Introduction

Transparent conductive electrode (TCE) is a critical component within a wide range of electronic and optoelectronic devices. To date, wide bandgap conductive metal oxides such as indium tin oxide (ITO) and Al-doped zinc oxide (AZO), have been the most successfully commercialized transparent conductive material. On the other hand, with the fast development of flexible and wearable electronics, flexible TCEs are highly desired and have been extensive researched in the past decades [1,2,3,4,5]. However, challenges still remain to be solved urgently for the flexible or stretchable TCEs, if the electronic devices would be integrated on wearable devices or freely attached on human skin without any discomfort [6,7,8]. During the past decades, many kinds of nanomaterials have been studied for the fabrication of flexible TCEs, such as graphene-based electrodes, metallic nanowires electrodes, conductive polymers and dielectric-metal-dielectric (DMD) electrodes. Most of the above nanomaterials possess good physical properties, while the vital drawbacks like high price, potential scarcity or brittleness, limited their commercialization [9, 10]. Silver nanowires (AgNWs) attracted great attention because of its excellent physical performances. AgNW is a kind of one-dimensional nanomaterial with high aspect ratio, which make it easy to establish planar conductive film than metallic particles or flakes. Besides, the AgNW networks show extremely higher electrical conductivity and excellent deformation properties, which were expected to be a good candidate for flexible TCEs [11,12,13].

In order to further realize the industrial application of AgNWs for flexible TCEs, the research community has committed to enhance the stability of AgNW networks. Many studies have shown that silver was easily oxidized or degraded when exposed to air, acid or sulfur-containing environment. Therefore, the flexible TCEs based on the AgNWs will be unstable if it works under severe conditions for a long time [14]. In addition, AgNWs tend to be spheroidized when subjected to high temperature, which will greatly affect the conductivity of the AgNW networks. This unstable phenomenon is also called Plateau–Rayleigh instability [15]. All these factors are the main problems when integrating AgNW networks into optoelectronic devices. It was reported that AgNW nanocomposites covering another capping material on the surface of the AgNW networks could improve the instability of the AgNWs. The capping materials commonly include nanoparticles, carbon-based conductive materials, polymers or metal oxides, etc [16,17,18,19,20]. The nanocomposite conductive structure of AgNW networks mainly has two purposes: one is to reduce the potential instability of AgNWs, and the other is to combine complementary materials to improve the comprehensive properties. Among the capping materials, metal oxides have been widely studied to modified the AgNW networks in recent years, exhibiting significant stability enhancements without reducing the optical transparency [21,22,23,24]. For example, Aghazadehchors et al. confirmed that the bilayer coatings of 70 nm ZnO/70 nm Al2O3 could enhance the thermostability of AgNW networks [25]. Song et al. covered a sol–gel coating of titanium dioxide (TiO2) on the surface of AgNWs to improve the thermal and chemical stabilities of AgNWs [26]. Furthermore, the metal oxide coatings can also enhance the adhesion of the AgNWs to the substrate and improve the stability and service life of overall structure by introducing surface modifiers to strengthen the chemical binding between AgNWs and metal oxide coatings [27, 28].

TiO2 film is a cheap semiconductor with superior optical and electrical properties, such as high surface area, excellent thermal and chemical stabilities, moderate electron transfer ability and wide band gap energy, and new processes have been developed to explore the potential application of TiO2 on AgNWs electrode modification and make it more widely used [29,30,31,32]. To superimpose the performance of the coating layer and the AgNWs, the TiO2 coating layer should be able to improve the bending performance of the AgNWs/TiO2 composites as far as possible without affecting the transmittance and working stability [26]. TiO2 film can be normally fabricated by the conventional methods of e-beam evaporation, sol–gel processing, sputtering, scratching, and rod coating. However, in view of the homogeneity, conformality and thickness controllability of the films, atomic layer deposition (ALD), a special CVD technique with excellent three-dimensional conformality, large-area uniformity, precise sub-monolayer film thickness control and low-temperature growth, is considered as the promising technique to deposited the TiO2 coating layer for AgNW networks to make it withstand a certain degree of bending and stretching [33,34,35,36].

