Ice-interface assisted large-scale preparation of polypyrrole/graphene oxide films for all-solid-state supercapacitors

In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. The morphology, chemical structure and electrochemical property were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS), respectively. The lamellar structure of GO and both strong interaction with ice and pyrrole could promote polymerization of pyrrole and improve the compactness of the film. With the aid of GO, the conjugation length of PPy increased, the resistance of the material decreased, and the electrochemical energy storage of the composite film was significantly enhanced. In the case of 2.5 wt% GO, the prepared PPy/GO nanocomposite supercapacitor exhibited a high area specific capacitance of 97.3 mF cm⁻² at 1 mA cm⁻². Furthermore, the PPy/GO film supercapacitor also showed excellent cycling stability and good flexibility.

A confirned polymerization method was employed to fabricate self-standing PPy/GO film for all-solid-state supercapacitor.     

Efficient multi-barrier thin film encapsulation of OLED using alternating Al2O3 and polymer layers

Organic optoelectronic devices, especially for OLEDs, are extremely susceptibility to water vapor and oxygen which limit their widespread commercialization. In order to extend the shelf-lifetime of devices, thin film encapsulation is the most promising and challenging encapsulation process. In this study, dyad-style multilayer encapsulation structures based on alternating Al₂O₃ layer and parylene C have been discussed as gas diffusion barriers, in which dense and pinhole-free Al₂O₃ films were grown by atomic layer deposition (ALD) and flexible parylene C layers were deposited by chemical vapor deposition (CVD). We found the particle in ALD deposited Al₂O₃ films process is the key killer to barrier property. The thickness of Al₂O₃ films is the key factor which limit the amount of strain placed on barrier films. With three dyads of the optimal thickness of 30 nm Al₂O₃ film and 500 nm parylene C, WVTR value is lower than 10⁻⁵ g m⁻² per day. In addition, the lifetime of OLEDs with and without encapsulation was 190 h and 10 h, respectively. All the results show that this TFE structure has the effective encapsulated property and does not cause degradation of the OLED devices.

The work demonstrates the WVTR value of 3 dyads alternative 30 nm Al₂O₃ and 500 nm parylene C encapsulation structure is less than 10⁻⁵ g m⁻² per day. And this TFE technology successfully applies for OLED device encapsulation.     

Large-scale preparation of graphene oxide film and its application for electromagnetic interference shielding

In this work, a large-scale preparation of graphene oxide (GO) film is reported, and the structure and the compositional variation was studied after thermal annealing. The electromagnetic interference (EMI) shielding performance of thermally reduced GO films was also investigated. Commercial GO clay was well dispersed by high-speed shearing and formed a stable slurry with a high solid content in water (5%), and this was chosen rather than organic solvent due to its optimal performance in coating procedures and film quality. The optimized thermal annealing procedure resulted in a significant enhancement of electric conductivity and EMI shielding efficiency, which reached 500 S cm⁻¹ and 32–42 dB with the thickness under 0.1 mm. The excellent EMI shielding efficiency of thermally reduced GO film, as well as the easily amplified pilot manufactoring procedure adaptive to commercial equipment, produce graphene for universal EMI shielding materials.

A large-scale preparation of graphene oxide (GO) film is reported, and annealing process improve the electromagnetic interference shielding performance of the film by structure and compositional variation.     

Rational and site-selective formation of coordination polymers consisting of d10 coinage metal ions with thiolate ligands using a metal ion-doped polymer substrate

Here, we report an interfacial approach for fabricating coordination polymers (CPs) consisting of d¹⁰ coinage metal ions with thiolate ligands on a polymer substrate. It was found that CPs were selectively formed on the polymer substrate, resulting in the formation of CP-based thin films. In addition, utilizing a mixed metal ion-doped polymer substrate leads to the formation of mixed-metal CP-based films.

We report an interfacial approach for fabricating coordination polymer (CP) crystal films and patterns on a polymer surface using a metal ion-doped polymer substrate.     

