Jixian Liu

Enhanced efficiency of polymer solar cells by incorporated Ag–SiO2 core–shell nanoparticles in the active layer

In this article, we creatively incorporated Ag–SiO2 core–shell nanoparticles (Ag–SiO2-NPs) into photo-/electro-active layers consisting of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) in polymer solar cells (PSCs). By this way, the photovoltaic performances of PSCs have largely been enhanced. The results demonstrate a 13.50% enhancement of short-circuit photocurrent density (Jsc) and a 15.11% enhancement of power conversion efficiency (PCE) as the weight percent of doped Ag–SiO2-NPs is 1.5 wt% in the active layer of corresponding PSCs. We attribute the enhancement to the localized surface plasmon resonance (LSPR) effect of Ag–SiO2-NPs, by which the incident light harvesting is enlarged. Whereas, the incorporated bare Ag nanoparticles (Ag-NPs) in the active layer of PSCs decreases the PCE, which is ascribed to the quenching of excitons at the surface of Ag-NPs and the poor dispersion of Ag-NPs in the active layer. Importantly, this work provides a new approach to enhance the performance of PSCs via the LSPR effect of Ag–SiO2-NPs other than via non-circular nanometals.

Effect of photocurrent enhancement in porphyrin–graphene covalent hybrids

Graphene oxide (GO) sheets were covalently functionalized with 5-p-aminophenyl-10,15,20-triphenylporphyrin (NH2TPP) by an amidation reaction between the amino group in NH2TPP and carboxyl groups in GO. The Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning and transmission electron microscopies reveal that NH2TPP covalent bonds form on the double surface of graphene oxide sheets, generating a unique nano-framework, i.e., NH2TPP-graphene-NH2TPP. Its UV-visible spectroscopy reveals that the absorption spectrum is not a linear superposition of the spectra of NH2TPP and graphene oxide, because a 59nm red shift of the strong graphene oxide absorption is observed from 238 to 297nm, with significant spectral broadening between 300 and 700nm. Fluorescence emission spectroscopy indicates efficient quenching of NH2TPP photoluminescence in this hybrid material, suggesting that photo-induced electron transfer occurs at the interface between NH2TPP and GO. A reversible on/off photo-current density of 47mA/cm(2) is observed when NH2TPP-graphene-NH2TPP hybrid sandwiches are subjected to pulsed white-light illumination. Covalently-bound porphyrins decrease the optical HOMO/LUMO band gap of graphene oxide by ≈1eV, according to UV-visible spectroscopy. Cyclic voltammetry predicts a small HOMO/LUMO band gap of 0.84eV for NH2TPP-graphene-NH2TPP hybrid sandwiches, which is consistent with efficient electron transfer and fluorescence quenching.

Preparation of Ag@SiO2 Dispersion in Different Solvents and Investigation of its Optical Properties

In this article, Ag-SiO2 composite nanoparticles with a core-shell structure were prepared by a very simple and rapid wet chemical method in different solvents such as methanol, ethanol and isopropanol, respectively, transmittance electron microscopy (TEM) images show that regular SiO2-covered silver nanoparticles (briefly-marked as Ag@SiO2) can be obtained in ethanol and isopropanol, but not in methanol. The x-ray diffraction (XRD) measurement indicates that the silver nanoparticles are face-centered cubic (fcc) structure with high crystallinity. X-ray photoelectron spectroscopy (XPS) measurement shows that the binding energy of O1 s in Si-O-Ag is lower than that in Si-O-Si, which means that the complex bonding is established between Ag core and SiO2 shell. Ultraviolet-visible (UV-vis) spectroscopy records that the plasmon resonance peak of silver nanoparticles is shifted after the coverage of SiO2. As capping effect, the fluorescence intensity related to surface plasmon resonance (SPR) of Ag core is reduced by SiO2 shell.

