Silver Nanowire-Based Flexible Transparent Electrodes: Fabrication and Applications

Abstract

Silver nanowire (AgNW) networks have attracted significant attention as leading candidates for flexible transparent electrodes owing to their unique combination of high electrical conductivity, optical transparency, and mechanical compliance. This review presents an overview of recent developments in AgNW-based transparent electrode technologies, with particular emphasis on strategies to improve network conductivity and long-term reliability, including junction engineering, surface modification, encapsulation approaches, and composite structure design. Representative applications in flexible optoelectronic systems, such as organic light-emitting devices, transparent heating elements, and electrochromic platforms, are also discussed. Finally, current challenges and future research directions toward scalable manufacturing and practical implementation of high-performance AgNW electrodes are outlined.

1. Introduction

Flexible electronic technologies—encompassing organic electronics [1,2,3,4,5], nanoelectronics [6,7,8,9], and printed electronics [10,11,12,13]—are rapidly emerging. Studies on rheology-controlled printable systems have shown that ink formulation, viscosity regulation, and shape retention strongly affect printing fidelity and structural stability [14,15,16,17]. For AgNW-based flexible transparent electrodes, recent advances in screen printing, inkjet printing, aerosol jet printing, and electrohydrodynamic printing further demonstrate the feasibility of scalable fabrication of conductive networks [18,19,20]. Compared to traditional rigid devices, flexible electronics offer superior portability, expanded functionality, and more intuitive interaction with users [21,22,23,24,25,26]. Flexible transparent electrodes (FTEs) are essential components in many flexible devices, including displays [27,28,29,30,31], solar cells [32,33,34,35,36], and sensors [37,38,39,40]. To achieve high-performance flexible electronics, FTEs must possess excellent optoelectronic properties and mechanical flexibility [41,42,43,44]. At the same time, industrial applications demand solutions that support low-cost, large-area fabrication. Currently, indium tin oxide (ITO) remains the dominant transparent conducting oxide material in commercial transparent electrodes owing to its high optical transparency, low sheet resistance, and mature deposition technology [45,46]. However, conventional ITO films are intrinsically brittle and are prone to cracking or electrical degradation under bending or tensile deformation because of the mechanical mismatch between the stiff oxide layer and flexible polymer substrates [47,48]. This limitation makes ITO unsuitable for applications that require flexible transparent electrodes capable of withstanding large mechanical strains (>10%) [49,50]. As a result, identifying alternative conductive materials that fulfill both performance and scalability requirements remains a significant challenge [20,51,52,53].

A variety of conductive materials have been explored for the fabrication of flexible transparent electrodes [16,54,55]. For instance, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) [56,57,58], a transparent conductive polymer, was among the first used for this purpose. However, due to its relatively low conductivity, PEDOT:PSS-based electrodes often fail to simultaneously achieve high transparency and high electrical performance. Graphene, known for its outstanding transparency, conductivity, and flexibility, is another promising candidate [59,60,61]. However, the large-area fabrication of high-quality graphene transparent electrodes, particularly CVD-grown graphene, still faces challenges related to high cost, complex manufacturing processes, high deposition temperatures, and transfer-induced degradation, which restrict their large-scale industrial application [62,63,64]. Carbon nanotubes (CNTs), a representative one-dimensional nanomaterial [65,66,67,68,69], have also been utilized in this field and are compatible with roll-to-roll manufacturing processes, which helps reduce production costs [70,71,72]. Nevertheless, the considerable contact resistance between individual nanotubes limits the overall conductivity of CNT-based flexible transparent electrodes.

In recent years, advancements in one-dimensional nanomaterial synthesis have introduced promising alternatives for the fabrication of flexible transparent electrodes [73,74,75,76]. Among these materials, silver nanowires (AgNWs) stand out as one of the most ideal candidates due to their low synthesis cost and excellent electrical conductivity [77,78,79,80]. In AgNW-based flexible transparent electrodes, the nanowires form an interconnected conductive network, while light can pass through the gaps between the wires, resulting in optoelectronic performance comparable to that of indium tin oxide (ITO), with transmittance around 90% and sheet resistance ranging from 10 to 20 Ω/sq [81]. Furthermore, the AgNW network can accommodate mechanical deformation by adjusting its structure, thereby fulfilling the requirements for high flexibility. These combined advantages have become key drivers in advancing the commercialization of AgNW-based flexible transparent electrodes. However, the contact resistance at the junctions of the AgNW network is high, leading to suboptimal conductivity [82,83]. Moreover, the AgNW network has poor thermal stability, and during long-term operation, the Joule heat generated by the current gradually damages the nanowires, resulting in poor long-term operational stability of the flexible transparent electrodes [84,85,86]. To reduce the contact resistance at the junctions of AgNWs, researchers worldwide have developed various connection methods, including heating methods, pressing methods, Joule heating methods, photonic sintering, electrodeposition, and chemical deposition.

