In the United States, the Massachusetts Institute of Technology (MIT) has developed a light concentration system for solar cells that has no need to track the sun. The method can utilize display glass and even window glass in homes and office buildings as solar concentrators. In addition, it helps reduce the cost of the solar cell system to a tenth or less.

Until now, Fresnel lenses and similar materials have been used in solar cell concentrators, but along with mechanisms to track the suns motion. The new concentrator has no lenses it merely uses a light guide. It consists of an organic thin film with fluorescent or phosphorescent properties placed on a sheet of glass with a high refractive index of about 1.8. Light enters the light guide, and only light of a specific wavelength is absorbed by the organic material, which emits light of a slightly longer wavelength. This emitted light travels inside the glass and is collected at the edges.

If solar cells were to be placed at window edges, it would be theoretically possible to use small solar cells to generate the same amount of electrical energy as a solar cell of the same area as the light guide. The concentration function of the light guide is not affected by the angle of incidence, making tracking mechanisms unnecessary. Light concentration efficiency is determined by the ratio of light guide area to the area of the solar cells mounted at the glass sheet edges, and by the efficiency with which light is transmitted to the edges by the light guide. If the light guide area is increased, the light concentration efficiency increases geometrically as the ratio of areas, but light guide efficiency drops. This imposes limits on maximum light guide area.

The effective efficiency of the newly developed solution is about 10-61 times higher than the solar cell area. An MIT source said the improvement is due to a better understanding of the organic materials, improved film growth technology and other factors. Only the light guide has been fabricated at present; measurements of performance when mated to an actual solar cell are scheduled for the future.

Source: techon.nikkeibp.co.jp

An untreated silicon solar cell only absorbs 67.4 per cent of sunlight shone upon it meaning that nearly one-third of that sunlight is reflected away and thus unharvestable. Dr. Shawn-Yu Lin, a physics professor at Rensselaer Polytechnic Institute, the United States, and his team have nano-engineered an anti-reflective coating that has absorbed 96.21 per cent of sunlight shone on it meaning that only 3.79 per cent of the sunlight was reflected away. This huge gain in absorption was consistent across the entire spectrum of sunlight, from ultraviolet to visible light and infrared, and moves solar power a significant step forward towards economic viability. A stationary solar panel treated with the coating would absorb 96.21 per cent of sunlight irrespective of the suns position in the sky. Along with significantly better absorption of sunlight, Dr. Lins discovery could thus enable a new generation of stationary, more cost-efficient solar arrays.

Source: nextbigfuture.com

Dye-sensitised solar cells designed for outdoor conditions typically have an efficiency of about 6 per cent at present. Dr. Michael Grtzel of the Swiss Federal Institute of Technology in Switzerland who co-invented dye-sensitised solar cells in 1991 had thought it might be possible to double the efficiency of his low-cost cells simply by designing one that collects light from both sides simultaneously. Working with Dr. Seigo Ito of the University of Hyogo, Japan, Dr. Grtzels team has now achieved just that. Their new dye-sensitised solar cell is almost as efficient at light-to-energy conversion when it strikes the rear side as when it strikes the front.

To achieve the trick, Dr. Grtzels team first replaced the opaque back panel with a second sheet of glass, making the entire device transparent to let light into the system also from the rear. The new panel, coated with tin oxide, acted as the second electrode, giving electrons back to the electrolyte and thus completing the circuit.

Dr. Grtzels team experimented with varying the thickness of the dye-filled layer. They found that if that layer was around 15 m thick, the solar cell converted 6 per cent of the light arriving through its front into electricity and a further 5.5 per cent of the light arriving through the rear. There is always an albedo effect [as light bounces off surfaces] and on a cloudy day, collecting light from both sides will buy you almost double the normal efficiency, says Dr. Grtzel. Other electrolytes have reached 10 per cent or even higher, he adds. Using those electrolytes in the new two-sided solar cell can help reach efficiencies of 15 to 20 per cent, which is better than the performance of silicon wafer solar cells under similar conditions.

Source: technology.newscientist.com

Researchers have developed some of the tiniest solar cells ever made. So far, they have managed to pull 11 volts of electricity from a small array of the organic cells, which are each just a quarter of the size of a grain of white rice, said Dr. Xiaomei Jiang from the University of South Florida, the United States, who led the research.

Because it is in a solution, you can design a special spray gun where you can control the size and thickness. You could produce a paste and brush it on, Dr. Jiang said. She envisions the solar cells being used eventually as a coating on a variety of surfaces, including clothing. The cells might generate enough energy to power small electronic devices or charge a cell phone, for example.

The tiny cells from Dr. Jiangs lab are made from an organic polymer that has the same electrical properties of silicon wafers but can be dissolved and applied to flexible materials. The main components are carbon and hydrogen materials that are present in nature and are environmentally friendly, she said. The researchers showed that an array of 20 of these cells could generate 7.8 V of electricity, about half the electricity needed to run a microscopic sensor for detecting dangerous chemicals and toxins. They are now refining the manufacturing process with the hope of doubling that output to 15 V.

Source: www.reuters.com

Belgiums IMEC has reported that its associate laboratory, Institute for Materials Research in Microelectronics (IMOMEC), has developed a method to stabilize organic solar cells, with multi-fold improvement in cell lifetimes. IMOMEC, located on the campus of the Hasselt University, said the research paves the way for commercial organic solar cells with an operational lifetime of more than five years. The researchers optimized the nanomorphology of the active layer, creating a more stable mix of organic compounds that can trap photons and transport them to an electrical contact.

