Abstract
Silver nanowires (AgNWs) are a promising candidate to replace indium tin oxide (ITO) as transparent electrode material. However, the loose contact at the junction of the AgNWs and residual surfactant polyvinylpyrrolidone (PVP) increase the sheet resistance of the AgNWs. In this paper, an argon (Ar) plasma treatment method is applied to pristine AgNWs to remove the PVP layer and enhance the contact between AgNWs. By adjusting the processing time, we obtained AgNWs with a sheet resistance of 7.2Ω/□ and a transmittance of 78% at 550 nm. To reduce the surface roughness of the AgNWs, a peel-off process was used to transfer the AgNWs to a flexible NOA63 substrate. Then, an OLED was fabricated with the plasma-treated AgNWs electrode as anode. The highest brightness (27000 cd/m2) and current efficiency (11.8 cd/A) was achieved with a 30 nm thick light emitting layer of tris-(8-hydroxyquinoline) aluminum doped with 1% 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5 H,11H-(1)-benzopyropyrano(6,7-8-I,j)quinolizin-11-one. Compared to thermal annealing, the plasma-treated AgNW film has a lower sheet resistance, a shorter processing time, and a better hole-injection. Our results indicate that plasma treatment is an effective and efficient method to enhance the conductivity of AgNW films, and the plasma-treated AgNW electrode is suitable to manufacture flexible organic optoelectronic devices.
Highlights
Flexible conductive electrodes play an important role in many optoelectronic devices, such as organic light-emitting diode (OLED)[1,2], organic solar cells[3,4], and touch screens[5]
The sheet resistance of the AgNWs gradually decreased when the processing time was within 15 min, and it became stable when processing time was between 15 min and 20 min
Our studies show that plasma treatment is a faster and more effective method than thermal annealing
Summary
Flexible conductive electrodes play an important role in many optoelectronic devices, such as organic light-emitting diode (OLED)[1,2], organic solar cells[3,4], and touch screens[5]. Silver nanowire films are usually prepared using solution-based processes, including spin-coating, drop-casting, rod-coating, and spray-coating During these processes, the connection between crossed AgNWs is mainly determined by gravity, van der Waal forces between them, and capillary forces from solvent evaporation[27]. Some groups tried to use low temperature plasma to remove the PVP layer on the surface of AgNWs. Zhu Siwei et al enhanced the conductivity of ultralong AgNWs by a room-temperature plasma treatment and obtained a high figure-of-merit (FOM) of 47140. Compared to the touch sensor, the electrode of OLED requires lower sheet resistance and higher work function to get a good hole-injection. The work function can increase by the plasma treatment Another problem with AgNWs is their large surface roughness, which can penetrate the soft organic layer of a laminated device and produce short circuit.
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