Ionic Liquid-Enhanced Assembly of Nanomaterials for Highly Stable Flexible Transparent Electrodes

The controlled assembly of nanomaterials has demon-strated significant potential in advancing technological devices.However,achieving highly efficient and low-loss assembly technique for nanomate-rials,enabling the creation of hierarchical structures with distinctive func-tionalities,remains a formidable challenge.Here,we present a method for nanomaterial assembly enhanced by ionic liquids,which enables the fabrication of highly stable,flexible,and transparent electrodes featuring an organized layered structure.The utilization of hydrophobic and non-volatile ionic liquids facilitates the production of stable interfaces with water,effectively preventing the sedimentation of 1D/2D nanomaterials assembled at the interface.Furthermore,the interfacially assembled nanomaterial monolayer exhibits an alternate self-climbing behavior,enabling layer-by-layer transfer and the formation of a well-ordered MXene-wrapped silver nanowire network film.The resulting composite film not only demonstrates exceptional photoelectric performance with a sheet resistance of 9.4Ωsq^(-1) and 93%transmittance,but also showcases remarkable environmental stability and mechanical flexibility.Particularly noteworthy is its application in transparent electromagnetic interference shielding materials and triboelectric nanogenerator devices.This research introduces an innovative approach to manufacture and tailor functional devices based on ordered nanomaterials.

Recent advances in nanofiber-based flexible transparent electrodes

Flexible and stretchable transparent electrodes are widely used in smart display,energy,wearable devices and other fields.Due to the limitations of flexibility and stretchability of indium tin oxide electrodes,alternative electrodes have appeared,such as metal films,metal nanowires,and conductive meshes.However,few of the above electrodes can simultaneously have excellent flexibility,stretchability,and optoelectronic properties.Nanofiber(NF),a continuous ultra-long one-dimensional conductive material,is considered to be one of the ideal materials for high-performance transparent electrodes with excellent properties due to its unique structure.This paper summarizes the important research progress of NF flexible transparent electrodes(FTEs)in recent years from the aspects of NF electrode materials,preparation technology and application.First,the unique advantages and limitations of various NF materials are systematically discussed.Then,we summarize the preparation technology of various advanced NF FTEs,and point out the future development trend.We also discuss the application of NFs in solar cells,supercapacitors,electric heating equipments,sensors,etc,and analyze its development potential in flexible electronic equipment,as well as problems that need to be solved.Finally,the challenges and future development trends are proposed in the wide application of NF FTEs in the field of flexible optoelectronics.

Bifunctional flexible electrochromic energy storage devices based on silver nanowire flexible transparent electrodes

Flexible electrochromic energy storage devices(FECESDs)for powering flexible electronics have attracted considerable attention.Silver nanowires(AgNWs)are one kind of the most promising flexible transparent electrodes(FTEs)materials for the emerging flexible devices.Currently,fabricating FECESD based on AgNWs FTEs is still hindered by their intrinsic poor electrochemical stability.To address this issue,a hybrid AgNWs/Co(OH)_(2)/PEDOT:PSS electrode is proposed.The PEDOT:PSS could not only improve the resistance against electrochemical corrosion of AgNWs,but also work as functional layer to realize the color-changing and energy storage properties.Moreover,the Co(OH)_(2)interlayer further improved the color-changing and energy storage performance.Based on the improvement,we assembled the symmetrical FECESDs.Under the same condition,the areal capacitance(0.8 mF cm^(−2))and coloration efficiency(269.80 cm^(2)C−1)of AgNWs/Co(OH)_(2)/PEDOT:PSS FECESDs were obviously higher than AgNWs/PEDOT:PSS FECESDs.Furthermore,the obtained FECESDs exhibited excellent stability against the mechanical deformation.The areal capacitance remained stable during 1000 times cyclic bending with a 25 mm curvature radius.These results demonstrated the broad application potential of the AgNWs/Co(OH)_(2)/PEDOT:PSS FECESD for the emerging portable and multifunctional electronics.

