Flexible, Stable, and Efficient Counter Electrode for Quantum-Dot-Sensitized Solar Cells Based on Carbon Nanotube Films.

With the rapid development in information, communication, energy, medical care, and other fields, the demand for light, strong, flexible, and stable materials continues to grow. Carbon nanotube (CNT) films possess outstanding properties, such as flexibility, good tensile properties, low density, and high electrical conductivity, making them promising materials for a wide range of applications. This paper reports an effective strategy that combines stretching treatment, laser etching, and electron beam deposition to fabricate an iron-deposited CNT film, which can serve as a counter electrode (CE) of quantum-dot-sensitized solar cells. The study also investigates the influences of processing parameters, such as stretching ratio and iron-depositing thickness on the film's stacking structure, electrical conductivity, and catalytic activity. Under optimized stretching ratios and depositing thicknesses, the catalytic activity of the reacted deposited layer and the high electrical conductivity of the flexible film basis can be fully utilized, allowing the photoelectric conversion efficiency (PCE) of the solar cells to reach approximately 4.58%. Additionally, the CE exhibits flexibility, light transmission, and good stability, with its primary properties remaining above 97% after nearly 50 days. Thus, this research provides innovative material options and development strategies for the development of electrode materials.

Analysis of transverse thermal conductivity for mesophase pitch-based carbon fibers and the through-thickness heat conduction of their composites.

A quantitative analysis method for the transverse thermal conductivity (TC) of carbon fiber is developed, which consists of three steps including TC and morphology characterization of unidirectional composite laminate, fiber contour extraction, and finite element inverse analysis. Two different pitch-based carbon fibers with folded-radial and onion-skin microstructure are characterized, and the influences of fiber volume fraction and microstructure on the heat conduction of their composites are investigated. The equivalent transverse TCs of TC-HC-800 and PCF-1 carbon fibers are measured to be 9.27 and 2.87 W m-1 K-1, respectively. The through-thickness TC of unidirectional composite exhibits rapid growth with the increase in fiber volume fraction. The finite element analysis reveals that more continuous heat conduction paths are formed with the increase in fiber volume fraction. Benefited from the bigger graphitization degree, larger cross-sectional area, and bigger aspect ratio, TC-HC-800 unidirectional composite shows higher through-thickness TC than PCF-1 composite at the same fiber volume fraction.

Temperature Dependence of Electrical Resistance in Carbon Nanotube Composite Film during Curing Process.

Carbon nanotube (CNT) film possesses excellent mechanical and piezoresistivity, which may act as a sensor for process monitoring and reinforcement of the final composite. This paper prepared CNT/epoxy composite film via the solution dipping method and investigated the electrical resistance variation (ΔR/R0) of CNT/epoxy composite film during the curing process. The temperature dependence of electrical resistance was found to be closely related to resin rheological properties, thermal expansion, and curing shrinkage. The results show that two opposing effects on electrical resistivity occur at the initial heating stage, including thermal expansion and condensation caused by the wetting tension of the liquid resin. The lower resin content causes more apparent secondary impregnation and electrical resistivity change. When the resin viscosity remains steady during the heating stage, the electrical resistance increases with an increase in temperature due to thermal expansion. Approaching gel time, the electrical resistance drops due to the crosslink shrinkage of epoxy resin. The internal stress caused by curing shrinkage at the high-temperature platform results in an increase in electrical resistance. The temperature coefficient of resistance becomes larger with an increase in resin content. At the isothermal stage, an increase in ΔR/R0 value becomes less obvious with a decrease in resin content, and ΔR/R0 even shows a decreasing tendency.

Influence of Electrical Heating Metal Mesh and Power Density on Resistance Welding of Carbon Fiber/PEEK Composite.

An experimental investigation on the resistance welding of carbon-fiber-reinforced polyetheretherketone (PEEK) composite laminate using three types of stainless steel (SS) meshes with different sizes and electrical resistances as heating elements is reported. The objective of this study is to determine the influence of the metal mesh on the welding process and performance at different power densities ranging from 29 to 82 kW/m2. Resistance welding equipment is used to monitor the temperature and displacement along the thickness of the laminate. The results show that the power density determines the welding time and heat concentration. A large power density results in a short welding time, but also increases the temperature gradient at the joining interface (almost 50 °C) and causes an obvious deformation of a contraction of more than 0.1 mm along the thickness of the laminate. A SS mesh with low resistance has a strong welding capability, i.e., a high welding efficiency under low power density. A lap shear strength of approximately 35 MPa can be obtained with the appropriate power density. The shear strength is affected by the bonding between the metal mesh and polymer, the metal mesh load bearing, and the metal mesh size.

The Fabrication and Properties of a Bendable High-Temperature Resistance Conductive Pitch-Based Carbon/CNT Film Nanocomposite.

This paper fabricates a carbon nanotube (CNT ) film-reinforced mesophase pitch-based carbon (CNTF/MPC) nanocomposite by using a hot-pressing carbonization method. During the carbonization, the stacked aromatic layers tended to rearrange into amorphous carbon, and subsequently generated crystalline carbon in the matrix. The continuous entangled CNT networks were efficiently densified by the carbon matrix though optimized external pressure to obtain the high-performance nanocomposites. The CNTF/MPC@1300 displayed a stable electrical conductivity up to 841 S/cm at RT-150 °C. Its thermal conductivity in the thickness direction was 1.89 W/m∙K, an order of magnitude higher than that of CNT film. Moreover, CNTF/MPC@1300 showed a mass retention of 99.3% at 1000 °C. Its tensile strength was 2.6 times the CNT film and the tensile modulus was two orders of magnitude higher. Though the CNTF/MPC nanocomposites exhibited brittle tensile failure mode, they resisted cyclic bending without damage. The results demonstrate that the CNTF/MPC nanocomposite has potential application in multi-functional temperature resistance aerospace structures.

