Study On Silver Nanowire Electrode In The Application Of Organic Light-emitting Devices

Organic light-emitting devices (OLEDs) have attracted more attention inrecent years due to their advantages of self-illumination, wide operationtemperature, lightweight, high luminance, and in particular, being sufficientlyductile for the organic material to undergo significant stress without cracking. Theflexibility of the OLEDs becomes a very attractive feature and is able to applying inflexible optoelectronic systems such as electronic newspapers and wearabledisplays. As we known, highly conductive and flexible electrodes on the flexiblesubstrate are the key issue for flexible optoelectronic devices. In general,indium-tin-oxide (ITO) has been most in common used transparent anode materialdue to its high optical transparency in the visible range, high electrical conductivityand high work function. However, ITO presents several key drawbacks, such as itshigh cost due to the scarcity of indium, its poor mechanical robustness andmanufacture incompatible with the plastic substrate due to the high temperatureproduction process, which is unsuitable for flexible OLEDs. So it is important tosearch for innovative materials for the next generation of optoelectronic devices.Towards this objective, different groups have pursued various alternatives ofpotential candidate materials in this field. The most significant materials amongthese are carbon nanotube (CNT) films, graphene films, conducting polymers,random networks of metallic nanowires, and hybrids of these. Carbon nanotubeshave been extensively explored, but the conductivity has not been high enough forhigh performance optoelectronic devices, due to the high contact resistance betweennanotubes. Although higher-quality and large-area graphene films have beenfabricated by a chemical vapor deposition (CVD) method, leading to high production costs. As to conducting polymers, on the basis of the merits of simpleand low-cost manufacturing, their conductivity is lower than that of ITO at thesame transmittance. For these reasons, metallic nanowire random networks,especially easily fabricated solution-processible silver nanowire (AgNW) films,have recently attracted a lot of attention for potential applications as transparentelectrodes, since their photoelectrical performance as transparent conductive filmsis close to ITO films. They can also provide outstanding mechanical flexibility onflexible films under repeating bending and stretching. Nevertheless, high surfaceroughness of the nanowire coating which can reach hundreds of nanometers hasbeen a major challenge for the fabrication of thin film devices on the nanowireelectrodes.In this communication, we have demonstrated a smooth transparent AgNWelectrode on a flexible substrate by template-stripping process. Compared to thefilms dropped-cast directly on glass, the AgNW electrodes fabricated bytemplate-stripping process have the same high transparency and low sheetresistance, but effectively reduced surface roughness from78.3nm to3.81nm,which make it possible to be used in OLEDs. The flexible OLEDs fabricated onphotopolymer substrates have shown good performance and superiority inflexibility. Then PEDOT:PSS has been used to combine with AgNWs to fabricatecomposite films on photopolymer substrates. The roughness has also been reducedby template-stripping process from27.2nm to0.372nm. The devices withcomposite electrode have exhibit excellent performance. The highest luminance andefficiency is5380cd/m2and51.3cd/A. In addition, the flexible OLEDs keep goodperformance under a small bending radius during bending50times.