In this work, we studied the modification of AgNW networks by TiO2 coating using ALD to obtain highly stable patterned flexible TCEs. Optical transmittance, electrical conductivity, mechanical properties and working stability of the flexible TCEs were investigated to determine the effects of TiO2 coatings on the AgNW networks. In addition, a novel patterning technique of AgNW networks was developed by using photolithography and ultrasonic concussion process. At last, the patterned flexible TCEs were applied to alternating current electroluminescent (ACEL) devices for further verification.

Experimental methods

Fabrication of AgNW networks

AgNWs ink was purchased from COLDSTONES TECH (CST-NW-S30). The average diameter and length of AgNWs were 30 ± 3 nm and 25 ± 5 μm, respectively. The solvent of AgNWs ink was isopropyl alcohol and the concentration of AgNWs was 10 mg/ml. Poly(dimethylsiloxane) (PDMS, Sylgard 184, Dow Corning) was used as substrate for AgNW networks, which prepared by mixing the base polymer with crossing-linking agent in a ratio of 10:1 and then spin-coated on glass substrates. The coated PDMS was cured at the temperature of 90 ℃ for 90 min to form solidified PDMS films with an average thickness of 300 ± 5 μm. Before spin-coating, the substrates were ultrasonic cleaned with detergent solution, acetone and deionized water for 15 min, respectively. Subsequently, the substrates were treated by oxygen plasma treatment for 5–10 min. Then, AgNWs ink was spin-coated on the substrate, and then passed for annealing at 130℃ for 15 min in the air to remove the solvent and welded the cross nodes between AgNWs to form a AgNW networks.

Deposition of TiO2 coating by ALD

The atomic layer deposition (ALD, BENEQ TFS-200) system was applied to deposit conformal TiO2 coating layers on AgNW networks. The temperature of the reaction chamber was kept at a low temperature of 90 ℃. Titanium tetrachloride (TiCl4) and water (H2O) were two precursors for the fabrication of TiO2 thin films. The carrier gas of precursors was high purity N2 (99.999%) with flow rate of 20 sccm. A reaction cycle of TiO2 contained the following pulses: TiCl4 pulse for 0.3 s, N2 purging for 2 s, H2O pulse for 0.3 s and N2 purging for 2 s. Thus, the ALD sequences were repeated to obtain the desired thicknesses. Different thicknesses of TiO2 thin films were investigated as the coating layers for AgNW networks.

Patterning of AgNW networks

AgNW networks with conformal coated TiO2 were patterned by a new developed photolithographic process by cooperating with ultrasonic concussion, as shown in Fig. 1. Briefly, AgNWs were firstly spinning coated on PDMS substrate to form a AgNW networks (step 1). Then, positive photoresist (PR, RZJ-304) was uniformly spin-coated on the AgNW network at 2000 rpm for 30 s, and was passed for annealing at 100 ℃ for 2 min (step 2). Next, the AgNW networks capped with PR layer were exposed to UV light for 20 s with a patterned photo-mask (step 3). The graphics of PR layer was developed by using positive developer (RZX-3038) for 30 s, followed by the rinse with deionized water, and annealing at 120 ℃ for 2 min (step 4). After that, the samples were transferred to ALD system to for the deposition of 30 nm TiO2 coating layers (step 5). The samples were then immersed in isopropyl alcohol solution, followed with ultrasonic concussion in a ultrasonic cleaner (Skymen, JTS-1030, power = 500 W) for 30 min to remove the PR together with the underneath AgNWs, while the AgNWs with TiO2 coatings remained due to the enhanced adhesion (step 6). Finally, the samples were purged by high purity N2 (99.999%) to remove the residual impurity and solution, and the patterned AgNW networks were successfully fabricated (step 7).

Figure 1
figure 1

Schematic illustration for the fabrication of patterned flexible TCEs for ACEL devices.