Organic solar cells deteriorate as the compounds tend to separate into different phases, reducing conversion efficiency. IMEC has shown that this phase segregation is related to the organic polymers mobility, and that fixing the nanomorphology of the polymers could improve their lifetimes.

To stabilize the nanomorphology of the active layer, IMOMEC developed conjugated polymers. Experiments on bulk heterojunction organic solar cells based on the material showed no degradation after 100 hours, whereas reference cells degraded after a few hours. The result, IMEC said, is a lifetime improvement by at least a factor of 10. The cells achieved efficiencies near 4 per cent, with an expectation that efficiencies could be improved to more than 10 per cent.

Source: www.semiconductor.net

Prof. Arie Zaban, Head of Bar-Ilan Universitys Nanotechnology Institute in Israel, claims he has created using nanotechnology a solar cell 100 times larger than a typical solar cell. An expert in photovoltaics, he demonstrated how metallic wires mounted on conductive glass can form the basis of solar cells with efficiency similar to that of conventional, silicon-based cells, but that are much cheaper to produce.

While Prof. Zabans earlier efforts produced photovoltaic cells 1 cm2 in size, he has now achieved a cell measuring 10 cm 10 cm, which he hopes would boost the techniques utility in producing commercial amounts of solar power. We have found a way to produce platinum nanodots tiny crystals measuring only a few nanometres in diameter, he said, adding that the technique helped reduce the amount of platinum needed by a factor of 40.

Prof. Zabans previous research had developed a low-cost process of depositing semiconductor material in a sponge-like array on top of flexible plastic sheets. Key to the system is the use of an organic dye that allows the semiconductor, transparent in its natural form, to absorb light.

Source: www.eetindia.co.in

Solar cell manufacturing depends on many vacuum-based processes, from plasma-enhanced chemical vapour deposition of silicon (Si) to lamination of the finished module. For these processes to meet the throughput needs of the solar cell industry, high pumping speeds and rapid chamber cycling are critical.

Solar cell manufacturing poses special challenges for pump designers. For example, the amorphous silicon (a-Si) cells that achieve the best conversion efficiency incorporate substantial amounts of hydrogen achieved at lower deposition rates. A slower deposition means that the chamber load and unload time is a smaller fraction of the total process time.

The hydrogen passivates dangling bonds and densifies the film, improving carrier lifetime and reducing recombination. However, as Mr. Clive Tunna, Technical and Commercialization Director for Oerlikon Leybold, explained, hydrogen is bad news for vacuum pump designers: the gas is notoriously difficult to pump. At 77K that the cold traps in standard cryopumps operate in, hydrogen is still a gas. Hydrogen molecules are small enough to leak through seals, and high concentrations of hydrogen anywhere in the system pose an explosion risk.

Another issue is that a-Si deposition chambers require to be cleaned often, usually by means of nitrogen trifluoride (NF3) etching. NF3 tends to corrode seals and pump components, a problem that Oerlikon Leybold addresses by flooding the components with purge gas. At the same time, the cleaning process generates a large volume of dust. Handling both dust and light gases in the same system requires careful optimization, Mr. Tunna said.

Problems with dust also appear in wafer-based solar cell manufacturing, as the crystal growth process produces large amounts of Si dust. This dust is hazardous because it spontaneously ignites below room temperature, and is reactive with water. To eliminate explosion risks, traditional system designs place a complex metal dust filter before the pump assemblies. Oerlikons pump design mixes air or oxygen with the Si dust, forming non-reactive silicon dioxide that can be captured by a less costly standard dust filter.

Vacuum processing appears in a different form towards the end of the solar cell assembly process, as wafer-based cells are laminated into the module frame and encapsulated in thin-film ethyl vinyl acetate (EVA) panels. These processes take place under vacuum to avoid trapping of air and water vapour. However, the volatile monomers from curing EVA can attack pump seals and react with pump oil. Standard pumps require oil replacement after as little as 200 hours in this environment, and dry pumps can be damaged if process gases infiltrate the gear box. Pumps that use oil-cooled rotors prevent polymerization of EVA by-products, while shaft seal purging helps isolate process gases from the pump oil.

Source: www.renewableenergyworld.com

Scientists in Australia have developed the first silicon solar cell to achieve the milestone of 25 per cent efficiency. The solar cell has been developed by scientists at the ARC Photovoltaic Centre of Excellence of University of New South Wales (UNSW).

The Centre of Excellence already held the world record of 24.7 per cent for silicon solar cell efficiency. Now, a revision of the international standard by which solar cells are measured, has delivered the significant 25 per cent record to the team led by Prof. Martin Green and Prof. Stuart Wenham. According to Prof. Green, new knowledge about the composition of sunlight was the basis for the jump in performance leading to the milestone. The new record has moved the UNSW team closer to the 29 per cent theoretical maximum efficiency possible for first generation silicon photovoltaic cells.

Blue light is absorbed strongly, very close to the cell surface where we go to great pains to make sure it is not wasted. Just the opposite, the red light is only weakly absorbed and we have to use special design features to trap it into the cell, said Dr. Anita Ho-Baillie, who heads the high efficiency cell research effort of the Centre. These light-trapping features make our cells act as if they were much thicker than they are, added Prof. Green. The focus of the Centre is now improving mainstream production.

Source: www.entertainmentandshowbiz.com