Ultra-thin and smooth transparent electrode for flexible and leakage-free organic light-emitting diodes

Abstract

A smooth, ultra-flexible, and transparent electrode was developed from silver nanowires (AgNWs) embedded in a colorless polyimide (cPI) by utilizing an inverted film-processing method. The resulting AgNW-cPI composite electrode had a transparency of >80%, a low sheet resistance of 8 Ω/□, and ultra-smooth surfaces comparable to glass. Leveraging the robust mechanical properties and flexibility of cPI, the thickness of the composite film was reduced to less than 10 μm, which is conducive to extreme flexibility. This film exhibited mechanical durability, for both outward and inward bending tests, up to a bending radius of 30 μm, while maintaining its electrical performance under cyclic bending (bending radius: 500 μm) for 100,000 iterations. Phosphorescent, blue organic light-emitting diodes (OLEDs) were fabricated using these composites as bottom electrodes (anodes). Hole-injection was poor, because AgNWs were largely buried beneath the composite's surface. Thus, we used a simple plasma treatment to remove the thin cPI layer overlaying the nanowires without introducing other conductive materials. As a result, we were able to finely control the flexible OLEDs' electroluminescent properties using the enlarged conductive pathways. The fabricated flexible devices showed only slight performance reductions of <3% even after repeated foldings with a 30 μm bending radius.

Foldable Transparent Substrates with Embedded Electrodes for Flexible Electronics

“…[12][13][14] For example, AgNWbased hybrid electrodes coated with graphene, carbon nanotube, and poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have been reported. 10,[14][15] This hybrid structure could improve the electrical properties and mechanical stability of the electrodes.…”

“…11,16 This approach provides a promising solution, particularly for the large R rms and the electric shorting of coated AgNW networks. 12,17 For example, the successful fabrication of flexible organic solar cells (OSCs) and organic light-emitting diodes (OLEDs) has been achieved on substrates with embedded AgNW networks. [10][11][12][17][18] However, the types of transparent polymer substrates in which AgNWs can be embedded are limited because the adhesion between the polymer and the AgNWs should be stronger than that between a release substrate and the AgNWs.…”

“…12,17 For example, the successful fabrication of flexible organic solar cells (OSCs) and organic light-emitting diodes (OLEDs) has been achieved on substrates with embedded AgNW networks. [10][11][12][17][18] However, the types of transparent polymer substrates in which AgNWs can be embedded are limited because the adhesion between the polymer and the AgNWs should be stronger than that between a release substrate and the AgNWs. 19 Hence, the low optical transmittance (T) of the polymer substrates is often 4 compensated for by the reduced R rms and the disconnected ends of the embedded AgNW networks.…”

Flexible and Stretchable Optoelectronic Devices using Silver Nanowires and Graphene

“…One group has developed improved AgNWbased OLEDs using a simple plasma treatment to remove the thin polymer overlayer. [ 23 ] Another group improved stretchable PLED devices using a GO soldered AgNW electrode. [ 24 ] Therein, the AgNW network was soldered with GO to increase the conductivity and mechanical stability of the transparent electrode.…”

Applications of Carbon Nanotubes to Flexible Transparent Conductive Electrodes

“…Actually, CNTs in some applications, which have low conductivity regardless of transmittance, are being commercialized. The rough surface of CNT films due to their tubular structures brings about a serious problem in the application of organic light-emitting diodes (OLEDs) [11]. In CNTs, furthermore, a relatively high contact resistance of the tube-tube junction may lead to insufficient sheet resistance [12].…”