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Results and discussion

TiO2 coating on AgNW networks by ALD

TiO2 films were deposited on the surface of AgNW networks to improve the stability. The surface morphology of the AgNW networks and the TiO2 coating state were observed by SEM. As shown in Fig. 2a and Figure S1(a), the AgNWs were randomly and uniformly distributed on the surface of the PDMS substrate after spin-coating and thermal annealing at 130 ℃ for 15 min. And the junctions between the AgNWs were then welded after thermal annealing, which could not only greatly improve the conductivity of the AgNW networks, but also enhanced the mechanical stability to a certain degree [37]. The effects of TiO2 coating layer by ALD with different thicknesses on the performance of AgNWs/TiO2 composites for flexible TCEs were further investigated. For clarity, the AgNW networks with 30 nm (50 nm or 80 nm) TiO2 coating were denoted as AgNWs@30 (50 or 80) nm TiO2, respectively. Figure 2b–d and Figure S1(b–d) show the SEM images for TCEs of AgNWs@30 nm TiO2, AgNWs@50 nm TiO2 and AgNWs@80 nm TiO2, respectively. It can be clearly seen that conformal TiO2 thin films with different deposition thicknesses were successful coated on the surface of AgNWs. This phenomenon also confirmed the three-dimensional conformal coatings of ALD technique on irregular surfaces. And the corresponding surface morphologies as well as the roughness of these films were further estimated using AFM (Figure S2), showing a significantly decreasing roughness with modification of TiO2 coating layer. Specifically, the root-mean-squared (RMS) values of surface roughness were 44.6 ± 2.3 nm, 22.6 ± 1.6 nm, 18.9 ± 1.3 nm and 8.74 ± 0.8 nm for the samples of the bare AgNW network, AgNWs@30 nm TiO2, AgNWs@50 nm TiO2 and AgNWs@80 nm TiO2, respectively. It was clearly that the TiO2 coating can reduce the surface roughness of AgNW networks, which should provide benefits for the fabrication of flexible devices. To further confirm the deposition of TiO2 coating layer, the cross-sectional image and the EDS maps of AgNWs@30 nm TiO2 were measured and illustrated in Figs. 2e and S3. It can be found that the AgNWs were isotropically coated with TiO2 thin film of around 30 nm. Besides, the surface of PDMS substrate also achieved continuous and uniform deposition of TiO2, which might increase the adhesion of AgNW networks on the substrate due to the infiltration and combination of TiO2 films with the free volume in the subsurface regions of the PDMS [38].

Figure 2
figure 2

SEM images of AgNWs/TiO2 composites for flexible TCEs: a bare AgNWs, b AgNWs@30 nm TiO2, c AgNWs@50 nm TiO2 and d AgNWs@80 nm TiO2. e The cross sectional image of AgNWs@30 nm TiO2. f Sheet resistances of AgNW networks with different surface density and different thicknesses of TiO2 coating. g Optical transmittances of the AgNW networks with different thicknesses of TiO2 coating; the surface density of AgNW networks were 13.3 μg/cm2.

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It is crucial to balance the conductivity and optical transmittance of AgNW networks because they constrain each other [39]. The optical transmittance and electrical conductivity were further optimized via the density of AgNW networks. Different surface densities were obtained by changing the concentration of AgNWs ink. Figure 2f shows the sheet resistances of the AgNW networks at different surface densities. It was obvious that the sheet resistance decreased with the increase of the AgNWs surface density, due to more overlap and connection probability between AgNWs. It was also found that the TiO2 coating layer affected the sheet resistances of AgNW networks, less than 20% of sheet resistances increased when the thicknesses of the TiO2 coating layer were less than 80 nm. And with the increase of TiO2 thickness, the sheet resistances of AgNW networks increased slightly, whose conductivity was well. This phenomenon might be attributed to the diffusion of Ag atoms through the semiconductor metal oxide [25, 40]. When the thickness of the metal oxide was thin, Ag atoms would diffuse through the coating, resulting in the network failure. On the contrary, when a large stress was applied, AgNW electrical resistance increased. Therefore, the sheet resistances of AgNW networks is related to the metal oxide thickness.

Since the silver is nearly opaque to light, higher surface density of AgNW network would lead to the lower optical transmittance. Considering the results of Figs. 2f and S4, the surface density of AgNW networks that applied in the subsequent studies was 13.3 μg/cm2, which showed surface resistance of 20.8 ± 1.0 Ω/sq and optical transparency of around 80% in the visible range. In addition, the effect of the TiO2 coating on optical transparency was also tested, as shown in Fig. 2g, from which, it can be seen that the optical transmittance of AgNW networks decreased with the increase of the TiO2 coating thickness. However, the optical transparency of the flexible TCEs could still remain about 70% under the coating thickness of 80 nm.

