Solar Cells: How To Transform More Solar Energy Into Electricity

Sagrario Domínguez-Fernández, a Spanish telecommunications engineer at CEMITEC, has managed to increase light absorption in silicon by means of nanostructures etched onto photovoltaic cells. This increases the efficiency obtained in these electronic devices which are made of this element and which transform solar energy into electricity.
solar cells

Over 30 percent of the sunlight that strikes a silicon is reflected, which means it cannot be used in the photoelectric conversion,” explained Sagrario Domínguez. “Because the nanostructures on the surface of a material have dimensions in the light wavelength range, they interfere with the surface in a particular way and allow the amount of reflected light to be modified.”

Sagrario Domínguez designed and optimised structures on a nanometric scaleto try and find one that would minimise the reflectance [ability of a surface to reflect light] of the silicon in the wavelength range in which solar cells function.” In their manufacturing process, she resorted to what is known as laser interference lithography which consists of applying laser radiation to a photo-sensitive material to create structures on a nanometric scale. Specifically, she used polished silicon wafers to which she gave the shape of cylindrical pillar and obtained a 77 percent reduction in the reflectance of this element.

Sagrario Domínguez then went on to modify the manufacturing processes to produce the nanostructures on the silicon substrates used in commercial solar cells. “These substrates have dimensions and a surface roughness that makes them, ‘a priori’, unsuitable for processes,” pointed out the researcher. Having overcome the difficulties, she incorporated nanostructures onto following the standard processes of the photovoltaics industry. “According to the literature, this is the first time that it has been possible to manufacture periodic nanostructures; they are the ones that on the surface of a material are continuously repeated on substrates of this type, and therefore, the first standard solar cell with periodic nanostructures,” pointed out the new MIT PhD holder. The efficiency obtained is 15.56 percent, which is a very promising value when compared with others included in the literature.


Smart Windows Clean Themselves, Save Energy

A revolutionary new type of smart window could cut window-cleaning costs in tall buildings while reducing heating bills and boosting worker productivity. Developed by University College London (UCL) with support from EPSRC, prototype samples confirm that the glass can deliver three key benefits:
Self-cleaning: The window is ultra-resistant to water, so rain hitting the outside forms spherical droplets that roll easily over the surface – picking up dirt, dust and other contaminants and carrying them away. This is due to the pencil-like, conical design of nanostructures engraved onto the glass, trapping air and ensuring only a tiny amount of water comes into contact with the surface.
 Energy-saving: The glass is coated with a very thin (5-10nm) film of window-cleaning of vanadium dioxide which during cold periods stops thermal radiation escaping and so prevents heat loss; during hot periods it prevents infrared radiation from the sun entering the building.
 Anti-glare: The design of the nanostructures also gives the windows the same anti-reflective properties found in the eyes of moths and other creatures that have evolved to hide from predators.

self cleaning windowA scanning electron miscroscope photograph shows the pyramid-like nanostructures engraved onto glass: at 200nm they are 100 times smaller than a human hair. Controlling the surface morphology at the nanoscale allows scientists to tailor how the glass interacts with liquids and light with high precision

This is the first time that a nanostructure has been combined with a thermochromic coating. The bio-inspired nanostructure amplifies the thermochromics properties of the coating and the net result is a self-cleaning, highly performing smart window, said Dr Ioannis Papakonstantinou of UCL. The UCL team calculate that the windows could result in a reduction in heating bills of up to 40 per cent.


New Cheap Catalyst For Hydrogen Electric Car

Graphene nanoribbons formed into a three-dimensional aerogel and enhanced with boron and nitrogen are excellent catalysts for fuel cells, used in hydrogen electric car, even in comparison to platinum, according to Rice University researchers. The reactions in most current fuel cells are catalyzed by platinum, but platinum’s high cost has prompted the search for alternative. A team led by materials scientist Pulickel Ajayan and chemist James Tour made metal-free aerogels from graphene nanoribbons and various levels of boron and nitrogen to test their electrochemical properties. In tests involving half of the catalytic reaction that takes place in fuel cells, they discovered versions with about 10 percent boron and nitrogen were efficient in catalyzing what’s known as an oxygen reduction reaction, a step in producing energy from feedstocks like methanol.
Ajayan’s Rice lab has excelled in turning nanostructures into macroscopic materials, like the oil-absorbing sponges invented in 2012 or, more recently, solid nanotube blocks with controllable densities and porosities.

