High-Efficiency Solar Cells Created
Researchers from Stanford and Oxford using tin and other abundant elements have created novel forms of perovskite solar cells—a photovoltaic crystalline material that is thinner, more flexible and easier to manufacture than silicon crystals. “Perovskite semiconductors have shown great promise for making high-efficiency solar cells at low cost,” said study co-author Michael McGehee, a professor of materials science and engineering at Stanford. “We have designed a robust, all-perovskite device that converts sunlight into electricity with an efficiency of 20.3 per cent, a rate comparable to silicon solar cells on the market today.” The new device consists of two perovskite solar cells stacked in tandem. Each cell is printed on glass, but the same technology could be used to print the cells on plastic.
Previous studies showed that adding a layer of perovskite can improve the efficiency of silicon solar cells. But a tandem device consisting of two allperovskite cells would be cheaper and less energyintensive to build, the authors said. A typical perovskite cell harvests photons from the visible part of the solar spectrum. Higher-energy photons can cause electrons in the perovskite crystal to jump across an ‘energy gap’ and create an electric current. A solar cell with a small energy gap can absorb most photons but produces a very low voltage. A cell with a larger energy gap generates a higher voltage, but lower-energy photons pass right through it.
An efficient tandem device would consist of two ideally matched cells, said co-lead author Giles Eperon, an Oxford postdoctoral scholar currently at the University of Washington. “The cell with the larger energy gap would absorb higher-energy photons and generate an additional voltage,” Eperon said. The smaller gap has proven to be the bigger challenge for scientists. Working together, Eperon and Leijtens used a unique combination of tin, lead, cesium, iodine, and organic materials to create an efficient cell with a small energy gap. The successful result was a tandem device consisting of two perovskite cells with a combined efficiency of 20.3 per cent.