| A flexible, highly transparent and conductive film(TCF) could considerably improve the development of flexible electronics, such as flexible OLED displays and flexible solar cells. Now, Indium Tin Oxide(ITO) is the most popular transparent conductive material. It is very stable, and has good conductivity and excellent optical transparency. However, the brittleness of ITO limits its application in flexible electronic devices. Also, the relatively complicated fabrication process of ITO films and the limited supply of Indium further will restrict its economic availability in the future. Many efforts have been made to develop comparable flexible transparent conductive materials, for example, conductive polymers, carbon nanotubes(CNTs), graphene, metal grids, and random networks of metallic nanowires. Silver nanowires(AgNW) with high electrical conductivity(6.3×107 S/m) are particularly promising, because they approach optoelectronic properties of ITO. However, the easily oxidized AgNW and the weak adhesion between AgNW and the substrate cause a huge increase in sheet resistance(Rs).The propose of this paper is to improve the transparency, conductivity, flexibility and stability of AgNW-based conducting network. Firstly, AgNW-based conducting network is prepared by spin-coating method; and then, a protective overcoating layer is deposited on AgNW network by spin-coating or drop-coating method to improve the properties of the conducting network. Some valuable research results are obtained. The main content of this paper are as the following:(1) The highly flexible, transparent, conductive and antibacterial film is prepared by spin-coating AgNW suspension on poly(ethylene terephthalate)(PET) substrate. The ZnO layer is covered the conductive AgNW network to protect the metal nanowires from oxidization and enhance the adhesion of wire-to-wire and wire-to-substrate. It is found that the density of AgNW coatings correlates with both the sheet resistance(Rs) and the transmittance of the AgNW/ZnO composite films. An excellent 92% optical transmittance in the visible range and a surface sheet resistance of only 9 Ω/sq has been achieved, respectively. Even after bending 1000 times(5 mm bending radius), no significant change is found in the sheet resistance or optical transmittance. The real-time sheet resistance measured as a function of bending radius also remains stable even at the small bending radius(?1 mm). Under the protection of the ZnO layer, the sheet resistance of the AgNW/ZnO composite TCFs remains nearly the same after kept at 80 ℃for half a year. The AgNW/ZnO composite films also show antibacterial effects which could be useful for the fabrication of wearable electronic devices.(2) In order to further improve the flexibility of the AgNW network, PVA(polyvinyl alcohol) is used to replace the ZnO layer and the PET substrate. Transparent conductive AgNW/PVA composite films are fabricated by burying the silver nanowires in the surface of PVA layer. The optical transmittance and electrical conductivity of the AgNW/PVA films can be controlled by silver nanowire deposition cycles, namely the density of silver nanowires. The AgNW/PVA film exhibits high optical transmittance(93.1% at 65 Ω/sq), low sheet resistance(10.1 Ω/sq at 81% transmittance), which outperforms commercial indium tin oxide(ITO) film. In addition, the films exhibit outstanding mechanical flexibility, which have no change in sheet resistance after 10 000 times bending cycles or at a 1 mm bending radius, which are better than the AgNW/ZnO films. The reliability and long-term stability of the AgNW/PVA TCF are greatly enhanced as the silver nanowires are buried in the surface of PVA. Heat performance of the films is excellent. As the operating voltage at 3 V, the AgNW/PVA film with sheet resistance of 6 Ω/sq can reach to 100 ℃ within 20 s. Thus, the optically transparent AgNW/PVA hybrid electrodes have extremely high potential application in flexible or defrosting devices. |
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