Cold Isostatic-Pressured Silver Nanowire Electrodes for Flexible Organic Solar Cells via Room-Temperature Processes

Flexible, Transparent and Conductive Metal Mesh Films with Ultra-High FoM for Stretchable Heating and Electromagnetic Interference Shielding

Despite the growing demand for transparent conductive films in smart and wearable electronics for electromagnetic interference (EMI) shielding, achieving a flexible EMI shielding film, while maintaining a high transmittance remains a significant challenge. Herein, a flexible, transparent, and conductive copper (Cu) metal mesh film for EMI shielding is fabricated by self-forming crackle template method and electroplating technique. The Cu mesh film shows an ultra-low sheet resistance (0.18 Ω □-1), high transmittance (85.8%@550 nm), and ultra-high figure of merit (> 13,000). It also has satisfactory stretchability and mechanical stability, with a resistance increases of only 1.3% after 1,000 bending cycles. As a stretchable heater (ε > 30%), the saturation temperature of the film can reach over 110 °C within 60 s at 1.00 V applied voltage. Moreover, the metal mesh film exhibits outstanding average EMI shielding effectiveness of 40.4 dB in the X-band at the thickness of 2.5 μm. As a demonstration, it is used as a transparent window for shielding the wireless communication electromagnetic waves. Therefore, the flexible and transparent conductive Cu mesh film proposed in this work provides a promising candidate for the next-generation EMI shielding applications.

Progress and Challenges Toward Effective Flexible Perovskite Solar Cells

The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous. The photoactive layer, i.e., the perovskite thin film, as a critical component of flexible perovskite solar cells (F-PSCs), still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity. This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs. We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance. Furthermore, we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films, such as internal stress engineering, grain boundary modification, self-healing strategy, and crystallization regulation. The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed. As concluding remarks, we propose our viewpoints on the large-scale commercial application of F-PSCs.

Flexible Quantum Dot Light-Emitting Device for Emerging Multifunctional and Smart Applications

Quantum dot light-emitting diodes (QLEDs), owing to their exceptional performances in device efficiency, color purity/tunability in the visible region and solution-processing ability on various substrates, become a potential candidate for flexible and ultrathin electroluminescent (EL) lighting and display. Moreover, beyond the lighting and display, flexible QLEDs are enabled with endless possibilities in the era of the internet of things and artificial intelligence by acting as input/output ports in wearable integrated systems. Challenges remain in the development of flexible QLEDs with the goals for high performance, excellent flexibility/even stretchability, and emerging applications. In this paper, the recent developments of QLEDs including quantum dot materials, working mechanism, flexible/stretchable strategies and patterning strategies, and highlight its emerging multifunctional integrations and smart applications covering wearable optical medical devices, pressure-sensing EL devices, and neural smart EL devices, are reviewed. The remaining challenges are also summarized and an outlook on the future development of flexible QLEDs made. The review is expected to offer a systematic understanding and valuable inspiration for flexible QLEDs to simultaneously satisfy optoelectronic and flexible properties for emerging applications.

Non-Embedded Silver Nanowires/Antimony-Doped Tin Oxide/Polyethylenimine Transparent Electrode for Non-Fullerene Acceptor ITO-Free Inverted Organic Photovoltaics

Indium tin oxide (ITO)-free solution-processed transparent electrodes are an essential component for the low-cost fabrication of organic optoelectronic devices. High-performance silver nanowires (AgNWs) ITO-free inverted organic photovoltaics (OPVs) usually require a AgNWs-embedded process. A simple cost-effective roll-to-roll production process of inverted ITO-free OPVs with AgNWs as a bottom transparent electrode requires solution-based thick metal oxides as carrier-selective contacts. In this reported study, we show that a solution-processed antimony-doped tin oxide (ATO)/polyethylenimine (PEI) electron-selective contact incorporated on the top of non-embedded AgNWs provides a high-performance ITO-free bottom electrode for non-fullerene acceptor (NFA) inverted OPVs.