hydrogen-electric car
The key to developing carbon-based catalysts is in the doping process, especially with elements such as nitrogen and boron,” he said. “The graphitic carbon-boron-nitrogen systems have thrown many surprises in recent years, especially as a viable alternative to platinum-based catalysts.”. The Rice process is unique, he said, because it not only exposes the edges but also provides porous conduits that allow reactants to permeate the material.
The research appeared in the American Chemical Society journal Chemistry of Materials.


How To Make Drinking Water From Air Humidity

Understanding how a desert beetle harvests water from dew could help to improve drinking water collection in dew condensers mimicking the nanostructure of the beetle’s back

Insects are full of marvels—and this is certainly the case with a beetle from the Tenebrionind family, found in the extreme conditions of the Namib desert. Now, a team of scientists from ESPCI Paristech – France – has demonstrated that such insects can collect dew on their backs—and not just fog as previously thought. This is made possible by the wax nanostructure on the surface of the beetle’s elytra. These findings by José Guadarrama-Cetina,and colleagues were recently published in EPJ E. They bring us a step closer to harvesting dew to make drinking water from the humidity in the air. This, the team hopes, can be done by improving the water yield of man-made dew condensers that mimick the nanostructure on the beetle’s back.
desert beerle
It was not clear from previous studies whether water harvested by such beetles came from dew droplets, in addition to fog.

Guadarrama-Cetina and colleagues also performed an image analysis of dew drops forming on the insect’s back on the surface of the elytra, which appears as a series of bumps and valleys. Dew primarily forms in the valleys endowed with a hexagonal microstructure, they found, unlike the smooth surface of the bumps. This explains how drops can slide to the insect’s mouth when they reach a critical size.

Super-Resolution Microscope For NanoStructure

Researchers from Purdue University have found a way to see synthetic nanostructures and molecules using a new type of super-resolution optical microscopy that does not require fluorescent dyes, representing a practical tool for biomedical and nanotechnology research.

Microscope for nanostructureA new type of super-resolution optical microscopy takes a high-resolution image (at right) of graphite “nanoplatelets” about 100 nanometers wide. The imaging system, called saturated transient absorption microscopy, or STAM, uses a trio of laser beams and represents a practical tool for biomedical and nanotechnology research.

Super-resolution optical microscopy has opened a new window into the nanoscopic world,” said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.”The diffraction limit represents the fundamental limit of optical imaging resolution,” Cheng said. “Stefan Hell at the Max Planck Institute and others have developed super-resolution imaging methods that require fluorescent labels. Here, we demonstrate a new scheme for breaking the diffraction limit in optical imaging of non-fluorescent species. Because it is label-free, the signal is directly from the object so that we can learn more about the nanostructure.


How To Analyse Nanometer-sized Devices Without Destroying Them

The nuclear magnetic resonance apparatus – developed by the University of Sheffield – Department of Physics and Astronomy – will allow for further developments and new applications for nanotechnology which is increasingly used in harvesting solar energy, computing, communication developments and also in the medical field. Scientists can now analyse nanostructures at an unprecedented level of detail without destroying the materials in the process, a limitation researchers across the world faced before the Sheffield experts’ breakthrough.

Dr Alexander Tartakovskii, who led a team of researchers, said: “We have developed a new important tool for microscopy analysis of nanostructures”. Development requires careful structural analysis, in order to understand how the nanostructures are formed, and how we can build them to enhance and control their useful properties. Existing structural analysis methods, key for the research and development of new materials, are invasive: a nanostructure would be irreversibly destroyed in the process of the experiment, and, as a result, the important link between the structural and electronic or photonic properties would usually be lost. This limitation is now overcome by our new techniques, which rely on inherently non-invasive nuclear magnetic resonance (NMR) probing.”

The results open a new way of nano-engineering, a full characterisation of a new material and new semiconductor nano-device without destroying them meaning more research and development and device fabrication processes.