Patterned Sandwich-Type Silver Nanowire-Based Flexible Electrode Through Simple Solution-Process Photolithography for Organic Photovoltaics

Organic semiconducting materials, which have been extensively researched in recent years, have the advantage that they can be applied to flexible devices such as organic photovoltaic cells (OPVs), organic light emitting diodes (OLEDs), and organic field effect transistors (OFETs). In order to realize a fully flexible optoelectronic device, a flexible transparent electrode (FTE) material that can replace the ITO electrode together with active materials is required. FTE materials for flexible organic devices must achieve high ductility, good mechanical durability, sufficient electrical conductivity and high optical transparency. Among various electrode materials, silver nanowires (AgNWs) have attracted considerable attention as alternative electrode materials for ITO because they can achieve high conductivity, transmittance, and flexibility at a low manufacturing cost.<br/>In this study, simple patterning of sandwich-type AgNW-based FTEs with high transparency and conductivity was successfully demonstrated using a specific underlayer and an overcoat layer capable of photo-crosslinking. Crosslinked polyvinyl cinnamate (x-PVCn) film was used as the underlayer to achieve a uniform distribution of AgNWs and improve the adhesion simultaneously. A solution (PHT solution) containing poly(sodium-4-styrene sulfonate) (PSS-Na+), photo-crosslinkable 2,4-hexadiyne-1,6-diol (HDD), and the non-ionic surfactant Triton X–100 were used as an overcoat layer material on the AgNWs layer, and millimeter/centimeter scale patterns were easily formed by irradiating with 254 nm UV light under a shadow mask. The AgNW-based flexible electrode exhibited excellent electrical and optical properties while achieving a uniform film with a smooth surface and mechanical flexibility. In order to evaluate its potential as an FTE, the aforementioned AgNWs-based patterned electrode was applied to flexible PSCs. The FTE-based PSC device showed as high efficiency as ITO-based devices. In addition, during the mechanical bending test, the FTE-based device exhibited superior durability compared to the ITO-based flexible PSC.