Highly Stable Silver Nanowires/Biomaterial Transparent Electrodes for Flexible Electronics

Flexible transparent electrodes (FTEs) possess excellent optoelectrical properties, mechanical robustness, and environmental adaptability are important for the industrial scale development of flexible electronics. Silver nanowires (AgNWs) are widely used in FTEs owing to their excellent optoelectrical properties and mechanical flexibility. However, the high surface roughness and poor stability of AgNWs FTEs still limit their practical applications. Here, highly stable FTEs are demonstrated via combining AgNWs and biomaterial propolis which is eco-friendly and antioxidative. The AgNWs/propolis composite transparent electrodes exhibit excellent optoelectrical performance as well as a smooth surface (root-mean-square roughness ∼ 6.2 nm). Meanwhile, the composite electrodes possess high mechanical stability (10,000 bending cycles), thermal stability, and environmental adaptability (60 °C and 85 ± 3% humidity for 700 h). The versatile composite FTEs show great potential applications in organic light-emitting diodes and pressure sensors, which exhibit high performance, mechanical stability, and environmental adaptability. Our strategy of introducing biocompatible materials into metallic nanowires opens up new possibilities to achieve high-quality FTEs in a simple and eco-friendly way.

Electrochemical Redox In-Situ Welding of Silver Nanowire Films with High Transparency and Conductivity

Silver nanowire (AgNW) networks with high transparency and conductivity are crucial to developing transparent conductive films (TCFs) for flexible optoelectronic devices. However, AgNW-based TCFs still suffer from the high contact resistance of AgNW junctions with both the in-plane and out-of-plane charge transport barrier. Herein, we report a rapid and green electrochemical redox strategy to in-situ weld AgNW networks for the enhanced conductivity and mechanical durability of TCFs with constant transparency. The welded TCFs show a marked decrease of the sheet resistance (reduced to 45.5% of initial values on average) with high transmittance of 97.02% at 550 nm (deducting the background of substrates). The electrochemical welding treatment enables the removal of the residual polyvinylpyrrolidone layer and the in-situ formation of Ag solder in the oxidation and reduction processes, respectively. Furthermore, local conductivity studies confirm the improvement of both the in-plane and the out-of-plane charge transport by conductive atomic force microscopy. This proposed electrochemical redox method provides new insights on the welding of AgNW-based TCFs with high transparency and low resistance for the development of next-generation flexible optoelectronic devices. Furthermore, such conductive films based on the interconnected AgNW networks can be acted as an ideal supporter to construct heterogeneous structures with other functional materials for wide applications in photocatalysis and electrocatalysis.

Realizing 17.5% Efficiency Flexible Organic Solar Cells via Atomic-Level Chemical Welding of Silver Nanowire Electrodes

Solution processable flexible transparent electrodes (FTEs) are urgently needed to boost the efficiency and mechanical stability of flexible organic solar cells (OSCs) on a large scale. However, how to balance the optoelectronic properties and meanwhile achieve robust mechanical behavior of FTEs is still a huge challenge. Silver nanowire (AgNW) electrodes, exhibiting easily tuned optoelectronic/mechanical properties, are attracting considerable attention, but their poor contacts at the junction site of the AgNWs increase the sheet resistance and reduce mechanical stability. In this study, an ionic liquid (IL)-type reducing agent containing Cl^- and a dihydroxyl group was employed to control the reduction process of silver (Ag) in AgNW-based FTEs precisely. The Cl^- in the IL regulates the Ag⁺ concentration through the formation and dissolution of AgCl, whereas the dihydroxyl group slowly reduces the released Ag⁺ to form metal Ag. The reduced Ag grew in situ at the junction site of the AgNWs in a twin-crystal growth mode, facilitating an atomic-level contact between the AgNWs and the reduced Ag. This enforced atomic-level contact decreased the sheet resistance, and enhanced the mechanical stability of the FTEs. As a result, the single-junction flexible OSCs based on this chemically welded FTE achieved record power conversion efficiencies of 17.52% (active area: 0.062 cm²) and 15.82% (active area: 1.0 cm²). These flexible devices also displayed robust bending and peeling durability even under extreme test conditions.