Recent reviews have summarized AgNW transparent conductive films from different perspectives, including AgNW synthesis, film fabrication, stability enhancement, uniformity control, and specific device applications [87,88,89]. These studies, together with broader bibliometric and metal-nanowire transparent electrode reviews that help identify emerging research trends and emphasize solution processing, mechanical flexibility, optoelectronic performance, uniformity control, and flexible/stretchable device integration [41,90,91], indicate that practical performance improvement remains a key issue for the scalable application of AgNW-based flexible transparent electrodes. Building on these studies, this review focuses on solution-processed AgNW-based flexible transparent electrodes from the viewpoint of practical performance improvement. Particular attention is paid to the relationship between network structure, post-treatment process, and electrode performance. The discussion first examines junction-engineering strategies for reducing contact resistance and improving electrical conductivity, followed by stabilization approaches based on surface modification, protective coatings, and composite structures. Representative applications in flexible optoelectronic devices, including OLEDs, transparent heaters, and electrochromic devices, are then discussed to illustrate how electrode design influences device-level performance. By linking conductivity enhancement, stability improvement, and flexible device integration, this review aims to provide a useful reference for the design and scalable fabrication of high-performance AgNW-based flexible transparent electrodes.

2. Post-Treatment Techniques for Reducing the Contact Resistance

The constructed AgNW network contains numerous junctions where the nanowires are in contact either at discrete points or along lines. These limited contact areas result in significant contact resistance, which prevents full utilization of the excellent electrical conductivity of AgNWs. Upon electrical operation, this contact resistance generates substantial Joule heating at the junctions, increasing the temperature of AgNW transparent electrodes and compromising their long-term operational stability. Additionally, during mechanical deformation, crossed nanowires are prone to sliding at these junctions, further reducing the mechanical stability of the electrodes [92]. Therefore, to fabricate high-performance AgNW transparent electrodes, it is essential to adopt joining strategies that enlarge the contact area at the junctions and reduce the corresponding contact resistance.

2.1. Thermal Annealing

Thermal annealing was the earliest technique proposed for welding AgNWs and remains the simplest approach. Lee et al. [93] used computer simulations to investigate how the sheet resistance of AgNW networks varies with network density under different contact resistances at the junctions. They found that the sheet resistance of the AgNW network decreases as the network density increases. However, as the contact resistance at the junctions increases, the overall sheet resistance of the network also increases. These simulation results indicate that contact resistance at the junctions significantly affects the network’s sheet resistance, and reducing this contact resistance can enhance the electrical conductivity of the AgNW network. Subsequently, thermal annealing at 200 °C was used to weld the AgNW network and reduce junction resistance, thereby improving conductivity. After heating at 200 °C for 20 min, the sheet resistance of the network dropped by more than an order of magnitude—from over 1 kΩ/sq to approximately 100 Ω/sq. This improvement is primarily due to two effects: first, heating removes the polyvinylpyrrolidone (PVP) coating on the surface of the AgNWs; second, it promotes the interdiffusion of Ag atoms at the junctions, increasing the contact area and reducing contact resistance. However, when the heating duration exceeds 40 min, the AgNWs begin to degrade, resulting in increased sheet resistance. Lagrange et al. [94] further optimized AgNW transparent electrodes by controlling nanowire density, nanowire dimensions, and thermal annealing conditions, and obtained excellent optoelectronic performance with a sheet resistance of 2.9 Ω sq⁻¹ and a transmittance of 89.2% at 550 nm.

In addition to requiring precise control of temperature and duration, thermal annealing is also unsuitable for thermally sensitive substrates, which limits its applicability. To address this issue, several milder or more localized welding strategies have been developed, including photonic sintering [95,96], laser welding [97,98,99,100], electrodeposition welding [81,101,102,103], and self-limited nanosoldering [92].

2.2. Photonic Sintering

Garnett et al. [95] first proposed using the strong surface plasmon resonance (SPR) effect at the junctions of AgNW networks to achieve nanowire connection. By irradiating the AgNW network with a broadband tungsten halide lamp at a power density of 30 W/cm² for 10 to 120 s, they successfully demonstrated a photonic sintering method for connecting AgNWs. Finite element simulation results from this study revealed that, under light irradiation, localized hotspots formed at the junctions where light energy was converted into thermal energy. The heat generated at these hotspots facilitated the mutual diffusion of Ag atoms at the junctions, enabling the formation of conductive connections. As the process continued, the hotspots gradually shifted toward the edges of the junctions; once the contact area became sufficiently large, the hotspots disappeared.

