J
jeremy
33 minutes
Reverse Bias Damage in Perovskite Modules: Partial Shading and Hot Spots
Reverse bias damage in perovskite modules happens when one cell is shaded. Cells in a module are wired in series, so the same current must flow through all of them. A shaded cell makes less current than its lit neighbours. They push current through it anyway, and that drives the shaded cell to a negative voltage, called reverse bias. On a J-V curve, this is the region to the left of zero volts, which a normal scan never shows. A silicon cell can hold off a large reverse voltage before it breaks down. Many perovskite cells break down at only a few volts. Then current crowds into weak spots, the spot heats up into a hot spot, and the cell can be scarred in minutes. The strong field also pushes ions, so iodide reaches the contacts faster and reacts with them. The damage may not heal when the shade moves. Defences come at the module level and the cell level. Bypass diodes give current a path around a shaded group of cells. Tougher contacts and barrier layers slow the reactions inside the cell. In a perovskite-silicon tandem, the silicon cell can share the reverse voltage and shield the top cell. After this Concept you can explain why a small shadow can harm a perovskite module and name the defences to look for on a data sheet.