Gentle plasma process for embedded silver-nanowire flexible transparent electrodes on temperature-sensitive polymer substrates

Abstract

The present study investigates processing routes to obtain highly conductive and transparent electrodes of silver nanowires (AgNWs) on flexible polyethylene terephthalate (PET) substrate. The AgNWs are embedded into a UV-curable polymer to reduce the electrode roughness and enhance its stability. For the purpose of device integration, the AgNWs must partially protrude from the polymer, which demands that their embedding is followed by a transfer step from a host substrate to the final substrate. Since the AgNWs require some sort of curing (thermal or plasma) to reduce the electrode sheet resistance, a thermally stable host substrate is generally used. This study shows that both thermally stable polyimide, as well as temperature-sensitive PET can be used as flexible host substrates, combined with a gentle, AgNW plasma curing. This is possible by adjusting the fabrication sequence to accommodate the plasma curing step, depending on the host substrate. As a result, embedded AgNW electrodes, transferred from polyimide-to-PET and from PET-to-PET are obtained, with optical transmittance of ∼80% (including the substrate) and sheet resistance of ∼13 Ω/sq., similar to electrodes transferred from glass-to-glass substrates. The embedded AgNW electrodes on PET show superior performance in bending tests, as compared to indium-tin-oxide electrodes. The introduced approach, involving low-cost flexible substrates, AgNW spray-coating and plasma curing, is compatible with high-throughput, roll-to-roll processing.

Implementation of Flexible Embedded Nanowire Electrodes in Organic Light‐Emitting Diodes

“…The high roughness value is mainly caused by holes in the Ormocomp from the plasma treatment and not by the sharp spikes which may cause shunts. [18] By overcoating the embedded NW with ZnO:PEI (Figure 2c), an even smoother surface (RMS ¼ 8.1 nm) is formed, which is close to the ITO/ZnO: PEI roughness of 5 nm ( Figure S2, Supporting Information).…”

“…Fabrication of NW Electrodes: The fabrication of the embedded NW electrodes was realized following the process described in a previous study. [18] Clogging of the spraying nozzle by the NWs was not observed, because the nozzle diameter (%3 mm) was far larger than the average NW length (10 μm), and in contrast to inkjet printing, spraying is a continuous process, which prevents the drying of the solution at any place in the tubing system. Further, the shaping air was set to its highest value, which removed almost all NW residuals from the nozzle surface.…”

“…[ 2,12–14 ] Other important TE materials include conductive polymers, [ 15 ] ultrathin metallic layers, [ 16 ] dielectric/metal/dielectric layers, [ 8 ] carbon nanotubes, [ 17 ] and metal nanowires (NWs). [ 5,18 ]…”

“…[ 20 ] For R2R processing, different deposition methods for NWs have been presented, such as electrostatic spraying, [ 21 ] wire bar coating, [ 22 ] inkjet printing, [ 23 ] air brush spraying, [ 24 ] and spray coating. [ 18 ]…”

“…[20] For R2R processing, different deposition methods for NWs have been presented, such as electrostatic spraying, [21] wire bar coating, [22] inkjet printing, [23] air brush spraying, [24] and spray coating. [18] Independent of the deposition technique, NW films feature two major drawbacks, namely their high roughness and their need for postdeposition treatments. High roughness is a bottleneck for thin-film device fabrication, as spikes from the one electrode may reach the opposing electrode and hence short circuit the device.…”