Silver Nanowire Networks: Ways to Enhance Their Physical Properties and Stability

Silver nanowire (AgNW) networks have been intensively investigated in recent years. Thanks to their attractive physical properties in terms of optical transparency and electrical conductivity, as well as their mechanical performance, AgNW networks are promising transparent electrodes (TE) for several devices, such as solar cells, transparent heaters, touch screens or light-emitting devices. However, morphological instabilities, low adhesion to the substrate, surface roughness and ageing issues may limit their broader use and need to be tackled for a successful performance and long working lifetime. The aim of the present work is to highlight efficient strategies to optimize the physical properties of AgNW networks. In order to situate our work in relation to existing literature, we briefly reported recent studies which investigated physical properties of AgNW networks. First, we investigated the optimization of optical transparency and electrical conductivity by comparing two types of AgNWs with different morphologies, including PVP layer and AgNW dimensions. In addition, their response to thermal treatment was deeply investigated. Then, zinc oxide (ZnO) and tin oxide (SnO2) protective films deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) were compared for one type of AgNW. We clearly demonstrated that coating AgNW networks with these thin oxide layers is an efficient approach to enhance the morphological stability of AgNWs when subjected to thermal stress. Finally, we discussed the main future challenges linked with AgNW networks optimization processes.

Rapid nanowelding of silver nanowires by focused-light-scanning for high-performance flexible transparent electrodes

Silver nanowires (AgNWs) have been considered as one of the most promising flexible transparent electrodes (FTEs) material for next-generation optoelectronic devices. However, the large contact resistance between AgNWs could deteriorate the conductivity of FTEs. In the present work, high-performance AgNWs FTEs were obtained by means of focused-light-scanning (FLS), which could lead to the large-area, rapid and high-quality welding between AgNWs within a short time, forming the reliable and stable AgNWs network. The results of the optoelectronic tests show that after FLS, the sheet resistance of the AgNWs FTEs sharply decreased from 5113 Ω/sq to 7.7 Ω/sq, with maintaining a high transmittance (∼94%). Finally, a high-performance flexible transparent heater was fabricated by using FLS, showing reach a relatively high temperature in a short response time and rapid response at low input voltage. The findings offer an effective pathway to greatly improve the conductivity of AgNWs FTEs.

Recent progress in post treatment of silver nanowire electrodes for optoelectronic device applications

Owing to the economical and practical solution synthesis and coating strategies, silver nanowires (AgNWs) have been considered as one of the most suitable alternative materials to replace commercial indium tin oxide (ITO) transparent electrodes. The primitive AgNW electrode cannot meet the requirements for preparing high performance optoelectronic devices due to its high contact resistance, large surface roughness and poor stability. Thus, various post-treatments for AgNW film optimization are needed before its actual applications, such as welding treatment to decrease contact resistance and passivation to increase film stability. This review investigates recent progress on the preparation and optimization of AgNWs. Moreover, some unique fabrication strategies to produce highly oriented AgNW films with unique anisotropic properties have also been carried out with detailed analysis. The representative devices based on the AgNW electrode have been summarized and discussed at the end of this review.

Digital printing of a novel electrode for stable flexible organic solar cells with a power conversion efficiency of 8.5

