Transparency - Page 5

Researchers at The University of Tokyo's Institute of Industrial Science (IIS) have made advancements in the design of transparent solar materials. These could be suitable for roof-mounted solar panels or ones that are placed on windows. Instead of silicon, the cell is based on a perovskite material. A thin perovskite layer absorbs sunlight to generate an electric charge, which is transmitted to an electrode layer sandwiched between perovskite and a glass backing.

A major challenge in the field of solar panels is to create a material that absorbs enough light to produce power, yet still manages to remain transparent. To achieve this, the IIS researchers exploited the properties of the human eye. They took account of the fact that, for visual purposes, not all colors are equal. In fact, the eye is much more sensitive to green light, in the middle of the spectrum, than red or blue. According to the rules of "human luminosity," a good supply of green light is the main priority for visibility. Their new material was therefore designed to mostly absorb red and blue light, while letting green through.

A research team at the Korea Advanced Institute of Science and Technology (KAIST) and Sungkyunkwan University developed a perovskite-based solar cell that is semi-transparent, highly efficient and functions very effectively as a thermal-mirror.

The team has developed a top transparent electrode (TTE) that works well with perovskite solar cells. In most cases, a key to success in realizing semi-transparent solar cells is to find a TTE that is compatible with a given photoactive material system, which is also the case for perovskite solar cells. The proposed TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive-index (high-index) layer and an interfacial buffer layer. This TTE, placed as a top-most layer, can be prepared without damaging ingredients used in perovskite solar cells.

Researchers at Pennsylvania State University have developed a transparent and electrically conductive material that could make large screen displays, smart windows, touch screens and solar cells more affordable and efficient. The material has the potential to replace indium tin oxide (ITO), the transparent conductor that is currently used for more than 90% of the display market but is expensive, scarce and brittle.

Along with display technologies, the researchers will investigate the new materials with a type of solar cell that uses organic perovskite materials. The team has reported a design strategy using 10 nm-thick films of an unusual class of materials called correlated metals. In most conventional metals, such as copper, gold, aluminum or silver, electrons flow like a gas. In correlated metals, such as strontium vanadate (a perovskite material) and calcium vanadate, they move more like a liquid. The electron flow produces high optical transparency along with high metal-like conductivity, the researchers said.

Researchers involved in the €10.6 million European research project called GRAFOL have reportedly demonstrated a cost-effective roll-to-roll production tool capable of making large sheets of graphene on an industrial scale, which could greatly contribute to flexible thin-film solar cells with transparent electrodes like perovskite PVs.

Researchers at the Helmholtz-Zentrum Berlin (HZB) developed a process for coating perovskite layers with graphene for the first time, so that the graphene acts as a front contact.

A traditional silicon absorber converts the red portion of the solar spectrum very effectively into electrical energy, whereas the blue portions are partially lost as heat. To reduce this loss, the silicon cell can be combined with an additional solar cell that primarily converts the blue portions and a particularly effective complement to conventional silicon is perovskite. However, it is normally very difficult to provide the perovskite layer with a transparent front contact. While sputter deposition of indium tin oxide (ITO) is common practice for inorganic silicon solar cells, this technique destroys the organic components of a perovskite cell.