Energy generation - Page 7

Researchers from MIT developed a new solar (photovoltaic) cell that is made from several graphene sheets coated with nanowires. They say that this flexible and transparent cell could be made on the cheap.

The new solar panels use graphene as a replacement for ITO. The new electrode material is cheaper and provides several advantages over ITO: flexibility, low weight, mechanical strength and chemical robustness. The idea is to use a series of polymer coatings to modify the graphene properties, allowing them to bond a layer of zinc oxide nanowires to it, and then an overlay of a material that responds to light waves—either lead-sulfide quantum dots or a type of polymer called P3HT. Despite these modifications, graphene's innate properties remain intact.

Researchers from Georgia Tech have developed a new low-temperature method to dope graphene films using self-assembled monolayers (SAM) that modify the interface of graphene and its support substrate. Using this method the researchers developed graphene p-n junctions.

The researchers used CVD to grow graphene on copper film and then transferred it to silicon dioxide substrates that were functionalized with the self-assembled monolayers. Thus they have shown that you can make fairly well doped p-type and n-type graphene controllably by patterning the underlying monolayer instead of modifying the graphene directly. All previous methods (such as substitution of carbon atoms for nitrogen atoms, compounds addition or graphene ribbons edge modification) or had disrupted the graphene lattice which reduced the electron mobility and the devices were not stable.

Researchers from Stanford University managed to build a solar cell made entirely from carbon. Solar panels made from such materials can provide high performance at a low cost. The entire panel can be built using a coating process (the materials are soluble) and can be made flexible.

The two electrodes in the device are made from graphene and single-walled carbon nanotubes. The active layer (sandwiched between the electrodes) is made from buckyballs (which can be used to create graphene quantum-dots, by the way).

Nobel Prize-winner (together with Andre Geim) Professor and Kostya Novoselov Professor Volodya Falko from Lancaster University have released a graphene roadmap. The roadmap discusses the different possible applications for graphene and also the different ways to produce the material.

The authors says that the first key application is conductors for touch-screen displays (replacing ITO), where they expect can be commercialized within 3-5 years. They also see rollable e-paper displays soon - prototypes could appear in 2015. Come 2020, we can expect graphene-based devices such as photo-detectors, wireless communications and THz generators. Replacing silicon and delivering anti-cancer drugs are interesting applications too - but these will only be possible at around 2030.

An artificial photosynthesis system converts sunlight into chemical energy (as opposed to a PV/solar system which produces electricity). Such a system could be used to produce renewable fuels - but developing an efficient system is very challenging. Now researchers form the Korea Research Institute of Chemical Technology and the Ewha Womans University in Seoul have discovered that a graphene-based photocatalysis could improve the efficiency of such a system.

The researchers coupled graphene to a porphyrin enzyme. The resulting material converts sunlight and carbon dioxide into formic acid. This material is highly functional in the visible light spectrum, and its overall efficiency is significantly higher than the efficiency of other photocatalysts.

Researchers from the University of Florida have managed to develop the most efficient graphene based solar cell to date. This was achieved by doping it with an organic material, and it increases the efficiency by more than four times (from 1.9% to 8.6%).

The researchers used a cheap and environmentally stable organic coating layer to reduce the graphene electrical resistance by adjusting the Fermi level. In the new solar cells, a single layer of graphene placed on top of a silicon wafer serves as a Schottky junction, the main component of simple photovoltaic devices called Schottky junction solar cells.

Researchers from the Institute of Photonic Sciences (ICFO) in Barcelona, Spain have developed a highly sensitive photodetector that uses graphene and quantum dots. They say that the new device is a billion times more sensitive to light than previous graphene-based photodetectors because of the quantum dots. A photo-detector such as this can be used in light sensors, solar cells, infrared cameras and biomedical imaging.

Graphene's external quantum efficiency (EQE) is low as it absorbs less than 3% of the light that falls on it. It is also quite difficult to actually extract the electrical current from the graphene. Adding the quantum dots on the graphene sheet helps both of these issues.

Researchers from the Michigan Technological University discovered that the addition of graphene augmented the conductivity of titanium dioxide, thus increasing the electricity production in a dye-sensitized solar cells by 52.4%. Graphene’s superior electrical conductivity enables it to function as bridges, thus speeding up electron transfer between the titanium dioxide and the photoelectrode.

The team also developed a low-cost, comparatively foolproof technique to synthesize titanium dioxide sheets embedded with the nanomaterial. The idea is to first create a graphite oxide powder and then form a paste by mixing the powder with titanium dioxide. The paste is then applied over a substrate (glass for example) and baked at high temperatures.

Researchers from the Hong Kong Polytechnic University claim that they have invented a new graphene-based battery that runs solely on ambient heat. If this is confirmed, it could lead the way towards a clean, continuous and limitless source of power!

The new battery electrodes harvest energy from ions in a solution - that move at room temperature. The thermal energy of these ions can reach several kilojoules per kilogram per Kelvin. The researchers used silver and gold electrodes connected to a strip of graphene, and a copper chloride solution. Six of these devices in series can produce a voltage of over 2 V - enough to drive a red LED.

Researchers from the University of Houston have used quantum mechanical calculations to show that graphene could be turned into a piezoelectric material by producing triangular-shaped holes in a specific pattern onto it and applying consistent pressure.

The team also says that the pseudo-piezoelectricity of graphene was as high as that of familiar piezoelectric materials such as quartz.