This photonic sintering approach leverages the strong SPR effect at the junctions to generate localized heating, inducing reliable nanowire joining without affecting regions of the nanowires beyond the junctions. The presence of coordination groups (e.g., PVP) on the AgNW surfaces results in nanoscale gaps at the junctions. Simulation results showed that the heat generation efficiency was maximized when this gap was approximately 2 nm. Gerlein et al. [96] demonstrated a photonic sintering method to rapidly weld AgNWs at their junctions via plasmon-induced localized heating (Figure 1). The process enables the fabrication of high-performance, flexible, and transparent conductive electrodes with excellent optoelectronic properties. By optimizing pulse fluence and nanowire density, the authors achieved electrodes with over 88% transmittance and a sheet resistance as low as 9.8 Ω/sq—outperforming conventional ITO by a factor of 2.6–2.7 in key performance metrics. The method is compatible with low-temperature substrates and industrial roll-to-roll manufacturing, making it ideal for wearable electronics, sensors, and solar energy applications.

2.3. Laser Sintering

Laser nano-welding is an effective technique for joining AgNWs at their junctions by locally inducing plasmonic heating through focused laser irradiation. When a laser beam interacts with the overlapping regions of AgNWs, surface plasmon resonance leads to a rapid and localized temperature increase, which promotes atomic diffusion and recrystallization at the contact points. This process significantly reduces the contact resistance between nanowires while maintaining the overall morphology of the network. Compared to thermal annealing, laser welding offers higher spatial precision, faster processing times, and compatibility with flexible, heat-sensitive substrates, making it highly suitable for the fabrication of high-performance transparent conductive electrodes. Dai et al. [97] used a continuous-wave laser to join AgNWs and observed that the laser’s irradiation position had a significant impact on the welding quality. Similarly, Nian et al. [98] utilized a 248 nm nanosecond laser to enhance the junction performance of AgNWs. After 2.5 µs of irradiation, the silver at the junction gradually melted and recrystallized, forming a robust metallurgical bond. Wang et al. [99] further demonstrated a 532 nm nanosecond-pulsed laser nano-welding method for fabricating high-performance AgNW flexible transparent electrodes. As shown in Figure 2, the as-deposited AgNW network showed loose junction contact before laser treatment. After laser nano-welding under appropriate fluence, the junctions became more closely connected because of localized surface plasmon resonance-induced heating. When the laser fluence increased from 10.0 to 27.9 mJ cm⁻², the junction welding became more effective and the sheet resistance decreased rapidly. However, excessive laser fluence, such as 37.9 mJ cm⁻², caused morphological deterioration of the AgNWs and an increase in resistance. Under optimized conditions, the laser-welded AgNW FTEs achieved a low sheet resistance of 11.3 Ω sq⁻¹ and a high optical transmittance of 85.9%, while the thermal effect on organic substrates was negligible.

Compared with nanosecond-pulsed laser welding, femtosecond laser welding provides a shorter energy-deposition time and a more localized heat-affected region. Hu et al. [100] presented a femtosecond laser nanowelding technique to improve the conductivity, uniformity, and mechanical stability of AgNW FTEs. By inducing localized melting at nanowire junctions without damaging the polyethylene terephthalate (PET) substrate, the method achieved a low sheet resistance of 16.1 Ω/sq, high transmittance of 91%, and excellent bending durability over 10,000 cycles. The process also enhanced adhesion between AgNWs and the substrate. This approach offers a promising, non-damaging solution for fabricating high-performance, flexible transparent electrodes for next-generation optoelectronic devices.

2.4. Electrodeposition Welding

The joining of AgNWs can also be achieved by electrodepositing metal materials onto their surfaces. The basic principle of electroplating involves using the AgNW transparent electrode as the cathode and the target metal as the anode. Both electrodes are immersed in an electrolyte containing the desired metal ions. When current is applied, the metal ions are reduced on the surface of the AgNWs, resulting in the deposition of metal atoms that effectively connect the nanowires at their junctions.

In 2014, Eom et al. [101] published the first report on joining AgNWs via electroplating. At a current density of 2.3 mA/cm², electroplating for 5, 20, 50, and 100 s gradually increased the diameter of the nanowires from 50 nm to 275 nm. This enhanced connectivity significantly reduced the sheet resistance of the AgNW transparent electrode from 31.1 Ω/sq to 10.0 Ω/sq. Additionally, nickel (Ni), being more chemically stable than silver, served as a protective layer. Upon immersion in Na₂S solution for 21 s, pristine AgNWs corroded, and the electrode lost conductivity. In contrast, Ni-coated AgNWs exhibited only a 6.4-fold increase in sheet resistance after 300 s, demonstrating the protective effect of Ni. Moreover, Wang et al. [102] found that Ni electroplating suppressed the surface diffusion of silver atoms, thereby improving thermal stability.

