Smart actuators have many potential applications in various areas, so the development of novel actuation materials, with facile fabricating methods and excellent performances, are still urgent needs. In this work, a novel electromechanical bimorph actuator constituted by a graphene layer and a PVDF layer, is fabricated through a simple yet versatile solution approach. The bimorph actuator can deflect toward the graphene side under electrical stimulus, due to the differences in coefficient of thermal expansion between the two layers and the converse piezoelectric effect and electrostrictive property of the PVDF layer. Under low voltage stimulus, the actuator (length: 20 mm, width: 3 mm) can generate large actuation motion with a maximum deflection of about 14.0 mm within 0.262 s and produce high actuation stress (more than 312.7 MPa/g). The bimorph actuator also can display reversible swing behavior with long cycle life under high frequencies. on this basis, a fish-like robot that can swim at the speed of 5.02 mm/s is designed and demonstrated. The designed graphene-PVDF bimorph actuator exhibits the overall novel performance compared with many other electromechanical avtuators, and may contribute to the practical actuation applications of graphene-based materials at a macro scale.

Lithium-ion hybrid supercapacitors (LIHSs), also called Li-ion capacitors, have attracted much attention due to the combination of the rapid charge–discharge and long cycle life of supercapacitors and the high energy-storage capacity of lithium-ion batteries. Thus, LIHSs are expected to become the ultimate power source for hybrid and all-electric vehicles in the near future. As an electrode material, graphene has many advantages, including high surface area and porous structure, high electric conductivity, and high chemical and thermal stability, etc. Compared with other electrode materials, such as activated carbon, graphite, and metal oxides, graphene-based materials with 3D open frameworks show higher effective specific surface area, better control of channels, and higher conductivity, which make them better candidates for LIHS applications. Here, the latest advances in electrode materials for LIHSs are briefly summarized, with an emphasis on graphene-based electrode materials (including 3D graphene networks) for LIHS applications. An outlook is also presented to highlight some future directions.

Although the performance of polymer solar cells has been improved significantly recently through careful optimization with different interlayers for the same materials, more improvement is needed in this respect for small-molecule-based solar cells, particularly for the electron-transport layers (ETLs). In this work, three different solution-processed ETLs, PFN, ZnO nanoparticles, and LiF, were investigated and compared in the performance of small-molecule-based devices, and power conversion efficiencies (PCEs) of 8.32, 7.30, and 7.38 % were achieved, respectively. The mechanism for the ETL-induced enhancement has been studied, and different ETLs have a significantly different impact on the device performance. The clearly improved performance of PFN is attributed to the combination of reduced bimolecular recombination and increased effective photon absorption in the active layer.

A high-performance graphene oxide (GO)-doped ion gel (P(VDF-HFP)-EMIMBF₄-GO gel) is prepared by exploiting copolymer (poly(vinylidene fluoride-hexafluoro propylene), P(VDF-HFP)) as the polymer matrix, ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate, EMIMBF₄) as the supporting electrolyte, and GO as the ionic conducting promoter. This GO-doped ion gel demonstrates significantly improved ionic conductivity compared with that of pure ion gel without the addition of GO, due to the homogeneously distributed GO as a 3D network throughout the GO-doped ion gel by acting like a ion “highway” to facilitate the ion transport. With the incorporation of only a small amount of GO (1 wt%) in ion gel, there has been a dramatic improvement in ionic conductivity of about 260% compared with that of pure ion gel. In addition, the all-solid-state supercapacitor is fabricated and measured at room temperature using the GO-doped ion gel as gel polymer electrolyte, which demonstrates more superior electrochemical performance than the all-solid-state supercapacitor with pure ion gel and the conventional supercapacitor with neat EMIMBF₄, in the aspect of smaller internal resistance, higher capacitance performance, and better cycle stability. These excellent performances are due to the high ionic conductivity, excellent compatibility with carbon electrodes, and long-term stability of the GO-doped ion gel.

A new reaction sequence for the chemical functionalization of graphene oxide (GO) consisting of the nucleophilic addition of n-butyllithium (n-BuLi) to the GO sheets and a subsequent coupling and etherification reaction of the intermediates (Bu-GO)ⁿ⁻Liⁿ⁺ and 2-ethylhexyl bromide leading to functionalized GO is developed. The reaction is investigated. The results show that the n-Bu and 2-ethylhexyl are covalently attached to the GO sheets and many sp³ carbons are formed by addition reaction of n-BuLi to the plane of GO. After functionalization, the dispersibility of functionalized GO in ortho-dichlorobenzene (ODCB) increases significantly to 0.4 mg mL⁻¹ and the structural integrity of the graphene sheets remained. Good electronic conductivity of the film prepared from functionlized GO (i-Octyl-Bu-GO) in ODCB is obtained after high temperature annealing.

