“In fact, not only do I believe that multiple gigawatts of tandem will be sold before the end of 2022, I am also confident that in a decade’s time, tandem will command more than 50% of our industry’s market share,” van Mierlo said.

“Is it that I no longer believe in the long-term role of silicon? No! In fact, it’s the remarkable success of silicon that now makes tandem modules the inevitable next step. With its low bandgap of 1.1 eV and its low cost, silicon is the ideal candidate for the bottom cell in a tandem configuration. In this position, a silicon bottom cell converts less than one-third the energy captured by the sun but still carries 100% of the cell cost. To make tandem work, you need the bottom cell to be extremely low cost. And, thanks to recent innovations such as the Direct Wafer furnace, we can achieve that cost target.”

“Which brings us to the tandem top cell, for which there are many excellent solutions. Thanks to the massive investment in thin film R&D, there are suitable materials already on the shelf. Moreover, new perovskites bring additional promise. Oxford PV and Swift Solar both vouch that it is possible to make a stable high-bandgap perovskite, but it is much harder for perovskites to match the excellent low-bandgap performance of silicon,” he said.

Swift Solar stacks perovskite solar cells to make tandem cells.

Other researchers have found that PV modules made with tandem solar cells will have to show efficiencies of 30% and offer the same lifetime and degradation rate as standard crystalline panels if manufacturers want to hit commercial production.