One of the main reasons that solar cells aren’t more efficient at converting sunlight into electricity is because much of that sunlight is reflected off the cell, or can’t be fully absorbed by it. A new sandwich-like material created by researchers at Princeton University, however, is claimed to dramatically address that problem – by minimizing reflection and increasing absorption, it reportedly boosts the efficiency of organic solar cells by 175 percent.
Developed by a team led by electrical engineer Prof. Stephen Chou, the material is known as a “plasmonic cavity with subwavelength hole array” or PlaCSH.
It consists of five very thin layers. On top is the “window layer” through which the sunlight first passes. It’s made from an extremely fine metal mesh, the diameter and spacing of its holes being measured in nanometers. Next is a layer of transparent plastic, followed by a layer of semiconductive material – although Chou used a plastic semiconductor, other materials could be used. This is followed by a layer of titanium oxide, with a layer of aluminum sitting at the bottom of the stack.
The combined thickness of all five layers is just 230 nanometers. This distance, along with the spacing and diameter of the holes in the mesh, is shorter than the wavelength of the sunlight itself. According to Chou, it is this property that allows only four percent of the light to be reflected, and up to 96 percent to be absorbed.
When it comes to converting direct sunlight into electricity, this translates into a 52 percent increase in efficiency over conventional organic solar cells. PlaCSH is also superior at capturing sunlight coming at steep angles, however. This ups its efficiency by an additional 81 percent, which when combined with other factors brings the total percentage of improvement to 175.
PlaCSH could reportedly be cost-effectively manufactured in large sheets. Besides providing greater efficiency, the material could also replace the costly indium-tin-oxide (ITO) electrodes in conventional organic solar cells, bringing their price down. As PlaCSH is more flexible than ITO, it should also make the cells less fragile.
Although Chou’s research regarding the use of PlaCSH in inorganic solar cells is not yet complete, he believes that the material should also allow them to achieve much greater efficiency. Additionally, because it could supposedly reduce the thickness of the silicon semiconductor in such cells by a thousand-fold, it should make them cheaper and more flexible.
A paper on the research was recently published in the journal Optics Express.
Source: Princeton University
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