Multiple-Ring Aromatic Spacer Cation Tailored Interlayer Interaction for Efficient and Air-Stable Ruddlesden–Popper Perovskite Solar Cells

2D Ruddlesden–Popper (2DRP) perovskites with hydrophobic bulky cations are proven to improve the environmental stability in photovoltaic devices significantly. However, these spacer cations lead to a weak interplay in the 2DRP perovskites, severely impacting the charge carrier transport and require a systematic understanding of the interaction between spacer cations and inorganic slabs. Herein, a series of novel perovskites (BA 1− x NMA x ) 2 MA 3 Pb 4 I 13 (NMA = 1-naphthalenemethylammonium, BA = n -butylammonium) are successfully fabricated to reveal the interaction of mixed spacers and inorganic slabs. Incorporating NMA cations enhances the N  H⋯I − hydrogen-bonding interaction between the spacer cations and [PbI 6 ] 4− slabs, resulting in a preferentially crystal vertical orientation of smoothed perovskite films with larger crystal grains. Thus, a significant reduction in the density of trap states of the resulting 2DRP perovskites is achieved which leads to highly efficient charge carrier transport. Consequently, the champion (BA 0.9 NMA 0.1 ) 2 MA 3 Pb 4 I 13 device yields a power conversion efficiency (PCE) of 14.21%, along with the unencapsulated devices that can retain 85% of their initial PCE for 1200 h under 35–65% relative humidity conditions. This work provides a simple and original method to modulate the interlayer interplay in 2DRP perovskites for highly efficient and air-stable perovskite solar cells.