In a thin perovskite film, a material for cheap solar cells, light creates pairs of charges: an electron and a "hole." They need to reach the electrodes and produce current, but many vanish along the way. Where exactly they go is the question that determines how efficient the cell will be.
The researchers measured the film's luminescence after a short laser pulse and the fraction of light converted into charges. Together, these data allowed them to build a model that reproduces all experiments. The model showed that the material has deep and shallow traps, as well as a special process — Auger capture. In this process, one charge gives energy to a neighbor, causing it to fall into a trap faster.
At the brightness of an ordinary sunny day, Auger capture becomes the main killer of charges. This means that even a perfectly clean perovskite will lose energy due to this mechanism. To increase the efficiency of solar cells, we need to learn how to suppress such capture — for example, by changing the composition or structure of the film.
So the path to better solar cells lies not only in removing defects, but also in controlling the interaction between charges.
The Auger effect is named after the French physicist Pierre Auger, who discovered it in the 1920s while studying X-rays.