Structure Design of GFRP Composite Leaf Spring: An Experimental and Finite Element Analysis.

Due to the high load-bearing capacity and light weight, composite leaf spring with variable width and variable thickness has been increasingly used in the automobile industry to replace the conventional steel leaf spring with a heavy weight. The optimum structural design of composite leaf spring is particularly favorable for the weight reduction. In this study, an effective algorithm is developed for structural optimization of composite leaf spring. The mechanical performance of composite leaf spring with designed dimensions is characterized using a combined experimental and computational approach. Specifically, the composite leaf spring with variable width and variable thickness was prepared using the filament winding process, and the three-dimensional finite element (FE) model of the designed composite leaf spring is developed. The experimental sample and FE model of composite leaf spring are tested under the three-point bending method. From experimental and simulation results, it is shown that the bending stiffness of the designed leaf spring meets the design requirement in the automotive industry, while the results of stress calculation along all directions meet the requirements of material strength requirement. The developed algorithm contributes to the design method for optimizing the stiffness and strength performance of the composite leaf spring.

Mechanical and electrical enhancement of super-aligned carbon nanotube film by organic and inorganic doping.

Inspired by the chemical and physical doping methods on traditional composites, bismaleimide (BMI) resin and graphene oxide (GO) are selected for doping modification of carbon nanotube (CNT) film in this paper. Based on the diverse enhancement effects of CNT film, the mechanisms and characteristics of resin crosslink and inorganic doping are compared. Due to the crosslinking network of resin, BMI is more beneficial for cooperative deformation and mechanical enhancement, while GO doping shows more advantages in improving electrical performance because of the numerous functional groups on the surface, and good intrinsic properties. With the appropriate doping method and optimized process conditions, the tensile property and electrical conductivity of CNT film can be improved by over 150% and 200% (e.g., tensile strength and modulus of 2990 MPa and 149 GPa, and electrical conductivity of 38 700 S m-1).

Piezoresistivity of resin-impregnated carbon nanotube film at high temperatures.

This paper presents the development of a continuous carbon nanotube (CNT) composite film sensor with a strain detecting range of 0%-2% for structural composites. The strain-dependent resistance responses of continuous CNT film and its resin-impregnated composite films were investigated at temperatures as high as 200 °C. The results manifest that impregnation with resin leads to a much larger gauge factor than pristine film. Both the pristine and composite films show an increase in resistivity with increasing temperature. For different composite films, the ordering of gauge factors is consistent with that of the matrix moduli. This indicates that a resin matrix with higher modulus and strong interactions between CNTs/CNT bundles and the resin matrix are beneficial for enhancing the piezoresistive effect. The CNT/PAA composite film has a gauge factor of 4.3 at 150 °C, an order of magnitude higher than the metal foil sensor. Therefore, the CNT composite films have great potential for simultaneous application for reinforcement and as strain sensor to realise a multifunctional composite.

Densification of chlorine-doped continuous CNT sheet/polyvinylidene fluoride sandwich film and improvement of the mechanical and dielectric properties.

The compact structure of a chlorine-doped continuous CNT sheet/polyvinylidene fluoride (Cl-CNT sheet/PVDF) was successfully optimized by means of a hot-press treatment to improve the mechanical and dielectric properties with a high densification degree. Then, the densified Cl-CNT sheet/PVDF dielectric layer was inserted between two PVDF insulating layers to fabricate a sandwich composite. It was found that the dielectric and mechanical properties were effectively enhanced, with a dielectric permittivity of 40.4 (@102 Hz), a dielectric loss of 0.16 (@102 Hz), a tensile strength of 139 MPa, and a tensile modulus of 4.4 GPa under a hot-pressing pressure of 20 MPa. Furthermore, the densified Cl-CNT sheet/PVDF was used as an electrode in a multilayer sandwich composite film, and good performance was obtained. The improvement mechanism was discussed and the studied CNT composite and other dielectric composites were compared. It demonstrates great potential for applications in dielectric and electrode materials to achieve structural and functional integration.

Tuning carbon nanotube assembly for flexible, strong and conductive films.

Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g(-1), greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive.

Highly aligned dense carbon nanotube sheets induced by multiple stretching and pressing.

The CNT sheet fabricated by the floating catalyst chemical vapor deposition (CVD) method has attracted great attention due to its easy fabrication process and promising mass production at low cost. However, the randomly oriented CNT sheet with a loose stacking density shows relatively poor mechanical properties. In this work, a highly aligned dense CNT sheet was successfully fabricated by a simple process of two-time stretching and pressing of a multilayered CVD-grown CNT sheet. Drastic nanotube rearrangements occurred during stretching and pressing processes. A polymer-like tensile necking behavior was observed during the stretching process, accompanied by inter-tube junction breakage due to long-distance slippage. Simultaneously the CNT sheet was thickened after the stretching process due to the increase of the inter-layer space, which could be effectively eliminated by the following pressing treatment. After two-time stretching and pressing, a highly aligned dense CNT sheet was fabricated with the volume density increasing to 0.98 g cm(-3) (by 109%) and the tensile strength increasing to 598 MPa (by 221%) compared to the as-prepared CNT sheet.