Solar panels with multiple stacked cells are currently breaking records. Remarkably, a team of researchers from the Eindhoven University of Technology and TNO at Holst Centre have now managed to make photodiodes – based on a similar technology – with a photoelectron yield of more than 200 percent. You would think that efficiencies of more than 100 percent are only possible using alchemy and other Harry Potter-like wizardry. But it can be done. The answer lies in the magical world of quantum efficiency and stacked solar cells.
René Janssen, professor at TU/e and co-author of a new Science Advances paper, explains. “I know, this sound incredible. But we’re not talking about standard energy efficiency here. What counts in the world of photodiodes is quantum efficiency. Instead of the total amount of solar energy, it counts the number of photons that the diode converts into electrons.
I always compare it to the days when we still had guilders and lira. If a tourist from the Netherlands received only 100 lira for their 100 guilders during their holiday in Italy, they might have felt a bit shortchanged. But because in quantum terms, every guilder counts as one lira, they still achieved an efficiency of 100 per cent. This also holds for photodiodes: the better the diode is able to detect weak light signals, the higher its efficiency.”
