Roll-to-roll slot-die coating of 400 mm wide, flexible, transparent Ag nanowire films for flexible touch screen panels

We report fabrication of large area Ag nanowire (NW) film coated using a continuous roll-to-roll (RTR) slot die coater as a viable alternative to conventional ITO electrodes for cost-effective and large-area flexible touch screen panels (TSPs). By controlling the flow rate of shear-thinning Ag NW ink in the slot die, we fabricated Ag NW percolating network films with different sheet resistances (30–70 Ohm/square), optical transmittance values (89–90%), and haze (0.5–1%) percentages. Outer/inner bending, twisting, and rolling tests as well as dynamic fatigue tests demonstrated that the mechanical flexibility of the slot-die coated Ag NW films was superior to that of conventional ITO films. Using diamond-shape patterned Ag NW layer electrodes (50 Ohm/square, 90% optical transmittance), we fabricated 12-inch flexible film-film type and rigid glass-film-film type TSPs. Successful operation of flexible TSPs with Ag NW electrodes indicates that slot-die-coated large-area Ag NW films are promising low cost, high performance, and flexible transparent electrodes for cost-effective large-area flexible TSPs and can be substituted for ITO films, which have high sheet resistance and are brittle.

unwinding and rewinding system, the flexible PET substrate was continuously passed through the slot die coating head. In addition, the tension of the flexible PET substrate was controlled by a load cell in the rolling system. PET substrate with a width of 500 mm and thickness of 125 μm was passed over the heating chamber and UV treatment zone as shown in Figure S1 c and d. The rolling speed of the PET substrate could be exactly controlled by the motor speeds of the unwind and rewind roller. A TACMINA pump with the property of non-pulsation was installed into the RTR coating system as shown in Figure S1e. The Ag NW network density was controlled by pump frequency (Motor RPM). Figure S1. (a) Pictures of the R2R slot-die coating system equipped with an unwinder, rewinder, heating chamber, UV zone, slot die coating head, Ag ink and over-coating ink tank with pump. Picture of (b) slot-die head for Ag NW ink coating, (c) heating chamber to remove solvent in the slot-die coated films, and (d) UV irradiation chamber. (e) Ink supply system for injecting Ag NW ink into the slot die using TACMINA pump. Figure S1e schematically illustrates process used to coat the Ag NW layer using slot-die coating head with a TACAMINA pump. With increasing the motor rpm, the amount of Ag NW ink coated on the PET substrate was increased through the slot die coating head. The Ag NW layer was coated onto the PET substrate by using a slot die coating head, and then passed through the heating chamber at 120 ºC by means of unwinding and rewinding at a roller constant speed of 2 m/min ( Figure S1c). After coating the Ag NW layer, an over-coating layer was coated on the Ag NW layer using the slot-die coating head and passed through the heating chamber at 80 ºC, after which the film was exposed to a UV-mercury type lamp with an intensity of 1000 mJ under a nitrogen ambient by means of unwinding and rewinding rollers at a constant speed of 2 m/min.

Slot-die coating process:
In the slot-die apparatus, liquid solution is pumped to the inner part of the slot-die head and ejected through a narrow slot, which is a gap between upstream lip and downstream lip 1,2 .

Figure S2a
show schematics of the slot-die apparatus for coating of Ag NW ink and over coating layer. In general, the shim, which is injected into the slot-die plays an important role to control the thickness and density of Ag NWs. In our slot-die coating process, we employed a shim with thickness of 100 μm as shown in Figure 2Sb. The 500 mm wide shim with a thickness of 100 μm was installed between upstream and downstream lips as shown in Figure   S2c. Finally, we controlled the pressure of Ag NW ink using the capsule filter, which is connected to the inner part of the slot die head, to optimize the uniformity of the Ag NW layer on PET substrate as shown in Figure S2d. This capsule filter also remove the bubble in the Ag NW ink.
Diamond-shaped patterning of OC/Ag NWs electrode films: OC-Ag NW films were annealed in box oven at 130 °C for 20 min to prevent film shrinkage as shown in Figure S3-a.  Then, the LPR-coated OC-Ag NW films were annealed at 90°C for 2min to bake in box oven as shown in Figure S3-c. The LPR-coated OC-Ag NW films were then exposed to UV light at 60 mJ using a positive diamond mask, as shown in Figure S3 d. The UV-exposed OC-Ag NW films were patterned by a hand-develop dipping process using a developing solution (EN-DT238E : tetramethylammonium hydroxide 3%, surfactant 2%, deionized water 95%).
Diamond-patterned OC-Ag NW films were subsequently etched by a hand-etch dipping process using etching solution (EO-NS100: nitric acid & deionized water). The wet-etched OC-Ag NW films were stripped by a hand-strip dipping process using stripping solution (EN-S800Mo: glycol ethers 10%, sodium gluconate 10%, EDTA 10%, surfactant 5%, deionized water 65%). Finally, the stripped OC-Ag NWs films were cleaned by a spray-type rinse system using deionized water, as shown in Figure S3