Molecular Interlayer with Large Cations Supports Efficient, Stable Perovskite Solar Cells

Low-dimensional (quasi-2D) perovskite interlayers can improve the power conversion efficiency and stability of perovskite solar cells (PSCs). These improvements are primarily due to the passivation of the defective perovskite surface. In this work, we designed molecular interlayers with triphenylamine-based bulky ammonium cations that are ionically bonded to the 3D perovskite surface. We found that the best-performing PSCs exhibited higher efficiency (19.44%) than those with the n-octylammonium-formed quasi-2D perovskite interlayer (18.92%). Characterization of structure, cross-sectional morphology, and charge transport demonstrated that the improved PSC performance is due to the suppressed formation of resistive quasi-2D perovskites on the 3D perovskite surface, and improved interfacial contact between the molecular interlayer and the hole transport layer derived from the same molecular building block. These results offer a more effective strategy to show how the performance of PSCs can be improved by enhancing the perovskite|HTL interfacial contact instead of passivating defective perovskites.