**5. Conclusion**

thermal conductivity of AgNWs and their degradation mechanism is lack of investigations. Mayousse et al. spend over 2 years to study the relationship between the stability of AgNW networks and the temperature, humidity, light, hydrogen sulfide and electrical stress [11]. Khaligh et al. [109] once modeled the random AgNW networks in MATLAB and analyzed the overall circuit with HSPICE. In their work, graphene can slow the degradation of AgNWs and uniform the surface temperature. In this case, the failure mechanism is not the nanowire degradation any more. It is changed into the melting of the substrate. Thus the most commonly used method is to use hybrid materials to improve both thermal and chemical stability. Also, the aging of flexible transparent electrodes under different working conditions is now lack of research. Song et al. compared the environmental stability of nanowires with

**Figure 10.** Schematic of the mechanism for treatments used to improve environmental stability and mechanical properties:

sure area but are unable to diminish the whole area. AgNWs with nanoparticles coating can

The sheet resistance of transparent AgNW electrodes shows negligible increase under bending test, quite different from that of ITO electrodes. AgNWs are able to conform to non-planar surface. They can easily fit to the surface, even the highly roughened surface. Though the flexibility makes AgNW a promising alternative to ITO, the high roughness of the network remains a serious problem which hinders the development of AgNW electrodes. The high roughness would lead to interlayer shorting, high leakage currents, and low quantum efficiency in OLEDs [33]. The buffer layer and the conductive material coating are investigated by many researchers to reduce the roughness of the networks [111–114]. Nevertheless, they would degrade the performance by increasing the driving voltage and the electron–hole imbalance [30]. Burying AgNW into polymer substrate is also a way to reduce the roughness, but the effective electrode areas decreased [33]. In order to overcome this problem, the plasma treatment was applied on AgNW-cPI composite electrodes to enlarge the conductive

coating [110]. As shown in **Figure 10(a)**, AgNWs can

S (dark gray). Nanoparticles can reduce the expo-

avoid AgNWs being exposed to sulfur ions and

coating [110], and (b) the conductive pathway

nanoparticle coating and sol–gel TiO<sup>2</sup>

**4.3. Mechanical properties**

34 Flexible Electronics

easily react with sulfur ions to form Ag<sup>2</sup>

(a) the protection mechanism for the nanoparticle coating and sol–gel TiO<sup>2</sup>

enlarging mechanism for the plasma treatment on AgNW-cPI composite electrodes [27].

still react with sulfur ions. The sol–gel TiO<sup>2</sup>

improve the chemical durability of AgNWs.

The aim of this chapter is to demonstrate the fabrication techniques of flexible transparent AgNW electrodes and the efforts made to enhance the performance. Though AgNW electrodes reported exhibit similar performances to ITO electrodes, there is still a long way to go for future commercialization. Firstly, new synthesis methods for fine-tuning the dimensions of AgNWs are needed. The performances of AgNW electrodes have a close relationship with the dimensions of AgNWs. Secondly, metals other than silver need investigations to reduce the cost of electrodes with similar performances, such as copper. Thirdly, the hybrid materials, such as core-shell Cu-Ni nanowires and sandwich structure, are also of interest. Fourthly, the stability optimization in real environments is lacking now. The evaluation of the intrinsic stability is an important value to prove the possibility of integrating nanowires into future devices. Finally, the toxicity of nanowires needs attention before being integrated into commercial devices.
