Homogeneous coverage of the low-dimensional perovskite passivation layer for formamidinium–caesium perovskite solar modules

The formation of a homogeneous passivation layer based on phase-pure two-dimensional (2D) perovskites is a challenge for perovskite solar cells, especially when upscaling the devices to modules. Here we reveal a chain-length-dependent and halide-related phase separation problem of 2D perovskite growing on top of three-dimensional perovskites. We demonstrate that a homogeneous 2D perovskite passivation layer can be formed upon treatment of the perovskite layer with formamidinium bromide in long-chain (>10) alkylamine ligand salts. We achieve champion active-area efficiencies of 25.61%, 24.62% and 23.60% for antisolvent-free processed small- (0.14 cm²) and large-size (1.04 cm²) devices and mini-modules (13.44 cm²), respectively. This passivation strategy is compatible with printing technology, enabling champion aperture-area efficiencies of 18.90% and 17.59% for fully slot-die printed large solar modules with areas of 310 cm² and 802 cm², respectively, demonstrating the feasibility of the upscaling manufacturing.