A new solar cell promises enhanced efficiency and a smaller environmental footprint. The new cell, developed by a team from Northwestern University, uses a perovskite structure composed of tin instead of the traditional lead as the light-absorbing material. It is a low-cost, easily manufactured, environmentally friendly solar cell. Cross-sectional view of a completed photovoltaic device using tin perovskite. Courtesy of Nature Photonics. The tin solar cell has an efficiency of around 6 percent, which the researchers said is a solid starting point. The tin material is unique in its ability to absorb most of the visible light spectrum and in that it can dissolve and reform without heat once the solvent is removed, the researchers said. They expect that the tin perovskite will eventually be able to match the efficiency of lead, which is 15 percent. “There is no reason this new material can't reach an efficiency better than 15 percent,” said lead researcher Mercouri G. Kanatzidis, an inorganic chemist with the Weinberg College of Arts and Sciences at Northwestern. “Tin and lead are in the same group in the periodic table, so we expect similar results.” The solid-state tin solar cell is a sandwich of five layers about 1 to 2 µm thick. The first is electrically conducting glass, which allows sunlight to enter the cell. Next is a layer of titanium dioxide that is deposited onto the glass. Together, these act as the electric front contact of the solar cell. The next layer is the tin perovskite, deposited in a nitrogen glove box to avoid oxidation. A hole transport layer is next, which closes the electrical circuit and creates a functional cell. The final portion consists of a thin layer of gold that is also deposited into the glove box and is the back contact electrode of the solar cell. “Solar energy is free and is the only energy that is sustainable forever,” Kanatzidis said. “If we know how to harvest this energy in an efficient way we can raise our standard of living and help preserve the environment.” The research is published in Nature Photonics (doi: 10.1038/nphoton.2014.82). For more information, visit: www.northwestern.edu.