Researchers at the University of Groningen are working on a special type of solar cell that is made of organic-inorganic hybrid perovskites. The team has been focusing on a material in which hot electrons retain their high energy levels for much longer, which might make it possible to use more of their energy to obtain a higher voltage.
Most hybrid-perovskite solar cells contain lead, which is toxic. The research group recently published a paper describing 9% efficiency in a hybrid-perovskite solar cell containing tin instead of lead. "When we studied this material further, we observed something strange", the team said. The results showed that the hot electrons produced in the tin-based solar cells took about a thousand times longer than usual to dissipate their excess energy.
"The hot electrons gave off their energy after several nanoseconds instead of some hundred femtoseconds. Finding such long-lived hot electrons is what everybody in this field is hoping for". Their longer lifespan makes it possible to harvest these electrons' energy before it turns into heat. Theoretical calculations show that by harvesting the hot electrons, the maximum efficiency for hybrid-perovskite solar cells could increase from 33% to 66%.
The next step is to find out why the tin-based hybrid perovskite slows down the decay of hot electrons. Then new perovskite materials could be designed with even slower hot electrons.