Enhancement of mechanical reliability and environmental stability of AgNW networks with TiO2 coatings

To investigate the mechanical properties of AgNWs/TiO2 composites for flexible TCEs, the adhesion of AgNWs to the substrate was investigated. It was puzzled that AgNW networks without additional treatments tended to be easily removed from the substrate by a gentle wiping force. In order to evaluate the effects of TiO2 coating on the adhesion of AgNW networks, both bare AgNW networks and the AgNW networks with TiO2 coatings were subjected to ultrasonic concussion. Figure 3a shows that the sheet resistance of the bare AgNW networks increased remarkably due to ultrasonic concussion induced stripping, while the sheet resistance of AgNW networks with TiO2 coatings changed slightly after ultrasonic concussion for 2 h. Peeling tests were also conducted for further verification of the adhesion enhancement with of AgNW networks with TiO2 coatings, as shown in Fig. 3b. It was found that the sheet resistances of AgNWs with TiO2 coating layers remained nearly unchanged after 10 cycles of peeling using 3 M tape, while the sheet resistance of the bare AgNW networks decreased rapidly owe to the constant peeling of AgNWs (shown in the inset). Both the ultrasonic concussion and 3 M tape peeling tests confirmed the strengthen effect of adhesion with TiO2 coating layer.

Figure 3
figure 3

Adhesion and mechanical reliability of AgNWs/TiO2 composites on PDMS for flexible TCEs: a by ultrasonic agitation (power = 500 W); b by 3 M tape peeling, the insert image shows the bare AgNW networks after 10 cycles of peeling test; c by cyclic bending test with bending radius of 5 mm, the insert image shows the TCEs of AgNWs@50 nm TiO2 after 500 cycles of bending test; d by uniaxial tensile straining test, the insert diagrams show the testing process.

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The enhancements of mechanical reliability of the AgNWs/TiO2 composites for flexible TCEs were investigated by bending tests and uniaxial tensile straining tests, the photographs of the testing process were shown in Figure S5. After 500 cycles of bending tests, both the bare AgNWs and AgNWs@30 nm TiO2 still kept the good sheet resistances, as shown in Fig. 3c. However, AgNWs with thicker TiO2 coatings over 50 nm would decrease the bending performance of AgNW networks. This phenomenon might be attributed to the rigid feature of inorganic material TiO2, which is prone to cracks due to the existence of film stress when it is bent, and with the increase of inorganic material thickness, the maximum stress of the films increases, leading to the cracks in the AgNW/TiO2 composites with TiO2 coatings over 50 nm after repeated bending. The insert SEM image shows the cracks in the TCEs of AgNWs@50 nm TiO2 after 500 bending cycles. In addition, the conductivity under uniaxial tensile straining test were also measured, as shown in Fig. 3d. It can be seen that the AgNW networks coated with thinner TiO2 layer had more stable sheet resistances under tensile states. Therefore, it could be concluded that an appropriate thickness of about 30 nm TiO2 coating layer can not only effectively enhance the adhesion of AgNWs on the substrate, but also improve the mechanical reliability.

In practical application, the thermal stability of AgNWs is also a major problem. The effects of TiO2 coatings on the thermal stability of AgNW networks were also investigated as a function of the thickness of TiO2 coating layer. The samples used for the tests were also fabricated with the surface density of 13.3 μg/cm2. The thermal stability of AgNW networks with and without TiO2 coatings was tested from 40 to 300 ℃ at a heating rate of 5 ℃/min. The initial sheet resistances of all the samples were nearly constant regardless of the thickness of TiO2 coating layer, indicating that TiO2 coating has little effect on the surface resistance of AgNW networks. It is shown in Fig. 4a that the surface resistance remained unchanged when the heating temperatures were less than 180 ℃. As the temperature further increased, the sheet resistances of the bare AgNW networks increased, while the sheet resistances of AgNW networks with TiO2 coating can stand against the change up to 240 ℃, and then suffered from a sharp increase. It was found that this drastic change had already destroyed the conductive networks of AgNW, as shown in Fig. 4c–d. This phenomenon was attributed to the Plateau–Rayleigh instability [41]. The spheroidization of the bare AgNWs leaded to the disconnection of the conductive network, as shown in Fig. 4c, whereas Fig. 4d shows that the sample of AgNWs@30 nm TiO2 retained the wirelike construction after the Plateau-Rayleigh instability, which also confirmed that the TiO2 coating could improve the thermal endurance of AgNW networks. What’s more, the barrier property of TiO2 coating was accessed because AgNWs were easily oxidized by oxygen and water vapor. The oxidation stability test was carried by monitoring the conductance of AgNWs in a controlled environment of 85 ℃ and 85% RH, the results were plotted as normalized conductance (R/R0) vs. time curves, as shown in Fig. 4b. As expected, the AgNW networks were effective encapsulated by a TiO2 coating layer. Although the resistances of AgNWs/TiO2 composites showed a subtle linear increase in the testing process, this phenomenon could be explained by the interaction of electron and phonon because of the long-time exposure to high temperature and humidity environment [42]. However, the bare AgNW networks showed the constant increase in resistance day by day. It was found that the surface of bare AgNWs generated many nano-particles after oxidation in a controlled environment of 85 ℃ and 85% RH for 30 days, as shown in Fig. 4e. It can be deduced that a non-conductive silver oxide layer was formed on the surface of bare AgNWs.