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) mixed with single-wall nanotubes (SWNTs) (10:1) and doped with (0.1 M) perchloric acid (HClO4) in a solution-processed film, working as an excellent thin transparent conducting film (TCF) in organic solar cells, was investigated. This new electrode structure can be an outstanding substitute for conventional indium tin oxide (ITO) for applications in flexible solar cells due to the potential of attaining high transparency with enhanced conductivity, good flexibility, and good durability via a low-cost process over a large area. In addition, solution-processed vanadium oxide (VOx) doped with a small amount of PEDOT-PSS(PH1000) can be applied as a hole transport layer (HTL) for achieving high efficiency and stability. From these viewpoints, we investigate the benefit of using printed SWNTs-PEDOT-PSS doped with HClO4 as a transparent conducting electrode in a flexible organic solar cell. Additionally, we applied a VOx-PEDOT-PSS thin film as a hole transporting layer and a blend of PTB7 (polythieno[3,4-b] thiophene/benzodithiophene): PC71BM (phenyl-C71-butyric acid methyl ester) as an active layer in devices. Zinc oxide (ZnO) nanoparticles were applied as an electron transport layer and Ag was used as the top electrode. The proposed solar cell structure showed an enhancement in short-circuit current, power conversion efficiency, and stability relative to a conventional cell based on ITO. This result suggests a great carrier injection throughout the interfacial layer, high conductivity and transparency, as well as firm adherence for the new electrode.

Effects of Concentration and Spin Speed on the Optical and Electrical Properties of Silver Nanowire Transparent Electrodes

In this paper, silver nanowires (AgNWs) with a diameter of 40 nm and a length of 45 μm were dispersed into an ethanol solution to prepare AgNW solutions with concentrations of 1, 2, and 3 mg/mL, respectively. The AgNW solutions were then deposited on a glass substrate using spin-coating at 1000, 2000, and 3000 rpm for 45 s, respectively, to prepare transparent electrodes. The results showed that the distribution of AgNWs on the substrate increased in density with the increase in the AgNW solution concentration and the decrease in spin speed. The effect of concentration on the distribution of AgNWs was greater than that of the spin speed. The transmittance of each electrode was between 84.19% and 88.12% at 550 nm, the average sheet resistance was between 20.09 and 358.11 Ω/sq, the highest figure of merit (FoM) was 104.42, and the lowest haze value was 1.48%. The electrode prepared at 1000 rpm with a concentration of 2 mg/mL and that prepared at 3000 rpm with a concentration of 3 mg/mL were very similar in terms of the average sheet resistance, transmittance at 550 nm, FoM, and haze value; thus, these two electrodes could be considered equivalent. The haze value of the electrode was positively correlated with the spin speed at low concentration, but that relationship became inverse as the concentration rose. For the AgNWs used in this experiment with an aspect ratio of 1125, the concentration of the AgNW solution should reach at least 2 mg/mL to ensure that the FoM of the electrode is greater than 35.

Polymer Ligand Design and Surface Modification of Ag Nanowires toward Color-Tone-Tunable Transparent Conductive Films

Ag nanowire suspensions are one of the indispensable materials in the design and fabrication of flexible transparent conductive films. Although the required properties of Ag nanowire films, such as their high transparency, low haze, low contact resistance, and suppression of yellowing, are strongly related to the nanowire surface phenomena, approaches for the surface modification of polyol-synthesized Ag nanowires have rarely been reported. Here, we report the design of a polymer ligand and surface modification of Ag nanowires with the designed polymer to obtain color-tunable transparent conductive films through a simple casting and drying process. In this approach, we synthesized a series of functional polymer ligands by partially grafting polyethyleneimine (PEI) with polyethylene glycol (PEG) chains (PEI-mPEG). The amine sites in PEI-mPEG were designed to act as adsorption sites as well as anchoring sites for an anionic blue dye for suppressing the yellow color tone of Ag nanowires. On the other hand, the PEG chains were designed to maintain the stability of the Ag nanowires in aqueous suspensions and to suppress corrosion of Ag nanowires, which is enhanced by the amine groups of PEI. The effect of the grafting ratio of PEG chains on PEI on the ligand-exchange behavior of the Ag nanowires, their dispersion stability in aqueous inks, and final film properties were investigated systematically. Furthermore, successful color tuning of the Ag nanowire film, without suppressing the conductive and optical properties, is demonstrated by loading anionic blue dye onto PEI-mPEG-modified Ag nanowires.

