Use In Flexible Electronic Devices Research Articles

Highly Durable Silicone-Based Elastomers Achieved Through the Synergy of Bi-Incompatible Soft Segments and Multi-Scale Hydrogen Bonds.

Developing a silicone elastomer with high strength, exceptional toughness, good crack tolerance, healability, and recyclability, poses significant challenges due to the inherent trade-offs between these properties. Herein, the design of silicone-based elastomers with a nanoscopic microphase separation structure and comprehensive mechanical properties is achieved by combining bi-incompatible soft segments and multi-scale hydrogen bonds. The formation of multi-scale hydrogen bonds involving urethane, urea, and 2-ureido-4[1H]-pyrimidinone (UPy) facilitates efficient reversible crosslinking of the synthesized polymer containing thermodynamically incompatible poly(dimethylsiloxane) (PDMS) and poly(propylene glycol) (PPG). The dynamic dissociation and recombination of hydrogen bonds, coupled with the forced compatibility and spontaneous separation of bi-incompatible soft segments, can effectively dissipate energy, particularly in the crack region during the stretching process. The obtained silicone-based elastomer exhibits a high break strength of 8.0 MPa, good elongation at break of 1910%, ultrahigh toughness of 67.8 MJ m-3, and unprecedented fracture energy of 31.8 kJ m-2 while maintaining their thermal stability, hydrophobicity, healability, and recyclability. This resilient and long-lasting silicone-based elastomer exhibits significant potential for use in flexible electronic devices.

Carboxylating Elastomer via Thiol-Ene Click Reaction to Improve Miscibility with Conjugated Polymers for Mechanically Robust Organic Solar Cells with Efficiency of 19.

Incorporating flexible insulating polymers is a straightforward strategy to enhance the mechanical properties of rigid conjugated polymers, enabling their use in flexible electronic devices. However, maintaining electronic characteristics simultaneously is challenging due to the poor miscibility between insulating polymers and conjugated polymers. This study introduces the carboxylation of insulating polymers as an effective strategy to enhance miscibility with conjugated polymers via surface energy modulation and hydrogen bonding. The carboxylated elastomer, synthesized via a thiol-ene click reaction, closely matches the surface energy of the conjugated polymer. This significantly improves the mechanical properties, achieving a high crack-onset strain of 21.48%, surpassing that (5.93%) of the unmodified elastomer:conjugated polymer blend. Upon incorporating the carboxylated elastomer into PM6:L8-BO-based organic solar cells, an impressive power conversion efficiency of 19.04% is attained, which top-performs among insulating polymer-incorporated devices and outperforms devices with unmodified elastomer or neat PM6:L8-BO. The superior efficiency is attributed to the optimized microstructures and enhanced crystallinity for efficient and balanced charge transport, and suppressed charge recombination. Furthermore, flexible devices with 5% carboxylated elastomer exhibit superior mechanical stability, retaining ≈88.9% of the initial efficiency after 40000 bending cycles at a 1mm radius, surpassing ≈83.5% for devices with 5% unmodified elastomer.

The effect of thinner SDS-coated Ag NPs and organic carrier PVAc on properties of low-temperature silver paste

Low-temperature silver paste (LT-SP) is a critical conductive material for its use in flexible electronic devices. The high-purity thinner-coated Ag NPs with a size of about 100–200 nm are important for their oxidation resistance. Here, by adjusting mixed reduction of ascorbic acid (Vc), glucose (Clu), and sodium citrate (Na(3)Cit), with n(AgNO3): n(SDS) at 3:1, the size of obtained Ag NPs can be decreased to 158.1 nm. A simple natural precipitation purification was performed to obtain large-scale, thinner SDS-coated Ag NPs with lower energy consumption. With the increase of purification times from 1 to 3 and 5, the purification time was longer and longer, the surface coating layer decreased from 3.716 to 1.429 and 1.093 wt.%, and the size of the initial soft agglomerated Ag NPs gradually dispersed from 481.4 to 153.5 and 97.6 nm, indicating that the surface coating layer gradually became thinner. Considering the properties requirement/time-cost, 3 times purification was chosen. To improve the properties of LT-SP, a single green–white glue (PVAc) with excellent adhesion was used as the organic carrier, which was added to the obtained Ag NPs to produce a series of LT-SP samples. When Ag-4.8 wt.% PVAc, a low resistance of 6.2 × 10−8 Ω cm could be obtained by sintering at 140 °C for 25 min, and excellent electrical conductivity was still maintained after 50,000 times bending. Its adhesion could reach the 4B standard confirmed by the Burger test. In summary, an excellent LT-SP can be large-scale produced with high-purity thinner SDS-coated Ag NPs and PVAc organic carriers.

