Flexible Ag Nanowires and Conducting Polymer Composite Electrodes for Organic Optoelectronic Devices

Abstract

Flexible display applications have been increasingly investigated due to the needs for paper-like displays which can be crumpled and even stretchable freely. In particular, great interest on flexible transparent electrodes has been suddenly imposed to realize flexible optoelectronic device applications. In respect of this tendency, ITO, widely used as transparent electrode material, should be replaced because it shows rigid property and it contains a rare earth resource indium that brings the price instability issue. Some newly developed materials such as graphene, carbon nanotube (CNT), conducting polymers and Ag nanowires (Ag NWs) have been raised as ITO-alternative materials and promising and practical candidates for flexible transparent conducting electrodes. The representative conducting polymer electrode material is PEDOT:PSS due to higher electric conductivity, compared to any other conducting polymers. However, pristine PEDOT:PSS is insufficient to be used as an electrode in commercial applications and a lot of techniques have been accordingly explored for the enhancement of electric conductivity of PEDOT:PSS. Over hundreds times of conductivity enhancement of PEDOT:PSS can be obtained through doping or surface treatment with various solvents such as sulfuric acid (H2SO4), dimethylsulfoxide (DMSO), ethylene glycol (EG), fluorosurfactants and ionic liquid. In this study, H2SO4, DMSO and a fluoro-surfactant were used to increase the electric conductivity of PEDOT:PSS films. However, it needs further improvement for the flexible organic optoelectronic applications. Ag NWs are one of promising ITO-alternative materials along with conducting polymers. Ag NWs show excellent electrical properties originated from its metallic nature and high transparency with achromatic color. However, nanowires mesh does not cover entire surfaces of substrates and can be disconnected at nano-scale patterns or under excessive deformation. In this study, we present a efficient way to remarkably enhance both electric conductivity and mechanical property using Ag NWs and PEDOT:PSS composite materials for flexible electrodes of polymer light-emitting diodes (PLEDs) and organic solar cells (OSCs). The efficiencies of PLEDs and OSCs with Ag NWs and PEDOT:PSS composite electrodes are comparable with those of ITO-based PLEDs and OSCs and it confirms that a Ag NWs and PEDOT:PSS composite electrodes can be utilize for flexible organic-optoelectronic devices