Enhanced stability of silver nanowire transparent conductive films against ultraviolet light illumination

Silver nanowires are susceptible to degradation under ultraviolet (UV) light illumination. Encapsulating silver nanowire transparent conductive films (AgNW TCFs) with UV shielding materials usually result in the increasing of the sheet resistance or the decrease of the visible light transparency. Herein, we combine a reducing species (FeSO₄) and a thin layer (overcoating) of UV shielding material to solve the stability and the optical performance issues simultaneously. The AgNW TCFs show excellent stability under continuous UV light illumination for 14 h, and their sheet resistance varies only 6%. The dramatic enhancement of the stability against UV light illumination for as-obtained TCFs will make them viable for real-world applications in touch panels and displays.

Progress in Stability of Organic Solar Cells

The organic solar cell (OSC) is a promising emerging low-cost thin film photovoltaics technology. The power conversion efficiency (PCE) of OSCs has overpassed 16% for single junction and 17% for organic-organic tandem solar cells with the development of low bandgap organic materials synthesis and device processing technology. The main barrier of commercial use of OSCs is the poor stability of devices. Herein, the factors limiting the stability of OSCs are summarized. The limiting stability factors are oxygen, water, irradiation, heating, metastable morphology, diffusion of electrodes and buffer layers materials, and mechanical stress. The recent progress in strategies to increase the stability of OSCs is surveyed, such as material design, device engineering of active layers, employing inverted geometry, optimizing buffer layers, using stable electrodes and encapsulation materials. The International Summit on Organic Photovoltaic Stability guidelines are also discussed. The potential research strategies to achieve the required device stability and efficiency are highlighted, rendering possible pathways to facilitate the viable commercialization of OSCs.

Realizing Ultrahigh Mechanical Flexibility and >15% Efficiency of Flexible Organic Solar Cells via a "Welding" Flexible Transparent Electrode

The power conversion efficiencies (PCEs) of flexible organic solar cells (OSCs) still lag behind those of rigid devices and their mechanical stability is unable to meet the needs of flexible electronics at present due to the lack of a high-performance flexible transparent electrode (FTE). Here, a so-called "welding" concept is proposed to design an FTE with tight binding of the upper electrode and the underlying substrate. The upper electrode consisting of solution-processed Al-doped ZnO (AZO) and silver nanowire (AgNW) network is well welded by utilizing the capillary force effect and secondary growth of AZO, leading to a reduction of the AgNWs junction site resistance. Meanwhile, the poly(ethylene terephthalate) is modified by embedding the AgNWs, which are then used to link with the AgNWs in the upper hybrid electrode, thus enhancing the adhesion of the electrode to the substrate. By this welding strategy, critical bottleneck issues relating to the FTEs in terms of optoelectronic and mechanical properties are comprehensively addressed. The single-junction flexible OSCs based on this welded FTE show a high performance, achieving a record high PCE of 15.21%. In addition, the PCEs of the flexible OSCs are less influenced by the device area and display robust bending durability even under extreme test conditions.

Over 14% Efficiency Folding-Flexible ITO-free Organic Solar Cells Enabled by Eco-friendly Acid-Processed Electrodes

Environment-friendly manufacturing and mechanical robustness are imperative for commercialization of flexible OSCs as green-energy source, especially in portable and wearable self-powered flexible electronics. Although, the commonly adopted PEDOT:PSS electrodes that are treated with severely corrosive and harmful acid lack foldability. Herein, efficient folding-flexible OSCs with highly conductive and foldable PEDOT:PSS electrodes processed with eco-friendly cost-effective acid and polyhydroxy compound are demonstrated. The acid treatment endows PEDOT:PSS electrodes with high conductivity. Meanwhile, polyhydroxy compound doping contributes to excellent bending flexibility and foldability due to the better film adhesion between PEDOT:PSS and PET substrate. Accordingly, folding-flexible OSCs with high efficiency of 14.17% were achieved. After 1,000 bending or folding cycles, the device retained over 90% or 80% of its initial efficiency, respectively. These results represent one of the best performances for ITO-free flexible OSC reported so far and demonstrate a novel approach toward commercialized efficient and foldable green-processed OSCs.