Mini Review on PEDOT:PSS as a Conducting Material in Energy Harvesting and Storage Devices Applications

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), one of the conducting polymers, is widely used as a conducting material in various applications. PEDOT:PSS possesses high electrical conductivity, optical transparency in visible light range, good chemical and physical stability in ambient state, etc. Furthermore, PEDOT:PSS offers the advantages of flexibility and possibility of solution-based process, which makes it suitable for use in flexible electronic devices. In this mini review, the applications of PEDOT:PSS as a conductive parts in energy harvesting and storage technologies are discussed and summarized.

Structural, Electronic, Optical, and Mechanical Properties of Cu(I)Au(III)‐Based Double Perovskites: A First‐Principles Study

Herein, the structural, electronic, optical, and mechanical properties of Cu(I)Au(III)‐based double perovskites using first‐principles calculations are investigated. Phonon calculation results confirm that pure halide Cs2CuAuX6 (X = Cl, Br), mixed‐halide Cs2CuAuBr4Cl2 and Cs2CuAuI4Br2, and strained Cs2CuAuI6 (by 3% strain) are dynamically stable. Subsequently, the optoelectronic and mechanical properties of these compounds are calculated. The calculations reveal that Cs2CuAuX6 exhibits slightly indirect‐bandgap semiconducting behavior, with the bandgaps of 1.169, 1.191, and 1.355 eV from the HSE06 hybrid functional for X = Cl, Br, and I, respectively. Meanwhile, the bandgap of Cs2CuAuI6 decreases with the increase of strain from 1% to 3% (1.271, 1.148, and 1.037 eV, respectively). In addition, the results show that Cs2CuAuI4Br2 (EgHSE06 = 1.278 eV) has a suitable bandgap, which is close to the ideal direct bandgap. Moreover, Cs2CuAuI4Br2 exhibits strong anisotropic visible light absorption with absorption coefficients exceeding 105 cm−1 and has a relatively large dielectric constant (εxxst = εyyst = 36.27) along the ab plane. Furthermore, its Pugh's ratio (Poisson's ratio) value of 2.94(0.35) exceeds the critical value of 1.75(0.26), indicating its ductility and potential for use in flexible electronic devices.

Electroactive and Stretchable Hydrogels of 3,4-Ethylenedioxythiophene/thiophene Copolymers.

Hydrogels are conductive and stretchable, allowing for their use in flexible electronic devices, such as electronic skins, sensors, human motion monitoring, brain-computer interface, and so on. Herein, we synthesized the copolymers having various molar ratios of 3,4-ethylenedioxythiophene (EDOT) to thiophene (Th), which served as conductive additives. With doping engineering and incorporation with P(EDOT-co-Th) copolymers, hydrogels have presented excellent physical/chemical/electrical properties. It was found that the mechanical strength, adhesion ability, and conductivity of hydrogels were highly dependent on the molar ratio of EDOT to Th of the copolymers. The more the EDOT, the stronger the tensile strength and the greater the conductivity, but the lower the elongation break tends to be. By comprehensively evaluating the physical/chemical/electrical properties and cost of material use, the hydrogel incorporated with a 7:3 molar ratio P(EDOT-co-Th) copolymer was an optimal formulation for soft electronic devices.