Figure 4
figure 4

a Thermal stability of AgNW networks with and without TiO2 coatings under different temperatures. b Dependence of the normalized conductance vs. time for AgNW networks with and without TiO2 coatings in a controlled environment of 85 ℃ and 85% RH. SEM images of TCEs after stability test: c bare AgNWs heating at 250 ℃ for 15 min; d AgNWs@30 nm TiO2 heating at 250 ℃ for 15 min; e bare AgNWs oxidation in a controlled environment of 85 ℃ and 85 RH for 30 days.

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Patterning of AgNWs/TiO2 composites and the application to the ACEL devices.

To further applied the flexible TCEs in reality, the patterned method of TCEs should be explored. According to the adhesion enhancement of AgNW networks to the substrate by TiO2 coatings, a simple method based on photolithography and ultrasonic concussion processes was carried out to obtain the patterned AgNW/TiO2 composites with various graphics, and finally AgNW/TiO2 composites were applied as TCEs for ACEL devices. The fabricating processes were concretely shown in Fig. 1.

In this work, TCEs with the graphics of a snail and strip electrodes were successfully fabricated and used for ACEL devices, as the displays, respectively, shown in Figs. 5a, b and S6. It could be seen that the ACEL devices equably display the graphics, which illustrate the excellent conductivity of the patterned TCEs. The microscope image of Fig. 5c shows the TCEs with the strip width of 200 μm, the surface of the electrode was flat without defects. The changing of the sample in the ultrasonic concussion process was shown in Fig. S1. It could be seen that positive photoresist (PR) together with the bottom AgNW networks, detached from the PDMS substrate after 5 min ultrasonic concussion. After 30 min ultrasonic concussion, the pattern PR layer was all peeled off from the substrate, so that the strip TCEs were successfully fabricated. Besides, from the thickness measurement in Fig. 5d, the thickness of the AgNW/TiO2 composites was about 120 ± 7.3 nm, it is worth mentioned that the strip TCEs show sharp and clearly edges. These results demonstrate the successful preparation of the patterned TCEs under the cooperation of photolithography, TiO2 coating and ultrasonic concussion processes, which was greatly attributed to enhancement effects of TiO2 coatings. Furthermore, the patternings of TCEs were also investigated by the way of traditional etching. After the photolithography process of Fig. 1, the AgNW networks were etched by dilute nitric acid. It was found that the strip widths of TCEs were all below the designing width of 200 μm, as the results shown in Fig. 5e. Because of the strong corrosivity of nitric acid, the etching would be quickly taken in the edge of the strip electrodes even if the protection by PR layer, while the ultrasonic concussion process could maintain the target graphics of TCEs, as Fig. 5f has shown. Thus, the patterning of AgNW/TiO2 composites by ultrasonic concussion process was more easily to control compared to the traditional etching method.

Figure 5
figure 5

Photographs of the ACEL devices based on patterned TCEs: a a snail, b electrode with the strip width of 200 μm. c Microscope images of TCEs after 30 min ultrasonic concussion. d Thickness measurement to the sample of Fig. 5(c). e The width of strip TCEs fabricated by ultrasonic concussion and etching, the design widths both were 200 μm. f The corresponding microscope images of the strip TCEs after fabrication by ultrasonic concussion and etching.