However, due to the crystal structure mismatch between Ni and Ag, the resulting Ni layer is relatively rough, increasing light scattering and significantly reducing the transmittance of the electrode. To address this, Kang et al. [81] explored the epitaxial deposition of silver onto AgNWs, which maintained a smooth surface while achieving reliable junctions. This method yielded AgNW transparent electrodes with a transmittance of 90% and a sheet resistance of 19 Ω/sq. Zhang et al. [103] electroplated a gold (Au) protective layer onto the surface of AgNW networks, effectively achieving AgNW joining (Figure 3A–D). Using finite element simulations, they analyzed the electric field distribution (Figure 3E,F). They also examined the elemental distribution (Figure 3G–J) and surface chemical states (Figure 3K,L) during the deposition process. The analysis confirmed the successful formation of the gold coating.

To provide a clearer comparison among different junction-engineering strategies,

Table 1. Quantitative comparison of representative post-treatment and protection strategies for AgNW-based flexible transparent electrodes.

Method	Refs.	Processing Condition	Sheet Resistance/Transmittance	FOM	Compatibility and Scalability	Stability/Durability	Advantages and Limitations
Thermal annealing	Lee et al. [93]; Lagrange et al. [94]	Thermal treatment at ca. 200 °C; optimized annealing of AgNW networks.	Rs decreased from >1 kΩ sq−1 to ca. 100 Ω sq−1 after 20 min; optimized electrodes can reach 16 Ω sq−1 at 86% T or 2.9–9.5 Ω sq−1 depending on network density and wire geometry.	ca. 0.014–0.11 Ω−1, depending on T/Rs combination.	Simple and scalable heating process, but only moderately compatible with flexible substrates; high temperature may damage PET or other low-Tg polymers.	Excessive annealing may cause AgNW degradation, spheroidization, or increased resistance.	Advantage: simple, low-cost and chemical-free. Limitation: strict temperature/time control and limited compatibility with heat-sensitive substrates.
Photonic sintering/plasmonic welding	Garnett et al. [95]; Gerlein et al. [96]	Broadband light or pulsed photonic irradiation; plasmon-induced localized heating at AgNW junctions.	9.81 Ω sq−1 at 88.27% T.	0.031 Ω−1.	Good compatibility with flexible substrates because heating is localized at junctions; suitable for high-speed and roll-to-roll processing.	Junction resistance can decrease by more than three orders of magnitude after plasmonic welding; rapid treatment improves network conductivity.	Advantage: rapid, non-contact and large-area compatible. Limitation: pulse energy, exposure time and nanowire density must be carefully optimized.
Laser welding	Dai et al. [97]; Nian et al. [98]; Wang et al. [99]; Hu et al. [100]	Continuous-wave, nanosecond or femtosecond laser irradiation; localized melting/recrystallization at AgNW junctions.	16.1 Ω sq−1 at 91% T.	ca. 0.024 Ω−1.	Good substrate compatibility under optimized laser parameters; more suitable for patterned or local treatment than whole-area low-cost processing.	Stable after 10,000 bending cycles; stable for 30 days at 85 °C and 85% RH in the reported femtosecond-laser-welded film.	Advantage: high spatial precision and improved adhesion/uniformity. Limitation: relatively high equipment cost and scanning-dependent throughput.
Ni electrodeposition welding	Eom et al. [101]; Wang et al. [102]	Ni electroplating on AgNW networks; representative deposition time of 5–100 s.	Pristine AgNW: 31.07 Ω sq−1, 85.27% T. After 5, 20, 50 and 100 s Ni deposition: 28.98, 26.03, 21.09 and 9.92 Ω sq−1; T decreases to 81.41%, 74.99%, 48.66% and 37.01%, respectively.	Reported FoM values: 72.62 for pristine AgNW; 60.04, 46.79, 20.62 and 29.51 after 5, 20, 50 and 100 s deposition, respectively.	Solution-based process compatible with flexible substrates when electrolyte and deposition time are controlled; scalable but needs electrochemical equipment.	After 14 days at 80 °C/85% RH, Ni-coated samples showed only 1.18–1.54-fold resistance increase; one sample showed only 6.44-fold increase after 300 s in Na2S solution.	Advantage: reduces junction resistance and improves oxidation/sulfurization resistance. Limitation: excessive Ni deposition strongly reduces optical transparency.
Ag epitaxial electrodeposition	Kang et al. [81]	Roll-to-roll galvanostatic Ag electroplating; epitaxial Ag growth on AgNWs and junctions.	ca. 19 Ω sq−1 at 90% T550.	ca. 0.018 Ω−1.	Good compatibility with PET-based flexible electrodes; roll-to-roll electroplating demonstrates high scalability.	Improves junction bonding and network integrity; applied to OLEDs, triboelectric nanogenerators and resistive touch panels.	Advantage: smooth Ag deposition reduces junction resistance while maintaining transparency. Limitation: excessive Ag growth may reduce transparency and requires precise process control.
Au shell/Ag@Au structure	Zhang et al. [103]; Zhu et al. [104]; Seong et al. [105]	Au coating or ultrathin epitaxial Ag@Au core–shell nanowire formation; Au shell thickness typically only several nanometers.	9.88 Ω sq−1 at 85% T; 17.52 Ω sq−1 at 90% T; 37.41 Ω sq−1 at 95% T.	ca. 0.020 Ω−1 at 90% T and 17.52 Ω sq−1.	Good compatibility with flexible PET after transfer; solution synthesis is feasible, but Au cost should be considered for scale-up.	No significant Rs change for 84 days at 80 °C/100% humidity; stable in PBS for more than 21 days and in air for more than 6 months.	Advantage: excellent chemical, thermal and humidity stability. Limitation: high noble-metal cost and possible optical/plasmonic loss if the Au layer is too thick.
Self-limited nanosoldering	Huang et al. [92]	Room-temperature self-limited nanosoldering through selective Ag nanosolder deposition at AgNW junctions.	AgNW film decreased from 18.6 to 7.7 Ω sq−1 at 90% T; heater electrode reached 3.7 Ω sq−1 at 82.5% T.	ca. 0.045 Ω−1 at 90% T and 7.7 Ω sq−1; ca. 0.039 Ω−1 for heater electrode.	Good compatibility with flexible substrates because the process occurs at room temperature; large-area 210 × 297 mm2 electrodes were demonstrated.	Transparent heater reached 145 °C at 6 V within 30 s with a heating rate of 4.8 °C s−1.	Advantage: room-temperature, simple and effective for transparent heaters. Limitation: optical transmittance decreases when very low sheet resistance is targeted.
Metal oxide nanoparticle modification	Liu et al. [106]	Modification of AgNW networks with ZnO, SnO2, Al2O3 or TiO2 nanoparticles generated by magnetron sputtering.	Resistance reduction: 75.6% for ZnO, 70.4% for SnO2, 53.2% for Al2O3 and 59.8% for TiO2 modification. Exact comparable T/Rs values depend on oxide type and thickness.	Not reported using the same FOM format.	Compatible with flexible transparent conductive films; sputtering is scalable but requires vacuum equipment.	Failure voltage increased up to 16 V; temperature non-uniformity decreased to 8.7%–10.4% compared with 40.6% for pristine AgNW films.	Advantage: improves electrical uniformity, thermal distribution and current-loading stability. Limitation: vacuum equipment and thickness control are required.

