Modulating phase composition and crystallization of 2D Ruddlesden-Popper perovskite films via a polyvinylidene...

Uncontrolled crystallization and phase distribution remain major challenges in two-dimensional (2D) Ruddlesden-Popper (RP) perovskite films, often leading to the formation of undesirable small-n phases, poor out-of-plane orientation, and high defect density. Although polymer interlayers have been applied to improve film morphology, the underlying mechanisms and their effectiveness in quasi-2D systems remain insufficiently clarified. In this study, we present an effective interfacial engineering strategy to control phase distribution in two-dimensional (2D) Ruddlesden-Popper (RP) perovskite by incorporating an ultra-thin polyvinylidene fluoride (PVDF) interlayer at the buried interface. Comprehensive characterization reveals that the PVDF-modified interface significantly suppresses the formation of low-n (n < 4) phases in BA₂MA₃Pb₄I₁₃ perovskite films while promoting preferential out-of-plane orientation and enhanced crystallinity. The optimized devices with enhanced film morphology and phase purity lead to improved charge transport properties compared to the control devices fabricated directly on PEDOT:PSS. As a result, the PVDF-modified 2D RP perovskite solar cells achieve a champion power conversion efficiency of 11.03%, representing a 17.47% enhancement over reference devices without interfacial modification.