Seawater soaks up the longer wavelengths of light, everything above about 630 nanometers, so only blue and green light survives at depth. That is why ordinary solar panels perform poorly underwater.
Researchers at Yunnan University built perovskite cells tuned to the 400 to 600 nanometer range. Ten meters down, they converted light at 34.71 percent efficiency. The same cells reach 17.08 percent on land, and typical land-based panels manage between 20 and 25 percent.
How much power
At a depth of two meters, 115 square centimeters of cells produced 1,416 milliwatt-hours over two hours. At 10 meters, the same area delivered 324 milliwatt-hours, three to six times more than expected.
The cells are sealed in glass, synthetic rubber and epoxy resin to keep seawater out. Lab tests point to a lifespan of about 5.5 years before output drops to 80 percent, while ordinary perovskite cells on land start degrading within a year.
Where they would work
The team tested the cells on small robots off Weizhou Island in the South China Sea. The authors list submarines, autonomous underwater vehicles, sensors, cameras and networked devices on the seafloor as possible uses.
"With submerged solar cells, submarines or autonomous underwater vehicles could achieve far greater range," says Wen-Hua Zhang, dean of the university's School of Materials and Energy, who led the work.
The study appeared in the journal Joule on September 11.
