At the Fraunhofer Institute for Solar Energy Systems (ISE), Germany, researchers claim that the new solar cells they devised convert sunlight into electricity at a rate of 41.1 per cent, beating their previous record of 39.7 per cent. The new record was achieved when the sunlight was concentrated by a factor of 454 and at the higher concentration of 880 they recorded an efficiency of 40.4 per cent.

The Group III-V: Epitaxy and Solar Cells, research team achieved success by finding a new way to combine the three component materials gallium indium phosphate and gallium indium arsenide on a germanium substrate. This was achieved by means of metamorphic crystal growth, which allowed the scientists to focus imperfections in the crystals into an inactive part of the solar cell.

Source: www.lowcarboneconomy.com

Current solar cells cannot convert all the incoming light into usable energy because some of the light can escape through the back of the cell. Additionally, sunlight comes in a variety of colours and the cell might be more efficient at converting bluish light than reddish light. The nanoparticle approach, described in a recent paper in Optics Express, describes a relatively new approach to solar cells lacing them with nanoscopic metal particles to address these problems.

The key to this new research is the creation of a tiny electrical disturbance called a surface plasmon. When light strikes a piece of metal, it can set up in the surface of the metal, electron waves that move about like ripples on the surface of a pond. If the metal is in the form of a tiny particle, the incoming light can make the particle vibrate, thus effectively scattering the light. If the light is in certain resonant colours, the scattering process is particularly strong.

In the study conducted at the Centre for Nanophotonics, FOM Institute for Atomic and Molecular Physics, the Netherlands, Dr. Kylie Catchpole and Dr. Albert Polman describe what happens when a thin coating of nanoscopic metal particles are placed onto a solar cell: the scattering process keeps more of the light inside the solar cell. Varying the size and material of the particles further improves light capture, at otherwise poorly performing colours.

In their work, Dr. Catchpole and Dr. Polman show that light capture for long wavelength (reddish) light can be improved by a factor of more than ten. Dr. Catchpoles team at the University of New South Wales had earlier shown that overall light-gathering efficiency for solar cells employing metallic nanoparticles could be improved by 30 per cent.

An important point about plasmonic solar cells is that they are applicable to any kind of solar cell, says Dr. Catchpole, who has now started a new group studying surface plasmons at the Australian National University. This includes the standard silicon or newer thin-film types.

Source: www.azonano.com

Recent experiments conducted by Dr. Greg Scholes and Dr. Elisabetta Collini at the Chemistry Department of University of Toronto, Canada, have provided new insights into the way molecules absorb and move energy. The chemists looked specifically at conjugated polymers, believed to be one of the most promising candidates for building efficient organic solar cells.

The research by Dr. Scholes and Dr. Collini found that quantum effects can be used to control what happens after light is absorbed by an organic solar cell one of the biggest obstacles to the development of organic solar cells. The finding opens the way to designing organic solar cells or sensors that capture light and transfer its energy much more effectively.

The scientists used ultrashort laser pulses to put the conjugated polymer into a superposition state or quantum coherence state, wherein it is simultaneously in the ground (normal) state and a state where light has been absorbed. Then they observed whether the quantum state can migrate along or between polymer chains. It turns out that it only moves along polymer chains, says Dr. Scholes. The chains chemical framework is crucial for enabling quantum coherent energy transfer. This means that a chemical property structure can be used to steer the ultrafast energy transfer using quantum coherence, he says.

Source: www.sciencedaily.com

Currently, solar cells are difficult to handle, expensive to purchase and complicated to install. Researchers at the Henry Samueli School of Engineering and Applied Science of University of California Los Angeles (UCLA), the United States, have found out that these limitations could be overcome. Dr. Yang Yang, a professor of materials science and engineering, and colleagues have described the design and synthesis of a new polymer that would bestow on solar cells notably greater sunlight absorption and conversion capabilities than other polymers.

Dr. Yang and his team found that a polymers photovoltaic properties are markedly improved by replacing a carbon atom with a silicon atom. This silole-containing polymer can also be crystalline, giving it great potential as an ingredient for high-efficiency solar cells. The efficiency reached 5.1 per cent during the time but improved to 5.6 per cent in the laboratory within a few months.

The UCLA team has shown that the photovoltaic material they use on their solar cells is one of the most efficient based on a single-layer, low-band-gap polymer. At a lower band gap, the polymer solar cell can absorb more sunlight. At a higher band gap, light is not easily absorbed and is wasted, reveals the study. Previously, the synthesizing process for the polymer was very complicated. We have been able to simplify the process and make it easier to mass produce, said Dr. Jianhui Hou, UCLA post-doctoral researcher and co-author of the study. We hope that solar cells will one day be as thin as paper and can be attached to the surface of your choice, added co-author Mr. Hsiang-Yu Chen, a UCLA graduate student in engineering.

Source: www.engineer.ucla.edu

The University of Surrey, the United Kingdom, will develop carbon nanotube-doped organic solar cells under a three-year programme. Dr. Ravi Silva, Director, Advanced Technology Institute at Surrey, explains, The best organic solar cells are currently 5-6 per cent efficient. We hope to be able to go up to above 10 per cent by the end of the project. A 10 per cent efficiency is viewed as the threshold, beyond which solar cells are commercially viable.

Carefully designed-in carbon nanotubes can increase organic solar cell efficiency in three ways: absorbing photons to create electron-hole pair excitons; separating excitons into available electron and hole carriers; and transferring these carriers to external loads. Unlike conventional solar cell materials, carbon nanotubes have a black body absorption spectrum, which is ideal for solar cell. You make an organic solar cell, tuning the size of the inorganic part [carbon nanotubes] to absorb other parts of the spectrum, says Dr. Silva. Introduced carbon also adds to available excitons separation sites. A heterojunction is produced wherever there is organic contact with defects in the nanotube.

Carrier mobility along carbon nanotubes is very high, and can boost the low conductivity of semiconducting organic materials. This will result in improved carrier transport to the cell electrodes. Although organic solar cells could suffer from UV degradation, lower lifetime is offset by low cost, says Dr. Silva.

Source: www.electronicsweekly.com

Local loss mechanisms often reduce the energy to current conversion efficiency of solar cells. Optical characterization techniques capable of providing spatially resolved information about the performance of a solar cell are therefore valuable. The Cooke Corporation from the United States and the Institute for Solar Energy Research Hameln (ISFH) in Germany have jointly investigated the use of camera-based electroluminescence (EL) imaging for the characterization of conversion efficiency of solar cells.

The recently introduced camera-based EL imaging technique allows a rapid solar cell characterization with a high spatial resolution. The intensity of luminescence radiation (IEL) is determined by the product of the electron and hole concentrations. The image captured with the CCD camera shows the distribution of IEL. EL images of real solar cells always show inhomogeneities, as the EL signal is considerably higher at the contact grid in comparison to a point midway between the contact fingers. Generally, all effects resulting in a local reduction of the carrier concentration are seen on an EL image. Even though the reason for such a local reduction in the carrier concentration can be varied, they can be clearly distinguished. Thus, local variations in the bulk carrier lifetime are clearly visible on the EL image, captured using a cooled 12 bit CCD camera system.

Source: www.advancedimagingpro.com