Transparent Flexible Ultra‐Low Permeability Encapsulation Film: Fusible Glass Fired on Heat‐Resistant Polyimide Membrane

Abstract

physics, and engineering. One of the key points lies in the development of flexible substrate materials and efficient packaging technology. The components of organic light-emitting devices (OLEDs) or organic photovoltaics (OPV), including the cathode materials and photoelectric conversion layer, are reactive; thus, thin films should encapsulate both the top and bottom surfaces of the devices to realize the desired property. [2-4] Barrier-coated plastic lids, ultrathin glasses, and vacuumdeposited thin films have been developed as thin-film encapsulation (TFE) approaches. [5] However, there are many issues with the current manufacturing methods for encapsulation films. The laser lift-off (LLO) process is widely used for flexible electronics manufacturing, requires evaporating each functional layer onto a substrate, then peeling the devices off the substrate using a laser; the product yield is high, but the productivity is low. In contrast, roll-to-roll (R2R) processing, which involves directly assembling the devices on a formed substrate, is more suitable for large-scale industrial production. [6,7] There are demanding performance requirements for the encapsulation film, such as light transmittance, flexibility, gas impermeability, and heat resistance. The encapsulation film in the direction of light transmission should be highly transparent. [8,9] The other functional layers in electronic devices can be fabricated with nanoscale thickness; thus, the flexibility of the completed devices mainly depends on the properties of the encapsulation materials. Encapsulation materials have gradually developed from rigid glass plates to flexible thin films in recent years. [6,10] The degree of gas permeability is the most important property of TFE materials because flexible electronics use reactive metals and organic matters in devices. It is generally required that the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) should be on the order of 10 −3-10 −6 g m −2 day −1 to provide flexible electronics to have a sufficient service life. [11,12] Furthermore, OLEDs, for example, use thin-film transistors (TFTs) to control brightness and grayscale. A flat/smooth surface (roughness average R a < 1 nm) is beneficial for the fabrication of its nanostructures, and as the manufacturing temperature of TFTs is very high, A good packing of flexible electronics is one of the most critical points to ensure its lifetime. However, efficient and straightforward packaging technology is still very challenging. In this work, a new strategy for preparing encapsulation film is reported by "enameling" a fusible glass layer on a polymer membrane. Careful consideration has been given to the materials properties and manufacturing process, and the obtained glass-coated polymer can combine the advantageous properties of polymers and inorganic materials unconventionally. The encapsulation films show exceptional overall properties, including transparency (<5% optical deterioration), flexibility (radius of curvature: 1.5 mm), and low ...

A Review on Emerging Barrier Materials and Encapsulation Strategies for Flexible Perovskite and Organic Photovoltaics

“…Exhibiting similar favorable properties as rigid glass sheets, various studies have been performed to investigate the barrier and encapsulation performance of flexible glass. [ 19,239–241 ] Glass flexibility is achieved when the film thickness reduces to below 200 µm, as seen in Figure 9 b. [ 190,242 ] This additionally results in an outstandingly lightweight and transparent barrier material.…”

“…designed a novel means of firing a thin (12 µm) glass layer onto a heat‐resistant polymer substrate with the multilayered film exhibiting an impressive WVTR of 5.7 × 10 −4 g m −2 d −1 and demonstrating a radius of curvature of 1.5 mm. [ 19 ] The fabrication process of this barrier material is shown in Figure 9a and indicates the small firing window where the maximum permittable temperature of the polymer overlaps with the lowest sealing temperature of the glass. The polymer membrane is coated with the glass slurry before drying, firing, annealing, and cooling to result in the final barrier film.…”

“…This glass “annealing” process resulted in exceptional flexible barrier materials with high optical transmittance, flexibility, and permeation resistance. Flexible glass substrates are also compatible with roll‐to‐roll processing, [ 19,240 ] resulting in the opportunity for high‐throughput fabrication of PSCs, OPVs, and other flexible electronics.…”

“…Various alternatives to rigid glass have been proposed in the literature to maintain a high barrier performance while also permitting a greater degree of mechanical flexibility and transmittance of solar irradiation. These alternatives include thin flexible glass substrates, [ 19 ] single or multilayer film structures, [ 20–24 ] and reactive polymer nanocomposite systems. [ 25–28 ]…”

What Is Driving the Growth of Inorganic Glass in Smart Materials and Opto-Electronic Devices?

“…Encapsulating materials is a very interesting area that inorganic flexible glass could also enter due to the characteristics discussed in this paper. This field is important with the contribution of polymers and graphene [ 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 , 206 , 207 ], although inorganic flexible glass materials also permeated the area with Willow ® Glass and thin glass/polymer composition using roll-to-roll processing [ 115 , 208 , 209 , 210 ]. However, there is still plenty of room for the inorganic glass influence to grow.…”