Synthesis of photocatalytic hematite nanotube array using a template-free solvothermal approach

The paper describes a template-free solvothermal synthesis of α-Fe2O3 hollow nanotube arrays over a large area. The columnar nanotubes on the substrate have closed tips and smooth defined walls. The thickness of the nanowall is about 10 nm, which could offer short diffusion distances and decrease recombination of electron–hole pairs. And the preferential orientation is the [110] axis. The cubic Au nanocrystals were decorated by a photocatalytic reduction process, and the corresponding EDX mappings intuitively display the distributions of the composites. Au nanocrystals matched the absorption of α-Fe2O3 hollow nanotube arrays, which improved photoactivity under visible light (wavelength > 420 nm). The photoactivity of the sample was investigated based on systematic photoelectrochemical (PEC) measurements. These revealed that the photocurrent density of Au/α-Fe2O3 is almost 6 times higher than that of pure α-Fe2O3. And its photocurrent density increases to 0.16 mA cm−2 at 1.23 VRHE under irradiation. The mechanism of enhanced visible light PEC activity has been discussed using schematics. Hence, the study presents not only a route for formation of α-Fe2O3 hollow nanotube arrays but also PEC applications of plasmonic composites.

Effective regulation of the micro-structure of thick P3HT:PC71BM film by the incorporation of ethyl benzenecarboxylate in toluene solution

In this work, ethyl benzenecarboxylate (EB) was creatively selected as the additive in a blend of poly(3-hexylthiophene)/phenyl-C71-butyric acid methyl ester (P3HT/PC71BM) in non-halogenated solvent toluene (TL). With the optimized incorporating concentration of EB (i.e. 2 vol%) in toluene, a great power conversion efficiency (PCE) enhancement of 4.11% was achieved without thermal annealing, whereas a maximum PCE of 4.82% with thermal annealing was achieved under the same conditions. According to our systematic characterization results, we could conclude that we successfully regulated the micro-structures, including phase separation, the domain sizes of P3HT or PC71BM and the crystallinity of P3HT by incorporating 2 vol% EB in TL solution. The effectiveness of EB as a TL additive in P3HT/PC71BM can be interpreted based on its Hansen solubility parameters (HSPs) and its high boiling point.

Leveling graphene sheets through electrospinning and their conductivity

This study provided a strategy to extend and level easily-curved graphene sheets through electrospinning. A suspension of graphene oxide (GO) sheets in polar polymers, such as polyacrylonitrile (PAN) and polyvinyl pyrrolidone (PVP), was first electrospun into a composite network in which the GO sheets were sandwiched and leveled under the drag force of the electrospun nanofibers at the surface and around the edge of the GO sheets. Then, the leveled GO sheets were reduced under the vapor of reducing agents and became graphene sheets. The scanning electron micrographical results confirm the extended and leveled shape of the graphene sheets. With this strategy, the problem of easy curvature of graphene sheets can be thoroughly dissolved. Very importantly, the pressed multilayer samples have a high conductivity of 103 S m−1. This indicates that wide potential applications of graphene materials from natural graphite in photo- and electro-devices will be developed.

A Nano-Silver Enhancement Effect on the Luminescence of a Ligand–Eu3+ Complex via a SiO2 Spacer

Luminescent rare earth complex (REC) nanocomposites, Eu(TTA)3Phen attached onto Ag@SiO2 nanoshells, were fabricated by facile wet chemistry and self-assembly techniques. Transmission electron microscopy, and fourier transform infrared and UV–Vis spectroscopy were used to investigate the step-by-step fabrication. The luminescence of REC was significantly enhanced using a silver core (size: 45 nm) surrounded by a 20-nm thick silica shell. Thicker or thinner silica shells afforded tuning of the metal-enhanced luminescence. The thiophene-TTA-containing REC fluorophore was able to etch the silver core, resulting in hollow silica shells, consequently displaying no luminescence enhancing capabilities. The etching efficiency was proportional to the concentration of Eu(TTA)3Phen, and decreased with increasing shell thickness.

