In this podcast episode, MRS Bulletin’s Laura Leay interviews Rasmus Neilsen from the Technical University of Denmark about his fabrication of a monolithic selenium/silicon tandem solar cell. The selenium forms the top cell of the tandem device, with silicon used as the bottom cell. Selenium-based single-junction solar cells have traditionally used fluorine-doped tin oxide. In this work indium-tin oxide was used as a transparent conductive layer that is easier to deposit and its use is more widespread. Neilsen and his research team controlled the thickness of the carrier-selective contacts in the silicon solar cell that protects the silicon layer from the processes used to deposit subsequent layers on top, thus enabling them to deposit the top cell directly onto the substrate. This work was published in a recent issue of PRX Energy.