Roll-to-roll processed,highly conductive,and flexible aluminum (Al) electrodes based on Al precursor inks

In this study, a roll-to-roll (R2R) process for the large-scale fabrication of aluminum thin films on flexible polyimide (PI) films is proposed. The R2R machine for Al-film coating assembled in the current work uses a previously reported Al etherate-based precursor ink as the source. After the PI substrate is exposed to a diluted catalyst, the Al precursor ink is coated directly on to the substrate by a slit-die coating method. To optimize the injection of the Al precursor ink, a low-flow limit was established. At a film speed of 5 cm s⁻¹, the width of the fabricated Al film was 130 mm. Such Al-coated films exhibit many advantageous features, including 5.87 × 10⁶ S m⁻¹ of high electrical conductivity at 60.9 nm film thickness and high durability with good adhesion. There was only a minor change in the resistance of the film when it was heated at 100 °C in an oven for 10 days or when it was exposed to H₂O or ethyl alcohol. Flexibility and tape testing was also conducted and the film showed robustness in both cases. Touch panels (7 cm × 9 cm) were fabricated using the fabricated Al-coated film as one side of the panel; the panel showed enough sensitivity to write recognizable letters on the computer. This indicates that the fabricated Al films can be applied in actual electronic devices without further complicated processing.

R2R machine is designed for the Al thin film coating to the flexible substrate, and the substrate can be applied to the flexible electronics.     

High-performance soy protein-based films from cellulose nanofibers and graphene oxide constructed synergistically via hydrogen and chemical bonding

Soybean protein isolate (SPI) shows a broad application prospect in the food and packaging industry. However, its inferior mechanical properties and water resistance limit its application. In this work, a series of SPI-based composite films were prepared by combining with cellulose nanofiber (CNF), graphene oxide (GO), GO/CNF, ethylene glycol diglycidyl ether (EDGE) or GO/CNF/EGDE. The results show that by adding a small amount of reinforced materials (3%), the water resistance, hydrophilicity, mechanical properties and thermal stability of composite films were improved. The filling effect and hydrogen bonding of the reinforcing materials contribute to the formation of film structure. EGDE cross-link SPI with CNF and GO build a chemical network to improve the properties of the film. In addition, they could make a synergistic effect to better enhance the performance of a protein film. Therefore, the tensile strength and elastic modulus of the SGCE film reached 469.21% and 367.58%, respectively.

Soybean protein isolate (SPI) shows a broad application prospect in the food and packaging industry.     

Highly transparent copper iodide thin film thermoelectric generator on a flexible substrate

Simultaneously transparent and flexible conductive materials are in demand to follow the current trend in flexible technology. The search for materials with compliant optoelectronic properties, while simultaneously retaining their electric conductivity at high strain deformation, comprises promising opportunities in modern nanotechnology. Copper iodide (CuI) is not only the most transparent and highly conductive p-type material, but its optimization has contributed to improved ZT values in planar thin-film thermoelectrics. In this work, the readiness of CuI thin films to transparent, flexible technology is evidenced. A maximum ZT value of 0.29 for single CuI thin films of ca. 300 nm in thickness is reported. Values of open-circuit voltage V_oc, short circuit current I_sc and power output of p–n thermoelectric modules of Gallium-doped zinc oxide (GZO) and CuI thin films deposited on a transparent flexible Kapton® (type CS) substrate are reported, and a prototype of a flexible transparent thermoelectric generator based on 17 p–n modules was constructed. Bending analysis of CuI thin films reveals interesting, distinct results when submitted to compression and tension analysis – a behaviour not seen in conventional semiconducting thin films under equivalent strain conditions. A plausible account for such diversity is also included.

Simultaneously transparent and flexible conductive materials are in demand to follow the current trend in flexible technology. A highly transparent and flexible thermoelectric generator of 17 p–n modules was constructed based on copper iodide thin films.     

