Jinquan Wei

Colloidal antireflection coating improves graphene-silicon solar cells.

Carbon nanotube-Si and graphene-Si solar cells have attracted much interest recently owing to their potential in simplifying manufacturing process and lowering cost compared to Si cells. Until now, the power conversion efficiency of graphene-Si cells remains under 10% and well below that of the nanotube-Si counterpart. Here, we involved a colloidal antireflection coating onto a monolayer graphene-Si solar cell and enhanced the cell efficiency to 14.5% under standard illumination (air mass 1.5, 100 mW/cm(2)) with a stable antireflection effect over long time. The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range. Our results demonstrate a great promise in developing high-efficiency graphene-Si solar cells in parallel to the more extensively studied carbon nanotube-Si structures.

Core-Double-Shell, Carbon Nanotube@Polypyrrole@MnO2 Sponge as Freestanding, Compressible Supercapacitor Electrode

Design and fabrication of structurally optimized electrode materials are important for many energy applications such as supercapacitors and batteries. Here, we report a three-component, hierarchical, bulk electrode with tailored microstructure and electrochemical properties. Our supercapacitor electrode consists of a three-dimensional carbon nanotube (CNT) network (also called sponge) as a flexible and conductive skeleton, an intermediate polymer layer (polypyrrole, PPy) with good interface, and a metal oxide layer outside providing more surface area. These three components form a well-defined core-double-shell configuration that is distinct from simple core-shell or hybrid structures, and the synergistic effect leads to enhanced supercapacitor performance including high specific capacitance (even under severe compression) and excellent cycling stability. The mechanism study reveals that the shell sequence is a key factor; in our system, the CNT-PPy-MnO2 structure shows higher capacitance than the CNT-MnO2-PPy sequence. Our porous core-double-shell sponges can serve as freestanding, compressible electrodes for various energy devices.

Graphene/Silicon Nanowire Schottky Junction for Enhanced Light Harvesting

Schottky junction solar cells are assembled by directly coating graphene films on n-type silicon nanowire (SiNW) arrays. The graphene/SiNW junction shows enhanced light trapping and faster carrier transport compared to the graphene/planar Si structure. With chemical doping, the SiNW-based solar cells showed energy conversion efficiencies of up to 2.86% at AM1.5 condition, opening a possibility of using graphene/semiconductor nanostructures in photovoltaic application.

Graphene sheets from worm-like exfoliated graphite

High quality graphene sheets have been prepared by a facile liquid phase exfoliation of worm-like graphite (WEG). This approach combining with the advances in large scale industry manufacturing of WEG could potentially lead to the development of new and more effective graphene products.

TiO2-Coated Carbon Nanotube-Silicon Solar Cells with Efficiency of 15%

Combining carbon nanotubes (CNTs), graphene or conducting polymers with conventional silicon wafers leads to promising solar cell architectures with rapidly improved power conversion efficiency until recently. Here, we report CNT-Si junction solar cells with efficiencies reaching 15% by coating a TiO2 antireflection layer and doping CNTs with oxidative chemicals, under air mass (AM 1.5) illumination at a calibrated intensity of 100 mW/cm2 and an active device area of 15 mm2. The TiO2 layer significantly inhibits light reflectance from the Si surface, resulting in much enhanced short-circuit current (by 30%) and external quantum efficiency. Our method is simple, well-controlled, and very effective in boosting the performance of CNT-Si solar cells.

Super‐Stretchable Spring‐Like Carbon Nanotube Ropes

Spring-like carbon nanotube ropes consisting of perfectly arranged loops are fabricated by spinning single-walled nanotube films, and can sustain tensile strains as high as 285%.

Tribological properties of oleic acid-modified graphene as lubricant oil additives

Liquid phase exfoliated graphene sheets were modified by oleic acid and dispersed in lubricant oils as additives. The tribological behaviours of graphene-contained oils were investigated using a four-ball tribometer. The lubricant with optimized graphene concentrations of 0.02–0.06 wt% showed enhanced friction and anti-wear performance, with friction coefficient and wear scar diameter reduced by 17% and 14%, respectively.

Ion doping of graphene for high-efficiency heterojunction solar cells

We demonstrated the p-type chemical doping by chlorine and nitrate anions to enhance the Schottky junction in the solar cell. Nitrate ions were found to be more effective for reducing the sheet resistance and enlarging the work function of graphene for effective charge separation and transport, and the efficiency was increased to 9.2% by a factor of 1.68 under AM 1.5 illumination.

Encapsulated carbon nanotube-oxide-silicon solar cells with stable 10% efficiency

We report a metal-insulator-semiconductor heterojunction solar cell by depositing a carbon nanotube film onto silicon substrate, followed by acid oxidation of the Si surface to form a thin oxide layer at the junction interface. The nanotube-oxide-Si solar cells with polymer encapsulation show stable efficiencies of above 10%, owing to enhanced photon absorption, inhibited charge recombination, and reduced internal resistance. Parallel and series connections without sacrificing cell efficiencies were demonstrated.

Carbon nanotube sponge filters for trapping nanoparticles and dye molecules from water

Carbon nanotube sponges show effective filtration for nanoparticles and dye molecules with different sizes and concentrations from water. The three-dimensional interconnected porous structure formed by entangled nanotubes can trap nanoparticles and molecules by physisorption without the need for chemical functionalization. The sponge filters are potential environmental materials for water treatment.