A solar cell is like a heart: if you force it to beat out of rhythm, it tires quickly. Usually, cells are tested by applying reverse voltage, but in real life, a shadow from a leaf or a bird forces neighboring cells to pass foreign current through themselves. The authors of this new study are the first to examine in detail what happens when a constant reverse current is driven through a perovskite cell.
The key lies in the interlayer between the perovskite and the transparent electrode. With a thick polymer layer (PTAA), the cell holds high voltage, but under a current comparable to operating levels, it burns out instantly and permanently. With a thin phosphonic layer (MeO-2PACz), the picture is different: degradation is gentle and gradual, and after resting, the cell almost fully recovers. The longer the current flows, the worse the damage — even if the total charge is the same.
Imaging of light-emitting regions on the cell showed that the damage is not linked to short circuits. Instead, electrochemical reactions occur at the layer interfaces: ions and charges rearrange the material, much like salt corrodes metal. This insight suggests how to choose materials for solar panels so they can survive shadows and faults without catastrophe.
Perovskite solar cells are named after the mineral perovskite, discovered in the Ural Mountains in 1839—but the cells use synthetic materials with a similar crystal lattice.
In Kim Stanley Robinson's novel 'Aurora,' the characters rely on solar sails and batteries that must withstand years of overload far from the Sun — the problem of current-induced degradation there would be a matter of life and death.