent conductive film after 1000 bending tests is less than 8%. The research shows that the proposed new method for fabricating embedded metal-mesh flexible transparent conductive film requires simple process steps and low production cost. The transparent conductive film produced has excellent photoelectric performance, low surface roughness and good mechanical flexibility. It provides a promising solution for high-efficiency mass production of high-performance transparent conductive films.