The research, which was enabled by the development of new ultrathin metal electrodes, represents a step toward developing completely transparent solar cells, say the researchers.
"Transparent solar cells could someday find a place on windows in homes and office buildings, generating electricity from sunlight that would otherwise be wasted," says Kai Wang, assistant research professor of materials science and engineering at Penn State and co-author of a paper on the study. "This is a big step - we finally succeeded in making efficient, semitransparent solar cells."
In attempts to create ever more efficient solar cells, scientists believe that traditional solar cells made from silicon are approaching the limits of the technology. Perovskite cells offer a promising alternative and stacking them on top of the traditional cells can create more efficient tandem devices, say the scientists.
"We've shown we can make electrodes from a very thin, almost few atomic layers, of gold," says Shashank Priya, associate vice president for research and professor of materials science and engineering at Penn State. "The thin gold layer has high electrical conductivity and at the same time it doesn't interfere with the cell's ability to absorb sunlight."
The perovskite solar cell that the researchers developed achieved 19.8% efficiency - a record for a semitransparent cell. And when combined with a traditional silicon solar cell, say the scientists, the tandem device achieved 28.3% efficiency, up from 23.3% from the silicon cell alone.
"A 5% improvement in efficiency is giant," says Priya. "This basically means you are converting about 50 watts more sunlight for every square meter of solar cell material. Solar farms can consist of thousands of modules, so that adds up to a lot of electricity, and that's a big breakthrough."
While ultrathin gold film has shown promise in previous research as a transparent electrode in perovskite solar cells, say the scientists, issues in creating a uniform layer resulted in poor conductivity. However, when chromium