summarizes representative post-treatment methods for AgNW-based flexible transparent electrodes, including their processing conditions, sheet resistance/transmittance, figure of merit, compatibility with flexible substrates, scalability, stability/durability, and main advantages and limitations.

3. Protective Coating Layers for Improving Stability

Through the polyol method and its improved variations, high-quality AgNWs can be synthesized in large quantities at relatively low cost, making their large-scale industrial application feasible [107,108]. However, the complete replacement of ITO materials with AgNWs for the preparation of transparent electrodes is still hindered by their insufficient long-term stability. The root cause of this instability lies in the enhanced surface reactivity and thermally induced morphological degradation of AgNWs. First, the nanoscale diameter of AgNWs gives them a large specific surface area and high chemical activity, making unprotected AgNW networks susceptible to oxidation, sulfurization, and corrosion under ambient or harsh operating conditions [109]. Second, Ag atoms on the nanowire surface can undergo thermally activated surface diffusion at temperatures far below the bulk melting point of silver, resulting in nanowire fragmentation, spheroidization, or network failure [86,87]. Therefore, improving the chemical and thermal stability of AgNWs is essential for developing flexible transparent electrodes with long-term operational reliability.

3.1. Metal Oxides

Silver has a melting point of 962 °C, while many metal oxides have melting points close to 2000 °C. By coating the surface of AgNWs with metal oxide nanoparticles or thin films, the diffusion of silver atoms on the nanowire surface can be effectively suppressed, thereby enhancing the thermal stability of AgNW networks. After sol–gel treatment with metal oxides, composite transparent electrodes with AgNWs protected by Al-doped ZnO (AZO), TiO₂, and ZnO films have been fabricated [110,111,112,113,114,115].