Two novel copolymers PBDT-DEAITN and PBDT-DOAITN containing the same backbone of isothianaphthene (ITN) quinoidal and benzodithiophene (BDT) donor units are synthesized and their organic photovoltaic (OPV) devices are fabricated. Although these two polymers have rather low optical bandgaps, 1.52 and 1.58 eV for PBDT-DEAITN and PBDT-DOAITN, respectively, their OPV cells exhibit rather limited power conversion efficiencies of 1.25% and 1.20% under an AM1.5G simulated solar light. The reasons for the low OPV performance are investigated by structure modeling calculation. Based on this and the screening results for the representative quinoidal polymers in the literatures, a strategy of designing high- performance planar polymers based on ITN unit is proposed.

As a promising two-dimensional nanomaterial with outstanding electronic, optical, thermal, and mechanical properties, graphene has been proposed for many applications. In this Progress Report we summarize and discuss comprehensively the advances made so far for applications of graphene in organic photovoltaic (OPV) cells, including that for transparent electrodes, active layers and interfaces layer in OPV. It is concluded that graphene may very likely play a major role in new developments/improvements in OPVs. The future studies for this area are proposed to focus on the following: i) improving the conductivity without comprising the transparency as a transparent electrode material; ii) controlling the sheet sizes, band structure and surface morphology for use as a electron acceptor material, and iii) controlling and improving the functionalization and compatibility with other materials as interface layer material.

Exceptionally high specific surface area, mechanical strength, electrical conductivity, and a special two-dimensional structure make graphene a highly promising material for electromechanical actuators. Electromechanical actuators are fabricated using flexible graphene-based paper prepared via a filtration process, and the stroke of these graphene-based actuators is directly measured during electrochemical double-layer charge injection. Actuation strain up to 0.064% was obtained for pristine graphene paper in response to an applied potential of –1 V in 1 M NaCl solution. Double-layer charge injection in graphene sheets is believed to induce actuation strain through a combination of coulombic and quantum-chemical-based expansion. To increase electrochemical-double-layer capacitance and actuator performance, Fe₃O₄ nanoparticles were used to partially prevent graphene sheets from restacking and allow the electrolyte ions to infiltrate the resulting magnetic graphene paper more easily. The magnetic graphene paper exhibits actuation strain as large as 0.1% at –1 V applied potential, which is about 56% higher than that of the pristine graphene paper.

Carbazole-based donor–acceptor compounds with tunable HOMO–LUMO gaps were synthesized by Suzuki and Sonogashira cross-coupling reactions. Their optical and electrochemical properties were fully characterized. The results show that materials with different emission colors ranging from blue to green to orange could be obtained. The experimental results were also supported by theoretical calculations.

A soluble graphene, which has a one-atom thickness and a two-dimensional structure, is blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction (BHJ) polymer photovoltaic cells. Adding graphene to the P3HT induces a great quenching of the photoluminescence of the P3HT, indicating a strong electron/energy transfer from the P3HT to the graphene. In the photovoltaic devices with an ITO/PEDOT:PSS/P3HT:graphene/LiF/Al structure, the device efficiency increases first and then decreases with the increase in the graphene content. The device containing only 10 wt % of graphene shows the best performance with a power conversion efficiency of 1.1%, an open-circuit voltage of 0.72 V, a short-circuit current density of 4.0 mA cm⁻², and a fill factor of 0.38 under simulated AM1.5G conditions at 100 mW cm⁻² after an annealing treatment at 160 °C for 10 min. The annealing treatment at the appropriate temperature (160 °C, for example) greatly improves the device performance; however, an annealing at overgenerous conditions such as at 210 °C results in a decrease in the device efficiency (0.57%). The morphology investigation shows that better performance can be obtained with a moderate content of graphene, which keeps good dispersion and interconnection. The functionalized graphene, which is cheap, easily prepared, stable, and inert against the ambient conditions, is expected to be a competitive candidate for the acceptor material in organic photovoltaic applications.

Despite great recent progress with carbon nanotubes and other nanoscale fillers, the development of strong, durable, and cost-efficient multifunctional nanocomposite materials has yet to be achieved. The challenges are to achieve molecule-level dispersion and maximum interfacial interaction between the nanofiller and the matrix at low loading. Here, the preparation of poly(vinyl alcohol) (PVA) nanocomposites with graphene oxide (GO) using a simple water solution processing method is reported. Efficient load transfer is found between the nanofiller graphene and matrix PVA and the mechanical properties of the graphene-based nanocomposite with molecule-level dispersion are significantly improved. A 76% increase in tensile strength and a 62% improvement of Young's modulus are achieved by addition of only 0.7 wt% of GO. The experimentally determined Young's modulus is in excellent agreement with theoretical simulation.