Ultra-Highly Cross-Aligned AgNWs Network by a Facile Liquid-Bridge Assisted Couette-Flow Solution Process:Toward Mass-Producing High-Performance Flexible Transparent Electrodes

Cross-aligned silver nanowires(CA-AgNWs),a unique networkwidely used in flexible transparent electrodes(FTEs),have been well developed using various solution processes.However,these approaches suffer from limitations of both the large alignment deviation and solution waste,especially in large-area fabrication,which deteriorates the performance of FTEs.Herein,we developed a facile liquid-bridge assisted Couette-flow solution shearing approach,which enables aligning AgNWs into a highly ordered horizontal array over a large area(120 cm^(2)).Particularly,the alignment deviation,evaluated by the statistic,full width at half-maximum,is rather small with a value of ca.12.6,several times lower than those made by other solution processes.The fibrous liquid-bridge is responsible for transferring liquid steadily onto the substrate,during which process AgNWs are aligned roughly by the solution shearing.It is worth noting that the enhanced shearing force(SF)by Couetteflow allows for further alignment.Consequently,the ultra-highly CA-AgNWs network was prepared,leading to a high-performance FTE with high conductivity(7Ωsq^(-1)),high transparency(93%),long lifetime(over 180 days),good adhesion-stability(200 times tape test),and good flexibility.Moreover,the strategy is applicable for mass-production,benefiting the practical applications of high-performance optoelectronic devices.

“Reinforced concrete”-like flexible transparent electrode for organic solar cells with high efficiency and mechanical robustness

Flexible transparent electrodes(FTEs) with robust mechanical stability are crucial for the industrial application of flexible organic solar cells(OSCs). However, their production remains challenging owing to the difficulty in balancing the conductivity,transmittance, and adhesion of FTEs to substrates. Herein, we present the so-called “reinforced concrete” strategy which finetunes the structure of silver nanowires(Ag NWs)-based FTEs with polydopamine(PDA) possessing good adhesion properties and moderate reducibility. The PDA reduces Ag+to form silver nanoparticles(Ag NPs) which grow like “rivets” at the Ag NW junction sites;PDA stabilizes the Ag NW skeleton and improves the adhesion between the Ag NWs and polyethylene terephthalate(PET) substrate and interface layer. The obtained Ag NW:PDA:Ag NP FTE exhibits excellent optoelectronic properties and high mechanical stability. The resulting flexible OSCs exhibit 17.07% efficiency, high flexibility during 10,000 bending test cycles, and robust peeling stability. In addition, this “reinforced concrete”-like FTE provides great advantages for the production of large-area flexible OSCs, thereby paving a new way toward their commercial application.

High-performance ultrathin Ag electrodes by chemical bond anchoring Ag atoms for stretchable organic light-emitting devices

The progress of stretchable organic light-emitting devices(OLEDs)has brought about new possibilities for highly functional wearable electronics.However,the efficiency and durability of stretchable OLEDs have been limited by the performance of stretchable transparent electrodes.Here,we proposed an interface engineering strategy that involves anchoring the growth of silver(Ag)atoms with amine-enriched biomaterials for high-quality stretchable transparent electrodes.The strong interactions between the Ag atom and the amine group enable the uniform Ag electrodes at an ultralow thickness of 7 nm,and provide remarkable mechanical flexibility and strain endurance to the Ag electrodes.The distinct effects of different amino acids were investigated,and a deep understanding of their unique contributions to the film formation process was gained.The resulting ultrathin Ag electrodes exhibit outstanding optoelectrical properties(transmittance of~98%and sheet resistance of~8.7Ω/sq)and excellent stretchability during 500 stretching cycles at 100%strain.Stretchable green phosphorescent OLEDs based on the Ag electrodes have been demonstrated with a current efficiency of up to~70.4 cd/A.Impressively,the devices show excellent stretching stability,retaining~89%of the original luminance and~78%of the original current efficiency after 200 stretching cycles at 100%strain.This work opens up new possibilities for stretchable transparent electrodes,fostering advancements in wearable displays and other innovative flexible devices.

