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

Abstract

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. Achieving uniform coverage of interfacial layers in perovskite solar cells is challenging, especially over large areas. Li et al. present design guidelines to fabricate these layers with uniform morphology, suppressed defects and improved charge transport.