Oxidation-degree-dependent moisture-induced actuation of a graphene oxide film

Multilayered films prepared from graphene oxide (GO) subjected to a single oxidation process (1GO) can actuate in response to moisture, whereas those prepared from GO subjected to two oxidation processes (2GO) lose this ability. To elucidate the origin of this difference, the structures and properties of various multilayered films and their contents were analyzed. According to atomic force microscopy images, the lateral size of the GO monolayer in 2GO (2.0 ± 0.4 μm) was smaller than that in 1GO (3.2 ± 0.4 μm), although this size difference did not affect actuation. Scanning electron microscopy images of the cross sections of both films showed fine multilayered structures and X-ray diffraction measurements showed the moisture sensitive reversible change in the interlayer distances for both films. Both films adsorbed 30 wt% moisture in 60 s with different water contents at the bottom moist sides and top air sides of the films. Nanoindentation experiments showed hardness values (1GO: 156 ± 67 MPa; 2GO: 189 ± 97 MPa) and elastic modulus values (1GO: 4.7 ± 1.7 GPa; 2GO: 5.8 ± 3.2 GPa) typical of GO, with no substantial difference between the films. On the contrary, the 1GO film bent when subjected to a weight equal to its own weight, whereas the 2GO film did not. Such differences in the macroscopic hardness of GO films can affect their moisture-induced actuation ability.

The moisture-induced actuation behavior of graphene oxide (GO) thin films was found to depend on their extent of oxidation.     

Room temperature two-photon-pumped random lasers in FAPbBr3/polyethylene oxide (PEO) composite perovskite thin film

Solution-processed organic–inorganic halide lead perovskites have attracted increasing attention due to their great potential in low-cost, effective, and versatile light emission applications and large-scale portable optoelectronic devices. In this paper, formamidinium lead tribromide perovskite thin films composited with polyethylene oxide (PEO) were fabricated by a solution processing method. Great enhancement of photoluminescence was observed and more attractively, two-photon-pumped random lasing action could be achieved at room temperature when pumped by a nanosecond pulse laser with excitation wavelength centered at 1064 nm. Evident transition from spontaneous upconversion emission to random lasing action was investigated by monitoring the log–log light emission slope and peak width at half height. The lasing threshold is at around 1.1 mJ cm⁻², which is comparable to that of other two-photon upconversion random lasers. The efficient random lasing emission originates from the multiple random scattering provided by the micrometer-scale rugged morphology and polycrystalline grain boundaries. Compared with conventional lasers that normally serve as a coherent light source, the perovskite random lasers show promise in fabricating low-cost thin-film lasing devices for flexible and speckle-free imaging applications.

Solution-processed organic–inorganic halide lead perovskites have attracted increasing attention due to their great potential in low-cost, effective, and versatile light emission applications and large-scale portable optoelectronic devices.     

Physicochemical characterisation of reduced graphene oxide for conductive thin films

Graphene is a desirable material for next generation technology. However, producing high yields of single-layer flakes with industrially applicable methods is currently limited. We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic acid) and thermal annealing at temperatures of <150 °C for times of <10 minutes, resulting in electrically conducting thin films with sheet resistances reducing by 8 orders of magnitude to as low as ∼1.3 kΩ □⁻¹, suitable for microelectronics, display technology and optoelectronic applications. The in-depth physicochemical characterisation of the products at different stages of GO preparation and reduction allows for further understanding of the process and demonstrates the suitability for industrial production methodologies due to an environmentally-friendly reducing agent, solution processability and no requirement for high temperatures. The presence of the vitamin C lowers the temperature required to thermally reduce the GO into an electrically conducting thin film, making the technique suitable for thermally sensitive substrates, such as low melting point polymers. Simultaneous spray coating and reduction of GO allows for large area deposition of conductive coatings without sacrificing solution processability, often lost through particle agglomeration, making it compatible with industrial processes, and applicable to, for example, the production of sensors, energy devices and flexible conductive electrodes for touchscreens.

We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic acid) and thermal annealing.     

