Dimensionality and Defect Engineering Using Fluoroaromatic Cations for Efficiency and Stability Enhancement in 3D/2D Perovskite Photovoltaics

State-of-the-art perovskite solar cells (PSCs) based on three-dimensional (3D) films have achieved high power conversion efficiencies (PCEs), but are relatively fragile in high-temperature and humid environments. This shortcoming must be addressed before PSCs can be fully commercialized. Herein, the use of a fluorinated aromatic organic spacer cation, 4-fluoro-phenethylammonium iodide (FPEAI), to fine-tune the dimensionality and surface morphology of perovskite films is demonstrated. Surface treatment with FPEAI can lead to in situ formation of a two-dimensional (2D) (FPEA)₂PbI₄ perovskite capping layer atop a 3D perovskite film, producing novel 3D/2D interface in perovskite films. Simultaneously, FPEAI treatment can induce a novel grain-boundary passivation effect on the film surface, which helps to suppress undesirable charge recombination. After FPEAI treatment, standard (0.09 cm²) and large-area (2.00 cm²) PSCs achieve PCEs of 20.53% and 16.82%, respectively. The FPEAI-treated PSCs also demonstrate superior air- and photo-stability due to the hydrophobic (FPEA)₂PbI₄ capping layer that reduces moisture ingress into perovskite structures. Furthermore, a 11.2 cm² large FPEAI-treated PSC module with a PCE of 13.66% are successfully fabricated. FPEAI passivation is a facile strategy to produce 3D/2D multi-dimensional PSCs with superior performance and stability.