Water-Repellent Low-Dimensional Fluorous Perovskite as Interfacial Coating for 20% Efficient Solar Cells

Hybrid perovskite solar cells have been capturing an enormous research interest in the energy sector due to their extraordinary performances and ease of fabrication. However, low device lifetime, mainly due to material and device degradation upon water exposure, challenges their near-future commercialization. Here, we synthesized a new fluorous organic cation used as organic spacer to form a low-dimensional perovskite (LDP) with an enhanced water-resistant character. The LDP is integrated with three-dimensional (3D) perovskite absorbers in the form of MA_0.9FA_0.1PbI₃ (FA = NH₂CH = NH₂⁺, MA = CH₃NH₃⁺) and Cs_0.1FA_0.74MA_0.13PbI_2.48Br_0.39. In both cases, a LDP layer self-assembles as a thin capping layer on the top of the 3D bulk, making the perovskite surface hydrophobic. Our easy and robust approach, validated for different perovskite compositions, limits the interface deterioration in perovskite solar cells yielding to >20% power conversion efficient solar cells with improved stability, especially pronounced in the first hours of functioning under environmental conditions. As a consequence, single and multijunction perovskite devices, such as tandem solar cells, can benefit from the use of the waterproof stabilization here demonstrated, a concept which can be further expanded in the perovskite optoelectronic industry beyond photovoltaics.