Graphene oxide obtention via liquid phase exfoliation from high-rank coal: A comparison of mineral matter removal by alkaline bath

Colombia is one of the world's leading exporters of coal and coke, with significant reserves of high-quality coal. Most of the coal exported from Colombia is used for power generation, but there is also a class of coal that is suitable for making coke. Coke is a raw material required for making steel, and it is produced by heating coal to high temperatures in the absence of air. Colombia is the third-largest global exporter of coke, with a significant portion of its exports going to the steel industry in countries such as Brazil, Mexico, and the United States. The country's high-quality coal reserves and proximity to major markets make it an important player in the global coal and coke trade. On the other hand, graphene and its derivative Graphene Oxide (GO) have unique properties that make them suitable for a wide range of commercial applications. Graphene has exceptional mechanical strength and high electrical conductivity, which make it an attractive material for a variety of electronic and structural applications. For example, graphene-based materials are being developed for use in flexible electronic devices, sensors, and high-strength composites. GO, on the other hand, is highly resistive but still retains exceptional mechanical strength. This makes it useful in applications where electrical conductivity is not necessary but mechanical strength and durability are important. Graphene production using current techniques can be expensive and inefficient, which limits its widespread adoption for commercial applications. However, new production methods, such as Liquid Phase Exfoliation (LPE), are being developed to address these challenges. LPE is a method for producing graphene and graphene oxide that involves using a liquid solvent to break apart graphite into individual graphene sheets. This method is more efficient and cost-effective than traditional methods such as mechanical exfoliation and chemical vapor deposition. In recent years, there has been increasing interest in using high-rank coal from Colombia as a raw material for graphene production using LPE. This is because high-rank coal from Colombia is known to have a high carbon content and low impurity levels, which makes it an ideal raw material for graphene production. Researchers have successfully produced GO using the LPE method and high-rank coal from Boavita, Colombia. This has the potential to significantly increase the supply of graphene and graphene oxide, making it more accessible for commercial applications. Additionally, using coal as a raw material for graphene production has the potential to create a new market for coal, which could benefit the Colombianeconomy. In order to synthesize GO, it is important to establish a suitable protocol for the grinding procedure and particle size selection. (i. more than 0.15 mm, ii. 0.15 mm to 0.05 mm, and iii. less than 0.05 mm) were defined. To compare the yield, the mineral matter removal procedure was carried out with a basic leaching bath. Coal oxidation was performed using the modified Hummers process, and GO was then obtained using LPE. This method has the following advantages:•It is feasible to produce GO from high-rank coal with acceptable quality and particulate size smaller than 0.15 mm, yields that are close to 5%, and flakes with fewer than 15 layers.•This approach also could eliminate dependence on graphite as the carbon feedstock for graphene production.•It is an alternative to manufacture GO from coal dust collected from mines.

Synthesis of oxidation-resistance copper nanowires-formate for high-performance transparent conductive electrodes

In this study, high-aspect-ratio (~1250) curved copper nanowires (CuNWs) composed of formate (FA) as the surface passivation layer were synthesized by the solvothermal method using sodium formate (HCOONa). Experimental data and density functional theory (DFT) simulations suggest that the growth of CuNWs-FA was due to the high chemisorption energy of FA on the [100] plane of Cu. The relative resistance ratio of CuNWs-FA increased by 1.67 and 1.72 after aging at 25 °C for 60 days and 60 °C for 5 days, showing FA passivation greatly improved the oxidation resistance of CuNWs. The transparent conductive electrodes (TCEs) fabricated from CuNWs-FA showed high transmittance (89.19%), low sheet resistance (Rs = 44.54 Ω sq−1), and excellent mechanical stability against 10,000 bending cycles. The TCEs-based transparent flexible heaters (TFHs) exerted a fast heating rate and a uniform temperature distribution within the 20 s response time, which is a testament to the CuNWs-FA in applications such as electrochromic and optoelectronic devices. This passivation approach sheds light on solving the major drawback of CuNWs oxidation and promotes its use in flexible electronic devices.

The optical and electrical properties of amorphous gallium/titanium co-doped indium oxide films based on oxygen flow dependence

Amorphous gallium/titanium (Ga,Ti) co-doped indium oxide (In2O3) (GTiIO) films present significant potential as transparent conducting electrodes for use in flexible electronic devices. Amorphous GTiIO films were grown on silicon and glass substrates using linear-facing target sputtering and various oxygen flow rates. Transmittance was as high as 80% in the visible range for O2 flow rates of 0.3, 0.7, and 1.0 SCCM. The lowest resistivity was obtained at f(O2) = 0.3 SCCM with 0.47 mΩ cm. Dielectric functions were determined, and optical gap energies were estimated as close to 3.4 eV using a Tauc formula. We show that Drude tail amplitude is proportional to the carrier density. An electronic transition was found at 2.7 eV from the optical spectra of the thin film at f(O2) = 0 SCCM; this transition was designated to be an inter-conduction band transition from the first to the second conduction band. Using Hall parameters and Drude tail amplitudes in dielectric functions, the effective mass of GTiIO films was determined as 0.398 m0 at f(O2) = 0.3 SCCM.

