A Novel Multiple-Ring Aromatic Spacer Based 2D Ruddlesden–Popper CsPbI₃ Solar Cell with Record Efficiency Beyond 16%

Two-dimensional (2D) Ruddlesden–Popper (RP) CsPbI₃ perovskite possesses superior phase stability by introducing steric hindrance. However, due to the quantum and dielectric confinement effect, 2D structures usually exhibit large exciton binding energy, and the charge tunneling barrier across the organic interlayer is difficult to eliminate, resulting in poor charge transport and performance. Here, a multiple-ring aromatic ammonium, 1-naphthylamine (1-NA) spacer is developed for 2D RP CsPbI₃ perovskite solar cell (PSC). Theoretical simulations and experimental characterizations demonstrate that the 2D RP CsPbI₃ perovskite using 1-NA spacer with extended π-conjugation lengths reduces the exciton binding energy and facilitates the efficient separation of excitons. In addition, its cations have a significant contribution to the conduction band, which can reduce the bandgap, promote electronic coupling between organic and inorganic layers, and improve interlayer charge transport. Importantly, the strong π–π conjugation of 1-NA spacer can enhance intermolecular interactions and hydrogen bonding, and prepare high-quality films with preferred vertical orientation, resulting in lower defect density, and directional charge transport. As a result, the (1-NA)₂(Cs)₃Pb₄I₁₃ PSC exhibits a record 16.62% performance with enhanced stability. This work provides an efficient approach to improve charge transport and device performance by developing multiple-ring aromatic spacers.