# NiO-Based Electronic Flexible Devices
## 5 Future Perspectives and Conclusions  
Flexible devices are largely in demand due to the rising tendency for good fitting, comfortable, easy-to-use tools and materials, which can feed the creativity of fashion designs. In addition, practicality, improved operativity and portability of smart devices for well-being aid the monitoring of vital parameters for personalized drug-delivery based on actual needs (all-in-all helping to maintain a healthy lifestyle). To a larger scale, modern, eco-sustainable architecture requires the use of materials which are adaptable, versatile, and energetically self-standing. The future development of flexible devices is very much connected to the development of integrated flexible components with homogenous characteristics of durability which ensure the proper functioning of the devices, a low-cost production and can be easily recharged if necessary. In this framework, some recently developed flexible tools were presented based on NiO as low-cost active material, which can give rise to improved flexible technology for the pursue of personalized items and tailored devices. NiO-based flexible supercapacitors may b achieved by the de-alloying, a technique that allows the fabrication of all-solid-state devices with associated advantages over the employment of liquid electrolytes (which may be affected by leakage and transport issues). These devices are characterized by a capacitance comparable to analoguesbased on 2D materials and higher resilience to repeated bending and deformation cycles [132]. The embedding of NiO is fundamental to enhance the electrochemical response of the plastisol towards specific targets such as H\({}_{2}\)O\({}_{2}\). Overall, the hybrid NiO-plastisol material has performances, to some extent, comparable to other non-flexible electrodes (see Table 3 in Ref. [103]), with the additional advantage of its flexibility. The examined NiO flexible temperature device showed a large resistance to harsh basic and acidic conditions (as compared, for instance, to graphene ribbons-based devices) and less sensitivity to the oxidative conditions in the synthesis procedure (which affects the reproducibility of the production of graphene derivatives-based devices) [133]. Flexible resistive random-access memory devices are usually achieved by employing a supple support topped by an active layer. Several options were suggested as active material, such as black phosphorous [134] or graphene oxide [135]. However, in both cases, limitations arise from the difficulty of handling the material in safe conditions or to achieve stability and/or stable performances (in addition to the employment of expensive connection Au layers) [135]. NiO-based electrochromic devices have better optical contrast, shorter coloring and bleaching times as compared to other inorganic analogues such as Ag-nanowire based ones [136], and cheaper manufacturing, due to lower cost of production materials. For solar cells the use of NiO is, in a way, essential, since it is routinely used as HTL, the real challenge being the insertion of the NiO component in flexible structures while keeping or improving the conversion efficiency. However, the manufacturing techniques may strongly impact the performances of the electronic devices. The retention of properties and consequent scalability of the processes is usually more favorable for flexible materials prepared by physical deposition methods. However, these are lengthy and costly procedures. Therefore, the development of solution-processable materials is preferred for device assembling. In this regard, the molding as well as the ink deposition and printing techniques are the most promising for the fabrication of devices. Furthermore, a correct assessment of the performances upon stress would require several deformation tests, including stretching and compression (besides bending), especially for the electronic materials destined to wearable devices. Therefore, a complete evaluation of performances under stress is advisable for the planning of a device.