German and Swedish researchers calculated the supply of materials to produce perovskite tandem PV at a multi-terawatt-scale, flagging the difficult supply of gold, indium and cesium, well as a need to streamline production of certain materials used for hole-transport layers. "In essence, we might be able to go post-fossil fuels, but we can't go post-minerals," the research's corresponding author, Lukas Wagner, told <b>pv magazine</b>.