An ultra-thin inorganic interlayer strategy for achieving efficient inverted planar perovskite solar cells and modules with high fill factor

The fill factor (FF) is a fatal parameter to determine the power conversion efficiency (PCE) of perovskite solar cells. Especially, for the large area solar cells and modules, the low FF is the bottleneck towards the high PCE. The FF is highly correlated with the carrier recombination caused by defects at interfaces. Herein, we propose that ultra-thin inorganic alkali metal fluorides interlayer passivate the interface defects by vapor evaporation method at the perovskite/electron transport layer (ETL) interface. We confirmed that the alkali metal fluorides (AF) layer can function as both defect passivation layer and physical barrier layer, showing the significant enhancement of PCE and ambient stability. Eventually, we achieve the highest FF (80.6%) for 1 cm2 size and highest FF (73.1%) for 10.8 cm2 size perovskite solar cell by potassium fluoride (KF) as passivation layer. This functional interlayer strategy paves the way to resolve the industrial requirements with low cost, high fill factor large area planar perovskite solar cells.