Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field.Read the abstract in Nature Energy (doi:10.1038/s41560-018-0278-x).TranscriptWelcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler. Researchers have made an all-perovskite tandem solar cell with a record high power-conversion efficiency of 21%.Tandem solar cells are more efficient than a single cell because each device in the stack can be tailored to absorb a different part of the light spectrum. Tandem perovskite/silicon cells are closer to market, but all-perovskite tandem cells would be easier and less costly.Making an all-perovskite tandem cell that is efficient has been a challenge. The bottom device in a tandem cell is prepared with a low-bandgap material to absorb all of the infrared photons passing through the top device. Despite many efforts, researchers have had difficulty making high-quality low-bandgap perovskite absorber layers.At the University of Toledo, Yanfa Yan and his colleagues made a high-quality layer by introducing 2.5% chlorine into a mixed tin–lead perovskite. This increased the grain size and crystallinity of the layer and reduced electronic disorder, which quashed the charge-carrier recombinations that produce heat and boost efficiency of the tandem cell. The cell retains 85% of this efficiency after 80 hours.This work was published in a recent issue of Nature Energy. My name is Bob Braughler from the Materials Research Society.For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.