Recent progress in flexible organic solar cells

Photovoltaic cells are one of the most promising renewable energy sources to address energy and environmental issues.Amongst the many photovoltaic technologies,organic solar cells(OSCs)have numerous advantages,such as low cost,light weight,semi-transparency,and flexibility.This last is a special merit of OSCs,arising due to the intrinsic flexibility of organic active layers.With promising applications in fields such as building-integrated photovoltaics and wearable electronics,flexible OSCs(F-OSCs)have developed rapidly,and significant process has been made in recent years.In this review,we summarize the recent progress in F-OSCs from the perspective of flexible transparent electrodes.In addition,large-area F-OSCs and their potential applications are briefly dis-cussed.Finally,challenges for the further development of F-OSCs are presented.

A transparent, conducting tape for flexible electronics

Transparent electrodes are essential components for optoelectronic devices such as displays and thin-film solar cells. Traditionally, the deposition of transparent conducting layers and the sealing of the device are separate steps. Here we report on a highly transparent, conductive, and flexible ＂tape＂, which can be obtained by transferring silver nanowire networks to conventional transparent tape. We utilized the viscidity of the tape to reduce the junction resistance between silver nanowires and further protect the nanowires from corrosion, oxidation and mechanical damage. By this simple method, we obtained a flexible tape with high transparency （-90% at 550 nm wavelength） and low sheet resistance （approaching 22 Ω.sq^-1）. The transparent tape can be attached and stuck firmly on complex surfaces, making the surface highly conductive. We demonstrated the use of the tape as both a conducting layer and a sealing layer for flexible electronics applications including in-situ temperature monitoring and electrochromic devices.

Copper nanowire-TiO2-polyacrylate composite electrodes with high conductivity and smoothness for flexible polymer solar cells

Copper nanowire （Cu NW） transparent electrodes have attracted considerable attention due to their outstanding electrical properties, flexibility and low cost. However, complicated post-treatment techniques are needed to obtain good electrical conductivity, because of the organic residues and oxide layers on the surface of the Cu NWs. In addition, commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, a TiO2 sol treatment was introduced to obtain Cu NW transparent electrodes with superb performance （13 Ω/sq @ 82% T） at room temperature within one minute. Polymer solar ceils with excellent flexibility were then fabricated on the copper nanowire- TiO2-polyacrylate composite electrode. The power conversion efficiency （PCE） of the cells based on a blend of poly（3-hexylthiophene） （P3HT） and phenyl-C61- butyric acid methyl ester （PC61BM） reached 3.11%, which was better than the control devices that used indium tin oxide （ITO）-PET electrodes, and outperforms other Cu NW based organic solar cells previously reported. The PCE of the solar cells based on Cu NW electrodes remained at 90% after 500 cycles of bending, while the PET/ITO solar cells failed after 20 and 200 cycles, with sheet resistance of 35 and 15 Ω/sq, respectively.

Graphene-based flexible and wearable electronics

Graphene with an exceptional combination of electronic, optical and outstanding mechanical features has been proved to lead a completely different kind of 2-D electronics. The most exciting feature of graphene is its ultra-thin thickness, that can be conformally contacted to any kind of rough surface without losing much of its transparency and conductivity. Graphene has been explored demonstrating various prototype flexible electronic applications, however, its potentiality has been proven wherever transparent conductive electrodes（TCEs） are needed in a flexible, stretchable format. Graphene-based TCEs in flexible electronic applications showed greatly superior performance over their conventionally available competitor indium tin oxide（ITO）. Moreover, enormous applications have been emerging, especially in wearable devices that can be potentially used in our daily life as well as in biomedical areas. However, the production of high-quality, defect-free large area graphene is still a challenge and the main hurdle in the commercialization of flexible and wearable products. The objective of the present review paper is to summarize the progress made so far in graphene-based flexible and wearable applications. The current developments including challenges and future perspectives arc also highlighted.