Xuezhen Huang

Dye‐Sensitized Solar Cell with Energy Storage Function through PVDF/ZnO Nanocomposite Counter Electrode

Dye-sensitized solar cells with an energy storage function are demonstrated by modifying its counter electrode with a poly (vinylidene fluoride)/ZnO nanowire array composite. This simplex device could still function as an ordinary solar cell with a steady photocurrent output even after being fully charged. An energy storage density of 2.14 C g(-1) is achieved, while simultaneously a 3.70% photo-to-electric conversion efficiency is maintained.

Actuators based on liquid crystalline elastomer materials

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including the unique, high-stroke reversible mechanical actuation when triggered by external stimuli. This article reviews some recent exciting developments in the field of LCE materials with an emphasis on their utilization in actuator applications. Such applications include artificial muscles, industrial manufacturing, health and microelectromechanical systems (MEMS). With suitable synthetic and preparation pathways and well-controlled actuation stimuli, such as heat, light, electric and magnetic fields, excellent physical properties of LCE materials can be realized. By comparing the actuating properties of different systems, general relationships between the structure and the properties of LCEs are discussed. How these materials can be turned into usable devices using interdisciplinary techniques is also described.

Energy Storage via Polyvinylidene Fluoride Dielectric on the Counterelectrode of Dye-Sensitized Solar Cells.

To study the fundamental energy storage mechanism of photovoltaically self-charging cells (PSCs) without involving light-responsive semiconductor materials such as Si powder and ZnO nanowires, we fabricate a two-electrode PSC with the dual functions of photocurrent output and energy storage by introducing a PVDF film dielectric on the counterelectrode of a dye-sensitized solar cell. A layer of ultrathin Au film used as a quasi-electrode establishes a shared interface for the I-/I3- redox reaction and for the contact between the electrolyte and the dielectric for the energy storage, and prohibits recombination during the discharging period because of its discontinuity. PSCs with a 10-nm-thick PVDF provide a steady photocurrent output and achieve a light-to-electricity conversion efficiency (η) of 3.38%, and simultaneously offer energy storage with a charge density of 1.67 C g-1. Using this quasi-electrode design, optimized energy storage structures may be used in PSCs for high energy storage density.

High Performance All-Solid-State Flexible Micro-Pseudocapacitor Based on Hierarchically Nanostructured Tungsten Trioxide Composite

Microsupercapacitors (MSCs) are promising energy storage devices to power miniaturized portable electronics and microelectromechanical systems. With the increasing attention on all-solid-state flexible supercapacitors, new strategies for high-performance flexible MSCs are highly desired. Here, we demonstrate all-solid-state, flexible micropseudocapacitors via direct laser patterning on crack-free, flexible WO3/polyvinylidene fluoride (PVDF)/multiwalled carbon nanotubes (MWCNTs) composites containing high levels of porous hierarchically structured WO3 nanomaterials (up to 50 wt %) and limited binder (PVDF, <25 wt %). The work leads to an areal capacitance of 62.4 mF·cm–2 and a volumetric capacitance of 10.4 F·cm–3, exceeding that of graphene based flexible MSCs by a factor of 26 and 3, respectively. As a noncarbon based flexible MSC, hierarchically nanostructured WO3 in the narrow finger electrode is essential to such enhancement in energy density due to its pseudocapacitive property. The effects of WO3/PVDF/MWCNTs composite composition and the dimensions of interdigital structure on the performance of the flexible MSCs are investigated.

One-step femtosecond laser patterning of light-trapping structure on dye-sensitized solar cell photoelectrodes

Light-trapping patterns were constructed in TiO2 photoelectrodes for dye-sensitized solar cells (DSSCs) by a one-step femtosecond laser structuring method that utilized ablation to create patterns at the surface of nanostructured TiO2 films. As a result, much more light was trapped in the photoelectrodes. Grating and orthogonal-grid patterns were studied, and the light trapping performance was optimized through the adjustment of pattern spacing, which was easily realized in the laser ablation process. With a 5-μm-spacing orthogonal-grid pattern, DSSCs showed a highest photon-to-electron conversion efficiency of 9.32% under AM 1.5G, a 13.5% improvement compared to the same cell without laser ablation. This simple and universal laser ablation method could be used to process many kinds of nanomaterials, and could be applied for various devices with nanostructures.