Bio-inspired nacre-like composites with excellent mechanical properties,gas-barrier function and fire-retardant performances based on self-assembly between hyperbranched poly(amido amine)s and montmorillonite

The fabrication of mechanically robust multifunctional nanocomposite (NC) films using simple but effective strategies is a long-term challenge. Inspired by natural nacre, we designed and fabricated high-performance nacre-like NC films (Na-MTM/HBP) through the self-assembly of the hyperbranched poly(amido amine) (HBP) and montmorillonite (Na-MTM) using a vacuum filtration approach. The optimal Na-MTM/HBP NC film shows excellent mechanical strength (106 MPa), which can be attributed to the formation of numerous hydrogen bonds and the electrostatic interactions between hyperbranched HBP and Na-MTM nanosheets. Such films also exhibit excellent gas barrier and fire–fire-retardant owing to the high aspect ratio of the Na-MTM nanosheets. In this work, a class of high-performance NC films exhibiting good mechanical, gas barrier, and flame retardancy properties have been developed. These NC films have great potential in packing or coating materials.

Nacre-like composites with excellent mechanical properties, gas-barrier function and fire-retardant performances are prepared by hyperbranched poly(amido amine)s and montmorillonite.     

Low-temperature atomic layer deposition of Al2O3/alucone nanolaminates for OLED encapsulation

Thin film encapsulation (TFE) is one of the key problems that hinders the lifetime and widespread commercialization of flexible organic light-emitting diodes (OLEDs). In this work, TFE of OLEDs with Al₂O₃/alucone laminates grown by atomic layer deposition (ALD) and molecular layer deposition (MLD) as moisture barriers were demonstrated. The barrier performances of Al₂O₃/alucone laminates with respect to the individual layer thickness and the number of dyads were investigated. It was found that alucone with suitable layer thickness could reduce the permeation to the defect zones of the inorganic layer by prolonging the permeation pathway, sequentially improving the moisture barrier performance. The water vapor transmission rate (WVTR) could be further lowered with increasing the number of dyads of the laminates, the WVTR value reached 1.44 × 10⁻⁴ g per m² per day for laminates with 5.5 dyads. These laminates were incorporated in OLEDs with pixel define layer (PDL), and were found to be able to evidently prolong the lifetime of the OLED.

Al₂O₃/alucone laminates were fabricated by atomic layer deposition (ALD) and molecular layer deposition (MLD), showing good barrier properties. These laminates were found to prolong the lifetime of organic light-emitting diodes (OLEDs) evidently.     

Investigation on optical temperature sensing behaviour via Ag island-enhanced luminescence doped β-NaGdF4:Yb3+/Tm3+ films/microfibers

In this study, silver (Ag) island modified up-conversion nano-particle (NaGdF₄:Yb³⁺/Tm³⁺) thin films were prepared via electrostatic layer by layer (LBL) and spin coating techniques. The spectroscopic results indicated that adding Ag nanoparticles could significantly enhance the up-conversion emission of NaGdF₄:Yb³⁺/Tm³⁺ thin films at 452 nm and 476 nm. The maximum enhancement factor of ∼15.6 was reached at 476 nm. Furthermore, we prepared microfibers from upconverting nanoparticles solution, the application of microfibers as active and passive waveguides was analyzed by observing the performance of microfibers with and without Ag under 980 nm excitation of the laser source. The fluorescence intensity ratio (FIR) method was adopted to evaluate microfiber sensitivity. The intensity-based temperature sensitivity of blue emission from a single microfiber containing up-conversion nanomaterials (NaGdF₄:Yb³⁺/Tm³⁺) and Ag nanoparticles reached up to 0.018 K⁻¹ at 310 K compared to 0.0029 K⁻¹ in Ag-free microfiber. Our results suggest that the novel material can be used to construct new nano-thermometers, useful both in biological experiments as well as industrial research.

In this study, silver (Ag) island modified up-conversion nano-particle thin films were prepared via electrostatic layer by layer (LBL) and spin coating techniques.     

