HONG KONG Researchers in Hong Kong have taken a new type of solar cell developed in Japan to the next level of efficiency, opening the door to a wide range of applications.
Perovskite solar cells, as they are called, use a thin film of perovskite crystal that combines metal atoms, such as lead, and organic substances containing elements such as bromine, to generate current. These cells can be produced cheaply and easily using printing technology to apply the material to a substrate or other object.
In 2009, researchers at Japan's Toin University of Yokohama confirmed that a thin film of perovskite crystal can function as a solar cell. The power conversion efficiency was initially less than 5% but was increased to over 10% in 2012. Researchers and companies around the globe have since been racing to achieve higher efficiency levels.
Among them is a group of researchers led by Hong Kong Polytechnic University professor Charles Chee Surya. His team came up with perovskite-silicon tandem solar cells. A perovskite solar cell functions as the top layer, harvesting short-wavelength light, while the silicon-coated bottom layer absorbs long-wavelength light.
The two layers enable the module to achieve a power conversion efficiency of 25.5%, the highest in the world for a perovskite cell, according to Surya. The previous highest rate was 22.8%, achieved by a Swiss team.
Perovskite cells are not only versatile, Surya's group also estimates that their power generation costs will be about 30% lower than those of conventional silicon cells. "The market for perovskite solar cells is going to grow quite substantially in the future," Surya said. He explained that the cells can be applied to a wide range of products, including wearable devices and sensors for home appliances.
But there are safety and durability problems that must be overcome before perovskite solar cells can be put to widespread use. One concern is the use of lead, which is tightly regulated in much of the world. The decline in power conversion efficiency seen after just a few days is another hurdle to practical application.