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Highly conductive PEDOT:PSS electrodes based on eco-friendly acid were exploited

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14.17% folding-flexible organic solar cells were realized

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The bending performance was significantly improved by interface bonding engineering

Electrodeposited Silver Nanowire Transparent Conducting Electrodes for Thin-Film Solar Cells

Silver nanowire (AgNW) networks have demonstrated high optical and electrical properties, even better than those of indium tin oxide thin films, and are expected to be a next-generation transparent conducting electrode (TCE). Enhanced electrical and optical properties are achieved when the diameter of the AgNWs in the network is fairly small, that is, typically less than 30 nm. However, when AgNWs with such small diameters are used in the network, stability issues arise. One method to resolve the stability issues is to increase the diameter of the AgNWs, but the use of AgNWs with large diameters has the disadvantage of causing a rough surface morphology. In this work, we resolve all of the aforementioned issues with AgNW TCEs by the electrodeposition of Ag onto as-spin-coated thin AgNW TCEs. The electrodeposition of Ag offers many advantages, including the precise adjustment of the AgNW diameter and wire-to-wire welding to improve the junction conductance while minimizing the increase in protrusion height because of the overlap of AgNWs upon increasing the diameter. In addition, Ag electrodeposition on AgNW TCEs can provide higher conductance than that of as-spin-coated AgNW TCEs at the same transparency because of the reduced junction resistance, which generates a superior figure of merit. We applied the electrodeposited (ED) AgNW network to a Cu(In,Ga)Se₂ thin-film solar cell and compared the device performance to a device with a standard sputtered transparent conducting oxide (TCO). The cell fabricated by the electrodeposition method showed nearly equal performance to that of a cell with the sputtered TCO. We expect that ED AgNW networks can be used as high-performance and robust TCEs for various optoelectronic applications.

Efficiency above 12% for 1 cm2 Flexible Organic Solar Cells with Ag/Cu Grid Transparent Conducting Electrode

With the rapid progress of organic solar cells (OSCs), improvement in the efficiency of large-area flexible OSCs (>1 cm2) is crucial for real applications. However, the development of the large-area flexible OSCs severely lags behind the growth of the small-area OSCs, with the electrical loss due to the large sheet resistance of the electrode being a main reason. Herein, a high conductive and high transparent Ag/Cu composite grid with sheet resistance <1 Ω sq-1 and an average visible light transparency of 84% is produced as the transparent conducting electrode of flexible OSCs. Based on this Ag/Cu composite grid electrode, a high efficiency of 12.26% for 1 cm2 flexible OSCs is achieved. The performances of large-area flexible OSCs also reach 7.79% (4 cm2) and 7.35% (9 cm2), respectively, which are much higher than those of the control devices with conventional flexible indium tin oxide electrodes. Surface planarization using highly conductive PEDOT:PSS and modification of the ZnO buffer layer by zirconium acetylacetonate (ZrAcac) are two necessary steps to achieve high performance. The flexible OSCs employing Ag/Cu grid have excellent mechanical bending resistance, maintaining high performance after bending at a radius of 2 mm.

PEDOT:PSS for Flexible and Stretchable Electronics: Modifications, Strategies, and Applications

Substantial effort has been devoted to both scientific and technological developments of wearable, flexible, semitransparent, and sensing electronics (e.g., organic/perovskite photovoltaics, organic thin-film transistors, and medical sensors) in the past decade. The key to realizing those functionalities is essentially the fabrication of conductive electrodes with desirable mechanical properties. Conductive polymers (CPs) of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have emerged to be the most promising flexible electrode materials over rigid metallic oxides and play a critical role in these unprecedented devices as transparent electrodes, hole transport layers, interconnectors, electroactive layers, or motion-sensing conductors. Here, the current status of research on PEDOT:PSS is summarized including various approaches to boosting the electrical conductivity and mechanical compliance and stability, directly linked to the underlying mechanism of the performance enhancements. Along with the basic principles, the most cutting edge-progresses in devices with PEDOT:PSS are highlighted. Meanwhile, the advantages and plausible problems of the CPs and as-fabricated devices are pointed out. Finally, new perspectives are given for CP modifications and device fabrications. This work stresses the importance of developing CP films and reveals their critical role in the evolution of these next-generation devices featuring wearable, deformable, printable, ultrathin, and see-through characteristics.