Properties of PEDOT nanowire/Te nanowire nanocomposites and fabrication of a flexible thermoelectric generator

Light-weight, mechanically flexible, transparent thermoelectric devices are promising as portable, and easy-to-integrate energy sources. Poly(3,4-ethylenedioxythiophene) nanowires (PEDOT NWs) possessing high electrical conductivity were synthesized by a facile self-assembled micellar soft-template method. And then, Te nanowires (Te NWs) with high Seebeck coefficient were easily synthesized by the solution process and then added as an inorganic filler to form the PEDOT NW/Te NW nanocomposite films via a simple and convenient vacuum filtration method. The thermoelectric (TE) properties of the nanocomposites were characterized in this research. A maximum power factor of 58.03 μW m⁻¹ K⁻² is obtained from the film containing 90 wt% Te NWs at room temperature, which is dozens of times that of the pure PEDOT NW film. This work uses the as-prepared PEDOT NWs/Te NW (90 wt%) nanocomposite film to fabricate a flexible thermoelectric generator and an output voltage of 2.8 mV was generated at a temperature difference of 13.5 K between the environment and human body.

Light-weight, mechanically flexible, transparent thermoelectric devices are promising as portable, and easy-to-integrate energy sources.     

The synthesis of CdZnTe semiconductor thin films for tandem solar cells

A new approach is adopted to grow cadmium zinc telluride (CdZnTe) thin films using the close spaced sublimation (CSS) technique. The deposition parameters for the growth of cadmium telluride (CdTe) thin films onto the glass substrate were optimized. A zinc telluride (ZnTe) thin film layer was deposited onto already-deposited CdTe thin film to fabricate the CdZnTe (CZT) thin film sample as a ternary compound. Annealing was done after the successful deposition of CZT thin films before further characterization of the CZT thin film samples. The structures of the CZT thin film samples were studied using X-ray diffraction (XRD) and cubic phases were found. A spectrophotometer was used to study the optical parameters, and the energy band gap was found to be in the range of 1.45 eV to 1.75 eV after annealing. The nature of the direct band gap predicts that it might be an ideal component in second-generation solar cells. A Hall measurement system was used to find that the electrical conductivity was in the range of 4.6 × 10⁻⁶ to 8.2 × 10⁻¹¹ (ohm cm)⁻¹. XPS analysis confirmed the presence of Zn in the CdTe thin films. A significant change in electronic properties was observed. These results show that these CZT thin film samples can not only play a key role in the tandem structures of high-efficiency solar cells but they could also be used in the detection of X-rays and gamma rays.

A new approach is adopted to grow cadmium zinc telluride (CdZnTe) thin films using the close spaced sublimation (CSS) technique.     

Rapid synthesis of thermoelectric SnSe thin films by MPCVD

Microwave plasma chemical vapor deposition (MPCVD) has been traditionally used to synthesize carbon-based materials such as diamonds, carbon nanotubes and graphene. Here we report that a rapid and catalyst-free growth of SnSe thin films can be achieved by using single-mode MPCVD with appropriate source materials. The analysis combining microscope images, X-ray diffraction patterns and lattice vibration modes shows that the grown thin films were composed of orthorhombic structured SnSe polycrystals. Further thermoelectric (TE) characterization of the SnSe films reveals the high-performance power factor of 3.98 μW cm⁻¹ K⁻² at 600 K. Our results may open an avenue for rapid synthesis of new types of materials such as IV–VI compounds and be useful for TE application of these materials.

Here we report that a rapid and catalyst-free growth of high quality SnSe thin films can be achieved by using single-mode MPCVD with appropriate source materials, the SnSe films exhibit high TE performance.     

