American scientists have discovered that there are many neglected organic or inorganic materials that can use sunlight underwater to efficiently power automatic submersibles. The study published in Joule recently developed guidelines for optimal band gap values ​​for different water depths, and clarified that a variety of wide band gap semiconductors are the best equipment for underwater use, rather than the narrow band gap semiconductors in traditional silicon solar cells. .
Jason A. R? Gohr, one of the authors of the paper and a postdoctoral researcher at the New York University Tandon School of Engineering, said: "As of now, the general trend is to use traditional silicon batteries, but we found that it is far from satisfactory. Absorb a lot of red light and infrared light, and water will also absorb these two lights. With our guidelines, more preferred materials will be developed. "
For example, submersibles used to explore the deep sea are currently limited by insufficient power on land or lack of onboard batteries, making long-distance and long-term navigation impossible. Solar cell technology has entered outer space from land, which gives submersibles more opportunities to roam freely. But the underwater world has unique challenges. Water can scatter and absorb most of the visible spectrum. At shallow depths, it absorbs red solar wavelengths, making silicon-based solar cells no chance to capture them.
Most previous attempts to develop underwater solar cells are based on silicon or amorphous silicon, which has a narrow band gap and is the best choice for absorbing light on land. However, when other light wavelengths disappear, blue and yellow light can still penetrate deeply into the water body, which indicates that wide band gap semiconductors not used in traditional solar cells may be a better choice for underwater functions.
To better understand the potential of underwater solar cells, R? Gohr and colleagues tested the clearest waters from the Pacific Ocean to the Atlantic Ocean, as well as the turbid waters of Finnish lakes, using a precisely balanced model to determine the solar cells at each location Efficiency limit. It was found that solar cells can absorb solar energy at a depth of 50 meters in the clearest water body of the earth, and cold water can further improve the efficiency of the battery.
The researchers calculated that the solar cell absorber can perform its best function at a water gap of 1.8 electron volts at 2 meters underwater or at a band gap of 2.4 electron volts at 50 meters underwater. These values ​​remain constant in all research waters, proving that solar cells should be designed based on specific working depths rather than water locations.
R? Gohr noted that low-cost organic material solar cells that can function well in low-light conditions and alloys made of 3 to 5 elements are also ideal materials in deep water. Although the materials that make up these semiconductors are different from terrestrial solar cells, the overall design is still similar.
"The sunlight absorption material must be changed, but the design of the answer does not require major changes." R? Gohr said, "In order to prevent damage to the environment, traditional silicon solar panels-that can be on the roof The kind found-after encapsulation. Research shows that these panels can be immersed in water for several months without sustained damage. The solar panels made of the preferred materials can be similarly packaged. "Now They have already revealed the key points for the efficient operation of underwater solar cells, and the researchers plan to develop optimized materials.
"It will be very interesting!" R? Gohr said, "We have researched unsealed organic batteries that are highly stable under water, but we still need to prove that these batteries are more efficient than traditional batteries. We believe that they will be on the market soon. I saw new and exciting solar cells. "(Jin Nan)
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