Adjustable Fluorescent Material of Terbium Hybrid in Poly (Methyl Methacrylate)—SiO2 Copolymer Host

In this work, the ternary copolymer of methyl methacrylate (MMA) and quadruple copolymer of MST-PEG (MSTE) were synthesized by sol-gel method. And their trivalent terbium complexes were prepared through hybrid strategy. FT-IR data confirmed that the cross-linked network of either ternary copolymer MST or quadruple copolymer of MSTE was formed by Si‒O‒Si, Si‒O‒C and Si-C bonding with molecular framework of poly (MMA-MSPMA). Trivalent terbium cooperates with ether characteristic groups of Si‒O‒Si, Si‒O‒C and C‒O‒C. The thermal behavior study of these samples by DSC indicated that MST, MST-Tb3+ and MSTE-Tb3+ behave a critical transition temperature (TTr) to accelerate the rate of sol-gel reactions while the PEG in MSTE- Tb3+ mitigates acceleration. The terbium-containing samples with or without PEG can emit sharp fluorescence at 548 nm and the fluorescent strength increases with the content of PEG. However, the emitting peak at 417 nm shows a maximum value at critical concentration of PEG. Based on the observations of microscopy and thermal history, this strength change goes with the domain conglomeration of silica crystalline.

Morphology and Luminescent Properties of Solid Micelles based on Europium(III) Complexes with Diblock Copolymers of Methyl Methylacrylate and Acrylic Acid

In this article, diblock copolymer (DBC), poly (methyl methacrylate)-block-poly (acrylic acid) was synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The DBC-Eu3+ solid micelles were prepared through the complex interaction between DBC and Eu3+ ions. As cross-linker, Eu3+ ions accept the electron donation of the ligand groups (carboxyl) sited on the polar PAA segments of DBC and form the DBC-Eu3+ solid micelles. The observations by transmission electron microscopy showed the embedment of Eu3+ ions in DBC and the nonpolar segments [poly (methyl methacrylate)] of DBC play a role of compatible agent for DBC-Eu3+ solid micelles to disperse in hydrophobic solvent [for example, dimethyl formamide] or polymer matrix. Very importantly, we found the dependence of the morphological structure (i.e. the size of solid micelles) on the molecular weight of DBC. On the other hand, the dependence of photoluminescent property of DBC-Eu3+ solid micelles on the molecular weight of DBC and the ratio of polar and nonpolar segments was confirmed through our experiments. The results showed the existence of enhanced photoluminescent property of DBC-Eu3+ solid micelles.

Electric-field-actuation of in situ composites that contain silver-coated carbon fibers in sodium sulfonate ionomers

In this research contribution, an electric-field-stimulated actuation system was developed by impregnating sodium-sulfonated ionomers, poly(styrene-co-butyl acrylate-co-sodium allyl sulfonate, PSBS) with in situ deposited silver-modified carbon fibers (SCCF). In the actuator, PSBS acts as an electrolytic medium for metal ion migration, and the SCCFs act as surface conductive electrodes on both sides of a sandwich configuration. The maximum bending angle of 98° is achieved after 11 s of stimulation when the electric potential difference is 5 V. This novel actuator has two outstanding characteristics: (1) in situ deposited SCCFs in PSBS form double-sided surface electrodes with high conductivity (10−3 Ω cm) and good interfacial binding with the PSBS matrix, which minimizes the drawbacks of electrochemical plating or electrode-less deposition of noble metals like Pt on the membrane surface of ionic polymer metal composites (IPMCs); and (2) it has the highest bending rate compared to currently existing IPMCs including Nafion and novel ones published recently. Additionally, the storage E′ and loss E′′ moduli of the PSBS–SCCF actuation system can be adjusted by selecting the appropriate ratio of butyl acrylate to styrene, where the latter comonomer increases the rigidity of the composite. The bending angle of this actuator can be controlled by the electric potential difference, water-uptake, and terpolymer composition. This fabrication technology exhibits significant advantages, such as process simplicity using non-toxic and low cost materials, rapid response, large bending angles, and reproducibility.