Liu et al. [110] prepared an AZO sol–gel, which was spin-coated onto the surface of AgNW transparent electrodes and then thermally treated to form a protective AZO film over the AgNW network. The AZO coating reduced the surface roughness of the transparent electrode and enabled the AgNWs to operate stably at 270 °C. Moreover, owing to the intrinsic conductivity of AZO, the electrical conductivity of the AgNW transparent electrode was further improved. Other metal oxide protection strategies have also been reported, including TiO₂-based [111,112,113] and ZnO-based [114,115] composite transparent electrodes, which improve the stability of AgNW networks by suppressing surface diffusion and protecting the nanowires from environmental degradation.

Moreover, Liu et al. [106] enhanced the electrical and thermal properties of AgNW FTEs by modifying AgNW networks with metal oxide nanoparticles through magnetron sputtering. Four metal oxides, namely Al₂O₃, SnO₂, TiO₂, and ZnO, were introduced onto the AgNW networks. As shown in Figure 4a, the pristine AgNW FTE consists of randomly distributed and relatively smooth AgNWs, with exposed wire surfaces and direct junction contacts. After metal oxide modification, obvious morphological differences can be observed in the AgNW networks. The AgNWs@Al₂O₃-TCFs and AgNWs@SnO₂-TCFs shown in Figure 4b,c still retain the interconnected nanowire network, while the oxide nanoparticles partially decorate the nanowire surfaces and junction regions. In comparison, the AgNWs@TiO₂-TCFs shown in Figure 4d exhibit a relatively smoother and more continuous surface morphology, whereas the AgNWs@ZnO-TCFs shown in Figure 4e display dense nanoparticle coverage along the AgNW surfaces and at the junctions. The corresponding cross-sectional SEM images further confirm that the oxide layers are distributed over the AgNW network and modify the surface topography of the transparent conductive films. These metal oxide nanoparticles significantly reduced the sheet resistance, with a maximum reduction of 75.6% for ZnO, and improved film uniformity, with the nonuniformity factor decreasing to as low as 8.7%. The modified films also exhibited higher failure voltages of up to 16 V and improved thermal stability, which can be attributed to the combined effects of reduced junction resistance and enhanced protection of AgNWs against oxidation and thermal degradation. Therefore, metal oxide nanoparticle modification provides an effective route to improve the electrical uniformity, current-loading capability, and thermal reliability of AgNW-based FTEs, showing promising potential for flexible electronics and transparent heater applications.

In addition to sol–gel treatment and magnetron sputtering, conformal metal oxide coatings have also been constructed by atomic layer deposition (ALD) and atmospheric-pressure spatial atomic layer deposition (AP-SALD). Duan et al. [116] fabricated a conductive-bridging ZnO layer on AgNW electrodes by low-temperature ALD, which improved the electrical contact and flexibility of the transparent electrode. Khan et al. [86] deposited conformal ZnO coatings on AgNW networks by AP-SALD and demonstrated that the ZnO coating significantly improved the thermal and electrical stability of the electrodes. Weng et al. [117] further introduced conformal TiO₂ coatings for AgNW networks, which enhanced both the stability and patterning capability of flexible transparent conductive electrodes. These studies indicate that the effectiveness of metal oxide protection depends not only on the oxide composition but also on coating conformality, processing temperature, thickness control, and compatibility with flexible substrates.

3.2. Noble Metals

Encapsulating AgNWs with noble metals to form core–shell structures can significantly enhance their chemical stability. The noble metal shell acts as a protective layer, preventing oxidation and corrosion of the Ag core while also introducing tunable surface properties for specific applications such as electrochemical devices. Metal nanoparticle/graphene hybrid electrodes have also been widely used to enhance interfacial charge transfer and surface functionality in electrochemical platforms [118,119]. Zhu et al. [104] reported the development of ultrathin-shell epitaxial Ag@Au core–shell nanowires with excellent chemical stability and performance (Figure 5). A room-temperature, solution-phase synthesis method was used to coat Ag nanowires with a smooth, conformal gold shell that prevents oxidation without compromising optical or electrical properties. The resulting nanowires exhibit long-term stability in air, moisture, and oxidative environments, and perform well in transparent electrodes, plasmonic waveguides, SERS substrates, and AFM probes. This work provides a universal and scalable strategy for stabilizing high-performance AgNW-based devices. Seong et al. [105] presented a novel oxidation-resistant, self-adhesive flexible transparent electrode (FTE) based on Ag–Au core–shell nanowires and 3D microstructures. By integrating high-aspect-ratio Ag nanowires with a conformal gold shell, the electrode achieves both superior oxidation stability and strong adhesion without external adhesives. Its sheet resistance can be tuned from ~340 to 5 Ω/sq, and optical transmittance ranges from ~90% to 70%, depending on coating dose. These electrodes maintain excellent conductivity and transparency even under heat, humidity, and bending, making them promising for flexible electronics, biointerfaces, and wearable optoelectronic applications.