Benzohexacene guide in accurate determination of field effect carrier mobilities in long acenes

Oligoacenes are promising materials in the field of electronic devices since they exhibit high charge carrier mobility and more particularly as a semiconductor in thin film transistors. Herein, we investigate the field effect charge carrier mobility of benzohexacene, recently obtained by cheletropic decarbonylation at moderate temperature. Initially, high performance bottom contact organic thin-film transistors (OTFTs) were fabricated using tetracene to validate the fabrication process. For easier comparison, the geometries and channel sizes of the fabricated devices are the same for the two acenes. The charge transport in OTFTs being closely related to the organic thin film at the dielectric/organic semiconductor interface, the structural and morphological features of the thin films of both materials are therefore studied according to deposition conditions. Finally, by extracting relevant device parameters the benzohexacene based OTFT shows a four-probe contact-corrected hole mobility value of up to 0.2 cm² V⁻¹ s⁻¹.

Four-probes mobility vs. V_GS in the linear regime (V_DS = −10 V) for benzohexacene based transistor.     

Facile preparation of flexible binder-free graphene electrodes for high-performance supercapacitors

A facile two-step strategy to prepare flexible graphene electrodes has been developed for supercapacitors using thermal reduction of graphene oxide (GO) and thermally reduced graphene oxide (TRGO) composite films. The tunable porous structure of the GO/TRGO film provided channels to release the high pressure generated by CO₂ gas. The graphene electrode obtained from reduced-GO/TRGO (1 : 1 in mass ratio) film showed great flexibility and high film density (0.52 g cm⁻³). Using the EMI-BF₄ electrolyte with a working voltage of 3.7 V, the as-fabricated free-standing reduced-GO/TRGO (1 : 1) film achieved a great gravimetric capacitance of 180 F g⁻¹ (delivering a gravimetric energy density of 85.6 W h kg⁻¹), a volumetric capacitance of 94 F cm⁻³ (delivering a volumetric energy density of 44.7 W h L⁻¹), and a 92% retention after 10 000 charge/discharge cycles. In addition, the solid state flexible supercapacitor with the free-standing reduced-GO/TRGO (1 : 1) film as the electrodes and the EMI-BF₄/poly (vinylidene fluoride hexafluopropylene) (PVDF-HFP) gel as the electrolyte also demonstrated a high gravimetric capacitance of 146 F g⁻¹ with excellent mechanical flexibility, bending stability, and electrochemical stability. The strategy developed in this study provides great potentials for the synthesis of flexible graphene electrodes for supercapacitors.

A supercapacitor electrode is developed with a free-standing graphene film by a facile two-step strategy. The graphene electrode achieved a gravimetric capacitance of 180 F g⁻¹ and a volumetric capacitance of 94 F cm⁻³.     

Difference in structural and chemical properties of sol–gel spin coated Al doped TiO2, Y doped TiO2 and Gd doped TiO2 based on trivalent dopants

In this research, pure titanium dioxide (TiO₂) and doped TiO₂ thin film layers were prepared using the spin coating method of titanium(iv) butoxide on a glass substrate from the sol–gel method and annealed at 500 °C. The effects on the structural and chemical properties of these thin films were then investigated. The metal doped TiO₂ thin film which exists as trivalent electrons consists of aluminium (Al), yttrium (Y) and gadolinium (Gd). The anatase phase of the thin films was observed and it was found that the crystal size became smaller when the concentration of thin film increased. The grain size was found to be 0.487 to 13.925 nm. The types of surface morphologies of the thin films were nanoporous, with a little agglomeration and smaller nanoparticles corresponding to Al doped TiO₂, Y doped TiO₂ and Gd doped TiO₂, respectively. The trivalent doping concentration of the thin films increased with a rising of thickness of the thin film. This can contribute to the defects that give advantages to the thin film when the mobility of the hole carriers is high and the electrons of Ti can move easily. Thus, Ti³⁺ existed as a defect state in the metal doped TiO₂ thin film based on lattice distortion with a faster growth thin film that encouraged the formation of a higher level of oxygen vacancy defects.

Ti³⁺ state in metal doped TiO₂ based on lattice distortion that encouraged the formation of oxygen vacancy defects.