Highly Conducting MXene-Silver Nanowire Transparent Electrodes for Flexible Organic Solar Cells

MXene, a new class of two-dimensional materials, offers a unique combination of metallic conductivity and hydrophilicity. This material has shown great promise in numerous applications including electromagnetic interference shielding, sensing, energy storage, and catalysis. In this paper, we report on the fabrication of transparent, conductive, and flexible MXene/silver nanowire (AgNW) hybrid films, resulting in the highest figure of merit (162.49) in the reported literature to date regarding an MXene-based transparent electrode. The hybrid films, prepared via a simple and scalable solution-processed method, exhibit good electrical conductivity, high transmittance, low roughness, work function matching, and robust mechanical performance. Following film fabrication, the hybrid electrodes were demonstrated to function as transparent electrodes in fullerene molecule PTB7-Th:PC71BM and nonfullerene molecule PBDB-T:ITIC organic photovoltaics (OPVs). In an effort to further improve the performance of flexible OPVs, a ternary structure of PBDB-T:ITIC:PC71BM was demonstrated, resulting in a power conversion efficiency (PCE) of 8.30%. Mechanical properties were also quantified, with the flexible ternary organic solar cells capable of retaining 84.6% of the original PCE after 1000 bending and unbending cycles to a 5 mm bending radius. These optoelectronic and mechanical performance metrics represent a breakthrough in the field of flexible optoelectronics.

High-Resolution and Large-Area Patterning of Highly Conductive Silver Nanowire Electrodes by Reverse Offset Printing and Intense Pulsed Light Irradiation

Conventional printing technologies such as inkjet, screen, and gravure printing have been used to fabricate patterns of silver nanowire (AgNW) transparent conducting electrodes (TCEs) for a variety of electronic devices. However, they have critical limitations in achieving micrometer-scale fine line width, uniform thickness, sharp line edge, and pattering of various shapes. Moreover, the optical and electrical properties of printed AgNW patterns do not satisfy the performance required by flexible integrated electronic devices. Here, we report a high-resolution and large-area patterning of highly conductive AgNW TCEs by reverse offset printing and intense pulsed light (IPL) irradiation for flexible integrated electronic devices. A conductive AgNW ink for reverse offset printing is prepared by carefully adjusting the composition of AgNW content, solvents, surface energy modifiers, and organic binders for the first time. High-quality and high-resolution AgNW micropatterns with various shapes and line widths are successfully achieved on a large-area plastic substrate (120 × 100 mm²) by optimizing the process parameters of reverse offset printing. The reverse offset printed AgNW micropatterns exhibit superior fine line widths (up to 6 μm) and excellent pattern quality such as sharp line edge, fine line spacing, effective wire junction connection, and smooth film roughness. They are post-processed with IPL irradiation, thereby realizing excellent optical, electrical, and mechanical properties. Furthermore, flexible OLEDs and heaters based on reverse offset printed AgNW micropatterns are successfully fabricated and characterized, demonstrating the potential use of the reverse offset printing for the conductive AgNW ink.