Processable, Ion-Conducting Hydrogel for Flexible Electronic Devices with Self-Healing Capability

Conductive, self-healing, and adhesive hydrogels are of great significance in wearable electronic devices. The most important properties of conductive self-healing hydrogels are the efficient recovery of both electrical and mechanical properties at room temperature and prolonged durability. In this work, we developed a novel double-network hydrogel consisting of poly(4-styrene sulfonate-co-methyl-uracil-imidazolium) chloride (PSS-MUI), gelatin, and ferric ions (Fe³⁺). Here, the MUI serves as a supramolecular crosslinker, while ferric ions act as ionic crosslinkers between gelatin and PSS functional groups. The hydrogel demonstrated excellent stretchability and outstanding ionic conductivity. The reversible nature of dynamic hydrogen bonding and ionic and metal coordination interactions rendered the hydrogel self-healing ability, strong adhesion, and rapid electrical performance recovery. Variation in the Fe³⁺ concentration proved to influence the time window of hydrogel processability and allowed tuning the hydrogel mechanical and ion-conducting properties. The optimal Fe³⁺ ion concentration for use in a processable, ion-conducting hydrogel was found to be 2 wt %. During repeated stretching, the hydrogel showed only small changes in its electrical resistance. An electric circuit was successfully assembled onto a flexible polyurethane (PU) substrate where the power supply, light-emitting diode, and resistor were connected with the hydrogel, serving as a conductive wire. Upon breakage of the wire, simple extrusion of the hydrogel precursor into the gap yielded instant repair of the circuit. Thus, the hydrogel demonstrated suitability for use in flexible electronic devices.

Flexible 3D Electrodes of Free-Standing TiN Nanotube Arrays Grown by Atomic Layer Deposition with a Ti Interlayer as an Adhesion Promoter.

Nanostructured electrodes and their flexible integrated systems have great potential for many applications, including electrochemical energy storage, electrocatalysis and solid-state memory devices, given their ability to improve faradaic reaction sites by large surface area. Although many processing techniques have been employed to fabricate nanostructured electrodes onto flexible substrates, these present limitations in terms of achieving flexible electrodes with high mechanical stability. In this study, the adhesion, mechanical properties and flexibility of TiN nanotube arrays on a Pt substrate were improved using a Ti interlayer. Highly ordered and well-aligned TiN nanotube arrays were fabricated on a Pt substrate using a template-assisted method with an anodic aluminum oxide (AAO) template and atomic layer deposition (ALD) system. We show that with the use of a Ti interlayer between the TiN nanotube arrays and Pt substrate, the TiN nanotube arrays could perfectly attach to the Pt substrate without delamination and faceted phenomena. Furthermore, the I-V curve measurements confirmed that the electric contact between the TiN nanotube arrays and substrate for use as an electrode was excellent, and its flexibility was also good for use in flexible electronic devices. Future efforts will be directed toward the fabrication of embedded electrodes in flexible plastic substrates by employing the concepts demonstrated in this study.

Chemical Postdeposition Treatments To Improve the Adhesion of Carbon Nanotube Films on Plastic Substrates.

The robust adhesion of single-walled carbon nanotubes (SWCNTs) to plastic substrates is a key issue toward their use in flexible electronic devices. In this work, semitransparent SWCNT films were prepared by spray-coating on two different plastic substrates, specifically poly(ethylene terephthalate) and poly(vinylidene fluoride). The deposited SWCNT films were treated by dipping in suitable solvents separately, namely, 53% nitric acid (HNO3) and N-methyl pyrrolidone. Direct evidence of SWCNT adhesion to the substrate was obtained by a peel-off test carried out with an adhesive tape. Moreover, these treatments caused enhanced film transparency and electrical conductivity. Electron microscopy images suggested that SWCNTs were embedded in the plastic substrates, forming a thin layer of conductive composite materials. Raman spectroscopy detected a certain level of doping in the SWCNTs after the chemical treatments, which particularly affected metallic nanotubes in the case of the HNO3 treatment. The microscopic adhesion and hardness of the SWCNT films were studied through a nanoscratch test. Overall, the efficiency of selected chemical postdeposition treatments for improving the SWCNT adhesion and the robustness of the resulting SWCNT films are demonstrated on flexible substrates of different chemical compositions.