Light Actuation of Graphene-Oxide Incorporated Liquid Crystalline Elastomer Nanocomposites

The authors demonstrate high-performance photo-actuation of nematic liquid crystal elastomer (LCE) nanocomposites incorporating graphene oxide (GO). The nematic LCE serves as the matrix with reversible thermomechanical response. The incorporated GO absorbs photons and converts the photonic energy to heat, thus actuating the LCE nanocomposite. Both infrared and visible lights of wide spectrum (white light) or various wavelength ranges irradiations are able to effectively actuate the LCE nanocomposites, thus proves that they can fully utilize the photo energy of a light source for their mechanical actuation. Attributed to the well dispersity of GO in LCE matrix, sensitive (in seconds) and reversible photo-induced strain of LCE nanocomposites with consistent shape-changing ratio and significantly enhanced mechanical properties are observed. The contraction of the LCE nanocomposite films under light irradiation is about one third of the original length. The effective load-actuation capability is elevated about 50%.

Recovering degraded quasi-solid-state dye-sensitized solar cells by applying electrical pulses

We discovered a method of applying a forward pulsed bias to recover the degraded quasi-solid-state dye-sensitized solar cells (DSSCs). Up to 30.7% of the power conversion efficiency (η) of a degraded poly(vinylidene fluoride) (PVDF) based DSSC was recovered by a double-pulse. The recovered η remained higher than that before the double-pulse treatment for at least 28 days. It is deduced that the blocking of ion-transport channels in the quasi-solid-state electrolyte causes degradation of the DSSCs. This study will shed light on the efficiency enhancement and long-term stability of quasi-solid-state DSSCs.

Reversible Photo Actuated Bulk Nanocomposite with Nematic Liquid Crystalline Elastomer Matrix

Liquid crystal elastomers (LCEs) are excellent actuator materials. However, current LCE materials are generally made in the forms with thin thickness, such as films or fibers, which have limitations in forming actuators. We have developed a bulk LCE material with the three-dimensional elastic skeleton network of polyurethane and the matrix of nematic LCE incorporating single-wall carbon nanotubes (SWCNTs). This LCE nanocomposite bulk (LCENB) exhibited sensitive and reversible photo actuation. It could evenly contract by up to 25% of the initial height under a uniform irradiation, or bend towards the incident light by up to 40° under an asymmetrical irradiation. A photo-driven scanning mirror with superior scanning angle, implementing this LCENB as the actuator, was also demonstrated.

Photo-thermo-mechanically actuated liquid crystalline elastomer nanocomposite reinforced by polyurethane fiber-network

ABSTRACT In this work, we develop a nanocomposite consisting of nematic liquid crystal elastomer (LCE) matrix incorporated with single-wall carbon nanotubes (SWCNTs) and the reinforcement phase of polyurethane fiber-network (PUFN). The photo-thermo-mechanical actuation of LCE matrix is realized by converting light into heat with assistant of SWCNTs. The PUFN enhances the mechanical properties of the material, thus the actuation capability. Under the irradiation from a wide-spectrum light source with an intensity on the order of 100 mW/cm2, the PUFNs/SWCNT/LCE nanocomposite contracts up to 27% of the original length in several seconds due to the photo-induced strain, and recovers to the original length in several seconds after the light source is switched off. The efficiency of actuation is not light-spectrum dependent. The maximum effective actuation force is about 260 kPa, much larger than that of the LCE material without the reinforcement of PUFNs. The tensile strength and the performance of anti-fatigue failure under multiple reversible actuations are also greatly improved. The mechanism of the actuation capability of LCE material involved in the fiber-network reinforcement phase is studied.

Two-step crosslinked liquid-crystalline elastomer with reversible two-way shape memory characteristics

ABSTRACT Liquid-crystalline elastomers (LCEs) possess large and equilibrium reversible anisotropic dimensional change in response to applied stimuli. The deformation behavior demonstrated by current LCE materials under the stimuli are generally determined by their own geometries and the alignment distributions of liquid crystal (LC) units in the LCE matrices. Here we report a LCE whose synthesis was through a two-stage crosslinking coupled with a mechanical reshaping process, where the shape was mechanically reset before the final crosslinking. It demonstrated reversible memory and change between the initial geometries formed during the first crosslinking stage and any reshaped geometries under the stimuli. Its deformation is not influenced by the geometries and the alignment distributions of LC units in the LCE matrix. This characteristic in LCEs holds promise in a wide range of application researches requiring sophisticated functions and smart structures.