Wenjin Zeng

Flexible Asymmetrical Solid-State Supercapacitors Based on Laboratory Filter Paper

In this study, a flexible asymmetrical all-solid-state supercapacitor with high electrochemical performance was fabricated with Ni/MnO2-filter paper (FP) as the positive electrode and Ni/active carbon (AC)-filter paper as negative electrode, separated with poly(vinyl alcohol) (PVA)-Na2SO4 electrolyte. A simple procedure, such as electroless plating, was introduced to prepare the Ni/MnO2-FP electrode on the conventional laboratory FP, combined with the subsequent step of electrodeposition. Electrochemical results show that the as-prepared electrodes display outstanding areal specific capacitance (1900 mF/cm(2) at 5 mV/s) and excellent cycling performance (85.1% retention after 1000 cycles at 20 mA/cm(2)). Such a flexible supercapacitor assembled asymmetrically in the solid state exhibits a large volume energy density (0.78 mWh/cm(3)) and superior flexibility under different bending conditions. It has been demonstrated that the supercapacitors could be used as a power source to drive a 3 V light-emitting diode indicator. This study may provide an available method for designing and fabricating flexible supercapacitors with high performance in the application of wearable and portable electronics based on easily available materials.

High-performance stretchable transparent electrodes based on silver nanowires synthesized via an eco-friendly halogen-free method

Silver nanowires (AgNWs) with high aspect ratio are usually prepared via complicated multi-step procedures or by a relatively tedious polyol method with the assistance of Xa−/O2 (Xa− represents the halide ion or sulfion) etching. In this paper, silver nanowires with both a high aspect ratio of 800–1600 and high purity were prepared via a simple, cost-effective, high-yield and eco-friendly method without the introduction of external halides or sulfides. Embedding the as-prepared silver nanowires beneath the surface of the poly(dimethylsiloxane) (PDMS) substrate, novel stretchable AgNW/PDMS electrodes with superior comprehensive performances were fabricated. The resulting AgNW/PDMS electrodes show high optoelectronic performance. Without annealing, transparent conductive films with both high conductivity and transmittance, Rs = 14 Ω □−1, T = 90% and Rs = 9 Ω □−1, T = 81% were fabricated, respectively. To the best of our knowledge, they are among the best AgNW/PDMS electrodes in terms of transparency and electrical conductivity. The transparent electrodes also possess excellent electromechanical performance and stretchability (no obvious changes in sheet resistance with strain up to 20%). What is more, the conductive layer of the as-prepared electrodes shows strong adhesion to the substrates, demonstrating their superior durability. They also show high flexibility, good chemical stability and high uniformity.

Controllable size-selective method to prepare graphene quantum dots from graphene oxide.

We demonstrated one-step method to fabricate two different sizes of graphene quantum dots (GQDs) through chemical cutting from graphene oxide (GO), which had many advantages in terms of simple process, low cost, and large scale in manufacturing with higher production yield comparing to the reported methods. Several analytical methods were employed to characterize the composition and morphology of the resultants. Bright blue luminescent GQDs were obtained with a produced yield as high as 34.8%. Moreover, how the different sizes affect fluorescence wavelength mechanism was investigated in details.

Copper salts mediated morphological transformation of Cu2O from cubes to hierarchical flower-like or microspheres and their supercapacitors performances.

Monodisperse Cu2O of different microstructures, such as cubes, flower-like, and microspheres, have been extensively synthesized by a simple polyol reduction method using different copper salts, i.e. (Cu(acac)2, Cu(OH)2, and Cu(Ac)2·H2O). The effects of copper salts on the morphology of Cu2O were investigated in details through various characterization methods, including X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV-Vis absorption spectra. The effects of morphology on the electrochemical properties were further studied. Among the different structures, Cu2O with the microspheric morphology shows the highest specific capacitance and the best cycling stability compared with those of the other two structures, thus bear larger volume charge during the electrochemical reaction due to the microspheres of small nanoparticles.

Self-propelled manganese oxide-based catalytic micromotors for drug delivery

A manganese oxide-based catalytic tubular micromotor (PEDOT/MnO2) is described that displays effective autonomous motion in hydrogen peroxide with high speed (318.80 µm s−1) and can operate in very low levels of fuel, down to 0.4%. The polymer bilayer micromotor also exhibits efficient locomotion in different biological media including bovine serum albumin and bovine serum. Moreover, the micromotor is applied to deliver a chemotherapeutic anticancer drug, camptothecin, using electrostatic interactions, offering considerable potential for diverse clinical and biomedical applications such as drug delivery for theranostic microsystems.

Morphology Analysis and Optimization: Crucial Factor Determining the Performance of Perovskite Solar Cells

This review presents an overall discussion on the morphology analysis and optimization for perovskite (PVSK) solar cells. Surface morphology and energy alignment have been proven to play a dominant role in determining the device performance. The effect of the key parameters such as solution condition and preparation atmosphere on the crystallization of PVSK, the characterization of surface morphology and interface distribution in the perovskite layer is discussed in detail. Furthermore, the analysis of interface energy level alignment by using X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy is presented to reveals the correlation between morphology and charge generation and collection within the perovskite layer, and its influence on the device performance. The techniques including architecture modification, solvent annealing, etc. were reviewed as an efficient approach to improve the morphology of PVSK. It is expected that further progress will be achieved with more efforts devoted to the insight of the mechanism of surface engineering in the field of PVSK solar cells.