Highly flexible transparent electrodes based on mesh-patterned rigid indium tin oxide

We developed highly bendable transparent indium tin oxide (ITO) electrodes with a mesh pattern for use in flexible electronic devices. The mesh patterns lowered tensile stress and hindered propagation of cracks. Simulations using the finite element method confirmed that the mesh patterns decreased tensile stress by over 10% because of the escaped strain to the flexible film when the electrodes were bent. The proposed patterned ITO electrodes were simply fabricated by photolithography and wet etching. The resistance increase ratio of a mesh-patterned ITO electrode after bending 1000 times was at least two orders of magnitude lower than that of a planar ITO electrode. In addition, crack propagation was stopped by the mesh pattern of the patterned ITO electrode. A mesh-patterned ITO electrode was used in a liquid-based organic light-emitting diode (OLED). The OLED displayed the same current density-voltage-luminance (J-V-L) curves before and after bending 100 times. These results indicate that the developed mesh-patterned ITO electrodes are attractive for use in flexible electronic devices.

Undercoordinated indium as an intrinsic electron-trap center in amorphous InGaZnO4

Undercoordinated indium (In*) is found to be an intrinsic defect that acts as a strong electron trap in amorphous InGaZnO4. Conduction electrons couple with the under-coordinated In* via Coulomb attraction, which is the driving force for the formation of an In*–M (M=In, Ga, or Zn) bond. The new structure is stable in the electron-trapped (2–) charge state, and we designate it as an intrinsic (In*–M)2− center in amorphous InGaZnO4. The (In*–M)2− centers are preferentially formed in heavily n-doped samples, resulting in a doping limit. They are also formed by electrical/optical stresses, which generate excited electrons, resulting in a metastable change in their electrical properties. Korean scientists have identified a key clue that can enhance the long-term stability of transparent semiconductors in ‘wearable’ computers. Recently, a glass-like oxide containing the metals indium, gallium and zinc (InGaZnO4) has found wide use in flexible electronic devices because its speedy transistor characteristics can drive high-resolution optical displays. However, the capabilities of this see-through semiconductor often degrade over time due to a phenomenon called charge trapping. Yong-Sung Kim from the Korea Research Institute of Standards and Science and co-workers simulated the amorphous structure of InGaZnO4 by performing first-principles quantum computations and discovered a previously unnoticed trapping site — ‘under-coordinated’ indium atoms that snare extra electrons through strong electron–ion interactions. Processing conditions that specifically supress populations of under-coordinated indium should be an essential part of future manufacturing efforts, suggest the authors. Undercoordinated indium (In*) is found to be an intrinsic defect that acts as a strong electron trap in amorphous InGaZnO4. Conduction electrons couple with the under-coordinated In* via Coulomb attraction, which is the driving force for the formation of an In*–M (M=In, Ga, or Zn) bond. The new structure is stable in the electron-trapped (2–) charge state, and we designate it as an intrinsic (In*–M)2− center in amorphous InGaZnO4. The (In*–M)2− centers are preferentially formed in heavily n-doped samples, resulting in a doping limit. They are also formed by electrical/optical stresses, which generate excited electrons, resulting in a metastable change in their electrical properties.

Solderable and electroplatable flexible electronic circuit on a porous stretchable elastomer

A variety of flexible and stretchable electronics have been reported for use in flexible electronic devices or biomedical applications. The practical and wider application of such flexible electronics has been limited because commercial electronic components are difficult to be directly integrated into flexible stretchable electronics and electroplating is still challenging. Here, we propose a novel method for fabricating flexible and stretchable electronic devices using a porous elastomeric substrate. Pressurized steam was applied to an uncured polydimethylsiloxane layer for the simple and cost-effective production of porous structure. An electroplated nickel anchor had a key role in bonding commercial electronic components on elastomers by soldering techniques, and metals could be stably patterned and electroplated for practical uses. The proposed technology was applied to develop a plaster electrocardiogram dry electrode and multi-channel microelectrodes that could be used as a long-term wearable biosignal monitor and for brain signal monitoring, respectively.