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The application of the AgNW/TiO2 composites on ACEL devices indicates a potential value for the development of flexible electronics. Therefore, mechanical reliability and stability of the ACEL devices should be checked. To verify the mechanical reliability, the ACEL devices were tested under bending and compression states. As the results of Fig. 6a has shown, the devices based on patterned TCEs of AgNWs@30 nm TiO2 and bare AgNWs, both has excellent emission properties after 500 cycles bending tests with the bending radius of 5 mm, while the TCEs of AgNWs@30 nm TiO2 showed a little superior than the bare AgNW networks. In the insert image, it is shown that the ACEL devices can maintain uniform emission under different deformation states. These excellent performances were mainly attributed to the highly stable and flexible AgNW/TiO2 composites. While under the uniaxial compression tests, the devices based on patterned TCEs of AgNWs@30 nm TiO2 and the bare AgNW networks show the same trends in the changes of luminance, as shown in Fig. 6b. The luminance increased as the increase in compression ratio. This was because that the thickness of EL layer decreased in compressed area, which leaded to the enhancement of electrical field between the top and bottom electrodes [43]. Thus, it was concluded that the ACEL device based on patterned TCEs of AgNWs@30 nm TiO2 could showed excellent mechanical properties. In addition, the degradation tests of ACEL devices were also investigated. As predicted from the result of AgNWs oxidation test, the lifetime of ACEL device could be prolonged by using the TCEs with TiO2 coating layer. It was found from the results of Fig. 6c, the ACEL device based on TCEs of AgNWs@30 nm TiO2 kept good emission property after degradation test in a controlled environment of 85 ℃ and 85% RH for 30 days. However, the luminance of the ACEL device based on bare AgNWs decreased day by day. It is reasonable to infer that the lifetime of ACEL device mainly depends on the electrodes, consequently the barrier performance of TiO2 coating layers improved the lifetime of ACEL device. Because of the high optical transparency, AgNW/TiO2 composites are more attractive. As Fig. 6d has shown, the transparency of the whole ACEL device was around 40%, and the display images before and after applying an alternating voltage can be clearly seen from the photographs in Figure S8. These features indicate the prospects of the AgNW/TiO2 compisites on applications to flexible electronics.

Figure 6
figure 6

a The normalized luminance of the ACEL device after the bending test with bending radius of 5 mm; the insert images show the devices (based on patterned TCEs of AgNWs@30 nm TiO2) after 0, 100, 300 and 500 bending cycles, the scale bar is 5 mm. b The normalized luminance of the ACEL device under different uniaxial compression ratios; the insert images show the devices (based on patterned TCEs of AgNWs@30 nm TiO2) under the compression ratios of 20%, 40%, 60% and 80%, the scale bar is 5 mm. c Dependence of the normalized luminance vs. time of the ACEL devices in a controlled environment of 85 ℃ and 85% RH. d The transparency of an ACEL device based on the TCE of AgNWs@30 nm TiO2.

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Conclusions

In summary, based on the conformal TiO2 coatings by atomic layer deposition (ALD), highly stable and patterned AgNW/TiO2 composites were successfully fabricated for flexible transparent conductive electrodes (TCEs). TiO2 coatings were introduced for the stability enhancement of AgNW networks. The measurements were conducted to determine the effects of the thickness of TiO2 coating on the mechanical property and stability of AgNW networks. It was found that TiO2 coating could not only enhance the adhesion of AgNWs to the substrate, but also improve the flexibility of AgNW networks. This was attributed to the three-dimensional conformal deposition of ALD technique on irregular surfaces, so that the surface of AgNWs and the substrate were coated with a uniform and conformal TiO2 thin film. Meanwhile, the thermal and oxidation stabilities of AgNW networks could be greatly improved because of the barrier performance of TiO2 coating layers. Besides, based on the adhesion enhancement by conformal TiO2 coating layers, a novelty patterning method of the AgNW networks were implemented by cooperating with photolithography and ultrasonic concussion process. The strip electrodes with the low width of 200 μm were well patterned, showing sharp edges without defects. At last, highly stable patterned AgNW/TiO2 composites were successfully applied as TCEs to alternating current electroluminescent (ACEL) devices. The graphics of ACEL display could be design as needed, and the whole ACEL device showed a high transparency of around 40%. As expected, the flexibility and the lifetime of ACEL devices were correspondingly improved owe to the enhancement by TiO2 coatings. These results proved that the highly stable patterned AgNW/TiO2 composites could be excellent TCEs for flexible or wearable electronics.