Highly Sensitive Flexible Pressure Sensor Based on Silver Nanowires-Embedded Polydimethylsiloxane Electrode with Microarray Structure

Flexible pressure sensors have attracted increasing research interest because of their potential applications for wearable sensing devices. Herein, a highly sensitive flexible pressure sensor is exhibited based on the elastomeric electrodes and a microarray architecture. Polydimethylsiloxane (PDMS) substrate, coated with silver nanowires (AgNWs), is used as the top electrode, while polyvinylidene fluoride (PVDF) as the dielectric layer. Several transfer processes are applied on seeking facile strategy for the preparation of the bottom electrode via embedding AgNWs into the PDMS film of microarray structure. The flexible pressure sensor integrates the top electrode, dielectric layer, and microarray electrode in a sandwich structure. It is demonstrated that such sensors possess the superiorities of high sensitivity (2.94 kPa-1), low detection limit (<3 Pa), short response time (<50 ms), excellent flexibility, and long-term cycle stability. This simple process for preparing such sensors can also be easily scaled up to construct pressure sensor arrays for detecting the intensity and distribution of the loaded pressure. In addition, this flexible pressure sensor exhibits good performance even in a noncontact way, such as detecting voice vibrations and air flow. Due to its superior performance, this designed flexible pressure sensor demonstrates promising potential in the application of electronic skins, as well as wearable healthcare monitors.

Low cost, high performance flexible asymmetric supercapacitor based on modified filter paper and an ultra-fast packaging technique

A flexible all-solid-state asymmetric supercapacitor (FAAS) was prepared via a low-cost method with commonly used paper fibers as the substrate and a modified polymer-based hydrogel as the electrolyte. In the designed structure of the positive electrode, a three dimensional network of stacked thin film based on paper fibers (PFs), chemically reduced graphene oxide (RGO) and the electro-polymerization of polyaniline (PANI) nanorods was prepared via an extended filtration assisted method. The fabricated PF–RGO–PANI electrodes exhibit large specific capacitance of 587 F g−1 at the current density of 0.8 A g−1 and excellent cycling stability (99.6% retention of initials specific capacitance even after 5000 cycles). PF–RGO film was introduced as the negative electrode for the designed asymmetric supercapacitor. During the preparation process of FAAS, a glutaraldehyde (GA) cross-linked PVA–H2SO4 hydrogel was not only used as the electrolyte but also explored as a separator and external packaging material prepared by a fast layer-by-layer assembly technique within one minute. The resulted FAAS exhibits a maximum energy density and power density of 175 W h kg−1 and 9200 W kg−1. Moreover, superior mechanical stability of the FAAS has been demonstrated by testing its bending and folding performance, which retains over 84% of its original specific capacitance even after 2000 cycles of bending and folding. The simple and low-cost preparation process of electrodes, the ultra-fast flexible supercapacitor assembling and the efficient packaging technique proposed in this study provide a good contribution to the development of FAAS for the next generation flexible energy storage devices.

Improved performances of inkjet-printed poly(3-hexylthiophene) organic thin-film transistors by inserting an ionic self-assembled monolayer

Inkjet printing is a promising technology because of the material conservation and facile patterning compared with other solution-processed techniques, facilitating the scalable fabrication and commercialization of organic electronics. In this study, organic thin-film transistors (OTFTs) based on poly(3-hexylthiophene) (P3HT) by inkjet printing were fabricated and explored by electrical analysis and morphological characterization. By optimizing the processing conditions, the comprehensive performance in terms of the field-effect mobility of inkjet-printed P3HT-based OTFTs was comparable to those of spin-coated P3HT-based OTFTs. More importantly, with the employment of an electrode buffer layer, namely Br(CH2)5N(CH3)3Br, the field-effect mobilities of both spin-coated and inkjet-printed OTFTs were improved in accordance with the expectations, resulting from the reduced contact resistance and improved film quality.

Understanding the Effect of Delay Time of Solvent Washing on the Performances of Perovskite Solar Cells

Uniform and dense perovskite films were realized by the one-step solution-processing method combined with toluene washing. The influence of the delay time applied for toluene washing on the film quality of CH3NH3PbI3 (MAPbI3) was investigated in a comprehensive manner. The optimal delay time was experimentally observed at the critical point when the color of the film changes from transparent to hazy. A detailed X-ray diffraction study suggested that such a color change was caused by the emergence of the MAPbI3 crystal nucleus. This finding provides a convenient method to determine the optimal time accurately. With the optimal delay time, the most uniformly distributed MAPbI3 grains with the largest average grain size and the smoothest surface were obtained. Owing to the realization of homogeneous MAPbI3 films combined with full coverage of perovskite on the substrate achieved by toluene washing at the critical point, open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 1.11 V, 18.24 mA/cm2, 77.47, and 15.54% were obtained.