3.3. PEDOT:PSS

PEDOT:PSS is commonly used as a protective coating for AgNW FTEs to enhance their stability and performance. It forms a uniform conductive polymer layer that adheres tightly to the AgNW network, acting as a barrier against oxidation, sulfurization, and mechanical damage. The PSS component provides good film-forming ability and adhesion, while PEDOT maintains high electrical conductivity. This encapsulation prevents direct exposure of silver to air and moisture, thereby improving long-term durability. Additionally, the flexible nature of PEDOT:PSS enhances mechanical robustness, making AgNW electrodes suitable for flexible and stretchable electronic applications. Xu et al. [120] demonstrated that coating AgNWs with PEDOT:PSS significantly reduces surface roughness from 33.9 nm to 6.4 nm, improving film uniformity and compatibility with OLEDs. The resulting AgNW/PEDOT:PSS electrodes exhibit high optical transmittance (~91% at 550 nm) and low sheet resistance (~40 Ω/sq) (Figure 6). When further combined with single-layer graphene, performance is enhanced (30 Ω/sq, 88.3% transmittance), enabling their use as transparent anodes in OLEDs. Although slightly less efficient than ITO, devices with these composite electrodes show comparable electroluminescence, confirming their potential as flexible, cost-effective ITO alternatives for optoelectronic applications. Wang et al. [121] reported the fabrication of AgNWs/PEDOT:PSS/graphene (SLG) composite transparent conductive films for OLED applications. PEDOT:PSS plays a key role in reducing the surface roughness of Ag nanowire networks from 33.9 nm to 6.4 nm, improving film uniformity and conductivity. After coating with PEDOT:PSS, the composite films achieve high optical transmittance (~91%) and low sheet resistance (~40 Ω/sq). The PEDOT:PSS layer also serves as a hole transport layer, enhancing charge injection. Overall, PEDOT:PSS improves film smoothness, electrical performance, and compatibility with optoelectronic devices, enabling OLEDs with performance comparable to ITO-based devices.

4. Applications

The improved conductivity, optical transparency, mechanical flexibility, and stability of AgNW-based flexible transparent electrodes enable their integration into a variety of flexible optoelectronic devices [122,123,124]. Among these applications, organic light-emitting diodes (OLEDs), transparent heaters, and electrochromic devices are representative systems because they place different requirements on electrode smoothness, current-carrying capability, thermal stability, and long-term operational reliability. Therefore, the following sections discuss these three applications to illustrate how AgNW electrode design affects device-level performance.

4.1. OLEDs

Organic light-emitting diodes (OLEDs) are advanced display and lighting devices that use organic semiconductor materials to emit light when an electric current is applied [55,125]. They offer several advantages over traditional displays, including high contrast ratio, wide viewing angles, fast response time, and flexibility. OLEDs are lightweight, energy-efficient, and capable of producing vibrant colors without the need for a backlight. These features make them ideal for use in smartphones, televisions, wearable electronics, and next-generation lighting systems. Ongoing research focuses on improving their lifespan, efficiency, and large-scale fabrication techniques. Lee et al. [126] fabricated a flexible, transparent electrode by embedding AgNWs into a poly(vinyl butyral) (PVB) matrix, followed by intense pulsed light (IPL) sintering (Figure 7). The resulting AgNW-PVB composite exhibited low sheet resistance (12.6 Ω/sq), high optical transmittance (85.7% at 550 nm), and excellent mechanical flexibility. This smooth and robust electrode was successfully used to fabricate flexible organic light-emitting diodes (OLEDs), which showed enhanced electroluminescence performance compared to conventional ITO/IZO electrodes. The work provides a simple, scalable method for creating high-performance electrodes suitable for next-generation flexible optoelectronic devices.

4.2. Heaters

Transparent heaters are thin, optically clear devices that generate heat when an electric current passes through them [31,127]. Made from conductive materials like AgNWs, graphene, or metal oxides, they combine high electrical conductivity with excellent optical transmittance. Transparent heaters are widely used in applications such as defogging and deicing of vehicle windows, smart windows, wearable devices, and flexible electronics. Their ability to provide uniform, fast, and controllable heating while remaining see-through makes them ideal for both industrial and consumer technologies, especially in compact or visually sensitive environments. Sun et al. [128] developed a high-performance flexible transparent electrode by embedding bundled AgNWs into a polyimide (PI) matrix (Figure 8). The AgNW bundle micromesh structure ensures excellent electrical conductivity, thermal stability, and uniform resistance distribution, while the PI encapsulation offers strong protection against heat, moisture, and mechanical deformation. The resulting Ag BMs/ePI electrodes were used to fabricate flexible transparent heaters, achieving fast response, high saturation temperature (~204 °C at 8 V), and stable operation even after 10,000 bending cycles. This work provides a scalable strategy for high-temperature-tolerant flexible electronics suitable for wearable and harsh-environment applications. Huang et al. [92] developed high-performance flexible transparent heaters by applying a self-limited nanosoldering method to AgNW electrodes. The nanosoldering selectively reduces contact resistance at nanowire junctions without sacrificing transparency. The resulting devices exhibit low sheet resistance (3.7 Ω/sq), high transmittance (82.5%), and fast, uniform heating up to 145 °C at low voltage (6 V).

