A team of researchers have disclosed in which location self-healing occurs for the future solar cells through the use of Photoconductive Atomic Force Microscope. The work entitles "Topological distribution of reversible and non-reversible degradation in perovskite solar cells" published in the prestigious scientific journal Nano Energy.

In this work the sample is illuminated from the back of the cell, with the help of a commercially available RGB LED light. While illuminating, a tiny metallic needle is placed on top of the active layer of the solar cell, in which the photocurrent is generated.

The needle collects the current which is displayed as a map, blue colors means higher current, and topography information available from standard topography with the AFM, correlating in which parts of the sample the cell is working correctly.

This simple explained methodology is used to disclosed in which parts self-healing occurs. These kinds of cells are formed of little grains, with sub-micrometer scale, which in total, forms the complete solar cell.

Each grain is separated from its neighbor, by a "grain boundary". By using Photoconductive AFM, researchers have proved that grain boundaries acts as seeds in which the degradation starts to spread towards the grain center.

Even more interesting is the fact that some part of the degradation can be reversed: the cell can be self-healed. This is done by degrading locally the sample using an applied negative bias.

Afterwards, researchers apply the contrary bias, in order to recover the initial state of the sample. However, not all the areas are recoverable, only the grains are. Once the grain boundaries are degraded, they do not recover any more.

Such fundamental study can have a direct application to device design, as grain boundaries are now spotted as the enemy to avoid the irreversible degradation of the future solar cells.