Highly Efficient Semitransparent Organic Solar Cells with Color Rendering Index Approaching 100

Neutral-colored semitransparent organic solar cells (ST-OSCs) have attracted considerable attention owing to their unique application in no-visual-obstacle building-integrated photovoltaics. Toward this promising potential application, a synergistic effect is first proposed by employing a dielectric mirror and ternary photoactive layer with near-infrared absorption to tune the color perception as well as ST-OSC performance precisely. As a result, a neutral-color ST-OSC with high average transmittance of over 21% is successfully constructed, and a remarkable color-rendering index approaching 100 and high power conversion efficiency (PCE) of 9.37% are simultaneously achieved. To the best of our knowledge, this is the highest PCE reported for neutral-color ST-OSCs to date. Importantly, this synergistic effect is demonstrated to be a universal strategy that is not only suitable for various photoactive layer systems, but can also be implanted in flexible substrate. The resulting neutral-color flexible ST-OSCs also show a promising PCE of 8.76%.

Influence of the average molar mass of poly(N-vinylpyrrolidone) on the dimensions and conductivity of silver nanowires

Improving the performance of Ag nanowire electrodes by adjusting the reaction conditions and the molar mass of PVP.

Effective passivation of Ag nanowire network by transparent tetrahedral amorphous carbon film for flexible and transparent thin film heaters

We developed effective passivation method of flexible Ag nanowire (NW) network electrodes using transparent tetrahedral amorphous carbon (ta-C) film prepared by filtered cathode vacuum arc (FCVA) coating. Even at room temperature process of FCVA, the ta-C passivation layer effectively protect Ag NW network electrode and improved the ambient stability of Ag NW network without change of sheet resistance of Ag NW network. In addition, ta-C coated Ag NW electrode showed identical critical inner and outer bending radius to bare Ag NW due to the thin thickness of ta-C passivation layer. The time-temperature profiles demonstrate that the performance of the transparent and flexible thin film heater (TFH) with the ta-C/Ag NW network is better than that of a TFH with Ag NW electrodes due to thermal stability of FCVA grown ta-C layer. In addition, the transparent and flexible TFHs with ta-C/Ag NW showed robustness against external force due to its high hardness and wear resistance. This indicates that the FCVA coated ta-C is promising passivation and protective layer for chemically weak Ag NW network electrodes against sulfur in ambient.

All-Solution-Processed Metal-Oxide-Free Flexible Organic Solar Cells with Over 10% Efficiency

All-solution-processing at low temperatures is important and desirable for making printed photovoltaic devices and also offers the possibility of a safe and cost-effective fabrication environment for the devices. Herein, an all-solution-processed flexible organic solar cell (OSC) using poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) electrodes is reported. The all-solution-processed flexible devices yield the highest power conversion efficiency of 10.12% with high fill factor of over 70%, which is the highest value for metal-oxide-free flexible OSCs reported so far. The enhanced performance is attributed to the newly developed gentle acid treatment at room temperature that enables a high-performance PEDOT:PSS/plastic underlying substrate with a matched work function (≈4.91 eV), and the interface engineering that endows the devices with better interface contacts and improved hole mobility. Furthermore, the flexible devices exhibit an excellent mechanical flexibility, as indicated by a high retention (≈94%) of the initial efficiency after 1000 bending cycles. This work provides a simple route to fabricate high-performance all-solution-processed flexible OSCs, which is important for the development of printing, blading, and roll-to-roll technologies.

Transparent Electrode Based on Silver Nanowires and Polyimide for Film Heater and Flexible Solar Cell

Transparent, conductive, and flexible Ag nanowire (NW)-polyimide (PI) composite films were fabricated by a facile solution method. Well-dispersed Ag NWs result in percolation networks on the PI supporting layer. A series of films with transmittance values of 53–80% and sheet resistances of 2.8–16.5 Ω/sq were investigated. To further verify the practicability of the Ag NWs-PI film in optoelectronic devices, we utilized it in a film heater and a flexible solar cell. The film heater was able to generate a temperature of 58 °C at a driving voltage of 3.5 V within 20 s, indicating its potential application in heating devices that require low power consumption and fast response. The flexible solar cell based on the composite film with a transmittance value of 71% presented a power conversion efficiency of 3.53%. These successful applications proved that the fabricated Ag NWs-PI composite film is a good candidate for application in flexible optoelectronic devices.