4.3. Electrochromic Devices

Electrochromic devices (ECDs) are smart systems that can reversibly change their optical properties—such as color, transparency, or reflectance—when a small voltage is applied [129,130,131]. This effect is achieved through electrochemical redox reactions in electrochromic materials like metal oxides or conductive polymers. ECDs are energy-efficient, maintain their state without constant power, and offer tunable optical control. They are widely used in smart windows, rear-view mirrors, displays, and anti-glare coatings. Their ability to dynamically modulate light and heat makes them valuable for energy-saving and user-responsive applications in buildings, vehicles, and wearable technologies. Zhang et al. [132] reported the fabrication of bifunctional flexible electrochromic energy storage devices (FECESDs) based on AgNW FTEs. AgNWs serve as highly conductive and flexible transparent conductors, while PEDOT:PSS acts as both an electrochromic material and a protective layer, enhancing electrochemical stability. The incorporation of a Co(OH)₂ interlayer further improves energy storage and optical modulation. The resulting device exhibits excellent performance with a coloration efficiency of 269.80 cm² C⁻¹ and an areal capacitance of 0.80 mF cm⁻², along with good mechanical flexibility, retaining performance after 1000 bending cycles. Shinde and Kim [133] developed highly stable AgNW FTEs by incorporating benzotriazole and Cs-doped TiO₂ layers. These electrodes exhibited excellent durability under heat, humidity, light, and acidic conditions. They were successfully applied in flexible electrochromic devices, showing stable optical modulation and cycling performance over 1000 cycles with strong transparency and conductivity. More broadly, recent studies on fully stretchable moisture-electric generators and high-precision printed biphasic conductive inks further suggest that interface-stable, mechanically compliant, and conformal conductive architectures are becoming increasingly important for next-generation wearable and biointegrated electronics [71,134,135,136]. These advances provide useful inspiration for the future design of AgNW-based flexible transparent electrodes, particularly in terms of interfacial adhesion, stretchability, high-resolution patterning, and stable biointerface integration (Figure 9).

5. Conclusions

This review systematically summarizes the recent advancements in AgNW FTEs, highlighting their exceptional potential to replace conventional indium tin oxide (ITO) in next-generation electronics. Through techniques such as thermal annealing, laser and photonic sintering, electrodeposition, and encapsulation with materials like metal oxides, noble metals, and PEDOT:PSS, researchers have effectively reduced junction resistance and enhanced the thermal, chemical, and mechanical stability of AgNW networks.

The application of AgNW FTEs in various flexible devices, including OLEDs, transparent heaters, and electrochromic systems, demonstrates their versatility and practicality. These devices exhibit outstanding optoelectronic performance, mechanical durability, and environmental stability, confirming that AgNWs are ideal candidates for future wearable and flexible electronics. Looking ahead, further research should focus on improving the long-term operational stability of AgNWs under extreme working conditions while ensuring scalable and eco-friendly fabrication. For the large-scale use of metal-based nanomaterials, safer-by-design strategies and environmental monitoring methods may provide useful guidance for balancing electrode performance with environmental responsibility [137,138]. Studies on extrusion-based printable gels and emulsion systems suggest that rheological control, component interactions, and formulation stability are also important for developing stable conductive inks [139,140,141]. For AgNW-based electrodes, these formulation principles should be combined with nanowire dispersion control, network connectivity optimization, and post-treatment-assisted welding. Moreover, optimizing the cost-performance balance, improving long-term mechanical durability, integrating AgNW-based electrodes into industrial roll-to-roll processes, and incorporating environmental assessment and source-apportionment methods to evaluate potential metal-related residues or emissions will be crucial for commercial viability [142,143,144,145]. The surface and subsurface reliability of AgNW electrodes under practical operating conditions should also be considered, especially when they are exposed to repeated deformation, friction, thermal loading, or complex device environments [146,147]. With continued innovation, AgNW FTEs are poised to play a central role in flexible electronic technologies, including transparent heaters and other flexible optoelectronic systems [91,128]. Future AgNW-based flexible transparent electrodes may also be extended to bioelectronic interfaces, where interfacial contact and multiphysical coupling are important design considerations [148,149,150]. In addition, advanced reliability-monitoring methods, including displacement/strain measurement, delamination detection, and crack monitoring, may provide useful guidance for evaluating electrode failure under repeated deformation [151,152,153].